HP 6236A Service manual

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HP Part No. 5950-1737
TRIPLE OUTPUT
POWER SUPPLY
MODELS 6236A AND 6237 A
OPERATING AND SERVICE MANUAL FOR;
MODEL 6236A, SERIALS 1507A-00141
AND ABOVE
MODEL 6237A, SERIALS 1507A-00101
AND ABOVE
*For Serials above 1507A-00141
or 1507A-00101,
achange page may be included.
Hewlett-Packard
Printed: February 1975

tions in additiola to the standard 104-127Vac 47-63Hz
unit and is furnished with a permanently attached 5-foot
3-wire grounding-type line cord.
1-8 SPECIFICATIONS
1-9 Table 1-1 lists detailed specifications for the power
supply.
SECTION I
GENERAL INFORMATION
I
INTRODUCTION
1-1
1-2 This manual covers two triple output power supply
models, the 6236A and the 6237 A. Both models are com-
pact general purpose bench supplies that are particularly
useful for powering developmental IC circuits, both linear
and digital. Unless one model or the other is specifically
identified, all information in this manual applies to both
the 6236A and the 6237 A.
1-10 OPTIONS
--- CAUTION ---
Carefully read Sections II and III of this
manual before
attempting to operate the
power supply.
1-11 Options are factory modifications of a standard
instrument that are requested by the customer. The follow-
ing
options are available for the instrument covered by this
manual.
OPTION NO. OESCR IPTION
---CAUTION---
1-13 ACCESSORIES
The user can convert an instrument from one line voltage
option to another by following the instructions in Para-
graph 3-4.
1-12 Before
the supply is shipped from the factory, an
internal line voltage
selector switch is set and the proper
fuse installed for the line voltage specified on the order. A
label
on the rear heat sink identifies this line voltage option.
Input Power: 87-106Vac,47-63Hz,
single-phase.
Input Power: 191-233Vac,47-63Hz,
single-phase.
Input Power: 208-250Vac, 47-63Hz,
single-phase.
220
240
100
Before applying power to the supply, make cer-
tain
that its line voltage selector switch (S3) is
set for the line voltage to be used. (See CA UTION
notice in Paragraph 3-2 for additional information
on S3).
1-5 All controls, meters, and output terminals are loca-
ted on the front panel. Two single-turn potentiometers con-
trol
the +6V (or +18V) and ±20V outputs. A three-position
meter switch selects one of the supplies for display of its
voltage
and current on two dual-range meters. The +6V
(or +18V) and ±20V outputs share a common output ter-
minal which
is isolated from chassis ground.
1-3 DESCRIPTION
1-4 Both models have adual output of 0 to ±20 volts
at 0 to 0.5amps. The voltages of the two 20-volt outputs
are adjusted by a si ngle front-panel control and track one
another within 1 %. The +20V and -20V outputs can also be
used
in series for asingle 0 to 40V 0.5A output. The third
output differs in the two models and is 0 to +6 volts at up
to 2.5amps in the 6236A and 0 to +18 volts at 0 to 1 amp
in the 6237 A /
1-6
All outputs are protected against overload or short-
circuit damage. The +18V output in the 6237 A and the
±20V outputs in both models are protected by circuits
which limit output current to 110% of its nominal maximum.
The overload protection circuit for the +6V output in the
6236A has a current foldback characteristic which reduces
the output current as an overload increases until only 1A
flows
through a short circuit. For this output, the current
limit depends on the output terminal voltage and varies
linearly
between 2.75A at 6V and 1A at zero volts.
1-7 The
instrument is available in three line voltage op- 1-14
The accessories listed below may be ordered from
your local Hewlett-Packard field sales office either
1-1

with the power supply or separately. (Refer to the list at
the rear of the manual for addresses.)
HP
PART NO.
14513A
14523A
DESCRIPTION
Rack Mounting Kit for mounting one
3 1/2" high supply in a standard 19"
relay rack.
Rack
Mounting Kit for mounting two
3 1/2" high supplies side by side in a
standard 19" relay rack.
ture. The first two digits indicate the year (10 = 1970, 11 =
1971, etc.) the second two digits indicate the week, and the
letter" A" designates the U.S.A. as the country of manufac-
ture. The second part is the power supply serial number; a
different sequential number is assigned to each power sup-
ply, starting with 001 01.
1-17 If the serial number on your instrument does not
agree with those on the title page of the manual, Change
Sheets supplied with the manual or Manual Backdating
Changes
define the difference between your instrument and
the instrument described by this manual.
1-15 INSTRUMENT AND
MANUAL
IDENTIFICATION 1-18 ORDERING
ADDITIONAL MANUALS
1-16 Hewlett-Packard power supplies are identified by a
two part serial number. The first part is the serial number
prefic, a number-letter combination that denotes the date
of a significant design change and the country of manufac-
1-19 One manual is shipped with each power supply.
Additional manuals may be purchased from your local Hew--
lett-Packard field
office (see the list at the rear of this manual
for addresses). Specify the model number, serial number
prefix, and the HP Part number provided on the title page.
NOTE
Table 1-1. Specifications, Models 6236A and 6237 A
TRACKING:
The +20V and -20V outputs track within 1 %.
Specifications apply to both models
unless otherwise indicated.
INPUT POWER:
Standard Option: 104:127Vac (120Vac nominal), 47-
63Hz, single-phase, 112W, 140VA (Other line voltage
options are listed in Paragraph 1-11.)
DC
OUTPUT AND OVERLOAD PROTECTION:
o to ±20V Outputs: Maximum rated output current is
0.5A. Short circuit output current is 0.55A ±5% and a
fixed current limit circuit limits the output of each sup-
ply
to this maximum at any output voltage setting. Unbal-
anced loads within current rating are permitted.
Model 6236A
o to +6V Output: Maximum rated output current is 2.5A
at 6V. The maximum available output current decreases
with the output voltage setting. A current foldback current
limits the output to 2.75A ±5% at 6volts and, with decreasing
voltage,
reduces the current limit linearly to 1A ±15% at zero
volts (short circuited).
Model 6237A
o to +18V Output: Maximum rated output current is
1.0A. Short circuit output current is 1.1 A±5% and a fixed
current limit circuit limits the output to this maximum at
any output voltage setting.
1-2
LOAD
EFFECT (Load Regulation):
All Outputs: Less than 0.01 %plus 2mV for afull load
to no load change in output current.
SOURCE EFFECT (Line Regulation):
All Outputs: Less than 0.01% plus 2mV for any line
voltage
change within rating.
PARD (Ripple and Noise):
All
Outputs: Less than 0.35mV rms and 1.5mV p-p
(20
Hi to 20 MHz).
DRIFT (Stability):
All Outputs: Less than 0.1 %plus 5mV (0 to 20 Hz)
during 8 hours at constant line, load, and ambient after an
initial warm-up time of 30 minutes.
LOAD TRANSIENT RECOVERY TIME:
All Outputs: Less than 50psec for output recovery to
within 15mV of nominal output voltage following aload
change
from full load to half load (or vice versa).
OUTPUT VOLTAGE OVERSHOOT:
All Outputs: During turn-on or turn-off of ac power,
output plus overshoot will not exceed 1V if the output
control is set for less than 1 V. If the control is set for 1V
or higher, there is no overshoot.

Table 1-1. Specifications, Models 6236A and 6237A (Continued)
TEMPERATURE COEFFICIENT:
All Outputs: Less than 0.02% plus 1 mV voltage change
per degree Celsius over the operating
range from 0 to 40°C
after 30 minutes warm-up.
*OUTPUT IMPEDANCE (typical):
o to +20V Output: 0.5mn plus 1.5/lH
o to -20V Output: 0.5mn plus 1.5/lH
Model
6236A
o to +6V Output: 0.3mn plus 1/lH
Model
6237A
o to +18V Output: 0.3n plus 1.5/lH
*Operating characteristics listed
as typical are provided for
the user's information only and are not warranteed specifi-
cations.
RESOLUTION:
(Minimum output voltage change obtainable using front
panel voltage control)
o to ±20V Outputs: 70mV
Model
6236A
o to +6V Output: 20mV
Model
6237A
o to +18V Output: 70mV
1-3
TEMPERATURE RANGES:
Operating: 0
to +40°C ambient. At higher temperatures,
output current is derated linearly to 50% at 55°C.
Storage:
-40° C to +75° C.
METER RANGES:
o to +20V Output: 0-25V,O-0.6A
o to -20V Output: 0-25V,O-0.6A
Model 6236A
o to +6V Output: 0-7V, 0-3A
Model 6237A
o to +18V Output: 0-21 V, 0-1.2A
METER
ACCURACY:
±4% of full scale
DIMENSIONS:
3 15/32 H x 87/32 W x 129/16 D
(88mm Hx208mm Wx319mm D)
WEIGHT:
9.5 Ib (4.3kg)

SECTION II
INSTALLATION
2-1 INITIAL INSPECTION
2-2 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, file
claim
with carrier immediately. The Hewlett-Packard Sales
and Service office should be notified as soon as possible.
2-3 Mechanical Check
2-4 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 scratch-
ed or cracked.
NOTE: ACCESSORY KITS FOR 19 INCH
RACK IIOUNTIIG AIlE:
HI' IIOOEL 1451~ FOR CIlE SUI'l\.Y
HP lOlELl4523A RJlTlI09..PPL£S
$10£ VIEW
2-5 Electrical Check Figure 2-1. Outline Diagram
2-6 The instrument should be checked against its elec-
trical
specifications. Section Vincludes an "in-cabinet" per-
formance check to verify proper instrument operation.
2-7 INSTALLATION DATA
2-8 The instrument is shipped ready for bench opera-
tion. Before applying power to the instrument, see the
CAUTION notice in Paragraph 3-2.
2-9 Location
2-11 Outline Diagram
2-12 Figure 2-1 illustrates the outline shape and dimen-
sions of this supply.
Figure 2-2. Rack Mounting, One Unit
Figure 2-3. Rack Mounting, Two Units
Rack Mounting
2-10 This instrument is air cooled. Sufficient space
should be allotted so that afree flow of cooling air can
reach the rear of the instrument when it is in operation. It
should be used in an area where the ambient temperature
does not exceed 40°C (up to 55°C with derating).
2-13
2-14 This instrument may be rack mounted in a standard
19-inch rack panel either by itself or alongside asimilar unit.
Figures 2-2 and 2-3 show the components of the rack mount-
ing kits available for this power supply. Ordering informa-
tion for rack mounting accessories is given in Paragraph 1-13.
2-1

2-15 Input Power Requirements
2-16 Depending on the line voltage option ordered, the
supply is ready to be operated from one of the power sources
listed in
Table 2-1. The input voltage range, and the input
current and power at high line voltage and full load is listed
for each option. Alabel on the rear heat sink identifies the
line voltage option of your supply. All options of this
model operate from a 47-63 Hz single-phase line.
2-17
If desired, the user can easily convert the unit from
any of these options to another by following the instructions
in Paragraph 3-4. A unit is converted by resetting an internal
line voltage
selector switch, replacing the fuse, and changing
the line voltage tag.
2-20
To preserve the protection feature when operating
the instrument from a two-contact outlet, use a three-prong
to two-prong adapter (if permitted by local regulations) and
connect the green lead on the adapter to ground.
2-21 Model 6236A and 6237 Asupplies are equipped
at the factory with a power cord plug appropriate for the
user's location. Figure 2-4 illustrates the standard configu-
rations
of power cord plugs used by HP. Above each draw-
ing
is the HP option number for that configuration of power
connector pins. Below each drawing is the HP part number
for a replacement power cord equipped with aplug of that
configuration. Notify the nearest HP Sales and Service
Office if
the appropriate power cord is not included with
the instru ment.
2-22 Repackaging for Shipment
-- CAUTION --
If the supply might possibly have been
converted to aline voltage
option other
than the one marked on its identifying
label without being relabeled in some way,
check the setting
of the line voltage selector
switch
and the fuse rating before applying
power. (See CAUTION in Paragraph 3-2)
2-23 To insure safe shipment of the instrument, it is
recommended that the package designed for the instrument
be used. The original packaging material is reusable. If it
is not available, contact your local Hewlett-Packard field
office
to obtain the materials. This office will also furnish
the address of the nearest service office to which the instru-
ment can be shipped and provide the Authorized Return
label necessary to expedite the handling of your instrument
return. Be sure to attach atag to the instrument which
specifies the owner, model number, full serial number, and
service required, or abrief description of the trouble.
2-18 Power Cable
8120-0050
OPTION 903
8120-1691
OPTION 902
8120-1369
OPTION 901
Figure 2-4. Power Cord Configurations
8120-1351
OPTION 900
2-19 To protect operating personnel, the National
Electrical
Manufacturers Association (NEMA) recommends
that the instrument panel and cabinet be grounded. "This
instrument 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 instru-
ment is grounded. The offset pin on the power cable three-
prong connector is the ground connection. In no event
shall this instrument be operated without an adequate cabi
net ground connection.
Table 2-1. Input Power Requirements
Option
Line Voltage Range
Input Current
Input Power
100 (100 Vac)
87-106 Vac
1.3A
140 VA
Standard
(120 Vac)
104-127 Vac
1.1A
140 VA
220
(220 Vac)
191-233 Vac
0.6A
140 VA
240 (240 Vac)
208-250 Vac
0.55A
140 VA
2-2

SECTION III
OPERATING INSTRUCTIONS
3-1
m =~=:: OU~~~/~~2~:
"If" _--- ........ 1
Figure 3-1. Controls and Indicators
TURN-ON CHECKOUT PROCEDURE
a. Connect line cord to power source and turn LINE
switch G) on. LINE ON indicator ®will light.
b.
Set METER switch ® to the +6V position and, with
no load connected, vary +6V VOLTAGE-control @over
its range
and check that the voltmeter responds to the con-
trol setting and the ammeter indicates zero.
c.
Set the +6V VOLTAG E control for a 6-volt meter
indication and short the +6V output terminal to COM
(common) terminal ® with an insulated test lead. The
ammeter should indicate a short-circuit output current of
approximately 1.0A (1.1A in the 6237A). Remove the
short from the output terminals.
d. Set the METER switch to the +20V position and,
with no load connected, vary ±20V VOLTAGE control ®
over its range and check that the voltmeter responds to the
control setting and the ammeter indicates zero.
3-2 The following steps describe the use of the Model
6236A or 6237 A front panel controls and indicators illus-
trated in Figure 3-1 and serve as a brief check that the sup-
ply is operational. This checkout procedure or the more
detailed performance test of Paragraph 5-6 should be follow-
ed when the instrument is received and before it is connect-
ed to any load equipment. Proceed to the more detailed
procedures beginning in Paragraph 5-6 if any difficulties
are encountered.
-- CAUTION--
e. Set the ±20V VOLTAGE control for a 20-volt meter
indication and short the +20V output terminal to the com-
mon terminal with an insulated test lead. The ammeter
should indicate a short-circuit output current of O.55A
±5%.
Remove the short from the output terminals.
f. Repeat steps (d) and (e), but substitute the -20V
position of the METER switch and the -20V output ter-
minal.
Figure 3-2. Line Voltage Selector (Set for 120 Vac)
Before applying power to the supply, make certain
that its line voltage selector switch
(53) is set for
the line voltage to be used. This switch
is mounted
on the circuit board behind the voltmeter and is
visible through the perforations in the top cover.
The positions
of the two white marks on the switch
indicate the switch setting
(see Figure 3-2). If the
switch setting does
not correspond to the intended
power source, proceed to
Paragraph 3-4 before
applying power.
.r-- 240----,
( r-
220
----,
0_ 0
L-,OO--.J
'---120 ---J
t
FRONT
OF
SUPPLY
NOTE
For the Model 6237A, substitute. +18V
for +6Vin the following steps.
3-1
3-3 If this brief checkout procedure or later use of the
supply reveals apossible malfunction, see Section V of this
manual for detailed test, troubleshooting, and adjustment
procedures.

3-4 LINE VOLTAGE OPTION CONVERSION
3-5 To convert the supply from one line voltage option
to another, the following three steps are necessary:
1.
After making certain that the line cord is discon-
nected from a source of power, remove the top cover from
the supply and. set the two sections of the li:1e voltage selec-
tor switch for the desired line voltage (see Figure 3-2),
2.
Check the rating of the installed fuse and replace
it
with the correct value, if necessary. For Options 100 or
120, use a normal time-constant 2-amp fuse (HP Part No.
2110-0002); for Options 220 or 240, use a normal time-
constant 1-amp fuse (HP Part No. 2110-0001).
3. Mark the instrument clearly with a tag or label
indicating the correct line voltage to be used.
3-6 OPERATION
3-7 This power supply can be operated individually or
in parallel with another supply (see Paragraph 3-17). All
output terminals are isolated from ground. The ±20V and
+6V or +18V outputs use asingle common output terminal.
This common (COM) terminal or anyone of the other output
terminals may be grounded to the chassis at the front panel
ground terminal ( G) in Figure 3-1), or all outputs may be
left floating. Loads can be connected separately between
each of the 0 to 20V output terminals and the COM ter-
minal,
or between the -20V and the +20V terminals for a
o to 40V output.
3-8 Overload Protection Circuits
3-9 ±20-Volt Current Limit. The +20V and -20V
outputs are individually protected against overload or short-
circuit damage by separate current limit circuits which are
adjusted at the factory to limit the output current to 0.55A
±5%. (This is 110% of the rated maximum output of 0.5A.)
The current limits can be set by adjusting resistor R6 for the
+20V output and R26 for the -20V output. (See Paragraph
5-47
for current limit calibration instructions.) No deteri-
oration of supply performance occurs if the output current
remains below the current limit setting. If asingle load is
connected between the +20V and -20V outputs, the circuit
set for the lesser current limit will limit the output.
3-10 +6V Current Foldback (Model 6236A). The over-
load and short-circuit protection circuit for the +6V output
of the Model 6236A reduces the output current limit as the
output terminal voltage decreases. (The operating region of
the +6V output is enclosed by heavy lines in Figure 3-3).
The maximum rated output current is 2.5A and the current
limit is factory-adjusted to operate at 2.75A ±5% when the
3-2
output is 6volts. At lower output voltages, the circuit
reduces the maximum obtainable output current linearly
until 1A
±15% flows vvhen the output is shorted. The short-
circuit current cannot be adjusted, but R46 can be set to
limit the maximum current at 6V to 2.75A ±5%. (See Para-
graph 5-47 for current limit calibration instructions.)
3-11 +18-Volt Current Limit (Model 6237 A). The +18-
volt output of the Model 6237 A is protected by a fixed cur-
rent limit circuit which operates at 1.1 A (110% of its max-
imum rated output of 1.0A). The circuit is similar to the
ones in the ±20-volt supplies. (See Paragraph 5-47 for
cal ibrati on i nstructi ons.)
3-12 Operation Beyond Rated Output
3-13 The supply may be able to provide voltages and
currents greater than its rated maximum outputs if the line
voltage
is at or above its nominal value. Operation can ex-
tend into the shaded areas on the meter faces without dam-
age to the supply, but performance cannot be guaranteed to
meet specifications. If the line voltage is maintained in the
upper end of the input voltage range, however, the supply
probably will operate within its specifications.
3-14 Connecting Loads
3-15 Each load should be connected to the power supply
output terminals using separate pairs of connecting wires.
This
minimizes mutual coupling between loads and takes
full advantage of the low output impedance of the power
supply. Connecting wires to the load must be of adequately
heavy gage to maintain satisfactory regulation at the load.
Each pair
of connecting wires should be as short as possible
and twisted or shielded to reduce noise pickup. If shielded
wire is used, connect one end of the shield to the power
supply ground terminal and leave the other end unconnect-
ed.
3-16 If load considerations require that the output power
distribution terminals be remotely located from the power
supply, then the power supply output terminals should be
connected to the remote distribution terminals by a pair of
twisted or shielded wires and each load separately connect-
ed to the remote distribution terminals.
3-17 Parallel Operation
3-18 Two or more power suppl ies can be connected in
parallel
to obtain a total output current greater than that
available from one power supply. The total output current
is the sum of the output currents of the individual power
supplies. The output voltage controls of one power supply
should
be set to the desired output voltage, and the other
power supply should be set for aslightly larger output volt-

NOTE:
THE LOWER END -POINT
OF THE
CURRENT
LIMIT LINE IS NOT AD-
JUSTABLE; THE UPPER END-POINT
IS SET AT THE FACTORY
FOR 2.75A
± 5%. BETWEEN ITS END- POINTS,
THE ACTUAL CURRENT
LIMIT IS A
STRAIGHT-LINE FUNCTION.
OPERATING
REGION
+6V SUPPLY, MODEL 6236A
2V
IV
5V ~-----+------+------+------+---~~-,4 __ --------4
4V ~-----+------+-----+------+-~~-+-"---+-------4
3V
OUTPUT
TERMINAL
VOLTAGE
6V
OUTPUT CURRENT (AMPERES)
o
0.5
t 1.0
\ 0.85A 115A
SHORT CIRCUIT CURRENT
MAY VARY ±15% FRav1
UNIT TO UNIT.
1.5 2.0
2.5 3.0
Figure 3-3: Current Limit Characteristics of the 6V Supply (Model 6236A)
3-21 Output Capacitance. An internal capacitor across
the output terminals of the power supply helps to supply
high-current pulses of short duration during constant volt-
age
operation. Any capacitance added externally will im-
prove
the pulse current capability, but will decrease the
load protection provided by the current limiting circuit. A
3-20 Pulse Loading. The power supply will automati-
cally cross over from constant voltage to current limit
operation in response to an increase in the output current
over the preset limit. Although the preset limit may be set
higher than the average output current, high peak currents
as occur in pulse loading may exceed the preset current limit
and cause crossover
to occur and degrade performance.
age. The supply set to the lower output voltage will act as
a
constant voltage source, while the supply set to the higher
output will act as a current-limited source, dropping its out-
put voltage until it equals that of the other supply. The
constant voltage source will deliver only that fraction of
its total rated output current which is necessary to fulfill
the total current demand.
3-19 Special Operating Considerations
high-current output pulse may damage load components
before the average output current is large enough to cause
the current limiting circuit to operate.
3-22 Reverse Current Loading. An active load connect-
ed to the power supply may actually deliver areverse cur-
rent to the power supply during a portion of its operating
cycle. An external source cannot be allowed to pump cur-
rent into the supply without loss of regulation and possible
damage
to the output capacitor. To avoid these effects, it
is necessary to preload the supply with a dummy load
resistor so
that the power supply delivers current through
the entire operating cycle of the load device.
3-23 Reverse Voltage Protection. Internal diodes con-
nected with reverse polarity across the output terminals
protect the output electrolytic capacitors and the driver
transistors from the effects of areverse voltage applied
across a
supply output. Since series regulator transistors
cannot withstand reverse voltage either, diodes are also
connected across them. When operating supplies in parallel,
these
diodes protect an unenergized supply that is in para-
llel
with an energized supply.
3-3

SECTION IV
PRINCIPLES OF OPERATION
4-1 OVERALL DESCRIPTION
4-2 This section presents the principles of operation of
the Models 6236A and 6237 ATriple Output Power Supply.
Throughout this section refer to the combined schematic
diagram of Figure 7-1.
NOTE
All information in this section applies to both
models unless otherwise indicated.
4-3 The two primary windings of the power transformer
are connected in one of four different ways by setting the
two slide switches mounted on the circuit board. These
switches select
one of the nominal ac input voltages for
which the supply is designed: 100V, 120V, 220V, or 240V.
4-4 The transformer secondaries, together with recti-
fiers
and capacitor filters, provide raw dc for the three out-
put regulator circuits and for another regulator which pro-
vides reference and bias voltages to the output regulators.
4-5 By comparing its output to ahigh-stability refer-
ence,
the 0 to +6-volt regulator (6236A) or 0 to +18-volt
regulator (6237 A) holds its output voltage at the value
determined by a front panel control. Any error in the
actual output as compared to the desired output is am-
plified by an operational amplifier and applied as fe~dback
to control the conduction of aseries regulator transistor.
As aresult, the voltage across the series transistor varies so
as to hold the output voltage constant at the desired level.
The high gain
of the voltage comparison amplifier and the
stability of the reference voltage ensure that input voltage
or load
current variations have Iittle effect on the output
voltage.
4-6
The 0 to +6-volt output in the Model 6236A is
protected by a current foldback limiter which minimizes
dissipation in
the series regulator transistor during overloads.
In a current foldback circuit, the current limit depends on
the output terminal voltage and in this regulator ranges
from 2.
75A ±5% at 6volts to 1A ±15% with the output short-
ed. (An
output of 2. 75A is 110% of the rated maximum of
2.5A at 6volts.) The operating region of the +6-volt regu-
lator output is enclosed by aheavy line in Figure 3-3. If
the operating point reaches the diagonal current limit line,
adecrease in load resistance moves
the operating point
4-1
down the line, reducing the output voltage and current.
Current foldback is controlled by a second operational
amplifier in the regulator which monitors the dc output
current. This current comparison amplifier takes control
of the 'output away from the voltage comparison amplifier
when the current reaches the design limit. Removing the
overload restores constant voltage operation automatically.
4-7 The +20-volt regulator has afixed current limit at
110% of its 0.5 amp maximum rated output but is otherwise
similar to the +6-volt regulator.
4-8
The 0 to -20-volt regulator is, in turn, similar to the
+20-volt regulator except that it resembles a complementary
mirror image of the latter. The output voltages of the +20-
volt
and -20-volt supplies are both set by the same front
panel control and track each other within 1%. Precise track-
ing
of the two outputs is achieved by controlling the positive
output conventionally and using that output as the reference
voltage
for the negative output.
4-9 The 0 to +18-volt regulator in the Model 6237 A
is similar to the +20-volt regulator. It has afixed current
limit at 110% of its 1.0 amp output.
4-10 The reference and bias supply provides reference
and bias voltages for the output regulators.
4-11
The turn-onlturn-off control circuit prevents out-
put transients when the supply is turned on or off. It does
this by delaying the application of certain bias and reference
voltages
at turn-on and removing them shortly after turn-off.
4-12 A three-position meter switch selects which of the
supplies has its output voltage and current indicated on the
front panel meters. The proper range of the dual-range
meters is selected automatically.
4-13 DETAILED CIRCUIT DESCRIPTION
4-14 0To
+20-Volt Regulator
4-15 Voltage Comparison Amplifier. The voltage com-
parison amplifier in the +20-volt supply controls the conduc-
tion of series regulator transistor Q1 so that the voltages at
the two inputs of the amplifier remain equal. Afixed volt-
age divider holds its inverting
input (U1-2) at -16mV. Its
non-inverting
input (U1-3) monitors the output voltage in

series with the voltage across R1. Since R2 is connected
between the -6.2V reference supply and a point which feed-
back action holds near -16mV, its current remains constant.
This current flows through R1 to produce avoltage drop
across R1 proportional to its resistance setting, thus the
output voltage of the supply is proportional to the resistance
setting of R1. At the output of the voltage comparison
amplifier (U1-1), apositive voltage change corresponds to a
decrease in the conduction of Q1.
4-16 CR2 and CR3 protect the input of the amplifier
against
transient overloads, C2 and R4 speed up loop re,.
sponse time, and C4 and R12 stabilize the supply's high
frequency characteristics.
4-17 OR-Gate. To permit either the voltage comparison
amplifier or the current comparison amplifier to control the
series regulator transistor, the outputs of both amplifiers
are
connected to the base of driver Q2 through an OR-gate
composed of CR5 and CR6. CR5 is normally reverse
biased by anegative
output from the current comparison
amplifier, permitting the voltage comparison amplifier to
drive Q2 through CR6. An overload drives the output of
the current comparison amplifier positive, forward biasing
CR5 and reducing the supply output. When the overload is
removed, CR5 is reverse biased again and the voltage com-
parison amplifier resumes control of the output.
4-18 Driver and Series Regulator. The -12.4 V output
of the bias supply provides the turn-on bias for series regu-
lator transistor Q1. Its complete current path includes Q15,
CR59, R14, and Q1, and returns to common through current
monitoring resistor R8. (It is because this bias current flows
through R8 that the output ammeter requires the zero off-
set bias circuit described in paragraph 4-43.) Through the
OR-gate, either the voltage or the current comparison ampli-
fier controls the conduction of driver Q2, which regulates
the flow of turn-off bias through Q1's base-emitter circuit.
The algebraic sum of the nearly constant turn-on bias through
R14 and the variable turn-off bias through Q2 controls the
conduction of series regulator transistor Q1.
4-19 Current limit Circuit. In the +20-volt regulator,
the current comparison amplifier compares the voltage
across
current monitoring resistor R8 to the fixed voltage
across part of current limit adjust potentiometer R6. The
current limit adjustment is set so that the input voltage to
the current comparison amplifier is negative in the normal
operating region, but becomes zero when the output current
increases to 0.55 amps. When the amplifier's input voltage
reaches zero, it
takes control of the regulator output voltage
and reduces it as necessary to keep the output current from
exceeding 0.55 amps. When the overload is removed, the
output of the current comparison amplifier goes negative,
reverse biasing
CR5 and returning control to the voltage
4-2
comparison amplifier.
4-20 Turn-On/Turn-Off Control. When the power supply
is turned on or off, Q15 in the turn-on control circuit with-
holds turn-on bias from Q1 while the regulator bias voltages
are
too low. This prevents an output voltage transient from
occurring before
the amplifiers are properly biased. The
output of the -6.2V reference supply is also temporarily
held at alow voltage by Q14, which conducts to short that
output.
4-21 Circuit Protection Components. Diodes CR1,
CR7,
and CR9 each protect the +20-volt supply from spe-
cific hazards.
Output diode CR1 protects the supply com-
ponents if areverse voltage is applied to the output terminals.
A
common way for this to occur is for an unenergized supply
to be connected in series with another that is energized. If
the output voltage is turned down quickly while alarge
capacitor is connected across the output, CR7 protects
driver Q2 from excessive dissipation by shunting some of its
base
current to common. The series regulator diode, CR9
protects the series regulator transistor from reverse voltage.
Series regulator voltage
could occur if adeenergized sup-
ply were
connected in parallel with an energized one.
4-22 0To -20-Volt Regulator
4-23 Instead of using an NPN driver and a PNP series
regulator in
the negative output line as in the +20-volt regu-
lator,
the -20-volt regulator uses a PNP driver and an NPN
series regulator in the positive output line. The -20-volt
regulator circuit is the complementary equivalent of the
+20-volt circuit in other respects, as well. Their current limit
circuits operate similarly. At the outputs of the current and
voltage comparison amplifiers in the -20-volt circuit, aneg-
ative voltage change corresponds to adecrease in series regu-
lator conduction. The turn-on bias for its series regulator
transistor, Q3, is supplied from apositive voltage source,
the +7.5V bias supply, and is switched on and off by Q13
in the turn-on control circuit.
4-24 The -20-volt supply uses the output of the +20-volt
supply
as its reference voltage. As aresult, both outputs are
set by asingle front panel control and track each other with-
in 1 %. Two resistors in resistor network Z1 are connected
in series between the +20-volt and -20-volt outputs. These
resistors are closely
matched in resistance and temperature
coefficient so that the voltage across each is exactly half of
the total. The midpoint of this divider is connected to the
non-inverting input of the -20-volt supply's voltage com-
parison amplifier.
The amplifier's inverting input is connect-
ed to common through R32 to hold it at zero volts. The
amplifier keeps its differential input voltage at zero by match-
ing the output voltage of the -20-volt supply to that of the
+20-volt supply.

4-25 0To +6-Volt Regulator (Model 6236A)
4-26 Except for differing component designations and
values, paragraphs
4-15 through 4-18,4-20, and 4-21, which
describe the voltage comparison amplifier, OR-gate, driver,
series regulator,
turn-on control, and circuit protection
components of the +20-volt regulator circuit, also apply to
the +6-volt regulator. The only difference in circuit opera-
tion lies in the control of the current comparison amplifier,
and thus the type of current limit the supply has.
4-27 Current Foldback Circuit. (For this discussion refer
to the Figure 7-1 schematic and to Figure 4-1.) The differ-
ential input signal to the current comparison amplifier is the
algebraic sum
of three circuit voltages:
1. The voltage across R49. ER49 remains constant
at
-305mV.
2. The voltage across the lower part of R46 (see Figure
4-1). ER46
is proportional to the regulator output
voltage and equals 440mV when the supply output
is 6volts.
3. The voltage across
current monitoring resistor R48.
ER48
is proportional to the sum of the regulator
output current and the 0.22A bias current that
flows through R54 and R48.
-12.4V
Z1 -1
-305mV 30K g~~~~~TSON
~t---_5"-i+ AMPLIFIER
put. When this happens, the output of this amplifier goes
positive and forward biases CR45. Since the current through
CR45 tends to reduce the output of the supply, the output
of the voltage comparison amplifier goes negative in oppo-
sition
to this change and reverse biases CR46 to leave the
current comparison amplifier in control of the output. Now
that the current comparison amplifier is in control and for
as long as the overload remains, the supply's output voltage
and
current vary so as to maintain this amplifier's differen-
tial input signal near zero volts. This results in the output
current limit characteristics shown in Figure 3-3.
4-29
If we assume for example that the voltage control
is set for 5volts and the load resistance is slowly decreased,
the supply
goes into current limit at about 2.47 amps. Here
is why it occurs at that value. At a 5-volt supply output,
ER46 is 5/6 of 440mV, or 367mV. In order for the algebraic
sum
of ER46 and ER48 to go as far negative as -305m Vand
drive the
amplifier output positive, ER48 must reach
-672mV. Once ER48 reaches this value, the current com-
parison
amplifier controls the series regulator transistor so
as to prevent ER48 (and thus the supply's output current)
from increasing further. At 0.25 ohms, R48 develops
-672mV at 2.69 amps. Since 0.22 amps of the current
through R48 is bias current for Q7, the nominal current limit
corresponding to a5-volt output is 2.69 amps minus 0.22
amps, or about 2.47 amps.
4-30
If the load resistance continues to decrease, it pulls
the
output voltage lower. This reduces ER46 until at azero
output voltage ER46 becomes zero, leaving ER48 equal in
magnitude
to ER49.This -305mV drop across R48 corre-
sponds
to a1.22-amp current through R48 and a1-amp short-
circuit current at the output of the supply.
CR45
U3
CR44
+--looT
6
R49
750
+
R47
23K
R48
_ 0.25 +
R46
3K
CURRENT +}
LIMIT _ER46
ADJ.
+--
lOUT +0.22A 07 BIAS
0.22A 07 BIAS
Figure 4-1. Foldback Current Limit Circuit in 6V Supply
4-31 In the +6-volt regulator, as in the +20-volt regulator,
the
turn-on bias current for the series regulator transistor is
switched on and off by Q15 in the turn-on control circuit
to prevent output voltage transients.
4-28 When the supply's
output current is below the cur-
rent
limit that corresponds to its output terminal voltage
(see Figure 3-3), the inv~rting input (U3-6) of the current
•comparison amplifier is more positive than its non-inverting
input (U3-5), which is held at -305mV. The negative am-
plifier output which results is clamped by CR44 and reverse
biases OR-gate diode CR45, leaving the voltage comparison
amplifier in control of the supply's output. If the load resis.:
tance is decreased, the higher output current increases ER48
until the algebraic sum of E
R48
and ER46 makes the cur-
rent comparison
amplifier's inverting input slightly more
negative than the
-305mV potential on its non-inverting in-
4-32 0To +18-Volt Regulator (Model 6237A)
4-33 Except for differing component designations and
values, paragraphs
4-15 through 4-21, which describe the
voltage comparison
amplifier, OR-gate, driver, series regu-
lator, current limit circuit, turn-on control, and circuit
protection components of the +2o-volt regulator circuit, also
apply to the +18-volt regulator. In the +18-volt regulator,
as in the +20-volt regulator, the turn-on bias current for the
series regulator transistor
is switched on and off by Q15 in
the
turn-on control circuit to prevent output voltage
transients.
4-3

4-34 Reference and Bias Supply
4-35 The reference and bias supply powers the operation-
al amplifiers and provides the bias and reference voltages used
throughout the supply. A shunt zener regulates its +7.5V
output. Aseries transistor regulates its -12.4 V output,
using 6.2-volt zener VR1 as its voltage reference. The -12.4V
output provides a constant current to VR 1, which is the pri-
mary voltage reference for the entire supply.
4-36 Two equal resistors are connected in series across
the -12.4V output. To regulate this output, voltage com-
parison amplifier U4 compares the voltage across one of
these resistors to the -6.2V reference and controls the con-
duction of series regulator 011 through driver 012. The
voltage drop across 011 is controlled by feedback so that
the voltages at the two inputs of U4 remain equal. Driver
012 controls 011 by shunting part of the base bias supplied
by R68.
4-37 During turn-on, the -6.2V reference supply is
temporarily shorted by 014 in the turn-on control circuit.
By trying to match this low reference, 011 is initially turned
off. While 011 is turned off, R69 bypasses current to the
-12.4V output until the output reaches -9 volts and the
turn-on control circuit removes the short from the reference
and enables the -12.4-volt regulator to operate normally.
4-38 Turn-On/Turn-Off Control Circuit
4-39 Immediately after the supply is energized and until
the output of the -12.4-volt regulator reaches about -9
volts, the turn-on control circuit withholds turn-on bias
from series regulator transistors 01, 03, and 07 and holds
4-4
the -6.2V reference at alow value. This prevents an out-
put voltage transient by ensuring that the operational am-
plifiers are energized and other essential bias voltages are
present before the series regulator transistors are turned on.
The circuit also prevents an output transient when the sup-
ply is turned off by removing the turn-on bias from the se-
ries regulators and shorting the -6.2V reference supply as
the voltage of the -12.4 Vsupply falls below -9 volts.
4-40 013 switches the bias to the -20-volt regulator on
and off, 014 switches the short across the -6.2-volt refer ...
ence supply, and 015 switches the bias to the +20-volt and
+6-volt or +18-volt regulators. 015 remains turned off until
VR2 conducts at 9volts to switch it on. While 015 is off,
it holds 013 biased off and 014 on; when 015 conducts,
it turns 013 and 014 off.
4-41 Meter Circuits
4-42 Voltmeter. Two of the resistors in resistor network
Z1 are range resistors for the voltmeter. The accurate ratio
of these resistors permits asingle calibration potentiometer,
R58 to adjust both ranges simultaneously.
4-43 Ammeter. The range switch connects the ammeter
across the current monitoring resistor of asupply: R48 in
the +6-volt or +18-volt supply, R8 in the +20-volt supply,
or R28 in the -20-volt supply. Each of these resistors con-
ducts a constant bias current for its series regulator transistor
in addition to the supply's output current. If no compen-
sation were used, this additional current would raise the
indicated output by up to 8% of full scale. The resistor net-
works connected to each range of the ammeter selector
switch apply abias to the meter to offset this error. R59
calibrates all ammeter ranges.

5-1
INTRODUCTION
SECTION V
MAINTENANCE
5-5 Table 5-1 lists the test equipment required to per-
form the various procedures described in this section.
5-2 Upon receipt of the power supply, the performance
test of Paragraph 5-6 can be made. This test is suitable for
incoming inspection. Section III contains a quick but less
comprehensive checkout procedure which can be used in
lieu
of the performance test if desired.
5-3 If a
fault is detected in the power supply while
making the performance test or during normal operation:
proceed to the troubleshooting procedure in Paragraph 5-32.
After troubleshooting and repair, repeat the performance
test to ensure that the fault has been properly corrected and
that no other faults exist. Before performing any mainte-
nance checks, turn on the power supply and allow ahalf-
hour warm-up.
5-4 TEST EQUIPMENT REQUIRED
5-6 PERFORMANCE TEST
5-7 The following test can be used as an incoming in-
spection check and appropriate portions of the test can be
repeated to check the operation of the instrument after
repairs. If the correct result is not obtained for a particular
check, proceed to the troubleshooting procedures of Para~
graph 5-32.
-- CAUTION--
Before applying power to the supply, make
certain
that its line voltage selector switch (S3)
is set for the line voltage to be used. (See
CA UTION notice in Paragraph 3-2 for addi-
tional information on S3.)
Table 5-1. Test Equipment Required
REQUIRED
RECOMMENDED
TYPE CHARACTERISTICS
USE MODEL
,
Digital
Sensitivity:
100J1V fyll scale Measure DC voltages: HP 3450A
Voltmeter
(min.). Input impedance:
calibration procedures
10 megohms (min.'.
Variable Range:
90-130 Vac Vary AC input ------
Voltage
Equipped with voltmeter
Transformer
accurate within 1 volt
Oscilloscope
Sensitivity:
100J1V/cm. Display
transient re- HP 180A with 1821A,
Differential
input.
sponse and ripple and
and 1801A or 1803A
noise waveforms.
plug-ins.
Repetitive
Rate: 60 Hz, 2J1sec.
Measure transient
See Figure 5-5.
Load Sw. rise
and fall time
response.
Resistive Val ue: See Paragraph 5-11.
Power supply load
James G. Biddle
Loads
Tolerance: ±5% resistor (fixed resistor
("Lubri-Tact"
or rheostat).
Rheostat)
Current
Value: See Paragraph 5-13. Measure
output current
Simpson Portable
Sampling
Accuracy:
1% (minimum)
Shunt, 06703.
Resistor (Shunt)
5-1

5-8 General Measurement Techniques
5-9 Connecting Measuring Devices. To achieve valid
results when measuring the load effect, PARD (ripple and
noise), and transient recovery time of the supply, measuring
devices
must be connected as close to the output terminals
as possible. A measurement made across the load includes
the impedance of the leads to the load. The impedance of
the load leads can easily be several orders of magnitude
greater than the supply impedance and thus invalidate the
measurement. To avoid mutual coupling effects, each
measuring device must be connected directly to the output
terminals by separate pairs of leads.
5-10 When
measurements are made at the front panel
terminals,
the monitoring leads must be connected at point
A, as shown in Figure 5-1, and not at point B. Connecting
the measuring device at point B would result in ameasure-
ment that includes the resistance of the leads between the
output terminals and the point of connection.
LOAD LEAD
Figure 5-1. Front Panel Terminal Connections
5-11 Selecting Load Resistors. Power supply specifica-
tions are checked with afull load resistance connected
across the supply output. The resistance and wattage of
the load resistor, therefore, must permit operation of the
supply at its rated output voltage and current. For example,
a supply rated at 20 volts and 0.5 amperes would require a
load resistance
of 40 ohms at the rated output voltage. The
wattage rating of this resistor would have to be at least 10
watts.
5-12 Either afixed
or variable resistor (rheostat) can be
used as
the load resistance. Using a rheostat (alone or in
series with afixed resistor) is often more convenient than
using fixed resistors as loads because the latter may be more
difficult to obtain in the exact resistance required. Asup-
plier
of rheostats appropriate for testing these supplies is
listed in Table 5-1.
5-13 Output Current Measurements. For accurate out-
put current measurements, a current sampling resistor
should be inserted between the load resistor and the output
of the supply. An accurate voltmeter is then placed across
the sampling resistor and the output current calculated by
5-2
dividing
the voltage across the sampling resistor by its
ohmic value. The total resistance of the series combination
should be equal to the full load resistance as determined in
the preceding paragraphs. Of course, if the value of the
sampling resistor is very low when compared to the full
load resistance,
the value of the sampling resistor may be
ignored. The meter shunt recommended in Table 5-1, for
example, has aresistance of only 1milliohm and can be
neglected when calculating the load resistance of the sup-
ply.
5-14 Figure 5-2 shows a
four terminal meter shunt. The
load current through a shunt must be fed to the extremes
of the wire leading to the resistor while the sampling con-
nections are
made as close as possible to the resistance
portion itself.
CURRENT SAMPLING
TERMINALS
TO UNGROUNDED TO GROUNDED
TER MI NAL OF "-.JV.'(/\r---~\/v\,,-I(",l--'" TE RM IN AL OF
POWER
SUPPLY POWER SUPPLY
Figure 5-2. Current Sampling Resistor Connections
NOTE
All instructions in this section apply to Models
6236A
and 6237 Aunless otherwise indicated.
5-15 Rated Output, Tracking, Meter Accuracy,
and
Current limit
5-16 To check that all supplies will furnish their maxi-
mum rated output voltage and current, that the ±20V out-
puts track each other, that the front panel meters are accu-
rate, and that the current limit circuits function, proceed
as follows:
Voltmeter Accuracy
a. With no loads connected: energize the supply, con-
nect adigital voltmeter between the +6V terminal (+18V
in Model 6237 A) and common (COM), and set the +6V
(+18V) VOLTAGE
control so that the DVM indication is as
near
as possible to 6volts (18 volts).
b.
Set the METER switch to the +6V (+18V) range and
check the front panel voltmeter indication. It should be
within 4%
of the DVM indication.
c. Check the +20V and -20V ranges of the panel volt-
meter similarly by connecting the DVM to each of these
outputs in turn, setting the ±20V VOLTAGE control for a

20V DVM indication, and verifying that the panel meter is
accurate within 4%.
Tracking
d. Connect the DVM to the +20V output, set the ±20V
VOLTAGE control for aDVM indication of 20 volts, and
reconnect the DVM to the -20V output without disturbing
the voltage control. The voltage at the -20V output should
be within 1% of the +20V output.
Rated Output and Ammeter Accuracy
e. Connect 40[2 10W load resistors across both of the
20V outputs of the supply and set the ±20V vaL TAG E
control for a ±20V output. (All three supplies must be
fully
loaded while checking the rated output voltage and
current of each supply.)
f. Connect the test setup shown in Figure 5-3 to the +6V
(or
+18V) output. Make the total resistance of RL and the
current sampling resistor 2.4 ohms for the Model 6236A (or
18 ohms for the 6237 A) to permit operating the output at
full load. RL should have a power rating of at least 20 watts.
g. Close the switch and set the +6V (+18V) VOLTAGE
control so that the DVM indicates avoltage drop across the
current sampling resistor that corresponds to a current of
2.5 amps (6236A) or 1.0 amp (6237 A).
h.
Set the METER switch to the +6V (+18V) range and
verify that the front panel ammeter indication is within 4%
of 2.5 amps ((6236A) or 1.0 amps (6237 A).
i. Connect the DVM directly across the output terminals
of the +6V (+18V) supply, record the DVM reading, and
then open the switch in the 6V (18V) load circuit without
disturbing the supply's output terminals. The DVM indica-
tion should not change by more than 2.6mV (6236A) or
3.8mV (6237 A).
j. Check the rated output and ammeter accur'!cy of the
+20V and -20V supplies similarly by connecting the test
setup of Figure 5-3 to each output in turn. For each 20V
supply: make the total resistance of RL and the current
sampling resistor 40 ohms, set the ±20V VOLTAGE con-
trol for a current indication on the DVM of 0.5A, check that
the panel meter indication is within 4% of 0.5A, connect the
DVM to the fully loaded output terminals, and compare the
output voltage before and after the load circuit is opened.
The voltage should not change by more than 4mV. While
checking each supply, the other two must be fully loaded.
Current Limit
k.
Disconnect all loads from the supply.
I. Connect the test setup shown in Figure 5-3 to the +20-
volt output. Substitute a short for RL and leave the load
circuit switch open.
m. Set the voltage of the :t20V supplies to 20 volts.
n. Close
the load switch and determine the current flow
through the current sampling resistor (meter shunt) by
measuring its voltage drop with the DVM. The current
5-3
should be 0.55A ±5%.
o. Check
the current limit of the -20V supply in the
same way. Its short-circuit current should also be 0.55A
±5%.
p. (Model
6237A only). Check the current limit of the
+18V supply similarly by setting its output for 18 volts and
using aDVM to measure the current which flows through
alow-resistance current sampling resistor. The short-circuit
current of the +18V supply should be 1.1 A±5%.
q. (Steps (q)
through (s) apply to the 6236A only.)
Connect the test setup shown in Figure 5-3 to the +6V out-
put. Close the switch, set the total resistance of R Land
the current sampling resistor to an initial value of 2.4 ohms
or greater, and set the output voltage to 6volts.
r. Reduce the value of RL gradually while observing the
output current indicated by the DVM. The current should
increase to a maximum of 2.75A ±5% before it begins to
decrease.
s. Connect a short across RL and then recheck the current
indicated by the DVM. The short-circuit current of this
output should be 1A ±15%. Disconnect the test setup from
the supply.
5-17 Load Effect (Load Regulation)
Definition: The change ~EOUT in the static
value of dc output voltage resulting from achange in load
resistance
from open circuit to avalue which yields maxi-
mum rated output current (or vice versa).
5-18
To check the load effect:
a. Connect afull load resistance and adigital voltmeter
across the output of the +20V supply.
b. Turn on the supply and adjust its voltage to its maxi-
mum rated value.
c.
Record the voltage indicated on the DVM.
d.
Disconnect the load resistance and recheck the DVM
indication. It should be within .01% plus 2mV of the read-
ing
in step (c).
e.
Repeat steps (a) through (d) for each of the remain-
ing
supply outputs.
POWER SUPPLY
UNDER TEST
-
COM.
+RL
0
()
("\.
)'
TV
1DIGITAL
(RHEOSTAT)
VOLTMETER
CURRENT + - G
SAMPLING
( (l9
RESISTOR
~
- f' .~ -
(SHUNT)
Figure 5-3. Output Current, Test Setup

5-19 Source Effect (Line Regulation)
Definition: The change, b. E
OUT
'in the static
value of dc output vcltage resulting from a change in ac
input voltage over the specified range from low line (typi-
cally
104 Vac) to high line (typically 127 Vac), or from
high line to low line.
rectification), an oscilloscope display showing a 120 Hz
fundamental component is indicative of a "c1ean" measure-
ment setup, while the presence of a 60 Hz fundamental
usually means that an improved setup will result in a more
accurate (and lower) value of measured ripple.
5-24 Figure
5-48 shows a correct method of measuring
the output ripple of a constant voltage power supply using
asingle-ended
scope. The ground loop path is broken by
floating the power supply output. To ensure that no poten-
tial difference exists between the supply and the oscilloscope,
it
is recommended that they both be plugged into the same
ac
power bus. If the same bus cannot be used, both ac
grounds must be at earth ground potential.
5-20 To test the source effect:
a. Connect avariable autotransformer between the in-
put power source and the power supply line plug.
b. Connect afull load resistance and adigital voltmeter
across the output of the +20V supply.
c. Adjust the autotransformer for alow line input.
d. Turn on the power, adjust the output of the supply
to its maximum rated voltage, and record the DVM indica-
tion.
e. Adjust the autotransformer for ahigh line input and
recheck the DVM indication. It should be within .01 %plus
2mV of the reading in step (d).
f. Repeat steps (b) through (e) for each of the remaining
supply outputs.
POWER SUPPLY CASE
•
OSCILLOSCOPE CASE
Figure 5-4. Ripple and Noise, Test Setup
AC-+---
ACC
GND
,..---f-..,.,....,~ AC
ACC
GND
I
I
I
VERTICAL I
.xr-+----~~G INPUT I
:--~~EG I
L ~_~~ __ ---_J
A. INCORRECT METHOD -GROUND CURRENT IG PRODUCES 60
CYCLE DROP IN NEGATIVE LEAD WHICH ADDS TO THE POWER
SUPPLY RIPPLE DISPLAYED ON SCOPE.
POWER
SUPPLY CASE
OSCILLOSCOPE CASE
AC f,C
ACC
ACC
GND
GND
++
-VERTICAL
GGINPUT
POWER SUPPLY CASE OSCILLOSCOPE CASE
AC
AC
ACC ACC
GND
GND ++
-VERTICAL
GG
INPUT
B. ACORRECT METHOD USING A SINGLE -ENDED SCOPE.
OUTPUT FLOATED TO
BREAK GROUND CURRENT LOOP,
TWISTED PAIR REDUCES STRAY PICKUP ON SCOPE
LEADS.
C. ACORRECT METHOD USING A DIFFERENTIAL SCOPE WITH
FLOATING INPUT. GROUND CURRENT PATH
IS BROKEN;
COMMON MODE REJECTION
OF DIFFERENTIAL INPUT SCOPE
IGNORES DIFFERENCE IN GROUND POTENTIAL OF POWER
SUPPLY 8SCOPE, SHIELDED TWO WIRE FURTHER
REDUCES
STRAY PICKUP ON SCOPE LEADS.
5-21 PARD (Ripple and Noise)
Definition: The residual ac voltage which is super-
imposed on the dc output of aregulated power supply.
Ripple and noise may be specified and measured in terms
of its rms or peak-to-peak value.
5-22 Measurement Techniques. Figure 5-4A shows an
incorrect method of measuring Pop ripple. Note that acon-
tinuous ground loop exists from the third wire of the input
power cord of the supply to the third wire of the input
power cord of the oscilloscope via the grounded power sup-
ply case,
the wire between the negative output terminal of
the power supply and the vertical input of the scope, and
the grounded scope case. Any ground current circulating
in this loop as aresult of the difference in potential EG
between the two ground points causes an IR drop which
is in series with the scope input. This IR drop, normally
having a 60 Hz Iine frequency fundamental, plus any pick-
up on the unshielded leads interconnecting the power sup-
ply
and scope, appears on the face of the CRT. The magni-
tude of this resulting signal can easily be much greater than
the true ripple developed between the plus and minus out-
put terminals of the power supply and can completely in-
validate
the measurement.
5-23 The same ground current and pickup problems can
exist if an rms voltmeter is substituted in place of the oscil-
loscope
in Figure 5-4. However, the oscilloscope display,
unlike
the true rms meter reading, tells the observer imme-
diately whether the fundamental period of the signal dis-
played is 8.3 milliseconds (1/120 Hz) or 16.7 milliseconds
(1/60 Hz). Since the fundamental ripple frequency present
on the output of an HP supply is 120 Hz (due to full-wave
5-4

c. Repeat for the remaining supply outputs.
OSCILLOSCOPE
RT
(NOTE 4)
NOTES:
I. THIS DRAWING SHOWS A
SUGGESTED METHOD OF
BUILDING ALOAD SWITCH.
HOWEVER. OTHER
METHODS COULD BE USED;
SUCH AS ATRANSISTOR
SWITCHING NETWORK.
MAXIMUM LOAD RATINGS
OF LOAD SWITCH ARE:
5AMPS.500V, 250W (NOT
2500W l.
2. USE MERCURY RELAY
CLARE TYPE HGP
1002
OR W.E. TYPE 276B.
3. SELECT CONTACT PRO-
TECTION NETWORK
ACCORDING TO MERCURY
RELAY MANUFACTURERS
INSTRUCTIONS
4. EACH RT IS EQUAL TO
TWICE THE
NORMAL FULL
LOAD RESISTANCE
(2 XRL)
USED IN PREVIOUS TESTS.
CONTACT
PROTECTION
NETWORK
r- (NOTE 3)------
r---- -----
IN.C.
I
I
I
I
-,
I
:t :
IN.C. I
I I
I
I
I
I
I
I
II
I REPETITIVE I
~~~ ~W~~_(!::02.E~) __ .J
+
POWER SUPPLY
UNDER TEST
Figure 5-5. Load Transient Recovery Time, Test Setup
5-29 Load Transient Recovery Time
Definition: The time "x" for output voltage
recovery
to within "Y" millivolts of the nominal output
voltage following a "Z" amp step change in load current,
where: "X" equals 50J,lsec, "Y" equals 15mV, and "z"
is the specified load current change, equal to half of the cur-
rent rating of the supply. The nominal output voltage is
defined as the dc level halfway between the static output
voltage before and after the imposed load change.
5-30 Measurement Techniques. Care must be taken in
switching the load resistance on and off. A hand-operated
switch in series with the load is not adequate since the re-
sulting
one-shot displays are difficult to observe on most
oscilloscopes and the arc energy occurring during switching
completely masks the display with anoise burst. Transistor
load switching devices are expensive if reasonably rapid load
current changes are to be achieved. Instead, a mercury-
wetted relay should be used for loading and unloading the
supply. Connect it in the load switching circuit shown in
Figure 5-5. When this load switch is connected to a 60 Hz
ac input, the mercury-wetted relay will open and close 60
times per second. The 25K control adjusts the duty cycle
of the load current switching to reduce jitter in the oscillo-
scope display. This relay
may also be used with a 50 Hz
ac input.
5-25 Either a twisted pair or, preferably, ashielded
two-wire cable
should be used to connect the output termin-
als of the power supply to the vertical input terminals of
the scope. When using a twisted pair, care must be taken
that one of the two wires is connected to the grounded in-
put terminal of the oscilloscope to ensure that the supply
output is safely grounded. When using shielded two-wire,
it
is essential for the shield to be connected to ground at
one end only to prevent ground current flowing through
this shield from inducing asignal in the shielded leads.
5-27
In most cases, the single-ended scope method of
Figure 5-4B will be adequate to eliminate non-real compon-
ents of ripple so that a satisfactory measurement may be
obtained. However, in more stubborn cases (or if high
frequency noise up to 20 MHz must be measured), it may
be necessary to use adifferential scope with floating input
as shown in Figure 5-4C. If desired, two single-conductor
shielded cables may be substituted in place of the shielded
two-wire cable
with equal success. Because of its common
mode rejection, a differential oscilloscope displays only the
difference in signal between its two vertical input terminals,
thus ignoring the effects of any common mode signal pro-
duced by the difference in the ac potential between the
power supply case and scope case. Before using adifferen-
tial
input scope in this manner, however, it is imperative
that the common mode rejection capability of the scope'
be verified by shorting together its two input leads at the
power supply and observing the trace on the CRT. it this
trace is a straight line, then the scope is properly ignoring
any
common mode signal present. If this trace is not a
straight line, then the scope is not rejecting the ground
signal-and must be realigned in accordance with the manu-
facturer's instructions until proper common mode rejection
is attained.
5-26 To verify that the oscilloscope is not displaying
ripple
that is induced in the leads or picked up from the
grounds, the (+) scope lead should be shorted to the (-)
scope lead at the power supply terminals. The ripple value
obtained when the leads are shorted should be subtracted
from the actual ripple-measurement.
5-28 Measurement Procedure. To measure the ripple
and noise on each supply output, follow the steps below,
If ahigh frequency noise measurement is desired, an oscil-
loscope
with sufficient bandwidth (20 MHz) must be used.
Ripple
and noise measurements can be made at any input
ac line voltage combined with any dc output voltage and
load current within rating.
a. Connect an oscilloscope or rms voltmeter across an
output of the supply as shown in Figures 5-4B or 5-4C.
b. Energize the supply and observe the oscilloscope or
meter indication. The ripple and noise should not be
greater than 0.35mV rms or 1.5mV peak-to-peak.
5-5

5-31 Measurement Procedure. To measure the load
transient recovery time, follow the steps below for each
supply output. Transient recovery time may be measured
at any input line voltage and any output voltage within
rating. For this supply the specified load change is between
half load and full load.
a. Connect the test setup shown in Figure 5-5. Both
load resistors (RT)are
twice the normal value of afull load
resistance.
b.
Turn on the supply and close the line switch on the
repeti+ive load switch.
c.
Set the oscilloscope for internal sync and lock on
either the positive or negative load transient spike.
d.
Set the vertical input of the oscilloscope for ac coup-
ling so that small dc level changes in the output voltage of
the power supply will not cause the display to shift.
e.
Adjust the horizontal positioning control so that the
trace starts at a point coincident with a major graticule
division. This
point then represents time zero.
f. Adjust the vertical centering of the scope so that the
tail ends of the no-load and full-load waveforms are symmet-
rically displaced about the horizontal center line of the oscil-
loscope. This
center line now represents the nominal output
voltage defined in the specification.
g. Increase the sweep rate so that asingle transient spike
can be examined in detail.
h.
Adjust the sync controls separately for the positive
and negative going transients so that not only the recovery
waveshape
but also as much as possible of the rise time of
the transient is displayed.
i. Starting from the major graticule division representing
time zero, count to the right 50psec and vertically 15mV.
Recovery should be within these tolerances, as illustrated
in Figure 5-6.
5-32 TROUBLESHOOTING
5-33 Before attempting to troubleshoot this instrument,
ensure that the fault is in the instrument itself and not in an
associated piece
of equipment. You can determine this with-
out removing the covers from the instrument by using the
appropriate portions of the performance test of Paragraph
5-6.
5-34 A
good understanding of the principles of opera-
tion is ahelpful aid in troubleshooting, and the reader is
advised to review Section IV of the manual before begin-
ning
detailed troubleshooting. Once the principles of oper-
ation are understood, proceed to the initial troubleshoot-
ing procedures in Paragraph 5-35.
-- CAUTION--
Before applying power to the supply, make
certain
that its line voltage selector switch (S3)
is set for the line voltage to be used. (See
CAUTION notice in Paragraph 3-2 for additional
information on S3.)
5-35 Initial Troubleshooting Procedure
5-36 If a malfunction is found, follow the steps below:
a.
Disconnect input power from the supply and remove
all loads from the output.
b. Table 5-2 lists the symptoms and probable causes of
several possible troubles. If the symptom is one of those
listed, make the recommended checks.
c. If
none of the symptoms of Table 5-2 apply, proceed
to Table 5-3. This table provides an initial troubleshooting
procedure that also directs you to the more detailed pro-
cedures which follow it.
Figure 5-6. Load
Transient Recovery Time Waveforms
POSITIVE OUTPUT-UNLOADING TRANSIENT LOADING TRANSIENT
NEGATIVE OUTPUT-LOADING TRANSIENT UNLOADING TRANSIENT
Open Fuse Troubleshooting
5-38
5-37 The numbered test points referred to in the trouble-
shooting procedures are identified on the circuit schematic
and on the component location diagram at the rear of the
manual.
5-39 Although transients or fatigue can cause afuse to
blow, it is a good idea to inspect the unit for obvious shorts
such as damaged wiring, charred components, or extraneous
metal parts or wire clippings in contact with circuit board
conductors before replacing the fuse. The rating of the
correct replacement fuse depends on the line voltage option
of the instrument: for Options 100 or 120, use anormal
time-constant 2-amp fuse (HP Part No. 2110-0002); for
Options 220 or 240, use a normal time-constant 1-amp
fuse (HP
Part No. 2110-0001).
v
15MV
~ 14----.~-- 50",
SECONDS
E
NOM
-r--,---------
50",
SECONDS
15 MV
T
5-6