I
DUAL OUTPUT POWER SUPPLY
Agilent MODEL E3620A
OPERATING AND SERVICE MANUAL
FOR INSTRUMENTS WITH SERIAL NUMBERS
KR71804262 AND ABOVE
For instruments with Serial Numbers above
KR71804262, a change page may be included.
Manual Part No. E3620-90001
April 2000
Edition 6
SAFETY SUMMARY
The following general safety precautions must be observed during all phases of operation, service, and repair of this instrument.
Failure to comply with these precautions or with specific warnings elsewhere in this manual violates safety standards of design,
manufacture, and intended use of the instrument. Agilent Technologies assumes no liability for the customer's failure to comply
with these requirements.
BEFORE APPLYING POWER.
Verify that the product is set to match the available line voltage and that the correct fuse is installed.
GROUND THE INSTRUMENT.
This product is a Safety Class I instrument (provided with a
protective earth terminal). To minimize shock hazard, the
instrument chassis and cabinet must be connected to an
electrical ground. The instrument must be connected to the
ac power supply mains through a three-conductor power
cable, with the third wire firmly connected to an electrical
ground(safety ground) at the power outlet. Any interruption of
the protective(grounding) conductor or disconnection of the
protective earth terminal will cause a potential shock hazard
that could result in personal injury. If the instrument is to be
energized via an external autotransformer for voltage reduction, be certain that the autotransformer common terminal is
connected to the neutral(earthed pole) of the ac power lines
(supply mains).
DO NOT OPERATE IN AN EXPLOSIVE ATMOSPHERE.
Do not operate the instrument in the presence of flammable
gases or fumes.
KEEP AWAY FROM LIVE CIRCUITS.
Operating personnel must not remove instrument covers.
Component replacement and internal adjustments must be
made by qualified service personnel. Do not replace components with power cable connected. Under certain conditions,
dangerous voltages may exist even with the power cable
removed. To avoid injuries, always disconnect power, discharge circuits and remove external voltage sources before
touching components.
SAFETY SYMBOLS
!
or
WARNING
CAUTION
NOTE
Instruction manual symbol; the product
will be marked with this symbol when it is
necessary for the user to refer to the
instruction manual.
Indicate earth(ground) terminal.
The WARNING sign denotes a hazard. It
calls attention to a procedure, practice,
or the like, which, if not correctly performed or adhered to, could result inpersonal injury. Do not proceed beyond a
WARNING sign until the indicated conditions are fully understood and met.
The CAUTION sign denotes a hazard. It
calls attention to an operating procedure,
or the like, which, if not correctly performed or adhered to, could result in
damage to or destruction of part or all of
the product. Do not proceed beyond
CAUTION sign until the indicated conditions are fully understood and met.
The NOTE sign denotes important information. It calls attention to a procedure,
practice, condition or the like, which is
essential to highlight.
DO NOT SERVICE OR ADJUST ALONE.
Do not attempt internal service or adjustment unless another
person, capable of rendering first aid and resuscitation, is
present.
Instruments that appear damaged or defective should be made inoperative and secured against unintended
operation until they can be repaired by qualified service personnel.
DO NOT SUBSTITUTE PARTS OR MODIFY INSTRUMENT.
Because of the danger of introducing additional hazards, do
not install substitute parts or perform any unauthorized modification to the instrument. Return the instrument to a Agilent
Technologies Sales and Service Office for service and repair
to ensure that safety features are maintained.
1-2
Table of Contents
SAFETY SUMMARY . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-2
GENERAL INFORMATION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-4
DESCRIPTION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-4
SAFETY CONSIDERATIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-4
SAFETY AND EMC REQUIREMENTS. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-4
INSTRUMENT AND MANUAL IDENTIFICATION. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-4
OPTIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-4
ACCESSORY . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-4
ORDERING ADDITIONAL MANUALS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-4
SPECIFICATIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-4
LINE FUSE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-5
INSTALLATION. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-5
INITIAL INSPECTION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-5
Mechanical Check . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-5
Electrical Check . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-5
INSTALLATION DATA . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-5
Location and Cooling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-5
Outline Diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-6
Rack Mounting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-6
INPUT POWER REQUIREMENTS. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-6
Power Cable. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-6
OPERATING INSTRUCTIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-6
INTRODUCTION. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-6
CONTROLS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-6
Line Switch . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-6
Voltage and Current Metering . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-6
Voltage Controls. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-6
TURN-ON CHECKOUT PROCEDURE. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-7
OPERATION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-7
Overload Protection Circuits. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-7
Operation Beyond Rated Output . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-7
Connecting Load . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-7
Series Operation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-7
Parallel Operation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-7
LOAD CONSIDERATIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-7
PULSE LOADING . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-7
REVERSE CURRENT LOADING . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-8
OUTPUT CAPACITANCE. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-8
REVERSE VOLTAGE PROTECTION. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-8
1-3
GENERAL INFORMATION
DESCRIPTION
The Model E3620A Dual Output Power Supply is a compact,
constant voltage/current limiting supply that delivers two isolated 0 to 25 V outputs rated at 1 A. It is an ideal power supply
for design and breadboard work where single or dual voltages
are required. Each output voltage is continuously variable
throughout its range and separate current limit circuits protect
each output against overload or short circuit damage.
Connections to the outputs are made to binding post type terminals on the front panel. The outputs can be used individually or in combination to satisfy any number of output
demands. The positive or negative terminal of each output
can be grounded or each output can be left floating. A chassis
ground terminal is located on the front panel of the supply.
The front panel also contains a line switch, output voltage
controls, an autoranging digital voltmeter and a single-range
digital ammeter, and two meter select pushbutton switches.
The meter pushbuttons select both voltage and current
monitoring for the output V1 and V2. The supply is furnished
with a detachable, 3-wire grounding type line cord. The ac
line fuse is an extractor type fuseholder on the rear heat sink.
SAFETY CONSIDERATIONS
This product is a Safety Class I instrument, which means that
it is provided with a protective earth ground terminal. This terminal must be connected to an ac source that has a 3-wire
ground receptacle. Review the instrument rear panel and this
manual for safety markings and instructions before operating
the instrument. Refer to the Safety Summary page at the
beginning of this manual for a summary of general safety
information. Specific safety information is located at the
appropriate places in this manual.
SAFETY AND EMC REQUIREMENTS
This power supply is designed to comply with the following
safety and EMC(Electromagnetic Compatibility) requirements:
n IEC 1010-1(1990)/EN 61010 (1993): Safety Require-
ments for Electrical Equipment for Measurement, Control,
and Laboratory Use
n CSA C22.2 No.231: Safety Requirements for Electrical
and Electronic Measuring and Test Equipment
n UL 1244: Electrical and Electronic Measuring and Testing
Equipment
n EMC Directive 89/336/EEC: Council Directive entitled
Approximation of the Laws of the Member States relating
to Electromagnetic Compatibility
n EN 55011(1991) Group 1, Class B/CISPR 11 (1990):
Limits and Methods of Radio Interference Characteristics
of Industrial, Scientific, and Medical(ISM) RadioFrequency Equipment
n EN 50082-1(1992) /
IEC 801-2(1991): Electrostatic Discharge Requirements
IEC 801-3(1984): Radiated Electromagnetic Field
Requirements
IEC 801-4(1988): Electrical Fast Transient/Burst
Requirements
INSTRUMENT AND MANUAL IDENTIFICATION
A serial number identifies your power supply. The serial number encodes the country of manufacture, the week of the latest significant design change, and a unique sequential
number. The letter "KR" designates Korea as the country of
manufacture, the first one digit indicates the year (4=1994,
5=1995, and so forth), and the second two digits indicate the
week. The remaining digits of the serial number are a unique,
five-digit number assigned sequentially.
If the serial number on your supply does not agree with those
on the title page of the manual, a yellow Change Sheet is
supplied with the manual to explain the difference between
your instrument and the instrument described by this manual.
The Change Sheet may also contain information for correcting errors in the manual.
OPTIONS
Options 0E3 and 0E9 determine which line voltage is
selected at the factory. The standard unit is configured for 115
Vac ± 10%, 47-63 Hz input.
Option No. Description
0E3: 230 Vac ± 10%, 47-63 Hz Input
0E9: 100 Vac ± 10%, 47-63 Hz Input
ACCESSORY
The accessory listed below may be ordered from your local
Agilent Technologies Sales Office either with the power supply or separately. (Refer to the list at the rear of the manual for
address.)
Agilent Part No. Description
5063-9240 Rack Kit for mounting one or two 3 1/2" high
supplies in a standard 19" rack
The rack mount kit is needed for rack mounting of the
E3620A power supply.
ORDERING ADDITIONAL MANUALS
One manual is shipped with each power supply. (Option 910
is ordered for each extra manual.) Additional manuals may
also be purchased separately for your local Agilent Technologies sales office (see the list at the rear of this manual for
addresses). Specify the model number, serial prefix, and the
Agilent Part Number provided on the title page.
SPECIFICATIONS
Instrument specifications are listed in Table 1. These specifications are performance standards or limits against which the
instrument is tested.
1-4
LINE FUSE
The line fuse is located by the ac line receptacle. Check the
rating of the line fuse and replace it with the correct fuse if
necessary as indicated below. These are slow-blow fuses.
Table 1. Specifications
Line Voltage Fuse Agilent Part No.
100/115 Vac 2 A 2110-0702
230 Vac 1 A 2110-0457
AC INPUT
Standard:
0E9:
0E3:
DC OUTPUT
Voltage span over which output may be varied using front
panel controls.
Output V1:
Output V2:
LOAD REGULATION
Less than 0.01% plus 2 mV for a full load to no load change in
output current.
LINE REGULATION
Less than 0.01% plus 2 mV for any line voltage change within
rating.
RIPPLE AND NOISE
Normal Mode Voltage:
(20 Hz-20 MHz).
Common Mode Current (CMI):
outputs (20 Hz-20 kHz).
OPERATING TEMPERATURE RANGE
0 to 40
output current is derated linearly to 50% at 55
temperature.
TEMPERATURE COEFFICIENT
Less than 0.02% plus 1 mV voltage change per
operating range from 0 to 40
115 Vac ± 10%, 47-63 Hz, 200 VA, 130 W
100 Vac ± 10%, 47-63 Hz, 200 VA, 130 W
230 Vac ± 10%, 47-63 Hz, 200 VA, 130 W
0 to 25 V at 1 A
0 to 25 V at 1 A
Less than 0.35 mV rms/1.5 mV p-p
Less than 1 mA rms for all
o
C for full rated output. At higher temperatures,
o
C after 30 minutes warm-up.
o
C maximum
o
C over the
STABILITY (OUTPUT DRIFT)
Less than 0.1% plus 5 mV (dc to 20 Hz) during 8 hours at
constant line, load and ambient after an initial warm-up time
of 30 minutes.
LOAD TRA NSIENT RESPONSE TIME
Less than 50 msec for output recovery to within 15 mV of
nominal output voltage following a load change from full
load to half load, or vice versa.
OUTPUT VOLTAGE OVERSHOOT
During turn-on or turn-off of ac power, output plus overshoot
will not exceed 1 V if the output control is set for less than 1 V.
If the control is set for 1 V or higher, there is no overshoot.
METER ACCURA CY: ±(0.5% of output + 2 counts)
o
C±5oC
at 25
METER RESOLUTION
Voltage:
Current:
DIMENSIONS
212.3 mmW x 88.1 mmH x 345.4 mmD
(8.4 inW x 3.5 inH x 13.6 inD)
WEIGHT
5.0 kg(11.0 lbs) net, 6.25 kg(13.8 lbs) shipping
10 mV (0 to 20 V),100 mV (above 20 V)
1 mA
INSTALLATION
INITIAL INSPECTION
Before shipment, this instrument was inspected and found to
be free of mechanical and electrical defects. As soon as the
instrument is unpacked, inspect for any damage that may
have occurred in transit. Save all packing materials until the
inspection is completed. If damage is found, a claim should
be filed with the carrier. The Agilent Technologies Sales and
Service office should be notified as soon as possible.
Mechanical Check
This check should confirm that there are no broken knobs or
connectors, that the cabinet and panel surfaces are free of dents
and scratches, and that the meter is not scratched or cracked.
Electrical Check
This instrument should be checked against electrical specifications. Perform the TURN-ON CHECKOUT PROCEDURE
in the following paragraph to confirm that the supply is
operational. Alternately, check the supply more fully using the
PERFORMANCE TEST in the service information section.
INSTALLATION DATA
The instrument is shipped ready for bench operation. Before
applying power to the supply, please read the INPUT
POWER REQUIREMENTS paragraph.
Location and Cooling
This instrument is air cooled. Sufficient space should be allowed
so that a free flow of cooling air can reach the sides and rear of
the instrument when it is in operation. It should be used in an
area where the ambient temperature does not exceed 40
1-5
o
C.
Outline Diagram
Figure 1 illustrates the outline shape and dimensions of the
supply.
Rack Mounting
This supply may be rack mounted in a standard 19-inch rack
panel either by itself or alongside a similar unit. Please see
the ACCESSORY, page 1-4, for available rack mounting
accessory. The rack-mounting kit includes complete installation instructions.
INPUT POWER REQUIREMENTS
Depending on the line voltage option ordered, the supply is
ready to be operated from one of the power sources listed in
Table 1. A label on the rear heat sink shows the nominal input
voltage set for the supply at the factory.
Power Cable
To protect operating personnel, the supply should be
grounded. This supply is equipped with a three conductor
power cable. The third conductor is the ground conductor and
when the cable is plugged into an appropriate receptacle, the
supply is grounded. The power supply is equipped at the factory with a power cord plug appropriate for the user's location.
Notify the nearest Agilent Sales and Service Office if the
appropriate power cord is not included with the supply.
Before applying power to the supply, check the label on the
heat sink to make certain that the supply's line voltage option
agrees with the line voltage to be used. If the option does not
correspond to your line voltage, refer to paragraph "LINE
VOLTAGE OPTION CONVERSION" in the service section
before applying power.
Figure 2. Front-Panel Controls and Indicators
Figure 1. Outline Diagram
OPERATING INSTRUCTIONS
INTRODUCTION
This section describes the operating controls and indicators,
turn-on checkout procedures, and other operating considerations for the Model E3620A Dual Output Power Supply.
CONTROLS
Line Switch
The LINE pushbutton switch ( , Figure 2) is pushed-in to
turn the supply ON and released (out position) to turn the
supply OFF.
Voltage and Current Metering
Two meter select pushbutton switches ( and ) permit the
output voltage and current of either output (V1 or V2) to be
monitored on the VOLTS/AMPS meter. The V1 and V2 output
select pushbuttons connect the desired output to the metering circuit when the applicable button is pushed in.
Be careful that both METER pushbuttons are not released
(out-position) or pushed in simultaneously.
Voltage Controls
The V1 and V2 voltage controls ( and ) set the voltage
level of the corresponding output. The voltage controls are 10
turn potentiometers.
1-6
TURN-ON CHECKOUT PROCEDURE
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The following steps describe the use of the Model E3620A
front panel controls illustrated in Fi
check that the suppl
cedure or the more detailed performance test of service information section when the instrument is received and before it
is connected to an
detailed performance test be
section if an
a. Connect line cord to power source and push LINE
switch ( ) in.
b. Push the V1 meter select pushbutton switch ( ) to in-
position to monitor suppl
load connected, var
ran
e and check that the voltmeter responds to the con
trol setting and the ammeter indicates zero.
c. Turn the V1 volta
short the +V1 output terminal ( ) to -V1 terminal ( )
with an insulated test lead. The ammeter should indicate a short-circuit output current of minimum 1.0 A +
5% at 25
nals.
d. Push the V2 meter select pushbutton switch to in-
position and repeat steps (b) and (c) for V2 output.
If this brief checkout procedure or later use of the suppl
reveals a possible malfunction, see the service information
section for detailed test, troubleshootin
cedures.
is operational. Follow this checkout pro-
load equipment. Proceed to the more
difficulties are encountered.
the V1 voltage control ( ) over its
e control ( ) fully clockwise and
o
C. Remove the short from the output termi-
ure 2 and serve as a brief
inning in service information
's V1 output voltage. With no
, and adjustment pro-
OPERA TION
The dual outputs of the E3620A can be used individually, in
series, or in parallel. Each output can be floated (up to 240
volts off
the suppl
Overload Protection Circuits
The outputs are individually protected against overload or
short circuit dama
circuits are factor
mum 1 A + 5%. The current limits are set b
the V1 suppl
dia
the output current remains below the current limit settin
round) or, the + or - terminal of either output can be
rounded to the chassis ground terminal which is located on
's front panel.
e by separate current limiting circuits. The
adjusted to limit the output current to mini-
adjusting R63 in
and R34 in the V2 supply (see the schematic
ram). No deterioration of supply performance occurs if
.
Operation Beyond Rated Output
The supply may be able to provide voltages and currents
reater than its rated maximum outputs if the line voltage is at
or above its nominal value. Operation can be extended up to
5% over the rated output without dama
performance can not be
above the rated output of 0 to 25 V at 1 A.
uaranteed to meet specifications
e to the supply, but
Connecting Load
Connect each load to the power supply output terminals usin
separate pairs of connecting wires. This will minimize mutual
couplin
the low output impedance of the suppl
of adequatel
at the load.
Make each pair of connectin
twist or shield them to reduce noise pick-up. If a shield is
used, connect one end of the shield to the power suppl
If load considerations require locatin
terminals at a distance from the power suppl
suppl
tribution terminals b
load should be connected to the remote distribution terminals
separatel
effects between loads and takes full advantage of
. Load wires must be
heavy gauge to maintain satisfactory regulation
wires as short as possible and
round terminal and leave the other end unconnected.
output power distribution
, then the power
output terminals should be connected to the remote dis-
a pair of twisted or shielded wires and each
.
Series Operation
The two outputs (V1 and V2) can be connected in series to
obtain a volta
le output. Each output control (V1 and V2) must be adjusted
sin
in order to obtain the total output volta
internall
capacitors a
plies are connected in series and the output is shorted.
e (up to 50 V) higher than that available from a
e. Diodes connected
across each output protect the supply's output filter
ainst reverse voltages. This could occur if the sup-
Parallel Operation
The V1 and V2 supplies can be connected in parallel to obtain a
total output current
The total output current is the sum of the output currents of the
individual supplies. The output volta
suppl
should be set to the desired output voltage, and the other
set for a slightly larger output voltage. The supply set to
suppl
the lower output volta
while the suppl
ited source, droppin
other suppl
fraction of its rated output current necessar
rent demand.
reater than that available from one supply.
e controls of one power
e will act as a constant voltage source,
set to the higher output will act as a current-lim-
its output voltage until it equals that of the
. The constant voltage source will deliver only that
to fulfill the total cur-
During the actual operation of the V1 and V2 outputs, if a load
e causes the current limit to be exceeded, the OVER-
chan
LOAD LED is li
V2 supplies will protect the load b
imum 1 A + 5%. The V1 and V2 supplies are self restorin
hted. If overload conditions occur, the V1 and
limiting the current to min-
;
that is, when the overload is removed or corrected, the output
e is automatically restored to the previously set value.
volta
LOAD CONSIDERATIONS
This section provides information on operating your suppl
with various types of loads connected to its output.
PULSE LOADING
The power supply will automatically cross over from constant-
e to current-limit operation in response to an increase in
volta
the output current over the preset limit. Althou
limit ma
1-7
be set higher than the average output current, high
h the preset
peak currents (as occur in pulse loadin
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g
g
y
g
g
g
g
y
preset current limit and cause crossover to occur and
de
rade performance.
) may exceed the
REVERSE CURRENT LOADING
An active load connected to the supply may actually deliver a
reverse current to the suppl
cycle. An external source can not be allowed to pump current
into the suppl
dama
effects, it is necessar
load resistor so that the supply delivers current through the
entire operatin
without risking loss of regulation and possible
e to the output capacitor of the supply. To avoid these
cle of the load devices.
during a portion of its operatin
to preload the supply with a dumm
OUTPUT CAP ACITANCE
An internal capacitor across the output terminals of the suppl
helps to supply high-current pulses of short duration durin
constant-voltage operation. Any capacitance added exter-
will improve the pulse current capability, but will
nall
decrease the load protection provided b
circuit. A high-current pulse may damage load components
before the avera
the current limitin
e output current is large enough to cause
circuit to operate.
the current limitin
REVERSE VOL TAGE PROTECTION
A diode is connected across the output terminals with reverse
. This diode protects the output electrolytic capacitors
polarit
and the series re
reverse volta
series re
either, diodes are also connected across them. When operatin
suppl
ulator transistors can not withstand reverse voltage
supplies in parallel, these diodes protect an unenergized
that is in parallel with an energized supply.
ulator transistors from the effects of a
e applied across the output terminals. Since
Figure 3. Reverse Current Loading Solution
1-8
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