Elenco 015V User Manual
AC/DC POWER SUPPLY KIT
MODEL K-11
Assembly and Instruction Manual
Copyright © 2014, 1989 by ELENCO®All rights reserved. Revised 2014 REV-N 753211
No part of this book shall be reproduced by any means; electronic, photocopying, or otherwise without written permission from the publisher.
ELENCO
®
-1-
PARTS LIST
If you are a student, and any parts are missing or damaged, please see instructor or bookstore.
If you purchased this AC/DC power supply kit from a distributor, catalog, etc., please contact ELENCO
®
(address/phone/e-mail is at the back of this manual) for additional assistance, if needed. DO NOT contact your
place of purchase as they will not be able to help you.
RESISTORS
Qty. Symbol Value Color Code Part #
! 1 R1 1kΩ 5% 1/4W brown-black-red-gold 141000
! 1 R3 2.7kΩ 5% 1/4W red-violet-red-gold 142700
! 1 R2 10kΩ Potentiometer 191516
CAPACITORS
Qty. Symbol Value Description Part #
! 1 C2 100µF Electrolytic 281045
! 1 C1 1000µF Electrolytic 291045
SEMICONDUCTORS
Qty. Symbol Value Description Part #
! 2 D1, D2 1N4001 Diode 314001
! 1 D3 1N5247 Zener Diode 315247
! 1 Q1 2N3904 Transistor 323904
! 1 Q2 2N6121 / HT1061 Transistor 326121
MISCELLANEOUS
Qty. Symbol Description Part #
! 1 T1 Transformer YD-1485 440111
! 1 PC board 518011
! 1 S1 Slide switch 541009
! 1 Heat sink 615002
! 1 Cable clamp 1/4” 628750
! 3 Screw 6-32 x 5/16” 641641
! 3 Nut 6-32 644600
! 1 Line cord 862100
! 1 Shrink tubing 2” 890120
! 1 Solder lead-free 9LF99
Resistor Transistors
Capacitor
Potentiometer
PARTS IDENTIFICATION
Electrolytic
Diode
Transformer
Switch
Heat Sink
Epoxy
Glass
BCE
Cable
Clamp
EBC
The electrical power that is supplied by your power
company is what is known as Alternating Current or
AC. This current is constantly changing amplitude and
polarity (see Figure 1). The electrons (current) move
back and forth at a rate of 60 times per second. This
type of current is not suitable for most electronic
circuits. It must be converted into a Direct Current or
DC which moves in one direction only. Your MultiPurpose Power Supply does exactly that. It converts
AC into DC. It also
allows you to vary the
amplitude of the
voltage from 0-15V
(0.25A - 12Vmax).
Also, your power
supply has an output
of 8.5VAC, 0.5A
without regulation.
-2-
INTRODUCTION
A block diagram of the system is shown in Figure 2. It
consists of five basic circuits needed to convert 120
volts of AC to a usable 0-15 volts of DC. We will
analyze each circuit for a better understanding of
power supplies.
VOLTAGE STEP-DOWN FUNCTION
In this circuit, 120 volts of AC is
reduced to two 13VAC out of
phase voltages. Thirteen volts
is the rms (effective) value. The
peak voltage is really 18 volts.
This step-down is achieved by
the use of a transformer. The
winding of the transformer is
shown in Figure 3A and the
voltage across each winding is
shown in Figure 3B. In a
transformer, the magnetic field
produced by the 120 volts of
current is induced into the
secondary winding. The voltage
across the secondary winding is
a ratio of the number of turns between the primary and
secondary winding. If the ratio was 1:1 (equal turns),
then the secondary voltage would be the same as the
120 volt input. In our transformer, the ratio is 120:13.
Therefore, the secondary voltage will be 13 volts. If
we were to put an oscilloscope between the common
lead of the two secondary windings and looked at the
other leads, we would see that the two voltages are
180 degrees out of phase. This is because the
windings are going in opposite directions from the
common point. This is an important point in converting
the AC to DC as we will see in the next section.
AC to DC CONVERSION - RECTIFICATION
This circuit that converts AC to
DC consists of two diodes D1
and D2. The purpose of a
diode is to pass current in only
one direction (see Figure 4). If
we were to take a battery and
connect it to a diode and lamp,
as shown in Figure 5, the lamp would only light when
the diode is in the conduction direction. If we replace
the battery with a transformer secondary winding, the
diode will only conduct on the positive cycle of the
voltage as shown in Figure 6. Note that the output of
the diode is a half-wave rectification with a hole in the
center. This voltage would be hard to filter out. It is
desirable to fill in this area. This is done by something
known as full wave rectification, which is using a
second winding out of phase with the first.
Figure 7A shows the circuit for a full wave rectification.
Note that diode D1 conducts the previously described
and diode D2, one half cycle later. The diodes
conduct only when the voltage goes positive and no
current flows on the negative half. The resulting
output voltage waveforms are shown in Figure 7B.
Note that there is no longer a gap between cycles.
This will make it easier to filter the output voltage.
THEORY OF OPERATION
Figure 1
336V
+168V
–168V
or
Time
Peak to
Peak (PP)
or 120V
rms
Volt age
Stepdown
Rectification
AC to DC
Volt age and
Current Control
DC
Filtering
Reference
Volt age
0-15V
Output
13VAC
Figure 2
Figure 3A
Figure 3B
120VAC
18V
AC Peak
AC Peak
–18V
18V
–18V
36Vpp
36Vpp
Figure 4
Direction of
Current Flow
Figure 5
Diode
Battery
Not Lit
Lamp
Output D1
Output D2
D1 & D2
D1
D2
Figure 7A
Figure 7B
Diode
Battery
Lamp
Figure 6
Resistor
Diode
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