Graymark 808 User Manual

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PARTS IDENTIFICATION AND INVENTORY EXPERIENCE

This experience is provided to acquaint you with the ous electronic components and fittings included in this

To assist you in proper identification of the major parts and

project. Unpack the project carefully and check

each

fittings, pictorial and schematic illustrations are given in

part and fitting against the PARTS LIST In case of incor-

Figure

rect, missing, or damaged parts, please refer to How to der Replacement Parts and Graymark’s Warranty.

Upon completion of the parts identification and inventory, have your instructor initial your Progress Guide.

DIODE, SIGNAL

INTEGRATED CIRCUIT

FUSE HOLDER

DIODE, POWER

TRANSFORMER

POWER RESISTOR

HEAT SINK

POST, RED,

POTENTIOMETER

RUBBER FOOT

SOLDER LUG

MACHINE SCREW

SELF-TAPPING SCREWS

AND 2.6 x

SPACER

AND

ELECTROLYTIC

CAPACITOR

PCB

BREADBOARD

__.

LOCK WASHER SPLIT

STRAIN RELIEF

AND INTERNAL STAR

TRANSISTOR

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FIG. 29A

29B

5”

TP17

, RlO

r----------

, .

l Tm

. . . .

YELLOW

connect the meter test leads from the power

24. Position the two portions of the AC power cord grommet around the cord where it extends out of

rear of the cabinet top, as shown in Fig. 29A. Using slip-joint pliers, insert the grommet into the hole in the rear of the cabinet top as shown in Fig.

will have to squeeze the grommet quite hard with the pliers so that the power cord is formed into a “U” inside the grommet, and the grommet is compressed enough to fit into the hole.

25. Locate the Printed Circuit Board (PCB) and the test points. Insert and solder

through into the PCB. The test points are inserted from the component side of the PCB and soldered to the copper on the solder side of the

Refer to Fig. 30 and the the silkscreened legend on the component side of the PCB for the test point

locations.

26.

From the solder side (bottom) of the PCB thread

the transformer leads through the holes in the

PCB as shown in Fig.

from the component side (top) of the PCB, thread the stripped and tinned wire ends through the holes marked YL, BL and

Solder these five wires to the PCB, and cut off any excess lead length. Note: This is done so when the board is handled during component installation and testing, the wires won’t bend and break at the weak points where the wire insulation stops and the tinned copper wire goes through the PCB.

AC VOLTAGE WAVEFORMS AND VALUES DISCUSSION Measuring a DC voltage is simple and straight forward.

Shown on a graph, the voltage of an automobile battery would appear as a straight horizontal line. In Fig.

the

axis shows the magnitude of the voltage being meas-

ured, and the horizontal axis represents time. The time

shown on the graph would be in the order of several

the time it takes for the meter pointer to stabilize and

for you to accurately read the

graph shows that

the meter test probes were connected to the the battery at

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time (T) 0, and removed immediately after the meter was read.

To show an AC voltage, we need to change our graph in two ways. It will have to indicate voltages of both polarities, positive and negative, and we will have to make the horizontal axis cover a much smaller period of time.The public utility companies in the United States provide 60 Hertz power. Hertz, abbreviated Hz, means cycles per second. 60 Hz means that the polarity of the voltage is reversing

120 times a second. Figure 32 is a graph of the voltage at a wall outlet.The

zontal axis only covers

of a second of time, or 16.67 milliseconds (mS).To observe what this graph shows, you will have to use an

AC voltage ranges of a VOM will indicate the rms voltage, but the meter cannot respond to the rapid changes of the 60 Hz. AC voltage, and even if it could your eye could not read meter pointer.

AC VOLTAGE OBSERVATION and

EXPERIENCE

Purpose: To observe and measure PEAK, and

Voltages.

Equipment: OSCILLOSCOPE

VOM or DMM

the rapidly moving

MEASUREMENT

PEAK,

7. 8

IO.

13.

Refer to Fig. 33. Mount the 1 Omm spacers on the solder side of the

using the four 20 x 3mm machine screws, the two 40mm spacers, and two 3mm nuts.

Place the cabinet top assembly, the power transformer and the PCB on a work surface as shown in Fig. 34.

Set the oscilloscope power switch to On. Adjust the Oscilloscope to 10

Set the

sweep rate to

Adjust the input controls to display an AC signal, and vertical positioning at the CENTER line.

Connect the scope ground lead to TP2 of the

and the probe to

Connect the power plug of the 808 to a 115 VAC power outlet.

Set the power switch to ON. Record your peak-to-peak reading

If your reading is about 60 Volts peak to peak,

then proceed to the next step. If your reading is

not about 60 Volts

stop, and check

your test set up or consult your instructor.

Remove the scope probe. Adjust the VOM or DMM to read 19 Volts AC. Connect one meter test lead toTP2 of the PCB,

and the other test lead to

Record your reading

If your reading is about 21 Volts AC, proceed to the next step. If your reading is not about 21 Volts AC, then stop and check your test set up or con-

sult your instructor.

Remove the test leads.

13.0

VOLTS-

TIME

TO READ

TIME FOR

METER TO

STABILIZE

FIG.

FIG. 32

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MATHEMATICAL

AND DEFINITIONS

Purpose: To demonstrate that the previous experience is in agreement with the mathematical formulas

The following formulas are used to calculate ROOT MEAN SQUARE, PEAK and PEAK-to-PEAK AC sine wave Voltages, Refer to Fig. 32.

VP 1.414 x V

P-P

2.828 x

P-P

x vp

PEAK VALUE (p): The amplitude of a voltage measured from zero or reference axis to its maximum value, when the voltage alternates between positive and negative half cycles.

PEAK-to-PEAK (p-p): The amplitude of a voltage meas-

ured from maximum positive peak to maximum negative

peak, when the voltage alternates between positive and

negative half cycles.

ROOT MEAN SQUARE (RMS): The effective or RMS val-

ue of a voltage is the SQUARE ROOT of the average (MEAN) of the squares of all the instantaneous values of the voltage over one cycle. For a sine voltage, the ue is equal to 0.707 times the maximum peak value of the voltage.

INSTANTANEOUS VALUE: The exact value of the amplitude of a voltage at a particular instant in time.

Using the above formulas, calculate the unknown voltages

in Fig. 35. This completes the AC VOLTAGE OBSERVATION and

MEASUREMENT EXPERIENCE.

Have your instructor

initial your progress guide.

MEASURED

VALUE

PEAK-TO-PEAK

PEAK

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DISCUSSION

Figure 36 is a partial block diagram and schematic of the 808 Power Supply, showing the rectifiers and associated

There are three basic types of rectifier circuits: the wave, the full-wave center-tapped, and the full-wave bridge. Each of these rectifier circuits uses a different number of diodes and requires a transformer winding with a different rating. Figures 36A and 37 identify some of the differences between these three types of circuits.

The first column in Fig. 37 contains the three types of rectifier circuits. The number of diodes used by each circuit is listed in the second column. The average diode current is shown in the third

value has significance because diodes with a higher current rating are required for half-wave circuits, as compared to those required by the other two

Power Rating column is also important, since each type of circuit requires a transformer or a transformer winding with a different power capacity. And, the larger the power capacity required, the greater the size and the cost of the transformer.

The Ripple column refers to the percentage of ac voltage contained in the DC output of the rectifier circuit. A decrease in the percentage of ripple offers a corresponding decrease in the amount of capacitance required in the

Stage. Since lower value capacitors are smaller in size and cost less, a low percentage of ripple from the rectifier circuit is desirable.

Finally, the Conversion Efficiency column indicates the eff ciency of each Rectifier Circuit in converting alternating current to direct current. Notice that the full-wave rectifier circuits are twice as efficient as the half wave circuit.

The heart of the rectifier circuit is the diode. Most diodes are made from silicon or germanium, both of which are

semiconductors. Silicon is used for almost all diodes used

in power supply rectifier circuits, as it is capable of operat-

ing a higher temperature than germanium. For a given size of device, a silicon diode can pass more current than a

manium diode. A diode is a component which will allow cur-

rent to flow in one direction

from cathode to anode. Refer

to Fig. 38.

Alternating current flows first in one direction, then the op-

posite direction, then reverses direction again. This alter-

nating action occurs continuously. Direct current, on the

other hand, flows in only one direction. A diode can be put

in the path of an alternating current to block the current flow

in one direction and permit the current flow in the opposite

direction. It is in this manner that alternating current is recti-

fied or converted into pulsating direct current.

The

Model 808 Power Supply uses four silicon diodes in a full-wave bridge rectifier circuit, and four more silicon diodes in a center-tapped full-wave bridge

rectifier circuit.

The center-tapped full-wave rectifier circuit combines features of the center-tapped full-wave and the full-wave bridge rectifier circuits. It is used in the 808 Power Supply to provide power for the 0 to

15 Volt and the 0 to

15 Volt outputs. Before going on to the FILTERING section, you will build and test four types of rectifier circuits.

POWER

TRANSFORMER

SEC

RECTIFIER

BLUE

TP4

FIG. 36

RECTIFIERS DISCUSSION Half-wave rectifier circuits are sometimes used where the

current requirements are low, in the order of 10 to 100 microamps, and voltages of 1

(1000 Volts) or higher are needed. Photomultiplier tubes and Ion chambers, which are used to detect and measure radiation, are examples of devices requiring this type of DC power. Utility power supplies, such as your

808, which are generally used to power solid state analog and digital devices, do not usually use half-wave rectifier circuits.

In the

RECTIFIER TEST, you will be viewing

the output of a half-wave rectifier on an oscilloscope. A

Ohm resistor (Rl 1) is connected across the output of

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Without it, dangerously high voltages could remain present

FULL WAVE BRIDGE

long after the input power has been turned off or

TYPES OF RECTIFIER CIRCUITS

disconnected.

36A

SIGNIFICANT RECTIFIER CIRCUIT CHARACTERISTICS

NUMBER

POWER

EFFICIENCY

REQUIRED

4Q.6

FIG. 37

DIODE

ANODE CATtiODE

ANODE

CATHODE

CURRENT FLOW

the rectifier circuitry. Figure 43 is a schematic of this circuit. Without this resistor, stray circuit capacitances could distort the waveform displayed on the scope. In the completed

Power Supply

1 serves as a bleeder resistor.

One of the functions of a bleeder resistor is to discharge or “bleed off” the electrical energy remaining in the filter capacitors

the power supply is turned off. In high voltage

supplies, the bleeder resistor is an important safety device.

FIG. 39

The output voltages of the Model 808 Triple Power Supply are not high enough to be hazardous to the person using it, but it is disconcerting when a power supply that has been turned off earlier generates a spark if an output is acciden-

tally shorted. In the 808 Power Supply, bleeder resistors,

along with the voltage regulators, serve to discharge the ter capacitors within seconds after the input power has been switched off or disconnected.

When you are building your 808, you will be instructed to install some components long before they are used in an

is to provide a discharge path for the filter

capacitors before the voltage regulators are installed.

In unregulated power supplies the bleeder resistor is is

often designed to draw 10

or more of the rated output

is to improve the voltage regulation of the sup-

ply under changing load conditions. CONSTRUCTION

Refer to Fig. 39 for the following steps.

Be sure the 808 power plug is

a power outlet. Mount diode Dl on the PCB. Be sure that the

banded end of the diode is oriented the same as

the diode outline that is silkscreened on the PCB.

Using a heat sink as shown in Fig. 40, solder the

diode leads to the PCB. cut off any excess lead

length.

Mount resistor

1 SK Ohm

red)

Watt, on the PCB. Solder the leads to the

PCB and cut off any excess length.

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Purpose: To observe the current blocking capability of a

diode.

Equipment: VOM or DMM

Be sure the 808 power plug is

a power outlet. Set the meter you are using to its lowest ohmme-

ter range. If your meter has an range marked with a diode symbol or the word “diode”, use that range instead. Connect the positive* meter test lead to TP8 and the negative* meter test lead to

, (If your uncertain what the asterisks after

the words “positive” and “negative” mean, review the last paragraph of the section titled USING AN OHMMETER ON POLARIZED CIRCUITS AND CIRCUITRY) Record the resistance reading.

Reverse the meter test leads and record the

reading.

Disconnect the

meter test leads from the test points.

In the 2nd step, you should have had an infinite resistance reading, indicating that the direct current from the ohmmeter was being blocked. In

the 3rd step, there should have been a much low-

er resistance reading, indicating that the current was passing through the diode. This illustrates the ability of a diode to permit current to flow in one direction, and to restrict its flow in the opposite direction. The difference between the two conditions depends upon the polarity of the voltage applied to the diode. The anode of a diode has to be at a more positive potential than the cathode for current to flow to occur.

RECTIFIER EXPERIENCE

Purpose: To observe the voltage waveform produced by a Half-Wave Rectifier circuit.

Equipment: Oscilloscope Refer to Fig. 39 for the following steps.

Be sure the 808 power plug is

a power outlet. Cut a

length of red 22 gauge wire, and

strip 6mm of insulation from each end.

Solder one end of the red wire to TP8, and the other end toTP17. Because these are temporary connections for testing purposes, its not necessary to make mechanical connections.

Turn the oscilloscope ON and let it warm up. Ad-

just it to display a 60 Volt (peak to peak) 60 Hertz

signal. Set the vertical (Y) input coupling

to DC. Connect the oscilloscope (scope) ground lead to

TP2, and the scope input probe to

Plug the 808 Power Supply plug into a power

the power switch ON.

the wave-

form displayed on the scope. It should look like

Fig. 41

is ac voltage which is present at the

secondary winding of the transformer.

TRANSFORMER

SECONDARY

AC VOLTAGE

FIG. 41

CATHODE OF Dl

RECTIFICATION

FIG. 42

CURRENT

FLOW

HALF WAVE RECTIFIER CIRCUIT

FIG. 43

7. Move the scope probe to TP17. The waveform should look like Fig.

waveform is the sult of diode Dl rectifying the ac voltage. Dl clips off the negative half of the waveform, leaving only the positive half. This is called

wave rectification. Current flow in a half-wave rectifier circuit is illustrated in Fig. 43.

8. Turn the 808 Power switch Off and disconnect the power plug from the outlet. Disconnect the scope common lead and input Probe. Leave the

red wire that is soldered to TP8 and

place.

9. This completes the

Rectifier Experience. Have your instructor initial your Progress Guide.

Page 25

CENTER-TAPPED RECTIFIERS DISCUSSION A

center-tapped rectifier circuit requires a transformer with a secondary winding which has a tap halfway between both ends of the winding (a center-tap). secondary number 2 of the 808 Power Supply transformer is a tapped winding. You have already used one half of this winding in the

Rectifier section.

CENTER-TAPPED

RECTIFIER EXPERIENCE

To observe the voltage waveform produced by a

Rectifier circuit.

Equipment: Oscilloscope Refer to Fig. 44 for the following steps.

12Be sure that the 808 power plug is

ed to a power outlet.

Solder the cathode lead of a

diode to

TP8 of the

and the anode lead toTP3. Do not cut the diode leads, or remove the red wire soldered to TP8. This is a temporary installation of D2. This diode will be removed after the wave filter test and installed later in its permanent location. Since the long leads isolate the heat of soldering from the diode itself, it is not necessary

to use a heat sink. Turn the scope ON and let it warm up. Adjust it

to display a 60 Volt (peak to peak) 60 Hz signal. Set the vertical input (Y) coupling to DC.

Connect the scope ground lead toTP2, and the

input probe to Connect the 808 Power Supply plug to a power

outlet. Turn the power switch ON. The waveform displayed on the scope should look like Fig. 45. Both halves of the ac cycle are now being rectified. Refer to Fig. 46.

rectifies the current from one half of the secondary winding, and diode D2 rectifies the current from the other half of the winding. Since the diode cathodes are connected together, both their waveforms are joined together to produce a composite waveform. This composite waveform is composed of two sets of positive voltage half cycles. One set is from Dl ,and the other set, which is 180 degrees out of phase with the first set, is from This is called full-wave rectification.

Turn the 808 Power switch OFF and disconnect the power plug from the outlet. Disconnect the scope common lead and input probe. Leave diode D2 and the red wire in place.

This completes the Full-Wave Center-Tapped

I--

r---------

RECTIFICATION, POSITIVE OUTPUT

NO CURRENT FLOW

CURRENT FLOW

NO CURRENT FLOW

CENTER-TAPPED RECTIFIER CIRCUIT

Rectifier Test. Have your instructor initial your Progress Guide.

FIG. 46

Page 26

bridge rectifiers are used in a wide range of pow-

rectifier circuits are among the most effi-

cient and cost effective for many applications.

Refer to Fig. 47 for the following steps.

Be sure the 808 power plug is Not connected to a power outlet.

Mount diodes

D6, D7 and D8 on the PCB Be sure the banded ends of the diodes are oriented the same as the diode outlines that are silk screened on the PCB. Using a heat sink, solder each diode lead to the

and cut off any

excess lead length.

BRIDGE RECTIFIER EXPERIENCE

the voltage waveform produced by a

Bridge Rectifier circuit.

Equipment: Oscilloscope

1. Be sure the 808 power plug is Not connected to a power outlet.

Refer to Fig. 47 for steps 3 through 6.

Solder a 1.5

(brown-green-red)

Watt re-

sistor toTP7 and

Cut the leads off close to the test points. This resistor is for testing purposes and will be left in place until the 5 Volt reg-

ulator is

Adjust the scope to display a 30 Volt (peak to peak) 60

signal. Set the vertical (Y) input

coupling to DC.

Connect the scope ground lead to TP7 and the input probe to

Plug the 808 Power Supply plug into an outlet. Turn the Power Switch ON. Observe the waveform displayed on the scope.

should look like

Fig. 45. Both the

and

the

Bridge produce the same wave-

form. Figure 48 illustrates current flow in a

Wave Bridge Rectifier circuit. Turn the 808 Power switch Off and disconnect

the power plug from the outlet. Disconnect the

scope ground lead and input probe from the test

points.

This completes the

Bridge Rectifier Test. Have your instructor initial your progress guide.

FIG. 47

RECTIFIER

FIG. 48

Page 27

CENTER-TAPPED

BRIDGE RECTIFIERS

DISCUSSION As mentioned before, the center-tapped full-wave bridge

rectifier circuit combines features of both the center-tapped full-wave and the full-wave bridge rectifier circuits. It has two equal voltage outputs of opposing polarity as referred to the transformer secondary center tap. Figures 49A and 49B are schematics of the same rectifier circuit. Figure 49A is drawn to illustrate that a center-tapped full-wave bridge rectifier is made by connecting two center-tapped full-wave rectifiers to a common center tapped transformer secondary winding. Figure 49B shows the same circuit, drawn differently to illustrate that a center-tapped full-wave bridge rectifier can also be considered to be a full-wave bridge rectifier with a added center-tap on the transformer winding.

CONSTRUCTION Refer to Fig. 50 tor the following steps.

Be sure the 808 power plug is not connected to

a power outlet.

Mount diodes D3 and D4 to the PCB. Be sure the banded ends of the diodes are oriented the same as the diode outlines that are silk screened on the PCB. Using a heat sink, solder each diode

lead to the PCB, and cut off any excess lead

3. Mount resistor Rl2,

Ohm

red),

Watt, on the PCB. Solder the resistor

leads to the PCB and cut off any excess length.

49A

CENTER-TAPPED FULL-WAVE BRIDGE RECTIFIER

EXPERIENCE

Purpose: To observe the voltages and waveforms pro- duced by a Full-Wave Center-Tapped Bridge Rectifier

Circuit

Equipment: Oscilloscope Refer to Fig. 50 for the following steps.

Be sure the 808 power plug is

a power outlet.

Cut a

length of green 22 gauge wire, and

strip 6mm of insulation from each end.

Solder one end of the green wire toTP6, and the other end

Because these are temporary connections for testing purposes, it is not necessary to make mechanical connections.

4. Adjust the scope to display a 60 Volt (peak to

peak) 60 Hz signal. Set the vertical (Y) input

coupling to DC.

5. Connect the scope ground lead to TP7 and the

input probe to

6. Connect the 808 Power Supply plug to a power the Power Switch

waveform displayed on the scope should look like Fig. 45. This is the same waveform being produced by the same circuitry as in the Full-Wave

Rectifier Test that you did earlier.

7. Move the scope input probe

The wave-

form displayed on the scope now should look like

PROBE

49B

FIG. 50

Page 28

FULL WAVE RECTIFICATION, NEGATIVE OUTPUT

CENTER-TAPPED

BRIDGE RECTIFIER

Fig. 51. Diodes D3 and

along with the tapped secondary winding that also is connected to diodes Dl and D2, form a Full-Wave Tapped Rectifier the output of which is negative

in respect to the transformer center-tap. These

two complimentary Full-Wave Center-Tapped

Rectifiers, sharing the same transformer winding, can also be correctly called a Center-Tapped

Bridge Rectifier. Figure 52 shows the

current flow in this type of

transformer primary winding and core symbol have been omitted so that the current flow in the rest of

can be shown clearly, but apart from that, it

is the same as Figs. 49A and 49B.

8. Turn the power switch Off and disconnect the power plug from the outlet. Disconnect the scope

leads.

9. Unsolder and remove the green wire running from TP6 to

Leave the red wire running

from

to TP17 and the diode connected to

TP3 and

in place, as you will be using them

later in another test.

-10

This completes the CENTER-TAPPED FULL WAVE BRIDGE RECTIFIER EXPERIENCE.

Have your instructor initial your Progress Guide.

FILTER SECTION DISCUSSION

In general, a filter is an electronic device used to pass a certain frequency or band of frequencies while rejecting or blocking another frequency or band of frequencies.

There are four types of filters commonly used in electronics:

LOW PASS

HIGH PASS A LOW PASS filter will pass all frequencies from DC to a cutoff frequency. All frequencies above this cutoff are attenuated. DC has a frequency of zero Hz; it is a straight line on an oscilloscope.

A HIGH PASS filter will pass all frequencies above a cutoff frequency, and attenuate all frequencies below that cutoff frequency.

filter will pass a band or group of frequen-

cies, and attenuate all frequencies outside that band. A

filter will attenuate a particular band of fre-

quencies and will pass all other frequencies. To remove the ripple from the output of the rectifier circuit,

most power supplies use a resistance/capacitance filter

(also called a

filter) of the low pass type.The resistance

part of the

filters in most DC power supplies is provided

by the resistance of the diode

and the power trans-

former secondary winding, along with the reactance of the

power transformer. The term reactance applies to devices

operating on alternating current and varying (pulsating)

output of a rectifier circuit is an example

of pulsating direct current. The resistance and reactance in a

filter used in a DC power supply serves to limit the peak current flowing through the rectifier diodes to a value that the particular diodes being used can handle safely. The

part of the

filter does not directly enter into the filter’s effectiveness.

Figure 53 shows part of the block diagram and schematic

of the 808 Power Supply, with the capacitive filters high-

lighted. Notice that

and

are not highlighted.

These components appear to be

low pass filters, but

are not. the resistors

and

are current sensing resistors used in the overcurrent detectors of the variable positive and negative power supplies. If

and

were not

in the circuit, capacitors C7 and C8 would not be

is due to the characteristics of the integrated circuit voltage regulators Ul and U2, And will be discussed in the External Control and Protection Circuitry Section. Capacitors C4,

and C6 are also required because of other characteristics of the voltage regulators. This will be explained later in the section on voltage regulators.

CAPACITIVE FILTERS

DISCUSSION

NO half-wave rectifier circuits are used in the

experience included tests using a half-wave recti-

fier because, when done along with tests using a full wave

rectifier, they will help you to understand the operation of

capacitive filters.

Figure

shows the circuit you built earlier for the

wave rectifier test. The voltage waveform across resistor

Page 29

1 is what you saw in step 7 (Fig. 42). If we could connect

the scope so that it would display the current flowing through

1, we would see that current waveform is the same as the voltage waveform. We can say that the current flowing through a resistor is in phase with the voltage across the resistor, and is proportional to this voltage. Ohms Law expresses this proportionality in the formula I

E/R or, current

voltage/resistance.

This direct correspondence of current and voltage are not true with other components such as

can display the waveform and magnitude of the current passing through a capacitor by using the test set up shown schematically in Fig.

voltage developed across the test resistor is proportional to the current flowing through it. As long as the resistance value of the test resistor is small compared to the resistances in the circuit being tested, the measurement error because of the added resistance will be small as

high sensitivity of the oscilloscope allows the current sensing test resistor to have a small resistance value.

FIG. 53

VOLTAGE

ACROSS RESISTOR

x 1.414

(FORWARD VOLTAGE DROP

ACROSS

29.2

0195 AMPERES OR

FIG. 54

PROBE CONNECTION TO MEASURE VOLTAGE ACROSS

PROBE CONNECTION TO

10 OHMS

SCOPE

Page 30

CAPACITIVE FILTER EXPERIENCE

Purpose: To obsetve the current through and the voltage across a capacitor when it is connected to a half wave

circuit.

Equipment: Oscilloscope

Clip Lead

1000

Capacitor

Test Resistor

Refer to Fig. 56 for the following steps.

Be sure the 808 power plug is

a power outlet.

2. Unsolder from TP3 the anode lead of the diode that was installed

and TP8 during

the Full-Wave Center-Tapped Rectifier Test.

Bend the anode lead so that is not touchingTP3

or any of the other parts or the PCB.

Solder the positive lead of a 1000

35 Volt ca-

pacitor toTP17. Make sure that the red wire from

TP8 remains soldered to TP17.

NOTE: The capacitors supplied in your 808 kit ail are

of the electrolytic type, and have both leads coming out of one end of the body of the capacitor. On the side of the capacitor there will be one or more minus signs

lead that is closest to these minus

the negative lead of the capacitor; the other lead is the positive lead. Also, the capacitors are with the positive leads longer than the negative leads as a further means of determining polarity.

It is important to observe polarity when using electrolytic capacitors. Failure to do so may result in damage to the capacitor and other components.

4. Solder the positive lead of a 10

50 Volt ca-

pacitor to the positive lead of the 1000

capac-

itor that you soldered to TP17 in step 3. Solder

one of the leads of the 10 Ohm

black)

Watt test resistor

other lead

of this 10 Ohm resistor and the negative leads of

the two capacitors are not connected to anything

at this time.

5. Adjust the scope to display a 30 Volt (peak) 60 Hz signal. Set the

input coupling to

6. Connect the scope ground lead toTP7, and the scope input probe to TP17.

7. Connect the 808 Power Supply plug to a power

the Power Switch

scope display should look like Fig. 57. You’ve seen this waveform before, its the output of a half wave rectifier.

8. Using a clip lead, connect the negative lead of the 10

test capacitor to the free lead of the 10

Ohm test

scope should now display the waveform shown in Flg. 58. Adjust the sweep and trigger controls as necessary to make the scope display closely match the waveform as

shown in Fig. 58. Notice that the peak voltage is

about 30 Volts, and the minimum voltage is about 9

peak to peak ripple voltage is

the difference between these two voltages, that

is, about 21

is a very large amount of ripple. If your stereo system were powered by a supply with this much ripple, you would hear a

very loud 60 Hz tone whenever it was turned on.

9. Remove the 808 power plug from the outlet for

Page 31

FIG.

12.

this step. Resolder the anode lead of the temporary D2 diode toTP3. Do not change the test set

Plug the 808 power plug back into the outlet. The waveform on the scope should now look Fig. 59. The peak voltage is still about 30 Volts, but the minimum voltage has gone up to 18 Volts, and the peak to peak ripple has gone down to 12 Volts. This shows that the output of a full wave rectifier is more easily filtered than the output of a half wave rectifier.

Disconnect the end of the clip lead that is connected to the negative lead of the 10

test ca-

pacitor, and connect it to the negative lead of the

1000

test capacitor. Observe the scope dis- play. (You may need to readjust the scope trigger control.) Using a colored pencil, draw this waveform on Fig. 59, over the printed is the approximate peak to peak ripple voltage now?

Move the Scope probe to the

Ohm test resis-

tor lead that is connected to the 1000

capacitor negative lead by the clip lead. You will need to change the scope vertical Volts/cm control to a more sensitive setting, as the voltage developed across the 10 Ohm resistor by the current

flowing through the test capacitor is quite low. The waveform displayed on your scope should

look like the one shown in Fig. 60. Notice that

the current flows through the capacitor in short

positive pulses. These current pulses occur

when the instantaneous voltage from the rectifier

diodes exceed the the relatively constant voltage across the capacitor. It is during these pulses that

the capacitor is charged or, to say it in another way, that electrical energy is stored in the capacitor. During the longer periods between the posi- tive current pulses the capacitor discharges, or gives up electrical energy to the load resistor

1 and the 10 Ohm current sensing resistor.

We can use Ohm’s law to calculate the current flowing through the capacitor during the charging

and discharging periods. The formula I

will give us the current

if the voltage (E) is di-

vided by the resistance

Using -0.2 Volts, the

voltage developed across across the current

sensing test resistor during capacitor discharge periods, and 10 Ohms, the resistance value of

the current sensing resistor, calculate the torcurrent.

Amps. Calculate the peak capacitor current during the capacitor charging period.

Amps. Hint: the voltage is

1.7 Volts.

Disconnect the 808 power plug from the power outlet and the scope probe and ground lead from your test setup. Unsolder the two capacitors, the test resistor, the diode and the red wire that were soldered to test points on the PCB. This completes the Capacitive Filter Experience. Have your instructor initial your progress guide.

Page 32

CAPACITIVE FILTER CALCULATIONS PERCENT OF RIPPLE

This term is often used to express how “clean” or free from periodic voltage variations a power supply output is. The voltage output of a battery supplying power to a constant load, such a fixed resistor, has a percent of ripple of 0.

To calculate the percent of ripple, the following formula is used:

Ripple

x 100

average

Where:

the rms value of the peak to peak

ripple voltage

We can use

times the peak to peak ripple voltage to determine the rms ripple voltage. While this conversion is only exact for sine waveforms, it is

reasonably accurate for full-wave ripple

waveforms. V

average

the average dc voltage output of the

power supply.

The dc voltage ranges of a VOM or a DMM read the average value of a pulsating dc voltage input.

Using the above formula, calculate the percentage of ripple in the voltage waveform shown in Fig. 59. Use 24.4 Volts

for V

Hint: the peak to peak ripple voltage can be calculated from

the voltage values given in Fig.

positive peak of the

ripple voltage is 30 Volts. The negative peak of the ripple

voltage is

Volts. Both of these voltages are positive in

respect to ground. The peak to peak ripple voltage is the

difference between these two voltages, that is, 12 Volts. Write your answer here.

CAPACITANCE REQUIRED FOR A PARTICULAR APPLICATION

we were designing a power supply, ho.w would we deter-

mine the value of capacitance needed for the capacitance

filter? Lets go through the process step by step, using the

positive 0 to

Volt power supply of the 808 as an example.

Figure 61 is the schematic of this power supply.

Determine the current required from the capacitive filter.

The rated output is

Volts at 300

Bleeder resistor

1 has a resistance value of 1500 Ohms. Using Ohm’s

law, E/R), we find the current through this resistor is .OIO Amps, or 10

To calculate the current flowing through the

and

circuit, we will have to get some values from

the ELECTRICAL CHARACTERISTICS OF THE

table in

SECTION of this manual. These values are the “Reference Voltage”, which appears across

and the “Adjustment

Reference Voltage is 1.30 Volts maxi-

mum.

is a 340 Ohm resistor. Using Ohm’s law again,

the same formula as above, the current through

cal-

culates to be 3.8

Since the Adjustment Pin Current

is a relatively low 100

(or .l

we will ignore it. If we wanted to include it, it would be added to the current flowing through

Since a current of 300

is not

enough to turn on the

protection

and

there is no current flowing

Dropout Voltage

-25

25 50 75

100 125 150

TEMPERATURE

through these three components. Its as if they were not there.

Adding these three currents gives us the total current that the filter capacitor (Cl

must provide during the time periods that the rectifier is not supplying current. See Fig. 60.

Rated output current:

300.0

Bleeder

1) current:

10.0

Voltage control circuit current:

3.8

Total current: 313.8

Determine the voltage required from the capacitive filter. The rated output is 15 Volts. To this we must add the “Drop Out” voltage of the voltage regulator, and the voltage drop across the overcurrent sensing resistor Rl. The drop out voltage of a regulator is the lowest voltage across its input to output terminals that can exist with the voltage regulator still functioning as a regulator. We will get voltage from the Dropout Voltage graph, from the National Semiconductor specification sheets for the LM

graph is shown in Fig. 60A. Using a current of

500

and a temperature of 25 C, the graph indicates

the input/output differential to be about 1.8 Volts. Ohm’s

I x

indicates the voltage drop across

1 Ohm

to be

Volts.

Rated output voltage: 15.0

Volts Regulator dropout voltage:

1.8

Volts

voltage drop:

0.314 Volts

Total Voltage: 17.114 Volts

This is the minimum voltage that Cl has to maintain between the time periods the rectifier is supplying current

if the output voltage is to be maintained at 15 Volts with a current of 300

If complete specifications for the power transformer and rectifier diodes are available, the peak voltage at the bridge rectifier output can be

specifications would have to include winding resistances, turn ratios,. and core losses at different power levels for the power transformer and forward voltage drops at different current levels for the rectifier diodes.

Page 33

PEAK VOLTAGE OF 22.2 VOLTS

A less math-intensive, more empirical method would be

tions the measured peak output voltage of the rectifier

to provide resistive loads for each rectifier output, and

is 22.2 Volts. We need to maintain a voltage of at least

measure the peak D.C. voltage available to charge the

17.1 Volts (which is 77% of the peak voltage) at

times

filter capacitor with an oscilloscope. (The word

to maintain a regulated power supply output of 15 Volts

cal” relates to information gained by observation and

at 300

How big a capacitor will be needed to do

experimentation.) All the outputs need to be loaded

this?

due to the primary winding resistance and core losses of the transformer, increasing the load on one winding will decrease the voltage output of the other

windings. Figure 62 shows schematically how this

measurement would be made.The load resistor values are calculated with the formula: E/l. For the variable supplies, we use the values of 17.1 Volts and 314

that we calculated earlier. The two load resistors

have a resistance value of 54 Ohms each.The load

sistor for the fixed

Volt supply was calculated in a simi-

lar manner, and has a resistance value of 6.8 Ohms.

The input voltage to the power transformer is reduced to 95 Volts, as this is the minimum input voltage specified for the 808 Power Supply. Under these test

Through calculation and measurement, we have determined that the power transformer and rectifier are capable of providing a full wave pulsating DC voltage of 22.2 Volts at full rated current with a line input voltage of 95

have also determined that to maintain a regu-

lated plus 15 Volts at a current of 300

at the variable positive output of the 808 Power Supply, the voltage from rectifier will have to be at least 17.1 Volts at all

times. Figure 63 shows this information graphically, along with the period of time that the capacitive filter will have to supply power during each cycle of the rectifier

calculate the size of the capacitor needed, we

will be using

time constant formulas.

Page 34

TIME CONSTANT EXPERIENCE

DISCUSSION

The time constant of the discharge of a capacitor through a resistor is the time required for the voltage or current to drop to 1

of its value at the time the discharge began.The

symbol “e” is the base of the natural or Napierian logarithm.

value is 2.718. The reciprocal of e (l/e) is 0.3679.

Consider the formulas:

or;

Where:

is the voltage across the capacitor at

the end of the discharge time period,

is the voltage across the capacitor at

the beginning of the discharge period,

e is 2.718,

is the discharge time in seconds,

x C, in seconds,

is resistance in Ohms,

and C is capacitance in Farads.

is expressed in

C in

in milliseconds

the formula is a little easier to handle.

Using a 1000

capacitor and a 10

resistor,T (that

is,

is 10,000

or 10 seconds. If

is 10 Volts, and

is 10 seconds,

then

10 x 0.3679’

3.679 Volts.

Figure 64 is a graph of

versus time, using the values giv-

en above.

Calculate the values for

0.5 and 2.0. Record your

answers. Compare your answers with the values you read from Fig.

CIRCUIT TEST

Purpose: To observe the action of an actual (hardware) circuit.

Equipment:

DC Power Supply Two Clip Leads Watch With Second Hand or Digital Readout

A completed

808 or 803 Power Supply, or any power supply capable of supplying 10 Volts at approximately 25

or more may be used. Be sure the power supply power plug is Not connected to a outlet, and that the voltage control is set for minimum voltage output. Refer to Fig. 65 for the following steps.

Connect a 1000

capacitor and the (brown-black-orange) test resistor from your 808 kit to the

as shown in Fig. 65. Solder the capacitor leads to the resistor leads. Do not make a mechanical connection of the leads before soldering, as these parts will be unsoldered at the end of this experience. Be sure to

the capacitor polarity when connect-

ing the power supply and meter.

1.5

2.0

Page 35

CAPACITANCE REQUIRED FOR A

(continued)

With some understanding of

time constants, we can

continue with the capacitive filter calculations that were be- gun

power transformer and rectifier circuitry for

the positive variable power supply of the 808 are capable

of supplying a full wave pulsating DC voltage of 22.2 peak Volts at full rated current with a line input voltage of 95 Volts.

For the voltage regulator and overcurrent protection circuit-

ry to maintain an output of

Volts at a current of 300

the voltage from the rectifier will have to be at least 17.1 Volts at all times.The length of time that the capacitive filter will have to periodically supply power to maintain this minimum voltage is 7.29

for

Hz input power. Refer to

Fig. 63 to review this information. The equivalent load resistance of the fully loaded voltage regulator and overcurrent circuitry is 54 Ohms.

The formula:

can be rewritten to solve for

0123456 8 10

FIG.66

Set the test meter to read a voltage of 10 Volts DC. Connect the power supply plug to an outlet and adjust the power supply for a meter reading of 10 Volts.

Disconnect one of the clip leads from the power supply, wait 20 seconds and then read the meter.

Put a dot on the blank graph in Fig. 66 where the voltage you read from the meter and the time you waited intersect.

Reconnect the clip lead (that was disconnected

in step 4) to the power supply. Notice how rapidly the capacitor is charged to 10 Volts. This is because the resistance, or

is now only the clip

lead resistances plus the internal resistance of the power

total of these resistances

is probably less than 100 Ohms.

Repeat steps 4 and 5, using waiting periods of

and 1 seconds. Place a dot in the appropriate place on the graph in Fig. 66 each time you repeat steps 4 and 5.

Connect the dots on the graph with a pencil line, using a

curve if possible. Does the graph

you just drew look like the one in Fig.

Be-

cause of the difficulty in reading the meter

when the voltage is changing rapidly, the dots you place near the left edge of the graph will be the least accurate. Also, the capacitance tolerances of electrolytic capacitors are large,

could affect the vertical location of the curve you generated on the graph, but not necessarily its slope.

Remove the power supply plug from the outlet. Disconnect the clip leads and the meter test leads Unsolder the capacitor and resistor leads.

This completes the

Time Constant Experi-

ence- Have your instructor initial your progress

guide.

x In

In is the natural log of, in this case,

It can be found by using a table of natural logarithms or a scientific calculator.

By expressing

in milliseconds and

C will be

in microfarads. Plugging in these values and solving for C, we get:

7.29

0.054 x In

this the value that should be used for the capacitive filter

for the positive variable supply in the

Because of one factor that we were not able to evaluate in our empirical design approach, the answer to that question has to be “no”.

Look at Fig. 60 again. This figure shows the voltage drop across a current sensing resistor connected between the rectifier and the capacitive filter. Because of the winding resistance and core losses of the power transformer, and losses in the rectifier circuitry, the spikes of current that oc-

cur when the capacitive filter is charging will reduce the

voltage available at the rectifier output.

Figure 67 shows the full wave rectifier output for the

tive variable supply of the

solid line shows the voltage waveform with a resistive load and no capacitive filter. The dashed line shows the voltage waveform when a capacitive filter is added. Notice how the voltage peaks are reduced with the addition of the filter.

To determine the values for the capacitive filters empirical-

ly, trial values for the capacitors must be connected and the

Page 36

power supply outputs evaluated under load until

capacitance values are found. Most engineering compa-

nies use a mathematical approach for the initial design

work, and then verify the design by building and testing a

prototype. Developments in computers and software allow tests using computer simulated prototypes, with savings in engineering time and expense.

A value of 1000

was selected for the capacitive filter of

the positive variable supply in the

808. The se-

lection of this value was based on further calculations.

CONSTRUCTION

Refer to Fig. 68 for the following steps.

Be sure the 808 power

a power outlet.

2. Mount diode D2 on the

Be sure that the banded end of the diode is oriented the same as the diode outline that is silkscreened on Using a heat sink as shown in Fig. 40, solder the diode leads to the PCB. Cut off any excess lead length.

Mount the following capacitors on the PCB, ing sure that the negative

leads are inserted

into the holes marked

-A. Cl,

Solder all the capacitor leads to the PCB and cut off any excess lead lengths.

5. Mount resistors RI and

on the PCB. Both

sistors are 1 Ohm

1 Watt. Solder the resistor leads to the PCB and cut off any excess lead length.

NOTE: The following components are being mounted on the PCB at this time to serve as bleeder resistors for capacitors Cl and C2 until the variable voltage

are

test resistor which was connected to TP7 and TP9 earlier serves as a bleeder for capacitor

until regulator U3 is installed.

Mount and solder resistors

and

(red-red-red),

Watt, on the PCB. Cut off the excess lead length. Save one of these leads for the next step.

Bend the piece of wire saved from the last step into a “U” shape, and use it for Jumper

insert this jumper wire from the component side of the PCB. Solder and cut off any excess lead length.

Mount the

diodes

Dll and

D12 on the PCB. These diodes are smaller than the rectifier diodes installed earlier. Be sure that the banded ends of the diodes are oriented as shown on the diode outlines printed on the PCB. Using a heat sink, as shown in Fig. 40, solder the diodes to the PCB. Cut off any excess lead

PCB TEST

that the PCB

been assembled

up to this point.

Equipment: VOM or

Watch with second hand or digital readout. (Counting out loud “One thousand one, one thousand two . . .

one thousand thirteen” etc.,

would be accurate enough for these tests.)

Review rule 9 of BUILDING YOUR POWER

SUPPLY BREADBOARD that appears earlier in

this manual.

With the 808 power plug connected to a power

outlet, turn the 808 power switch ON, wait 1

and turn it

all the diodes and pacitors C7 and C8 with your finger to tell if any of them are warm or hot. Bigger components take longer to heat up if something is wrong. By checking smaller components after a short power ON period, even if something is wrong the components probably will not be damaged, and will work satisfactorily after the fault is wrrected.

If any of the wmponents called out above are warm, something is wrong. Check the PCB carefully, and consult with your instructor if necessary.

Repeat step 2, leaving the power ON for onds. Recheck all the diodes, and capacitors C7 and C8 to tell if they are warm. In addition, touch

capacitors Cl, C2 and C3 to tell if they are getting warm.

Repeat step 2 again, leaving the power ON for

this time. Recheck all diodes and

pacitors for heating.

If none of the diodes or capacitors heated up in steps two through four, power up the 808 again and measure the dc voltage between the pairs of test points listed below. For an input line voltage of from 105 to 125 Volts, the voltages you measure should be within the ranges listed below.

A. TP7 and TPQ (TPQ should be positive),

to 16 Volts dc.

B. TP7 and

should be

tive), 25 to 31 Volts dc.

C. TP7 and TP12 (TP12 should be

tive), 25 to 31 Volts dc.

Turn OFF the power switch of the 808 Power

Supply, and remove its power plug from the

the FILTER SECTION. Have

your instructor initial your progress guide.

Page 37

is adjustable from -1.2 to -37 Volts. It is used in the negative variable supply of the

specifications for

the

are shown in Fig. 70.

The 808 uses three voltage regulators as follows. The

and

are interchangeable devices for the

VDC supply.

(Ul

for the VDC supply

(U2) for the

VDC supply

(or

(U3) for the

5 VDC supply

The

is a nonadjustable three terminal device, and

is used to regulate the

5 VDC supply so the output volt-

age is constant under varying load and line

is an integrated circuit, and all of the circuitry to do

it’s job is contained within the

Current limiting is also in-

cluded in the design of the

to limit the output current

to safe value. The

also has internal thermal shut-

down protection circuitry to prevent it from overheating. If

the internal power dissipation becomes too great, the

will shutdown to prevent damage to itself. Figure

shows the specifications for the

The

is a three terminal adjustable positive voltage

regulator. Refer to Fig. 69. Its output is adjustable from

37 Volts. As used in the

its output is guaranteed to be adjustable upward to a minimum of a regulated 15 Volts under worst case conditions, that is, 300

output current and low input line voltage (95 Volts AC). The output voltage is adjustable down to 0 Volts. This is made possible by the design of the external control circuitry. This will be discussed in the EXTERNAL CONTROL AND PROTECTION CIRCUITRY section.

The three voltage regulators will be installed and tested one at a time. Some of the associated circuit components have

already been installed so that tests could be performed, and some of the voltage control components will be in- stalled

time so that the regulators can be tested.

The

is an integrated circuit

All of the circuitry

for the

to do it’s job, with the exception of the voltage

divider

that controls the the output voltage, is con-

tained within the

Current limiting is also included in the

design of the

to limit the output current to a safe value.

The

also has internal thermal shutdown circuitry to

prevent the

from overheating. When the regulator reaches its maximum safe operating temperature, the regulator will shutdown to prevent damage to itself by excessive

heating. All protection circuitry remains fully functional even if the adjustment terminal becomes disconnected.

Refer to Fig. 72 for the following steps.

sure the 808 power plug is not connected to

a power outlet.

2. Mount resistor

340 Ohm

black-black)

Watt

on the PCB. Solder the

leads to the PCB and cut off any excess length.

3. Solder the leads of a 3.9 red)

Watt test resistor to test pointsTP13 and

resistor temporarily takes the place of

The LM337 is similar to the

except that its output

variable resistor

for test purposes.

Absolute Maximum Ratings

Input-Output

internally

Input

Voltage

4ov

Operating

Temperature

to l

Storm

SPECIFICATIONS

Load

Storage

SPECIFICATIONS

100% All

Preconditioning

Limit

100% Ail

Electrical Characteristics (Note 1)

Characteristics

MAX

CONDITIONS

0.1 003 50

0.2

1.20 1.25

0.02

0.3

0.5 0.8

5V 5V

- 5

25°C. 20 ms

I 5

225

250

-1250

1300

007

100 50 S

0.2 5 IJA

130

0.05 0.02 0.07 WV

50 20 70

03 15

5 3.5

2 5V

40V.

40V

2 5V

40V

40V.

VOUT

40V

hdLJ$,J

40V

5 5V

* 40V

K J”d T PJchJtfJ

10 Hz

23 3 2.3 3

RJUO

1000

.fuf!ctton

CJsJ

J tow

PERMISSION

CORPORATION

PERMISSION Of NATIONAL SEhflCOM?UCTOff

Page 38

Repeat step 2 again, this time leaving the power ON for

If none of the components heated up in the previ-

ous

power up the 808 again. Measure the

dc voltage between test points TP7 and TP17.

TP17 should be positive, and the voltage should

be between 12.7 and 15.8

reason that a range of voltages is given is that the tolerances of a number of components can affect the regula-

tor output voltage. If the voltage is not in this

range, check resistor

and the 3.9

resistor installed temporarily between TP13 and TP14. Make sure they are the correct resistors for these locations. Consult with your instructor

if necessary.

Turn OFF the 808 power switch and remove the

power plug from the power outlet.

Mount 10

capacitor C4 on the PCB, making

4 sure that the negative lead is inserted in the hole marked

Solder the capacitor leads to the PCB

and cut off any excess length. Locate the positive variable voltage regulator, U 1

one of the small heat sinks, a 3 x 8mm machine screw, a 3mm split lock washer and a 3mm hex nut.

Bend the three leads of the

regulator as

shown in Fig. 73. A long nose pliers is

tool

to use for this.

Refer to Fig. 74. Mount the

regulator

and heat sink on the

using the hardware

called out in step 5.

recommends the

use of heat sink compound on the surfaces of

the voltage regulators and heat sinks where they contact each other.

Before tightening the machine screw and nut that holds the heat sink and regulator to the PCB, tate the heat sink on the machine screw so that its cooling fins are oriented as shown in Fig. 72. Then tighten the machine screw and nut.

Solder the regulator leads to the PCB, using a small alligator clip heat sink on each lead between the plastic regulator package and the top surface of the PCB. Cut off any excess lead

length.

Refer to Fig. 72 for the following steps.

1. Be sure the 808 power plug is not connected to a power outlet.

2. Mount resistor

340 Ohm

Watt 1%, on the PCB. Solder the

leads to the PCB and cut off any excess length.

3. Solder the leads of a 3.9 red)

Watt test resistor to test pointsTP15 and

resistor temporarily takes the place of

variable resistor

for test purposes.

15 VOLT REGULATOR TEST

1. Connect the 808 power plug to a power outlet.

2. Turn the 808 power switch ON, wait 1 second and turn it

the components that were

installed in the construction steps that were just

completed. If any of these components are warm, there is something wrong. Check the PCB

and components carefully, and consult with your instructor if necessary.

4. Mount 10

capacitor C5 on the PCB, making sure that the negative lead is inserted in the hole marked

Solder the capacitor leads to the PCB

and cut off any excess length.

5. Locate the negative variable voltage regulator (U2,

one of

small heat sinks, a 3 x 8mm machine screw, a 3mm split lock washer and a 3mm hex nut.

3. Repeat step 2, leaving the power ON for 5 onds this time.

6. Bend the three leads of the LM337 regulator as shown in Fig. 73. A long nose pliers is a good tool to use for this.

Refer to Fig 74. Mount the LM337 regulator and

heat sink on the PCB, using the hardware called

out in step 5.

recommends the use of

Absolute Maximum Ratings

to to

SPECIFICATIONS

Storage

to +150°C

Electrical Characteristics

15 15

5.2

2.5

4.6

25v

25.T

5.2 50

0.5

0.0

CORPORATION

FIG. 71

FIG. 72

Page 39

SCREW

COMPOUND

3mm SPLIT

/LOCK WASHER

NUT

FIG. 74

heat sink compound on the surfaces of the voltage regulators and heat sinks where they contact each other.

Before tightening the machine screw and nut that holds the heat sink and regulator to the rotate the heat sink on the machine screw so that its cooling fins are oriented as shown in Fig. 72. Then tighten the machine screw and nut.

Solder the regulator leads to the PCB, using a

small alligator clip heat sink on each lead between the plastic regulator package and the top surface of the

Cut off any excess lead

length.

VOLT REGULATOR TEST

Connect the

power plug to a power outlet.

Turn the 808 power switch ON, wait

second

and turn it

the components that were installed in the construction steps that were just completed. If any of these components are

warm, there is something wrong. Check the PCB

and components carefully, and consult with your

instructor if necessary.

Repeat step 2, leaving the power ON for seconds this time.

Repeat step 2 again, this time leaving the power ON for 15 seconds.

If none of the components heated up in the previous steps, power up the

again.

Measure the dc voltage between test pointsTP7 and TP18.

should be negative, and the

voltage should be between 12.7 and 15.8 Volts.

The reason that a range of voltages is given is

that the tolerances of a number of components can affect the regulator output voltage. If the voltage is not in this range, check resistor

and

the 3.9

resistor installed temporarily betweenTP15 and TPl6. Make sure they are the correct resistors for these locations. Consult with

your instructor if necessary. Turn OFF the 808 power switch and remove the

power plug from the power outlet.

CONSTRUCTION Refer to Fig. 72 for the following steps.

1. Be sure the 808 power plug is not connected to a power outlet.

2. Mount 10

capacitor C6 on the PCB, making

sure that the negative lead is inserted in the hole marked

Solder the capacitor leads to the PCB

and cut off any excess length.

3. Locate the positive fixed voltage regulator the large heat sink, two 3.5 x

machine screws, two

split lock washers

Page 40

and two

nuts.

Refer to Fig.

Mount the

regulator and

heat sink on the PCB, using the hardware called

out in step 3.

the use of heat sink compound on the surfaces of the voltage regulators and heat sinks where they

contact each other. Be sure that the larger machine screws

diameter) are

fasten the

and heat sink to the PCB. If you use the smaller 3mm diameter screws for this purpose, it is possible for the heat sink to short

to the

leads.

Solder the regulator leads to

PCB. Cut off any

excess lead length.

VOLT

TEST

th8 808 power plug to a power outlet.

Turn th8 808 power switch ON, wait 1

and turn it

the components that were installed in the construction steps that were just completed. If any of these components are warm, there is

wrong. Check the PCB

and components carefully, and consult with your instructor if necessary.

step 2, leaving

power ON for 5

this time.

step 2 again, this time leaving the power

ON for 15

If none of the components heated up in the

previous steps, power up the

again.

Measure the dc voltage between* test points

9 and

should

positive, and the

voltage should

between 4.6 and 5.4 This range of voltages allows for the specified output voltage tolerance (4.7 to 5.3 Volts), plus approximately 2

measurement error. voltage is not in this range, check your work carefully, and consult with your instructor if

Turn OFF the 808 power switch and remove the power plug from the power outlet.

Page 41

Figure 76 is a partial block diagram and schematic of the 808 Power Supply, showing the voltage regulators and associated circuitry.

A power supply requires regulation to maintain a constant voltage level with variations in load, AC line voltage, and environmental conditions. Voltage regulators provide the regulation which will enable the supply to maintain a constant output voltage under these changing conditions. The

808 is voltage regulated triple power supply. The following are the definitions of load, and line regulation: LOAD REGULATION: Load regulation is a supply’s ability

to maintain a constant voltage or current output level with changes in a resistive load.

increases.This is because of the internal resistance of the power supply. When the load resistance decreases, the

load current increases, causing a proportional increase in the voltage drop across the internal resistance of the power supply. This results in a decrease in the voltage at the

power supply output. Refer to Fig. 78.

LINE

Line regulation is a supply’s ability to

maintain a constant voltage or current output level with changes in the input AC line voltage.

Figure 77 shows four voltage graphs plotted with a

common X axis, representing the passage of time.The top

graph is of AC line voltage. It appears that some other large

loads on this line are being switched on and off, resulting

in variations of the AC line voltage.

If the value of FULL LOAD voltage is equal to the value of NO LOAD voltage, the LOAD VOLTAGE REGULATION

Two power supplies are connected to this power line. One

is 0%, which is the ideal

value means the power

is unregulated, the other is a regulated power supply. Both

supply is a true voltage source, where the output voltage

of these power supplies have nominal output ratings of

is independent of the current drawn from the supply.

Volts DC at 300

Both power supplies are driving

identical loads. These loads periodically change between

In an UNREGULATED power supply the output voltage

no load (infinite resistance),

load (100 Ohms resistance)

decreases as the amount current drawn from the supply

REGULATOR

. ,

Page 42

and full load (50 Ohms

changing condition

following formula:

of these loads is shown by the second graph.

Figure 78 is the equivalent circuits of the unregulated and

regulation

(no load) (full load) x

the regulated power supplies. The boxes labeled INPUT

(full load)

POWER CONDITIONING represent the input circuitry,

At the nominal line input voltage of 115 Volts.

power transformer, rectifiers and input filters. The resistors labeled

represent all the losses and resistances in the

(no load) occurs at the point on the Unregulated Power

components mentioned above.

Supply Output graph that is marked with the letter A.

(full load) occurs at the point marked with the letter

In the equivalent circuit of the regulated power supply, the

variable resistor labeled

represents the Darlington

transistor in the voltage regulator that controls the current

that flows through the regulator to the load resistors. The

load resistors are shown with push-button switches,

ganged together between the two loads. With this setup,

the load conditions shown in the second graph could be

duplicated by manipulating the switches.

Calculate the

load voltage regulation for this power

supply and write your answer in the space provided.

The bottom graph in Fig. 77, shows the regulated power supply output

little “glitches’ appearing on this graph indicate that the voltage regulator cannot instantly compensate for input voltage and load changes. More about that later.

How voltage regulators actually work will be discussed in

more detail a little later. Right now we just want to see the

differences in the output voltages of unregulated and

regulated power supplies with varying line input voltages

and loads. The third graph from the top shows the output voltage of the

unregulated power supply. What is the worst case voltage

variation in Volts?

Most real life regulators won’t provide the zero percent regulation shown on the graph, but the voltage regulators in your

808 Power Supply will provide considerably better than 1% combined line and load regulation.

Figure 79 shows the schematic diagram of the voltage regulator. Transistors, resistors, Zener diodes and

Under what conditions is the output voltage the highest?

capacitors are formed in a small piece of silicon, often called a

help understand how a voltage regulator

Input line.

Load.

functions, we will be using a functional schematic, which

Under what conditions is the output voltage the lowest?

is shown in Fig. 80.

Input line.

Load.

The operation of all three of the

voltage regulators used

in the

808 Power Supply is based on the same

To calculate the

load voltage regulation, use the

general principles. The following discussion applies to the

INPUT

LINE 115

VOLTAGE

FULL LOAD

(50 OHMS)

LOAD

(100 OHMS)

NO LOAD

23 21

UNREGULATED

POWER SUPPLY

OUTPUT (VOLTS) 17

REGULATED

POWER SUPPLY 15

OUTPUT (VOLTS)

FIG. 77

Page 43

the

and the LM337. The LM337 is a

negative

is, its input and output voltages are negative in respect to ground. This results in different polarities inside the

but it operates according to the

same principles as the

and

POWER SUPPLY

PERMISSION OF NATIONAL SEMICONDUCTOR

INPUT

TRANSISTOR

OUTPUT

The two overlapping circles and the arrow in the upper left hand corner of the schematic form the symbol for a current source. A current source will pass a constant current, in this case

despite variations of the voltage appearing across its terminals. This current source provides a constant current for the Volt Zener diode that supplies the reference voltage for the regulator.

Resistors

and

form a voltage divider.

has three

times the resistance in Ohms of

so when the voltage

at the regulator output terminal is

Volts, the voltage at the

junction of

and

is 1.25

operational amplifier (op amp) compares this portion of output voltage of the regulator to the 1.25 Volt reference voltage. As long as the two input terminals of the op amp are at the same voltage, there is very little current flowing either into or out of the op amp output terminal.

The adjustable voltage regulators are a little different.

and

are external to the

will be discussed later in the EXTERNAL CONTROL AND PROTECTION CIRCUITRY section.

If we increase the voltage regulator load by connecting a resistor between the regulator output and ground, the additional current flowing through the regulator will cause the output voltage to drop below 5

voltage at the op amp input terminal marked with the minus sign drops as well. The op amp responds to this input change by

moving its output in a positive direction, causing an increase in the base current of the Darlington transistor

shown at the right side of Fig. The Darlington transistor is named after the person who

invented this particular way of connecting two transistors and a resistor together to form the equivalent of one

transistor. A Darlington transistor requires very little base

input current to control the collector output current, and can respond to rapid changes of the base current.

A transistor can be thought of as a valve that controls the flow of electrons, that is, the current in a circuit. The “valve handle” of the transistor is its base. The amount of current flowing through the transistor from emitter to collector is controlled by a much smaller current flowing from the emitter to the base.

Another way of looking at a transistor is to consider it as a variable resistor, where an increase in the base current causes a decrease in the resistance.

At this point, the output of the voltage regulator is below

Volts because an additional load resistor was connected between its output terminal and ground. This lowered output voltage caused the voltage at the inverting input of

the op amp to become lower as

op amp responds

to this input voltage change by by moving its output in a

positive direction, increasing the base current of the Darlington transistor.

The resulting decrease of resistance between the Darlington transistor’s emitter and collector causes an increase in the current flowing through the voltage regulator and the load resistors. In accordance with Ohm’s law, (voltage

current x resistance), the output voltage of

the voltage regulator heads back up to 5 Volts. Figure 81 shows the effects of connecting a load resistor

to the output of a voltage regulator. The conditions shown in the right portion of the figure occur after the load resistor

FIG. 80

Page 44

is connected, but before the voltage regulator. is able to

Equipment:

compensate for this change in load resistance.

takes much longer to describe the operation of a voltage

regulator than it takes for the regulator to

some time delay from the instant that a load change or input voltage change takes place and causes the output voltage to change until the voltage regulator is able to

compensate and restore the correct output voltage. This

time delay occurs mostly in the op amp and Darlington

transistor circuitry. Figure 82 is from the specification sheets, and illustrates the time required for the

regulator to respond to a load change. Notice

that it is a very short time, about 1 micro second. The output filter capacitor for the fixed supply, C6, reduces

the amplitude of these voltage spikes. C6 has a capacitance of 10

It does not need to have a large capacitance like C3, the input filter capacitor, because of the short periods of time it must provide or absorb electrical

energy to keep the output voltage constant. Look again at Fig.

time that the input filter capacitor must provide electrical energy is about 6 milliseconds, which is 6000 times as long as 1 microsecond.

The circuitry symbolized by the rectangle labeled

PROTECTION CIRCUITRY can divert the op amp output

current away from the base of the Darlington transistor.

Normally, when the op amp output moves in the positive direction, we want to increase the current flowing through the voltage regulator and load resistor. But when this current reaches the maximum value the regulator can safely handle, we don’t want it to increase any more.

The voltage across resistor

is directly proportional to the current flowing through it. (Ohm’s law again, voltage current x resistance. As the output current of the regulator increases, the voltage across

increases as well. When this voltage reaches a level that indicates the maximum safe current is flowing, the protection circuitry begins to divert current away from the Darlington transistor base.

OVERCURRENT PROTECTION EXPERIENCE

Clip Lead

Be sure that the 808 power plug is NOT

connected to a power outlet. Refer to Fig. 83 for the following steps.

Remove the 1.5

test resistor which is

soldered toTP7 and Connect the positive meter lead toTP8 and the

negative meter lead

meter will read

the voltage across the current sensing resistor

Set the meter range selector to read a DC

voltage of 2.5 Volts. Connect the 808 power plug to a power outlet. Turn the 808 power switch ON. While observing

the meter, connect the clip lead from TP7 to TP17. This is a short circuit across the positive variable regulator,

This represents a

heavy overload for the power transformer and

current sensing resistor

. Read the meter and

quickly remove the clip lead. Write down the meter reading here.

Volts

Using Ohm’s law, calculate how much current is flowing through the regulator.

Amps. Notice that

when using a 1 Ohm current sensing resistor, The voltage across the resistor in Volts is the same as the current flowing through the resistor in Amps. The same correspondence occurs when voltage is in millivolts, the current is then in milliamps. How does the current you measured compare to the value given on the

National Semiconductor Electrical Characteris-

tics specification sheet for the Turn OFF the 808 power switch and remove the

power plug from the power outlet. Disconnect the

clip lead and the meter test leads.

Purpose: To observe the operation of the internal

Just how hot a voltage regulator becomes when it is

limiting function of a voltage

operating depends on a number of variables. The input

POSITIVE

FROM

FILTER

POSITIVE

INPUT FROM

CURRENT

WILL INCREASE

DARLINGTON TRANSISTOR

RESISTANCE WILL DECREASE

IS STABLE

LOAD RESISTOR

NEGATIVE

FROM

FILTER

LOAD RESISTOR

NEGATIVE INPUT

FROM FILTER

FIG. 81

Page 45

LOAD TRANSIENT RESPONSE

FIG.

voltage, along with the output current and voltage, affect the amount of power that the regulator has to dissipate.The size of the heat sink and the amount air flow around it affects how much the temperature of the regulator must rise to dissipate this power.

a voltage regulator gets too hot, it will be damaged, even

though the current flowing through it is within safe limits. The protection circuitry on the voltage regulator chip

includes a temperature sensor. When the chip temperature reaches its maximum safe limit, the protection circuitry begins to divert some of the op amp output current from the Darlington transistor base, just as it did when the regulator output current reached its maximum safe value, as we discussed earlier.

OVER TEMPERATURE PROTECTION

DISCUSSION

To force the

voltage regulator into its over

temperature protection mode without risking damage to

other power supply components, the regulator will be operated without a heat sink attached while supplying approximately the maximum rated current of the power supply. The 50 Ohm 5 Watt test resistor that will be used for a load draws between 254 and 316

with the

regulator output voltage between 12.7 and

Volts. The

3.9

test resistor that was installed in place of variable

resistor

sets the regulator output within this range. If you wish to, refer back to step 5 of the VOLT TEST

TEMPERATURE PROTECTION EXPERIENCE

Purpose: To observe a voltage regulator and its output

when if is in the over temperature protection mode.

Equipment: Oscilloscope

or 50 Ohm 5 Watt Test Resistor Drinking Straw

1. Be sure that the 808 power plug is NOT connected to a power outlet.

Refer to Fig. 84 for the following steps.

Temporarily remove the mounting hardware and

heat sink for the

regulator from the

Solder the 50 Ohm test resistor leads toTP7 and TPl7.

Connect the ground lead of the scope and the negative lead of the DVM or the

to the test resistor lead going to TP7. Connect the scope probe and the positive lead of the meter to the

test resistor lead going toTPl7. Adjust the meter and scope to read and display a 15 Volt DC signal.

Connect the 808 power plug to a power outlet.

Turn the 808 power switch ON. Watch the meter

and scope display. Depending on the ambient temperature and the power line voltage, it may take a minute or more for the voltage regulator to

reach the temperature at which the over

Page 46

OHM

T&T

RESISTOR

FIG. 84

temperature protection circuitry begins to operate. When the over temperature circuit is activated, the voltage across the test resistor will begin to drop. Wait approximately

minute

longer. What is the meter reading?

Volts

While watching the meter and scope display, use the drinking straw to blow on the regulator. What happens?

8. Turn OFF the 808 power switch and remove the power plug from the power outlet. Disconnect the test equipment and unsolder the test resistor.

Replace the heat sink and mounting hardware

that was removed in step 2.

This completes the TEMPERATURE PROTECTION EXPERIENCE. Have your instructor initial your progress chart.

EXTERNAL CONTROL AND PROTECTION

CIRCUITRY SECTION

VOLTAGE CONTROL DISCUSSION Figure 85 is a partial block diagram and schematic of the

808 Power Supply, with the external voltage

control circuitry highlighted. Figure 86 is a functional diagram of the positive adjustable

regulator and its external voltage control circuitry. The

negative adjustable regulator is similar, but with reversed voltage polarities. Comparing this schematic with the functional schematic of the fixed voltage regulator shown

in Fig. 80, we see that resistors

and

are now outside the regulator, and that the ground terminal has become the adjustment terminal.

Because the adjustment

Is the control Input of the

voltage regulator, the current necessary to operate the op

amp and protection circuitry inside the regulator must flow from the input

the regulator circuitry and

through the output

is why there needs to be some output current flowing whenever the regulator is operating. The bleeder resistor and the voltage control resistors,

and Rb, provide the load needed to cause this

current flow. ADJUSTMENT VOLTAGE EXPERIENCE The voltage that is applied to the adjustment terminal of a

voltage regulator determines the output voltage of that

regulator. The op amp inside the regulator adjusts the resistance of the Darlington transistor so that the voltage at the op amp’s inverting input (marked with a minus

sign) is the same as the voltage at its non-inverting input

(marked with a plus

sign).

Purpose: To demonstrate how an adjustable voltage

output responds to different voltages at the

adjustment terminal.

Equipment:

Clip Lead

Be sure the 808 power plug is not connected to

a power outlet.

Refer to Fig. 87 for the following steps.

Connect the negative meter lead

7 and the

positive meter lead

17. Set the meter to a

range that will read up to 20 Volts DC. Connect the 808 power plug to an outlet and turn

the power switch ON. Write the voltmeter reading

down in Fig. 88 in the “Output Voltage” column and the Clip Lead Connections “None” row (in

the box marked

1). Move the negative meter

lead

13 and write the voltmeter reading in

the “Output to Adjustment Voltage Difference”

column and the Clip Lead Connections “None” row (box

2). Set the meter range selector to a

lower range if necessary for an accurate reading. Connect the clip lead

13 and TP 2. Write the

meter reading down in box

3. Move the negative meter lead back to TP 7 and write the meter reading down in box

Disconnect the negative meter lead from TP 7

Page 47

INPUT

DARLINGTON TRANSISTOR

ADJUSTMENT

COMMON

VOLTS

FIG. 86

FIG. 87

while you change one end of the clip lead from TP 2 to TP 14. Reconnect the negative meter lead to TP 7 and write the meter reading in box

Move the the negative meter lead from TP 7 to TP 13 and write down the meter reading in box

Notice that while the output voltage changed when the adjustment terminal of the voltage regulator was connected to different voltages, the output-to-adjustment voltage difference remained the same.The op amp was controlling the Darlington transistor resistance so that the op amp’s input terminals remained at the same voltage- The

Volts across the output and

regulator output voltages.

When the adjustment terminal is connected to ground, the regulator output voltage is Volts. To be able to adjust the output voltage to 0 Volts, two diodes connected in series are forward biased by the unregulated negative supply, through

The exact voltage drop across the diodes will vary with the current flowing through them and their temperature, but it is approximately 1.4 Volts, or 0.7 Volts for each diode.This results in the variables supplies being adjustable to and a little beyond zero Volts. With

the voltage controls turned all the way down, the

adjustment terminals of the regulator is actually the voltage of the voltage reference inside the

regulator.

VOLTAGE

NONE

Later, when you connect potentiometers

and

TP13 TO

to the PCB, they will control the adjustable

TP13 TO

Page 48

positive variable supply will have an output of about

0.2 Volts, and the negative supply an

output of about

0.2 Volts.

This can be useful in some test situations, where

it is is helpful if a voltage can be adjusted to zero and a little beyond. If the utmost in stability is required from the adjustable supplies, then the

diode pairs

and

l-l 2 could be

jumpered. This would make the lowest voltage

setting obtainable 1.25 Volts, but the output voltages would be more stable with changes in

power line voltage, load, and ambient

Turn OFF the 808 power switch, and remove its

power plug from the outlet. This completes the ADJUSTMENT VOLTAGE EXPERIENCE. Have you

instructor initial your Progress Guide.

PROTECTION CIRCUITRY DISCUSSION

Figure 89 is a partial block diagram and schematic of the 808, with the external protection circuitry highlighted.

The overcurrent and over temperature protection

built into the voltage regulators that are used in Your

808 do a good job of protecting the regulators themselves, but under some conditions over current damage could occur to other power supply components. With this in mind, circuitry has been designed into the 808 to give additional protection.

We have already talked about current sensing resistors

and

and used them to determine the current flowing

through the voltage regulators in tests that were done

earlier. Transistors

and

monitor the voltage drop that

occurs across these resistors. The collector current of a transistor depends on the voltage

applied from collector to emitter, and the current flowing between the emitter and

emitter to base current depends primarily on the voltage applied between the transistors base and emitter, and secondarily on the

temperature of the transistor. At normal operating temperatures, base current starts to

flow when the voltage of the base in respect to the emitter is about

0.50 Volts for an NPN transistor, and about

Volts for a PNP transistor. With the transistor base and emitter leads connected across a 1 Ohm resistors, base current begins to flow when the current through the resistors reaches about 500

As the base current of a transistor increases, the collector current will increase as well. A given change in the base current of a transistor results a larger change in the collector current. We could say that as base current increases in a transistor, resistance between the emitter and collector of that transistor decreases. In the positive adjustable power supply of the 808,

collector current of

flows through

and increases the base to emitter

voltage of

This results in a drop in the emitter to

collector resistance of

Since

is connected in

parallel with

the result is the same as if the resistance

was reduced, and the output voltage of the

voltage regulator is reduced as well. The voltage regulators can become unstable and cause

rapid changes or oscillations in the output voltage if there is too much resistance or reactance between the filter capacitor, in this

and the regulator input terminal.

is provided to prevent this oscillation.

All the polarities are reversed in the over current protection circuit for the negative adjustable power supply, but this circuit operates in the same-manner as the one described above.

Be sure that the 808 power plug is not connected to a power outlet. Refer to Fig. 90 for the following steps.

2. Mount resistor

and

on the

These

resistors are both 6.8

(blue-gray-red), Watt. Solder the resistor leads to the PCB and cut off any excess length. Save one of these

010

CURRENT

DETECTOR

1 1

CURRENT

DETECTOR

Page 49

FIG.

pieces of wire for the next step. Bend the piece of wire saved from the previous

step into a U shape and use it for jumper wire Insert this wire from the component side of the

Solder it to the PCB and cut off any excess

length. Locate the two transistors that are marked 9015.

There may be other numbers or letter as well, such as

QC, but the numbers 9015 will appear within the sequence of are the PNP transistors and are used for

and

Spread the leads to form a triangle, and

mount these transistors on the

making sure that they are oriented the same as the D shaped transistor outlines that are silk screened on the PCB. Solder the leads to the PCB, using a heat sink as shown in Fig. 40 on each lead as you solder it.

Repeat Step 4, using the transistors marked

9014. These are the NPN transistors and are used for

and

This completes the construction of the external protection circuitry. Have your instructor initial your progress guide.

Connect the 808 power plug to a power outlet. Turn the 808 power switch ON, wait 1 second

and turn it OFF touch the components that were

installed in the construction steps just completed. If any of these components are warm, there is something wrong. Check the PCB

and components carefully, and consult with your

instructor if necessary.

Repeat step 2, leaving the power ON for 5

seconds this time.

Repeat step 2 again, leaving the power ON for

15 seconds this time.

If none of the components heated up in the previous steps, power up the 808 again. Measure the DC voltage between test pointsTP7 and TP17. TP17 should be positive,and the voltage should be between 12.7 and 15.8 Volts.

Then measure the DC voltage betweenTP7 and

TP18 should be negative and the voltage should again be between 12.7 and 15.8 Volts. If these voltages are not within these ranges, check transistors

through

for proper

location and orientation. Consult with your

instructor if necessary.

PROTECTION EXPERIENCE

Purpose: To demonstrate the operation of the external

protection circuitry used in the

Power Supply

Equipment:

Clip Lead

Be sure that the 808 power plug is not connected to a power outlet. Refer to Fig. 91 for the following steps.

2. Connect the positive meter lead

8 and the

negative meter lead to TP 10. Set the meter

range selector switch to a range that will read

to 1 Volt DC.

3. Connect the 808 power plug to an electrical outlet and turn the power switch ON. What is the meter reading?

The meter

reading

the voltage drop across

the 1 Ohm current

sensing resistor. What is the current flowing

through the resistor? Use the short cut way of

calculating the current value that was discussed earlier in this manual.

4. Connect the clip lead to TP7 and TP17. This provides a very low resistance load for the positive variable power supply, and will activate its external overcurrent protection

How

much current is flowing now?

It should be about 500

Page 50

BLACK 18 GAUGE

GREEN 2

Disconnect both meter leads and reconnect the

be used.

positive meter lead to TP 11 and the negative

lead

meter will now read the voltage

between the emitter and base of

is the

meter reading now? (The clip lead should still be connected

and TP Remove the clip lead fromTP7 and TP 17. What

is the voltage across the base

emitter junction

now?

VOLTAGE CONTROL OPERATIONALTEST

To determine that the external voltage control

circuitry is working properly

In step

the voltage across the base

emitter

junction was more than 0.5 Volts, and current

was flowing from the collector to the emitter. In this step the voltage from the base to the emitter of

was very low, so there was almost no

current flowing from the collector to the emitter.

7. Turn OFF the 808 power switch and disconnect the power plug from the power outlet. Remove the test clip and meter leads. Remove the two 3.9

test resistors from

3, TP14,

5 and

TP16.

6. Repeat step 5, this time using the two red wires and the second potentiometer.

Insert the free ends of the green wires in the PCB

holes that are nearest to the silk screened

designation

Solder the wires to the PCB and cut off any excess length. It doesn’t matter which of the two wires goes into which of the two holes.

Repeat step 7, this time using the free ends of the two red wires and the two holes on the PCB closest to the designation

CONSTRUCTION

Be sure that the 808 power plug is not connected

to a power outlet. Refer to Fig. 92 for the following

steps.

Cut two 200mm pieces of green 22 gauge wire

and strip 6mm of insulation from all four ends. Twist the exposed strands of fine wire together on each end and tin them.

Repeat step 2, cutting and preparing two

pieces of red 22 gauge wire.

Locate the two 5

potentiometers. Bend the small metal tab on each potentiometer as shown in

93 so that it won’t interfere when the

potentiometer is mounted on the cabinet top.

Connect and solder the two green wires

prepared in step 2 to one of the potentiometers

as shown in Fig. 93. It is important that the

correct solder terminals of the variable resistors

During this test be careful not to let the terminals of the potentiometers touch the PCB or any of the components. Rotate the control shafts of both potentiometers to the full counter clockwise position. Adjust the range selector of your VOM or DMM to measure up to 20 Volts DC. Connect the negative meter lead to TP7. Connect the positive meter lead to

Power up the 808. The voltmeter should read between 0 and

0.3 Volts. Rotate the Shaft of the

potentiometer connected to the red wires to the

full clockwise position.The voltmeter should now

read between 15.5 and 20 Volts. Remove the voltmeter leads fromTP17 and

Reconnect the positive meter lead toTP7 and the Negative lead

voltmeter should read

between 0 and

0.3 Volts. Rotate the shaft of the potentiometer connected to the green wires to the full clockwise position. The meter should

now read between 15.5 and 20 Volts.

Turn OFF the 808 power switch and disconnect the power plug from the power outlet.

This completes the VOLTAGE CONTROL

OPERATIONAL TEST Have your instructor initial your progress guide.

Page 51

FINAL PCB ASSEMBLY

1. Be sure that the 808 power plug is NOT connected to a power outlet. Refer to Fig. 92 for the following steps.

Locate the four

lengths of 18 gauge wire.

strip 6mm of insulation from each end of each of the four wires. Twist the fine strands of exposed wire on each of the ends together and tin them.

Form one of the tinned ends of each of the wires

into a hook shape with a long nose pliers.

Connect and solder these hooked wire ends to the following test points on the PCB.

A. The black wire to TP 7.

The red wire to TP 19.

C. The orange wire to TP 17.

The gray wire to TP 18.

Cut a 1

piece of green 22 gauge wire. Strip

6mm of insulation from each

small

strands of wire together, and tin both ends.

Connect and solder the

solder lug to one

end of the green wire that you prepared in the

previous step. Connect and solder the other end

of this wire to the PCB. Use the unmarked hole

near TP 7. Cut off any excess wire.

5. This completes the FINAL PCB ASSEMBLY. Have your instructor initial your progress guide.

CABINET ASSEMBLY

CAUTION!

Be sure that the AC Cord is NOT plugged into an electrical outlet during this Cabinet Assem

Section.

Mount two rubber feet to one end of the cabinet bottom, using two 3 x 8mm self-tapping screws. Refer to Fig. 94.

Repeat the previous step for the other end of the cabinet bottom.

3. Remove the protective plastic from the breadboard.

4. Place the cabinet top face up on your work

BEND TAB

SELF-TAPPING SCREWS

FIG. 94

surface, so the printing on the

top is

readable.

Page 52

Position the breadboard on the cabinet top, so

the printing on the breadboard is readable. While holding the breadboard in place, turn the cabinet top over.

Refer to Fig. 95 for the following steps.

Refer to

11.

Attach the breadboard to the cabinet top using eight 2.6 x

self-tapping screws. Do not

over tighten the screws. Attach the breadboard bus strip to the cabinet

top using two 2.6 x

self-tapping screws. Do

not over tighten the screws.

Fig. 96 for the following steps.’

Position the transformer so the side with the two white wires is next to the cabinet side. Mount the transformer to the cabinet bottom using two 3 x 8mm machine screws, two 3mm flat washers, two 3mm lockwashers, and two 3mm nuts. Place the solder lug which is attached to the green wire from the PCB between the transformer and the cabinet bottom as shown in Fig. 96. This wire provides an electrical connection between Common (ground) on the PCB and the metal

cabinet. Unscrew and remove the four screws which are

holding the standoffs at each corner of the PCB. Using the screws, standoffs and nuts removed in

the previous step, mount the PCB to the cabinet bottom. Place four 3mm lockwashers between the top of the PCB and the two 3mm nuts and the two long standoffs. Position the PCB so that

Ul is next to the transformer.

Connect and solder the black wire from

the solder

on the black binding post which

was installed on the cabinet top earlier, Cut off

wire that sticks out beyond the

solder lug.

Repeat Step 11, connecting the red wire from

to the red

5V binding post.

2.6 SELF-TAPPING SCREWS (10 PLACES)

15. Place a 7mm lo&washer over the threaded bushing of the potentiometer which is connected

to the PCB with two green wires. Mount the

potentiometer in the hole in the cabinet top

marked 0 to

using a 7mm flat washer and

hex nut.

Repeat Step 11, connecting the orange wire

from TP17 to the red 0 to

binding post.

16. Repeat the previous step using the

Repeat Step 11, connecting the gray wire from

potentiometer connected to the PCB with two

TP18 to the red 0 to -15V binding post.

red wires, mounting it in the hole marked 0 to

Page 53

LOCK

WASHERS /

’

FLAT

WASHERS

Page 54

Page 55

Refer to Fig. 97 for the following steps.

Refer to Fig. 98 for the following steps.

Place the cabinet bottom on your work surface

22,

as shown in Fig. 97.

Make sure that all four brackets are lined up perpendicular with ‘the cabinet top before proceeding.

Hold the cabinet top so that it can be folded onto

the cabinet bottom like a hinge. Carefully

position all wires so that they will not be pinched

between any metal or other parts when the

cabinet top is assembled to the cabinet bottom.

Gently lower the cabinet top onto the cabinet bottom. Observe the wires to be sure they are not pinched between any parts.

21. Once the cabinet top is positioned firmly onto the

cabinet bottom, hold the two cabinet halves tightly together while you turn the unit over.

Continue to hold the cabinet tightly together.

While holding the cabinet together, install four

(4) 3 x 8mm screws with 3mm

into

the four (4) holes in the bottom of the cabinet-

THESC-

Install three (3) 3 x 8mm screws with 3mm lockwashers into the three holes on the left side

of the cabinet.

three (3) 3 x 8mm screws with 3mm

lockwashers into the three (3) holes on the left

side of the cabinet.

NOT

Tighten the screws installed in Step 22.

Tighten the screws installed in Step 23. Tighten the screws installed in Step 24. This completes construction of your

Model 808 Triple Power Supply/Bread board.

Page 56

FINAL TEST

To verify that

three power supplies work

properly after cabinet assembly

Equipment:

2 3

10. 11

12.

13. 14

17.

50 Ohm 5 Watt Resistor

Connect one end of the

Ohm resistor to the

terminal. Connect the other end to the

VDC terminal. Adjust the meter to read

VDC.

Connect the negative meter lead to the COM terminal.

Connect the positive meter lead to the VDC terminal.

Connect the 808 power plug to an electrical outlet and turn the power switch ON.

The voltmeter should read between 4.7 and 5.3

Volts. If the voltage is correct, proceed to the next step. If it is not correct, STOP, turn power OFF and remove the power plug from the check the resistor and meter connections. If all connections are correct, you may have pinched or broken a wire during the cabinet assembly.

Turn the power switch OFF Adjust the DC Voltmeter to read

15 VDC.

Disconnect the resistor lead and the positive meter lead from the

VDC terminal.

Reconnect both to the 0 to

15 VDC terminal.

Turn the power switch ON.

Monitor the voltage while turning the adjustment potentiometer using a small screwdriver. You should be able to adjust the supply between 0 and 15 Volts. If the voltage is correct, proceed to the next step. If it is not correct, STOP, turn power OFF and remove the power plug from the outlet. Then check the resistor and meter connections.

If all connections are correct, you may have

pinched or broken a wire during the cabinet assembly.

Turn the power switch OFF Adjust the DC Voltmeter to read

VDC.

Disconnect the resistor lead from the 0 to

VDC terminal. Reconnect it to the 0 to

VDC

terminal.

Disconnect both meter leads.

Adjust the meter to read

15 VDC.

Connect the negative meter lead to the 0 to

terminal.

Connect the positive meter lead to the COM

terminal. Turn the power switch ON.

Monitor the voltage while turning the adjustment

potentiometer. You should be able to adjust the

supply between 0 and 15 Volts. You should be

21 22

able to adjust the supply between 0 and 15 Volts.

If the voltage is correct, proceed to the next step. if it is not correct, STOP, turn power OFF and remove the power plug from the outlet. Then check the resistor and meter wnnections. If all

wnnections are

you may have pinched

or broken a wire during the cabinet assembly. Turn the power switch OFF

Disconnect the voltmeter and resistor from the Model 808.

This completes the Final Test.

OPERATION

The Breadboard portion of your Model 808 is populated with 2,420

leads of

wmponents such as integrated circuits, transistors, resistors and capacitors, as well as wires, can be inserted into these holes By inserting electronic components and wires into the Breadboard, you can design and

experimental (prototype) circuits. Before you can use the Breadboard, however, you must understand how the 2,420 holes are interwnnected.

The Breadboard is comprised of eight sections, five bus strip sections and threecomponent sections, as shown in

Fig 99. The bus strips are used to distribute or “bus”

power and electronic signals to different areas of the

Breadboard. The component sections are where the

electronic components are mounted.

Various wire sizes can be accommodated by the Breadboard, as well as the following component leads:

SIP and DIP Integrated Circuits

Watt Resistors Most Capacitors Most Small Transistors

Bus Each of the five bus strips wntains four segments of 25

holes each. Each segment is identified by a blue or red stripe printed next to the segment.The 25 holes which are next to each stripe are connected together, so that a wire or component lead inserted into any of the 25 holes will be connected to any wire or wmponent which is inserted into any of the remaining 24 holes in that segment.

Component Sections

Each of the three component sections contains 128 segments of five holes each.The segments are horizontal

rows, and each segment is identified by a number (1 to 64) printed next to the segment.The five holes in the row next to each number are wnnected together, so that a wire or component lead inserted into any of the five holes will be connected to any wire or wmponent which is inserted into any of the remaining four holes in that segment.

In each wmponent section, for reference only, the columns are identified by letters A, B, C, D

E, and

G, H, J.

A portion of the Breadboard is shown in Fig. 104 to illustrate

Page 57

l o***

l oooo'

. . ...2

. . .

. . . . .

I I

. . . . .

l l a a a

l l

. . .

l . . . . 11

l mo*m

. . .

I I

l . l . . 14

19 . . . . .

I I

a.. .

. . .

5 VOLTS

9 10

11 12 13 14

20 21 22 23 24

31 32 33

l l

l l l l

l l

l l l

100

101

Page 58

l l l l l l . l l l l l l l l l l l l l

l l l l l l l l l l l

l l l

l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l

l l l l l l oeee l l l l l l l l l l

20 l l l l l

l l l l l

l eeee l eeee

l l l l

l eeee l l l l l

l l l l

l eeee2

l eeee l eeee l eeee l eeee b l eeee l eeee l eeee 9 l l l l l 10 l l l l l l l l l l 12 l l l l l l l l l l 14 l l l l l 15 l l l l l l l l l l l l l l l l l l l l 19 l l l l

l l

l l l

l 22

l l l

l l

l l 24

l l l l l 2b l l l l l 27 l l l l l

l l l l l

l l l l l l l l l l

l l l l l

l l l l l l l l l

l eeee

l l l l l

10 l l l l l 11

l l l l l

l eeee

14 l eeee

15 l eeee lb l l l l l

l l l l l

19 l l

l l

l l l

l eeoo l eeee

l l

l l l l l

FIG. 102

l l l

l l l l l 15 l l l l l

l eoe*l7

l l l l l l l l l l 19 l l l l l 20 l l l l l l l l

22 23

l l l 24

l 29

l l l l l 27

l eee*

l l l l l

l l l

l l l l l

l eeee

l l l l l eeee

l l l

l eeee l l l l

l l l l l

l l l

l l a l l

l eeee l eeee 3 l e*e* 4 l eeee 5 l eeee l eeee l eo*e l eeee 9 l l l

l 10

l l l l

l ee*e 12 l l l l l 13 l l l l

l l l l l 15 l l l l l lb l

l l l I?

l l l

l l

l l 19

l l 0

l l l 21 l l l 22 l l l l

l l l

l l l l

l l

0 27

l l l

l 28

the interconnections in both the bus strip and the

component sections.

Sample Circuit

Equipment: VOM or DMM

Two 3.9

Resistors

To demonstrate how the Breadboard can be

construct circuits, you can build the voltage divider circuit shown

Fig.

Refer to Fig.

for the following steps.

Connect one end of a wire to the COM terminal.

Insert the other end of the wire into the hole in the

upper bus strip as shown. Insert one end of a wire into the hole in the upper

bus strip as shown. Insert the other end into the

hole in the vertical bus strip as shown.

Insert one end of a 3.9

resistor into the hole in the vertical bus strip as shown. Insert the other end in hole Al 0 in the center component section.

Insert one end of another 3.9

resistor into

hole El

Insert the other end into the hole in the

vertical bus strip as shown.

Insert one end of a wire into the hole in the

vertical bus strip as shown. Insert the other end

into the hole in the upper bus strip as shown.

6. Insert one end of a wire into the upper bus strip as shown. Connect the other end to the

terminal.

7. Adjust the meter to read

8. Connect the positive meter lead to the

resistor lead

is in hole

Connect the

negative

meter lead to the COM terminal.

Plug the Model 808 into a VAC outlet and turn the Power ON.

Read the meter. It should read approximately 2.5

VDC, showing that the voltage divider circuit is operating as expected, you know that the circuit

which you built on the Breadboard is connected

in accordance with the schematic in Fig. 101.

11. Turn the Power OFF and unplug the Model 808.

12. Remove the meter and all wires and resistors from the Breadboard.

NOTE: Due to the nature of the design, when the Positive and Negative Variable Voltage control pots (R8 and

are set to the full counter-clockwise position (for minimum output), the output voltage level can go past zero and produce an output in the opposite polarity. Levels upwards of one to two hundred millivolts (0.1 Volts) of reversed polarity are possible, and can adversely affect some semiconductor devices, Make sure that you have

Page 59

the two Variable Voltage Outputs set to the desired level before connecting them to the breadboarded circuit, and do not randomly adjust the control pots during operating.

If your

project does not operate correctly, the

following steps will help you to isolate the

are three basic steps to follow when servicing any

electronic device.

Isolate the defective section. Isolate the defective component or connection.

Ill. Repair or replace the defective component or

connection.

Check off each step as you proceed.

1. Check ALL solder connections. Poorly soldered

for their part numbers. Each

must be in the

connections should be reheated to form good

correct location.

joints. Refer to the HOW TO SOLDER section for

examples of good and poor solder connections.

4. If the above procedures fail to locate the problem, performing the experiences located

2. Check the placement of ALL components. Make sure that the

leads of

capacitors

are going into the PCB holes marked

Be certain that you have installed the proper capacitors in the right locations. It is easy to get confused by the numbers on capacitors. Check that all resistors have been installed in their proper locations. Resistor values can be determined by the RESISTOR COLOR CODE

section.

throughout the manual will be helpful in locating the problem, especially if you built the Power Supply using Mode

These experiences demonstrate how the various sections of your Power Supply operate. If you find results that differ greatly from those described, you will know where to look for trouble in your Power Supply.

Be sure that each

has been installed in the

proper location. Ul and U2 look similar, except

TEST POINT DESCRIPTIONS

DESCRIPTION

1 2

Transformer Secondary

Start (Blue)

Transformer Secondary #1

Tap (Black)

(Ground)

6 7

10 11 12 13 14 15 16

18 19

Transformer Secondary #1 Finish (Blue) Transformer Secondary

Start (Yellow)

Transformer Secondary

Finish (Yellow)

Volts, Unregulated

(Ground)

22 Volts, Unregulated

11 Volts, Unregulated Positive Regulator Input Terminal Overcurrent Protection Transistor Base Negative Voltage Regulator Input Terminal Positive Voltage Regulator Adjust Terminal Minus 1.4 Volt Voltage Control Bias Negative Voltage Regulator Input Terminal Positive 1.4 Volt Voltage Control Bias

0 to

15 Volt Output, Regulated

0 to

Volt Output, Regulated

Page 60

WHITE

BLUE

3.2

OHMS

YELLOW

SECONDARY

(NO LOAD)

LESS THAN

1 OHM

YELLOW

POWER TRANSFORMER SPECIFICATIONS

TAB CONNECTED TO OUTPUT

TAB CONNECTED TO INPUT

INPUT

OUTPUT

ADJUST

OUTPUT

INPUT

ADJUST

309 TOP VIEW

RESISTOR COLOR CODE

Your kit contains precision resistors which may use two types of color code: a four band code and a five band code.

FIVE BAND COLOR CODE

l First color (color nearest the end of the

represents the first

figure in the resistor value.

l Second color represents the second

in the resistor value.

l Third color represents the third

in the resistor value.

l Fourth color represents the multiplier of the first three figures. l Fifth color represents the resistor tolerance.

1st

2nd

3rd

4th

5th

COLOR COLOR

COLOR

FIRST

FIGURE FIGURE

MULTIPLIER TOLERANCE

1 1

2 2

100

3 3 3

1,000 4 4 4 5 5 5

100,000

FOUR BAND COLOR COOE

l First color (color nearest the end of the

represents

the first

in the resistor value.

l Second color represents the second figure in the resistor

value.

l Third color represents the multiplier of the first two figures. l Fourth color represents the resistor tolerance.

2nd

3rd

4th

COLOR COLOR COLOR

COLOR

FIRST

FIGURE

TOLERANCE

10%

GOLD

BLACK

BROWN

1 1

100

3 3

1 .ooo

YELLOW

10.000

GREEN

100.000

6 6

EXAMPLES

GRAY

YELLOW SILVER BROWN BROWN GREEN GREEN BROWN

100,000

equals 1.84 ohms equals

ohms or

Page 61

This project has afforded you the opportunity of expanding

your knowledge of electronic& and electronic devices

have learned, and the amount of knowledge you have acquired from building this project. The theory and skills

through experiments and related technical information.

which were covered are:

You will probably be surprised at the number of skills you

THEORY

Transformers

Rectification

Center-Tap Rectification

Bridge Rectification

Bridge With Center-Tap Rectification

Capacitive Filters

Unregulated Power Supplies Fixed Voltage Regulators Variable Voltage Regulators Overcurrent Protection

Electronic Component Identification Schematic Symbol identification Reading Schematic Diagrams Reading Block Diagrams Reading Resistor Color Code Test Equipment Use Soldering

Hand Tool Use

SPECIFICATIONS

POWER SOURCE: 110 VAC

POWER

VDC, 1 Amp

0 to

15 VDC, 300

0 to

-15

300

INTEGRATED CIRCUITS:

TRANSISTORS:

DIODES:

HOW TO ORDER REPLACEMENT PARTS

REPAIR POLICY

If you require a part, follow the instructions below.

If your

project does not operate properly, and

ment parts will be shipped subject to the warranty terms.

you have completed the steps outlined in SERVICING, you

Do not return the original component unless requested.

may return the project to

for inspection and

The Factory Warranty does not cover components

repair. aged through carelessness or incorrect assembly. Mail your request for replacement parts to Graymark.

Enclose the following:

1. Your name and mailing address.

2. Date kit was purchased.

3. Part number and description (as shown on Parts List)

4. If the part is not covered by warranty, you must also:

A B

Carefully pack the completed project so it

not

be damaged in shipment. Enclose a letter explaining the problem. Include

your name, address and phone number. Allow 4 weeks for repair and return. Send your kit to:

INTERNATIONAL, INC.

Show replacement price from Parts List.

Add $1

for postage

handling.

If you are a

resident, add

purchase price.

Tustin, CA 92680

Enclose a money order or check for the full amount. Sorry, COD not accepted.

Page 62

FACTORY WARRANTY

international, inc. warrants that each project was

complete and ready to assemble at the time of shipment.

shortage claims must be made within

days from

ceipt of goods representing each project.

warrants that, for a period of ninety (90) days from date of purchase, all merchandise is free of defects and workmanship, under normal conditions of use and service. The

under this warranty is limited to repair or

placement of those parts upon verification that they are de-

fective in this

does not in-

clude labor required to service or repair any project.

This warranty is completely void and

not

replace, or service any project or parts thereof on

which acid core

paste

or corrosive solders have been used in assembling the project. Any modification of the project will void the warranty.

This warranty is extended solely to the original buyer and only to the extent above expressed. No dealer or agent is authorized to make any other or additional guarantee or warranty.

no event shall

be liable for any anticipated profits, consequential damage, loss of time, or other losses incurred by

the buyer in connection with the

OTHER

KITS

There are many other

electronic projects

will enjoy building. Send your name and address to:

BOX 2015,

CA 92681

for your personal copy of Graymark’s latest catalog

includes:

ROBOTS

RADIOS

TOOLS

STROBE LIGHT

ELECTRONIC ACCESSORIES

POWER SUPPLIES

An extensive selection of low-cost KOMPONENT KITS is also described in the catalog.