HP BENCH Series Service manual

DC POWER SUPPLY
BENCH SERIES
MODEL 6215A
OPERATING AND SERVICE MANUAL
FOR SERIALS 8G250I - 4200
For Serials Above 8G4200
Check for inclusion of
change page.
For Serials Below 8G2 501
Refer to Appendix A.
100 Locust Avenue, Berkeley Heights, New Jersey 07922
HP Part No. 06215-90001 Printed: January, 1969

TABLE OF CONTENTS
Section Page No.
I GENERAL INFORMATION 1-1
1-1 Description 1-1
1-5 Specifications 1-1
1-7 Options 1-1
1-9 Accessories 1-1
1-11 Instrument/Manual Identification 1-1
1-14 Ordering Additional Manuals 1-1
Section page No.
IV PRINCIPLES OF OPERATION (CONTINUED)
II INSTALLATION
2-1 Initial Inspection
Mechanical Check
Electrical Check
Installation Data
Location
2-11 Outline Diagram
2-13 Rack Mounting
2-15 Input Power Requirements
Connections for 230V Operation
Power Cable
2-3
2-5
2-7
2-9
2-17
2-19
2-22 Repackaging For Shipment
111 OPERATING INSTRUCTIONS
2-1
2-1
2-1
2-1
2-1
2-1
2-1
2-1
2-2
2-2
2-2
2-2
3-1
3-1
Turn-On Checkout Procedure
3-1
3-3
Operation
3-1
3-5
Constant Voltage
3-1
3-7
Changing Current Limit
3-1
3-9
Connecting Load
3-1
3-12
Operation of Supply Beyond
Rated Output
3-2
3-14
Optional Operating Modes
3-2
3-15
Series Operation
3-2
3-17
Parallel Operation
3-2
3-19
Special Operating Considerations 3-2
3-20
Pulse Loading
3-2
3-22
Output Capacitance
3-2
3-24
Reverse Current Loading
3-2
PRINCIPLES OF OPERATION
4-1
4-1
Simplified Discussion
4-1
4-5
Detailed Circuit Analysis
4-2
4-6 Feedback Loop
4-11 Series Regulator
4-13 Constant Voltage Input Circuit
4-17 Driver and Error Amplifier
4-20 Current Limiting Circuit
4-22 Reference Circuit
4-2 6 Meter Circuit
V MAINTENANCE
5-1 Introduction
5-3 Cover Removal and Replacement
5-6 General Measurement Technique
5-11 Test Equipment Required
5-13 Performance Test
5-15 Rated Output and Meter Accuracy
5-18 Load Regulation
5-20 Line Regulation
5-35 Output Impedance
5-38 Current Limit
5-40 Transient Recovery Time
5-46 Troubleshooting
5-48 Trouble Analysis
5-53 Repair and Replacement
5-55 Adjustment and Calibration
5-57 Meter Mechanical Zero
5-59 Meter Calibration
5-61 Zero Volts Output Adjustment
5-63 Output Current Limit Adjustment
VI REPLACEABLE PARTS
6-1 Introduction
6-4 Ordering Information
Reference Designators
Abbreviations
Manufacturers
6-8 Code List of Manufacturers
Parts List Table
4-2
4-2
4-2
4-3
4-3
4-3
4-3
5-1
5-1
5-1
5-1
5-2
5-3
5-3
5-3
5-3
5-6
5-7
5-7
5-8
5-8
5-11
5-13
5-13
5-13
5-13
5-13
6-1
6-1
6-1
6-2
APPENDK A
A-1

MANUAL CHANGES
DC POWER SUPPLY
Model 6215A
Manual Serial Number Prefix 8M
Make all corrections in the manual according to errata below, then check the following table for your power
supply serial number and enter any listed change (s) in the manual.
SERIAL
MAKE
CHANGES
Prefix
Number
9C 4201 - 4450 1
ALL
-
Errata
9C
4451 - up 1,2
CHANGE 1:
In replaceable parts table, make the following
change:
R12: Change to IKn. ±5% 3W, Part No. 0813-
0001.
ERRATA:
On Page 5-4, Figure 5-5, change Rl for Models
6215A and 6216A to 62.5,^..
Change Paragraph 3-18, third sentence to read as
follows:
"The output of each power supply can be set
separately."
CHANGE 2:
In replaceable parts table, make the following
change:
R28: 820^, ±5%, ^W, ($ Part No. 0686-8215.
ERRATA:
On the Title Page, change the serial number in
formation to read: "FOR SERIALS 8G2501-4200.
For Serials Below 8G2501, Refer to Appendix A."
4-27-70

TABLE OF CONTENTS (CONTINUED)
LIST OF TABLES
Table
I-I
5-1
5-2
5-3
Specifications
Test Equipment Required
Common Troubles
Reference, Bias, and Filtered DC
Troubl e s hooting
Page No.
1-2
5-2
5-9
5-10
Table
5-4
5-5
5-6
5-7
Low Output Voltage Troubleshooting
High Output Voltage Troubleshooting
Selected Semiconductor
Characteristics
Calibration Adjustment Summary-
Page No.
5-10
5-11
11
13
LIST OF ILLUSTRATIONS
Figure
1-1
2-1
2-2
2-3
3-1
4-1
5-1
5-2
DC Power Supply
Outline Diagram
Page No.
i V
2-1
Rack Kit with Three BENCH Supplies 2-1
Input Power Transformer Connections 2-2
Front Panel Controls and Indicators 3-1
Simplified Schematic 4-1
Front Panel Terminal Connections 5-1
Output Current Measurement
Technique 5-1
Figure Page No.
5-3 Differential Voltmeter Substitute
Test Setup 5-3
5-4 Output Current, Test Setup 5-3
5-5 Load Regulation, Test Setup 5-4
5-6 Ripple and Noise, Test Setup 5-5
5-7 Noise Spike Test Setup 5-6
5-8 Output Impedance, Test Setup 5-6
5-9 Transient Recovery Time, Test Setup 5-7
5-10 Transient Recovery Time, Waveforms 5-8
5-11 Servicing Printed Wiring Boards 5-12
iii

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Figure 1-1. DC Power Supply
iv

SECTION I
GENERAL INFORMATION
1-1 DESCRIPTION
1-2 This power supply, Figure 1-1. is completely
transistorized and suitable for either bench or relay
rack operation. It is a compact, regulated. Con
stant Voltage/Current Limiting supply. The output
voltage can be continuously adjusted throughout the
output voltage range. The power supply is fully pro
tected from overloads by a fixed current limit which
is set by means of an internal adjustment. The cur
rent limit circuit permits series and parallel connec
tion of two or more supplies when greater voltage or
current is desired.
1-3 Either the positive or negative output terminal
may be grounded or the power supply can be opera
ted floating at up to a maximum of 300 volts off
ground.
1-4 A single meter is used to measure either out
put voltage or output current in volts and milliamps,
respectively. The voltage or current range is selec
ted by the METER switch on the front panel.
1-5 SPECIFICATIONS
1-6 Detailed specifications for the power supply
are given in Table 1-1.
1-7 OPTIONS
1-8 Options are factory modifications of a stand
ard instrument that are requested by the customer.
The following options are available for the instru
ment covered by this manual. Where necessary, de
tailed coverage of the options is included through
out the manual.
Option No. Description
28 230Vac, 50-400Hz, Single-Phase
Output: Factory modification consists
of reconnecting the input transformer
for 230Vac operation. Refer to Section
II for further details.
1-9 ACCESSORIES
1-10 The accessories listed in the following chart
may be ordered with the power supply or separately
from your local Hewlett-Packard field sales office
(refer to list at rear of manual for addresses).
(fe Part No. Description
1452lA 3|-" High Rack Kit for mounting up to
three BENCH supplies. (Refer to Sec
tion II for details.)
14522A 7" High Rack Kit for mounting up to
six BENCH supplies. (Refer to Sec
tion II for details.)
1-11 INSTRUMENT/MANUAL IDENTIFICATION
1-12 Hewlett-Packard power supplies are identified
by a three-part serial number tag. The first part is
the power supply model number. The second part is
the serial number prefix, which consists of a num
ber-letter combination that denotes the date of a
significant design change. The number designates
the year, and the letter A through L designates the
month, January through December respectively. The
third part is the power supply serial number.
1-13 If the serial number prefix on your power sup
ply does not agree with the prefix on the title page
of this manual, change sheets are included to up
date the manual. Where applicable, backdating
information is given in an appendix at the rear of
the manual.
1-14 ORDERING ADDITIONAL MANUALS
1-15 One manual is shipped with each power sup
ply. Additional manuals may be purchased from
your local Hewlett-Packard field office (see list at
rear of this manual for addresses). Specify the
model number, serial number prefix, and ($i stock
number provided on the title page.
1-1

Table 1-1. Specifications
INPUT:
105-125Vac, single phase, 50-400Hz.
OUTPUT:
0-25Vdc, 0-400mA.
LOAD REGULATION:
Less than 0.01% plus ImV for a full load to no
load change in output current.
LINE REGULATION:
Less than 0.01% plus 4mV for any line voltage
change within the input rating.
RIPPLE AND NOISE:
Less than 200|j.Vnns/lmV p-p (dc to 20MHz).
TEMPERATURE RANGES:
Operating: 0 to 55°C. Storage: -40 to +85°C.
TEMPERATURE COEFFICIENT:
Less than 0.02% plus ImV per degree Centi
grade.
STABILITY:
Less than 0.10% plus 5mV total drift for 8 hours
after an initial warm-up time of 30 minutes at
constant ambient, constant line voltage, and
constant load.
INTERNAL IMPEDANCE AS A CONSTANT VOLT
AGE SOURCE:
Less than 0.03 ohms from dc to IkHz.
Less than 0.5 ohms from IkHz to lOOkHz.
Less than 3.0 ohms from lOOkHz to IMHz.
TRANSIENT RECOVERY TIME:
Less than 50[j.sec for output recovery to within
lOmV following a full load current change in the
output.
OVERLOAD PROTECTION:
A fixed current limiting circuit protects the
power supply for all overloads including a direct
short placed across the output terminals in con
stant voltage operation.
METER:
The front panel meter can be used as either a
0-30V voltmeter or as a 0-500mA ammeter.
OUTPUT CONTROLS:
Coarse and fine voltage controls set desired
output voltage. Meter switch selects voltage or
current.
OUTPUT TERMINALS:
Three "five-way" output posts are provided on
the front panel All power supply output terminals
are isolated from the chassis and either the posi
tive or negative terminal may be connected to the
chassis through a separate ground terminal located
on the output terminal strip.
COOLING:
Convection cooling is employed. The supply
has no moving parts.
SIZE:
5i"/13,34cm W x 3i"/8,26cm H x 7"/l7„78cm D.
Using a Rack Mounting Kit, three units can be
mounted side by side in a standard 19" relay rack.
■WEIGHT:
5.25 lbs./2,38 kg. net, 71bs./3,17kg. shipping.
FINISH: DarkCray
POWER CORD:
A three-wire, five-foot power cord is provided
with each unit.
1-2

SECTION II
INSTALLATION
mnTTTTm
-
REAR
Figure 2-1. Outline Diagram
2-1 INITIAL INSPECTION
2-2 Before shipment, this instrument was inspec
ted and found to be free of mechanical and electri
cal defects. As soon as the instrument is unpacked,
inspect for any damage that may have occurred in
transit. Save all packing materials until the in
spection is completed. If damage is found, proceed
as described in the Claim for Damage in Shipment
section of the warranty page at the rear of this
manual.
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 scratched or cracked.
2-5 ELECTRICAL CHECK
2-6 The instrument should be checked against its
electrical specifications. Section V includes an
"in-cabinet" performance check to verify proper in
strument operation.
2-7 INSTALLATION DATA
2-8 The instrument is shipped ready for bench
operation. It is necessary only to connect the in
strument to a source of power and it is ready for
operation.
2-9 LOCATION
2-10 This instrument is air cooled. Sufficient
space should be allotted so that a free 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 ex
ceed 550c.
2-11 OUTLINE DIAGRAM
2-12 Figure 2-1 illustrates the outline shape and
dimensions of Models 62I3A through 62I8A.
2-13 RACK MOUNTING
2-14 This instrument may be rack mounted sepa
rately or with a maximum of two other BENCH
Series supplies as shown in Figure 2-2. The
Figure 2-2. Rack Kit with Three BENCH Supplies
2-1

units are placed in the Rack Mounting Frame. The
Rack Mounting Frame is then fastened to the rack
frame.
2-15 INPUT POWER REQUIREMENTS
2-16 This power supply may be operated continu
ously from either a nominal 115 Volt or 230 Volt
50-400HZ power source. The unit as shipped from
the factory, is wired for 115 Volt operation. The
input power required when operated from a 115 Volt
power source at full load is:
Model Input Current
6213A and 6214A 0.29A
6215A and 6217A 0.25A
6216A and 6218A 0.25A
Input Power
28W
26W
26W
2-17 CONNECTIONS FOR 230 VOLT OPERATION
(Figure 2-3)
2-18 Normally, the two primary windings of the
input transformer are connected in parallel for op
eration from 115 Volt source. To convert the power
supply to operation from a 230 Volt source, the
power transformer windings are connected in series
as follows:
a. Unplug the line cord and remove the top
cover as described in Paragraph 5-3.
b. Remove the jumpers between taps 4-2 and
3-1. Solder a jumper between taps 3-2 on the input
power transformer Tl, see Figure 2-3.
c. Replace existing fuse with a 0.5 Ampere,
230 Volt fuse.
d. Replace existing line cord plug with a
standard 230 Volt plug.
2-19 POWER CABLE
2-20 To protect operating personnel, the National
Electrical Manufacturers Association (NEMA) recom
mends 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
TRANSFORMER PRIMARY
CONNECTED FOR
115-VOLT OPERATION
TRANSFORMER PRIMARY
CONNECTED FOR
230-VOLT OPERATION
Figure 2-3. Input Power Transformer, Connections
into an appropriate receptacle, the instrument is
grounded. The offset pin on the power cable three-
prong connector is the ground connection.
2-21 To preserve the protection feature when oper
ating the instrument from a two-contact outlet, use
a three-prong to two-prong adapter and connect the
green lead on the adapter to ground.
2-22 REPACKAGING FOR SHIPMENT
2-23 To insure safe shipment of the instrument, it
is recommended that the package designed for the
instrument be used. The original packaging mate
rial is reusable. If it is not available, contact
your local Hewlett-Packard field otfice to obtain
the materials. This office will also furnish the ad
dress of the nearest service office to which the in
strument can be shipped. Be sure to attach a tag
to the instrument which specifies the owner, model
number, full serial number, and service required, or
a brief description of the trouble.
2-2

SECTION III
OPERATING INSTRUCTIONS
3-1 TURN-ON CHECKOUT PROCEDURE
3-5 CONSTANT VOLTAGE
3-2 The following checkout procedure describes
the use of the front panel controls and indicators
and ensures that the supply is operational;
a. Set AC toggle switch (1) upward to on
position; indicator (2) should light.
VOLTS
20 30 40
10 L L__/ 50
VOLTAGE
COARSE FINE
METER SELECTION
vOLTS^yjUgl^mA
+ GND
Figure 3-1. Front Panel Controls and Indicators
b. Set METER SELECTION switch (4) to
VOLTS position.
c. Turn COARSE (6) and FINE (5) VOLTAGE
controls fully ccw to ensure that output decreases
to OV, then turn the VOLTAGE controls fully cw to
ensure that output voltage increases to the maxi
mum rated output voltage.
d. Connect a milliammeter across the out
put of the supply (3) to check that the current
limit circuit within the supply is limiting the out
put current to:
Model Current Limit
6213A 1300 ±50mA
6215A 475 ±10mA
6217A 250 ±10mA
e. Remove milliammeter and connect load
to output terminals.
3-3 OPERATION
3-4 The power supply can be operated as a
single unit (normal operation), in parallel, or in
series. The output of the supply can be floated
up to 300 volts off ground.
3-6 To select a constant voltage output turn on
the supply and, with no load connected, adjust
the VOLTAGE controls for the desired output volt
age. To check the current limit, connect an ex
ternal ammeter across the output of the supply,
turn the VOLTAGE controls fully clockwise, and
observe the reading. The current limit is factory
adjusted in excess of the current rating of the
supply. If the existing current is not compatible
with the anticipated load requirements, the limit
can be changed as outlined in the following para
graphs.
3-7 CHANGING CURRENT LIMIT
3-8 The current limit can be varied by adjusting
resistor R50, located on the printed wiring board.
This adjustment procedure is described in Para
graph 5-63. The range of the current limit control
R50 is as follows:
Model Current Limit Range
6213A 800 - 1700mA
6215A 300 - 540mA
6217A 180 - 300mA
The current limit is normally adjusted to a
value far in excess of the current rating of the
supply to prevent the deterioration of line and
load regulation. Therefore, if for any reason the
current limit is adjusted so that the output current
is close to this value, the performance will not
meet the published specifications.
3-9 CONNECTING LOAD
3-10 Each load should be connected to the power
supply output terminals using separate pairs of
connecting wires. This will minimize mutual coup
ling effects between loads and will retain full ad
vantage of the low output impedance of the power
supply. Each pair of connecting wires should be
as short as possible and twisted or shielded to re
duce noise pickup. (If shield is used, connect
one end to power supply ground terminal and leave
the other end unconnected.)
3-11 If load considerations require that the output
power distribution terminals be remotely located
from the power supply, then the power supply out
put terminals should be connected to the remote
distribution terminals via a pair of twisted or
shielded wires and each load separately connected
3-1

to the remote distribution terminals.
3-12 OPERATION OF SUPPLY BEYOND RATED
OUTPUT
3-13 The shaded area on the front panel meter
face indicates the amount of output voltage or
current that is available in excess of the normal
rated output. Although the supply can be operated
in this shaded region without being damaged, it
cannot be guaranteed to meet all of its performance
specifications. However, if the line voltage is
maintained above 115 VAC, the supply will probably
ODerate within its specifications.
3-14 OPTIONAL OPERATING MODES
3-15 SERIES OPERATION
3-16 Normal Series Connections. Two or more
power supplies can be operated in series to obtain
a higher voltage than that available from a single
supply. When this connection is used, the output
voltage is the sum of the voltages of the individual
supplies. Each of the individual supplies must be
adjusted in order to obtain the total output voltage.
The power supply contains a protective diode con
nected internally across the output which protects
the supply if one power supply is turned off while
its series partner(s) is on.
3-17 PARALLEL OPERATION
3-18 Normal Parallel Connections. Two or more
power supplies can be connected in parallel to ob
tain a total output current greater than that avail
able from one power supply. The total output cur
rent is the sum of the output currents of the indi
vidual power supplies. The output CURRENT con
trols of each power supply can be separately set.
The output voltage controls of one power supply
should be set to the desired output voltage; the
other power supply should be set for a slightly
larger output voltage. The supply set to the lower
output voltage will act as a constant voltage
source; the supply set to the higher output will act
as a current limit source, dropping its output
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
3-20 PULSE LOADING
3-21 The power supply will automatically cross
over from constant voltage to current limit
operation in response to an increase (over the
preset limit) in the output current. 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. If this cross
over limiting is not desired, set the preset limit
for the peak requirement and not the average.
3-22 OUTPUT CAPACITANCE
3-23 An internal capacitor, across the output
terminals of the power supply, helps to supply
high-current pulses of short duration during con
stant voltage operation. Any capacitance added
externally will improve the pulse current capabil
ity, but will decrease the safety provided by the
current limiting circuit. A high-current pulse may
damage load components before the average output
current is large enough to cause the current limit
ing circuit to operate.
3-24 REVERSE CURRENT LOADING
3-25 Active loads connected to the power supply
may actually deliver a reverse current to the power
supply during a portion of its operating cycle. An
external source cannot be allowed to pump current
into the supply without loss of regulation and pos
sible damage to the output capacitor. To avoid
these effects, it is necessary to preload the sup
ply with a dummy load resistor so that the power
supply delivers current through the entire operating
cycle of the load device.
3-26 Reverse Voltage Protection. A diode is con
nected across the output terminals with reverse
polarity. This diode protects the output electro
lytic capacitors and the series regulator transistors
from the effects of a reverse voltage applied across
the output terminals. For example, in series oper
ation of two supplies, if the AC is removed from
one supply, the diode prevents damage to the un-
energized supply which would otherwise result from
a reverse polarity voltage.
Since series regulator transistors or driver
transistors cannot withstand reverse voltage,
another diode is connected across the series tran
sistor. This diode protects the series transistors
in parallel or Auto-Parallel operation if one supply
of the parallel combination is turned on before the
other.
3-2

SECTION IV
PRINCIPLES OF OPERATION
^CIO 48V
REGULATOR
Q9.QII
6.2V
12.4V
+ OUT
METER
CIRCUIT
S2
CURRENT
SERIES
REGULATOR
07
CURRENT
+ 6.2V
RI2
CONSTANT
VOLTAGE
PULLOUT
SAMPLING
RESISTOR
CURRENT
LIMIT AMPL
03
CR30
-*o-x>o-o
SI
ON/OFF
SWITCH
VOLTAGE
INPUT
CIRCUIT
01 .02
CR 4
DRIVER
05
NOTE I; MAIN SUPPLY
OUTPUT VOLTAGES ARE:
MODEL VDC
AMPL
04
NOTE I
Rll
COARSE
VOLTAGE
62I3A
62I5A
62I7A
RIO
FINE
VOLTAGE
£
Figure 4-1. Simplified Schematic
4-1 SIMPLIFIED DISCUSSION
4-2 The power supply, as shown on the simplified
schematic diagram of Figure 4-1, consists of a
power transformer, rectifier and filter, series regu
lator, error amplifier and driver, constant voltage
input circuit, current limiting circuit, reference
regulator circuit, and a metering circuit.
4-3 The input line voltage passes through the
power transformer to the rectifier and filter. The
rectifier-filter converts the ac input to raw dc
which is fed to the positive terminal via the regu
lator and current sampling resistor network. The
regulator, part of the feedback loop, is made to
alter its conduction to maintain a constant output
voltage. The voltage developed across the current
sampling resistor is the input to the current limit
ing circuit. If the output current that passes
through the sampling resistor exceeds a certain
predetermined level, the current limiting circuit
applies a feedback signal to the series regulator
which alters the regulator's conduction so that the
output current does not exceed the current limit.
The constant voltage input circuit obtains its input
by sampling the output voltage of the supply. Any
changes in output voltage are detected in the con
stant voltage input circuit, amplified by the error
4-1

amplifier and driver, and applied to the series
regulator intiie correct phase and amplitude to
counteract the change in output voltage. The ref
erence regulator circuit provides stable reference
voltages which are used by the constant voltage
input circuit for comparison purposes. The meter
circuit provides indications of output voltage or
current in either operating mode.
4-4 Diode CR14, connected across the output
terminals of the power supply, is a protective de
vice which prevents internal damage that might
occur if a reverse voltage were applied across the
output terminals.
4-5 DETAILED CIRCUIT ANALYSIS (Refer to overall
schematic diagram at rear of manual)
4-6 FEEDBACK LOOP
4-7 The feedback loop functions continuously to
keep the output voltage constant, during constant
voltage operation, and the output current at a safe
limit during current limit operation. For purposes
of this discussion, assume that the unit is in con
stant voltage operation and that the programming
resistors RIO and Rll have been adjusted so that
the supply is yielding the desired output voltage.
Further assume that the output voltage instantane
ously rises (goes positive) due to a variation in
the external load circuit.
4-8 Note that the change may be in the form of a
slow rise in the output voltage or a positive going
AC signal. An AC signal is coupled to the voltage
input circuit through capacitor C1 and a DC volt
age is coupled through RIO and Rll.
4-9 The rise in output voltage causes the voltage
at the base of Q1 to decrease (go negative). Q1
now decreases its conduction and its collector
voltage rises. The positive going error voltage is
amplified and inverted by Q4 and fed to the base
of series transistor Q7 via emitter follower Q5.
The negative going input causes Q7 to decrease
its conduction so that it drops more of the line
voltage, and reduces the output voltage to its
original level.
4-10 When the external load resistance decreases,
the output current increases until the current limit
is reached. The positive voltage developed at the
wiper of R50 causes Q3 to conduct. CR4 becomes
forward biased and controls the conduction of Q5
and Q7. Any further decreases in load resistance
increase the negative voltage on the base of Q5
which decreases the conduction of Q7. Thus,
through feedback action the output current is limi
ted to the value at which CR4 conducts.
4-11 SERIES REGULATOR
4-12 The series regulator consists of transistor
stage Q7 (see schematic at rear of manual). The
regulator serves as a series control element by
altering its conduction so that the output voltage
is kept constant and the current limit is never ex
ceeded. The conduction of Q5 is controlled by the
feedback voltage obtained from driver Q4. Diode
CR7, connected across the regulator circuit, pro
tects the series transistor against reverse voltages
that could develop across it during parallel or auto-
parallel operation if one supply is turned on before
the other.
4-13 CONSTANT VOLTAGE INPUT CIRCUIT (Refer
to overall schematic at rear of manual)
4-14 The circuit consists of the coarse and fine
programming resistors (RIO and Rll), and a differ
ential amplifier stage (Ql, Q2, and associated
components). Drift due to thermal differentials is
minimized, since both transistors operate at es
sentially the same temperature.
4-15 The constant voltage input circuit continu
ously compares a fixed reference voltage with a
portion of the output voltage and, if a difference
exists, produces an error voltage whose amplitude
and phase is proportional to the difference. The
error output is fed back to the series regulator,
through the error and driver amplifiers. The error
voltage changes the conduction of the series reg
ulator which, in turn, alters the output voltage so
that the difference between the two input voltages
applied to the differential amplifier is reduced to
zero. The above action maintains the output volt
age constant.
4-16 Stage Q2 of the differential amplifier is con
nected to a common (+S) potential through imped
ance equalizing resistor R6. Resistors RS and R7
are used to zero bias the input stage, offsetting
minor base-to-emitter voltage differences in Ql
and Q2. The base of Ql is connected to a sum
ming point at the junction of the programming
resistors and the current pullout resistor, R12.
Instantaneous changes in output voltage result in
an increase or decrease in the summing point
potential. Ql is then made to conduct more or
less, in accordance with the summing point volt
age change. The resultant output error voltage is
fed back to the series regulator via the remaining
components of the feedback loop. Resistor Rl, in
series with the base Ql, limits the current through
the programming resistors during rapid voltage
turn-down. Diodes CRl and CR2 form a limiting
network which prevents excessive voltage excur
sions'from over driving stage Ql. Capacitor Cl,
4-2

shunting the programming resistors, increases the
high frequency gain of the input amplifier.
4-17 DRIVER AND ERROR AMPLIFIER (Refer to over
all schematic at rear of manual)
4-18 The error and driver amplifiers amplify the
error signal from the constant voltage input circuit
to a level sufficient to drive the series regulator
transistor. Driver Q5 also receives a current
limiting input if GR4, the current limiting diode,
becomes forward biased.
4-19 Stage Q4 contains a feedback equalizer net
work, C3 and R17, which provides for high fre
quency roll off in the loop gain in order to stabi
lize the feedback loop.
4-20 CURRENT LIMITING CIRCUIT
4-21 Current limiting occurs when transistor Q3
conducts. This is determined by the voltage drop
across current sampling resistor R33 and the adjust
ment of current limit potentiometer R50. When the
output current reaches the limit value, the positive
voltage (with respect to+S) on the wiper arm of R50
causes Q3 to conduct. Diode CR4 becomes forward
biased clamping the base of C5 to a potential which
decreases the conduction of the series regulator,
thus limiting the output current. Potentiometer R50
permits the base potential of C3 to be varied and
thus changes the current limiting threshold.
4-22 REFERENCE CIRCUIT (Refer to schematic at
rear of manual)
4-23 The reference circuit is a separate power
supply similar to the main supply. It provides
stable reference voltages which are used through
out the unit. The reference voltages are all de
rived from smoothed dc obtained from the full wave
rectifier (CRIO and CRll) and filter capacitor C5.
The -6. 2V reference voltage is derived from VRl
which is a second dc source regulating at 6. 2vdc.
Current for VRl is supplied by the (-) side of C5
and flows through VRl, the base-emitter junction
of Q7, R20, and back to the positive side of C5.
4-24 The base-emitter junction of Qll is held
constant by 6. 2V zener diode VR7 which regulates
line voltage changes that alter the voltage across
C5. Thus Qll is a constant current source feeding
12. 4V zener diode VR4 and 6. 2V temperature-com
pensated zener diode VR6.
4-25 Resistors R27 and R30 form a voltage divider
across the stable 6. 2 volts developed by VRl. The
base-emitter junction of Q9 is therefore held con
stant by the voltage developed across R27. Thus
Q9 provides a constant current to zener diode VR3,
which regulates the -6. 2V source.
4-26 METER CIRCUIT
4-27 This circuit provides indications of output
voltage or output current. With METER SELECTION
switch 82 set to VOLTS position the meter, in
series with R38, is connected directly across the
output of the supply. With S2 set to the MA posi
tion the meter, in series with R37 and R47, is
connected across the current sampling resistor
R33. Potentiometer R47 adjusts the electrical
meter zero in the MA position.
4-3

SECTION V
MAINTENANCE
5-1 INTRODUCTION
5-2 Upon receipt of the power supply, the per
formance check (Paragraph 5-13) should be made.
This check is suitable for incoming inspection. If
a fault is detected in the power supply while
making the performance check or during normal op
eration, proceed to the troubleshooting procedures
(Paragraph 5-46). After troubleshooting and repair
(Paragraph 5-53), perform any necessary adjust
ments and calibrations (Paragraph 5-55). Before
returning the power supply to normal operation,
repeat the performance check to ensure that the
fault has been properly corrected and that no other
faults exist. Before doing any maintenance checks,
turn-on power supply, allow a half-hour warm-up,
and read the general information regarding measure
ment techniques (Paragraph 5-6).
5-3 COVER REMOVAL AND REPLACEMENT
5-4 To remove the top and bottom covers, pro
ceed as follows:
a. Insert a small screwdriver in each of the
four notches at the front of the unit at the top and
bottom. Push the screwdriver under the front panel
and gently pry toward the front of the unit to re
lease the holding mechanism.
b. Pull the front panel forward until it clears
the top and bottom covers.
c. Remove the rear cover by repeating step a.
d. Pull the rear cover until it clears the top
and bottom covers. Then lift off the top cover and
lift the unit out of the bottom cover.
5-5 To replace the top and bottom covers, pro
ceed as follows:
a. Place the unit into the bottom cover
(identified by the four protruding feet) and align
the heat sink into the track in the bottom cover.
b. Place the top cover over the unit and
align the track over the heat sink.
c. While holding the covers together at the
rear of the unit, carefully push on the rear panel.
d. Position the front panel so that the two
slotted ears at the bottom of the panel align with
the printed wiring boards.
e. Carefully push on the front panel.
5-6 GENERAL MEASUREMENT TECHNIQUES
5-7 The measuring device must be connected as
close to the output terminals as possible when
measuring the output impedance, transient re
sponse, regulation, or ripple of the power supply
in order to achieve valid measurements. A meas
urement made across the load includes the imped
ance of the leads to the load and such lead lengths
can easily have an impedance several orders of
magnitude greater than the supply impedance, thus
invalidating the measurement.
5-8 The monitoring device should be connected
as shown in Figure 5-1. Note that when measure
ments are made at the front terminals, the monitor
ing leads are connected at A, not B, as shown in
Figure 5-1. Failure to connect the measuring de
vice at A will result in a measurement that includes
the resistance of the leads between the output
terminals and the point of connection.
OUTPUT TERMINAL-
LOADLEAD
MONITOR HERE-
Figure 5-1. Front Panel Terminal Connections
5-9 For output current measurements, the current
sampling resistor should be a four-terminal resis
tor. The four terminals are connected as shown in
Figure 5-2. In addition, the resistor should be of
the low noise, low temperature coefficient (less
than 30 ppm/°C) type and should be used at no
more than 5% of its rated power so that its temper
ature rise will be minimized.
CURRENT SAMPLING
TERMINALS
EXTERNAL
TO UNGROUNDED
TERMINALOF
POWER SUPPLY
SAMPLING
RESISTOR \
LOAD
TERMINALS
TO GROUNDED
TERMINALOF
\ POWER SUPPLY
Figure 5-2. Output Current Measurement Technique
5-10 When using an oscilloscope, ground one ter
minal of the power supply and then ground the case
5-1

of the oscilloscope to this same point. Make certain
that the case is not also grounded by some other
means (power line). Connect both oscilloscope in
put leads to the power supply ground terminal and
check that the oscilloscope is not exhibiting a rip
ple or transient due to ground loops, pick-up, or
other means.
5-11 TEST EQUIPMENT REQUIRED
5-12 Table 5-1 lists the test equipment required to
perform the various procedures described in this
Section.
Table 5-1. Test Equipment Required
TYPE
REQUIRED
CHARACTERISTICS
USE
RECOMMENDED
MODEL
Differential
Voltmeter
Sensitivity: ImVfull scale (min.).
Input impedance: 10 megohms (min.).
Measure DC voltages;
calibration procedures
3420 (See Note)
Variable
Voltage
Range: 90-130 volts. Equipped with
voltmeter accurate within 1 volt.
Vary AC input
AC Voltmeter
Accuracy: 2%. Sensitivity: ImV
full scale deflection (min.).
Measure AC voltages and
ripple
403B
Oscilloscope
Sensitivity: lOOpV/cm. Differ
ential input.
Display transient response
waveforms
($)140A plus 1400A
plug-in. 1402A
plug-in for spike
measurements only.
Oscillator
Range: 5Hz to 500KHz. Accuracy:
2%. Output: lOVrms.
Impedance checks
200CD
DC Voltmeter
Accuracy: 1%. Input resistance:
20,000 ohms/volt (min.).
Measure DC voltages
412A
Repetitive
Load Switch
Rate: 60-400Hz, 2|a,sec rise and
fall time.
Measure transient response
See Figure 5-9.
Resistive
Loads
Values: See Paragraph 5-16.
Power supply load resistors
Current Sam
pling Resistor
See R33 in Parts List (Section VI).
Measure current; calibrate
meter
Resistor
IKn. ±1%, 2 watt non-inductive.
Measure impedance
Resistor
100 ohms, ±5%, 10 watt.
Measure impedance
Capacitor
500|j.f, 50WVdc.
Measure impedance
NOTE
A satisfactory substitute for a differen
tial voltmeter is to arrange a reference
voltage source and null detector as
shown in Figure 5-3. The reference
voltage source is adjusted so that the
voltage difference between the supply
being measured and the reference volt
age will have the required resolution
for the measurement being made. The
voltage difference will be a function of
the null detector that is used. Examples
of satisfactory null detectors are: (^419A
null detector, a dc coupled oscilloscope
utilizing differential input, or a 50mv
meter movement with a 100 division
scale. For the latter, a 2mv change in
voltage will result in a meter deflection
of four divisions.
5-2

POWER SUPPLY
UNDER TEST
I^VVV
LOAD
REFERENCE
VOLTAGE
SOURCE
OO
NULL
DETECTOR
9-P 9
POWER SUPPLY
UNDER TEST
iF -
0 o o
Rs»
MODEk NO.
Rl
62I3A/62I4A
62I5A/62I6A
62I7A/62I8A
ICQ , IOW,i5%
65n., low, ±5%
250n , IOW,i5%
LOAD
RESISTOR
CURRENT
SAMPLING
RESISTOR
'WV
DIFFERENTIAL.
VOLTMETER
- F- G
9 Q_P
• REFER TO R33 IN PARTS LIST (SECTION VI)
Figure 5-3. Differential Voltmeter
Substitute Test Setup
-CAUTION-
Care must be exercised when using an
electronic null detector in which one
input terminal is grounded to avoid
ground loops and circulating currents.
5-13 PERFORMANCE TEST
5-14 The following test can be used as an incom
ing inspection check and appropriate portions of
the test can be repeated either to check the oper
ation of the instrument after repairs or for periodic
maintenance tests. The tests are performed using
a 115-VAC 60 Hz, single phase input power source.
If the correct result is not obtained for a particular
check, do not adjust any controls; proceed to
troubleshooting (Paragraph 5-48).
5-15 RATED OUTPUT AND METER ACCURACY
5-16 Voltage. To check the output voltage, pro
ceed as follows;
a. Connect load resistor (Rl) indicated in
Figure 5-4 across the output terminals of supply.
b. Connect differential voltmeter across (+)
and (-) terminals of supply observing correct po
larity.
c. Set METER SELECTION switch to VOLTS
and turn on supply.
d. Adjust VOLTAGE controls until front panel
meter indicates exactly the maximum rated output
voltage.
e. Differential voltmeter should indicate
maximum rated output voltage within ±2%.
5-17 Current. To check the output current, pro
ceed as follows:
a. Connect test setup shown in Figure 5-4.
Figure 5-4. Output Current, Test Setup
b. Set METER SELECTION switch to MA
position.
c. Turn on supply and adjust VOLTAGE con
trols until front panel meter indicates maximum
rated output current.
d. Differential voltmeter should read as
follows: Model No. Reading (Vdc)
6213A 1 ±0.03V
6215A 1.2±0. 036V
6217A 1.2±0. 036V
5-18 LOAD REGULATION
Definition: The change AEqut in the
static value of DC output voltage re
sulting from a change in load resist
ance from open circuit to a value
which yields maximum rated output
current (or vice versa).
5-19 To check the constant voltage load regula
tion, proceed as follows:
a. Connect test setup as shown in Figure
5-5.
b. Set METER SELECTION switch to MA
position.
c. Turn on supply and adjust VOLTAGE
controls until front panel meter indicates maximum
rated output current.
d. Read and record voltage indicated on
differential voltmeter.
e. Disconnect load resistor.
f. Reading on differential voltmeter should
not vary from reading recorded in step d by more
than 4mV.
5-20 LINE REGULATION
Definition: The change, AEquT' the
static value of DO output voltage result
ing from a change in AC input voltage
over the specified range from low line
(usually 105 volts) to high line (usually
125 volts), or from high line to low line.
5-3

POWER SUPPLY
UNDER TEST
MODEL NO.
Rl
62I3A/62I4A
62I5A/62I6A
62I7A/62I6A
ion , [ow,t5%
65n, I0w,t57o
250n, I0w,±57o
DIFFERENTIAL
VOLTMETER
V G
Figure 5-5. Load Regulation, Test Setup
5-21 To test the line regulation, proceed as fol
lows:
a. Connect variable auto transformer be
tween input power source and power supply power
input.
b. Connect test setup shown in Figure 5-5.
c. Adjust variable auto transformer for 105
VAC input.
d. Set METER SELECTION switch to VOLTS
position.
e. Turn on supply and adjust VOLTAGE
controls until front panel meter indicates exactly
the maximum rated output voltage.
f. Read and record voltage indicated on dif
ferential voltmeter.
g. Adjust variable auto transformer for 125V
ac input.
h. Reading on differential voltmeter should
not vary from reading recorded in step f by more
than 4mV.
5-22 Ripple and Noise.
Definition: The residual ac voltage
which is superimposed on the dc out
put of a regulated power supply.
Ripple and noise may be specified and
measured in terms of its RMS or (pre
ferably) peak-to-peak value.
Ripple and noise measurement can be made at any
input ac line voltage combined with any dc output
voltage and load current within rating.
5-23 The amount of ripple and noise that is present
on the power supply output is measured either in
terms of the RMS or (preferably) peak-to-peak
value. The peak-to-peak measurement is particu
larly important for applications where noise spikes
could be detrimental to a sensitive load, such as
logic circuitry. The RMS measurement is not an
ideal representation of the noise, since fairly
high output noise spikes of short duration could
be present in the ripple and not appreciably in
crease the RMS value.
5-24 The technique used to measure high frequency
noise or "spikes" on the output of a power supply
is more critical than the low frequency ripple and
noise measurement technique; therefore the former
is discussed separately in Paragraph 5-32.
5-25 Ripple and Noise Measurements. Figure
5-6A shows an incorrect method of measuring p-p
ripple. Note that a continuous 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 supply
case, the wire between the negative output termi
nal of the power supply and the vertical input of
the scope, and the grounded scope case. Any
ground current circulating in this loop as a result
of the difference in potential Eq 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 line frequency fundamental, plus
any pickup on the unshielded leads interconnect
ing the power supply and scope, appears on the
face of the CRT. The magnitude of this resulting
noise signal can easily be much greater than the
true ripple developed between the plus and minus
output terminals of the power supply, and can
completely invalidate the measurement.
5-26 The same ground current and pickup problems
can exist if an RMS voltmeter is substituted in
place of the oscilloscope in Figure 5-6. However,
the oscilloscope display, unlike the true RMS
meter reading, tells the observer immediately
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
supply is 120 Hz (due to full-wave rectification),
an oscilloscope display showing a 120 Hz funda
mental component is indicative of a "clean"
measurement 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.
5-27 Figure 5-6B shows a correct method of meas
uring the output ripple of a constant voltage power
supply using a single-ended scope. The ground
loop path is broken with a 3 to 2 adapter in series
with the power supply's AC line plug. Notice,
5-4

POWER SUPPLY CASE
OSCILLOSCOPE CASE
GND-ii>- 1 D
I -I +c
[f
-Overt icAL
c:
-AC
-ACC
.|-GND
I
L
"G I
A/W
A. INCORRECTMETHOO- ground CURRENTIs PRODUCES 60
CYCLE DROP IN NEGATIVE LEAD WHICH ADDS TO THE POWER
SUPPLY RIPPLE DISPLAYED ON SCOPE.
POWER SUPPLY CASE
OSCILLOSCOPE CASE
GND*^^-| A
TWISTED PAIR
VERTICAL
NPUT
USE 3-T0-2
adapter to
BREAK GND PATH
B. A CORRECT method USING A SINGLE-ENDED SCOPE.
3-T0-2 ADAPTER BREAKS GROUND CURRENT LOOP, TWISTED
PAIR REDUCES STRAY PICKUP ON SCOPE LEADS.
POWER SUPPLY CASE
OSCILLOSCOPE CASE
AC
ACC
GND-
+0
SHIELDED
TWO -WIRE
&
-O VERTICAL
-O INPUT
c:
•AC
•ACC
hGND
C. A CORRECT 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 S
SCOPE, SHIELDED TWO WIRE FURTHER REDUCES STRAY
PICK-UP ON SCOPE LEAD.
ed up from the grounds, the (-h) scope lead should
be shorted to the (-) scope lead at the power sup
ply terminals. The ripple value obtained when the
leads are shorted should be subtracted from the
actual ripple measurement.
5-30 In most cases, the single-ended scope
method of Figure 5-6B will be adequate to eliminate
non-real components of ripple and noise so that a
satisfactory measurement may be obtained. How
ever, in more stubborn cases, or in measurement
situations where it is essential that both the power
supply case and the oscilloscope case be connect
ed to ground (e. g. if both are rack-mounted), it
may be necessary to use a differential scope with
floating input as shown in Figure 5-6C. If desired,
two single conductor shielded cables may be sub
stituted 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 introduced because of
the difference in the AC potential between the
power supply case and scope case. Before using
a differential 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. If this trace
is a straight line, the scope is properly ignoring
any common mode signal present. If this trace is
not a straight line, then the scope is not reject
ing the ground signal and must be realigned in ac
cordance with the manufacturer's instructions until
proper common mode rejection is attained.
Figure 5-6. Ripple and Noise, Test Setup
however, that the power supply case is still con
nected to ground via the power supply output ter
minals, the leads connecting these terminals to
the scope terminals, the scope case and the third
wire of the power supply cord.
5-31 To check the ripple and noise output, pro
ceed as follows:
a. Connect the oscilloscope or RMS volt
meter as shown in Figures 5-6B or 5-6C.
b. Adjust VOLTAGE control until front panel
meter indicates maximum rated output voltage.
c. The observed ripple and noise should be
less than 200p.Vrms and ImV p-p.
5-28 Either a twisted pair or (preferably) a shield
ed two-wire cable should be used to connect the
output terminals of the power supply to the verti
cal input terminals of the scope. When using a
twisted pair, care must be taken that one of the
two wires is connected both to the grounded ter
minal of the power supply and the grounded input
terminal of the oscilloscope. When using shield
ed two-wire, it is essential for the shield to be
connected to ground at one end only so that no
ground current will flow through this shield, thus
inducing a noise signal in the shielded leads.
5-29 To verify that the oscilloscope is not dis
playing ripple that is induced in the leads or pick-
5-32 Noise Spike Measurement. When a high fre
quency spike measurement is being made, an in
strument of sufficient bandwidth must be used; an
oscilloscope with a bandwidth of 20 MHz or more
is adequate. Measuring noise with an instrument
that has insufficient bandwidth may conceal high
frequency spikes detrimental to the load.
5-33 The test setups illustrated in Figures 5-6A
and 5-6B are generally not acceptable for measur
ing spikes; a differential oscilloscope is neces
sary. Furthermore, the measurement concept of
Figure 5-6C must be modified if accurate spike
measurement is to be achieved:
1. As shown in Figure 5-7, two coax
5-5

son.
TERMINATION
POWER SUPPLY
CASE
T-CONNECTOR
AC-
ACC-
6ND-
0.01 uf
+ O-
50 '
f'
Li^
n
OSCILLOSCOPE
CASE
(t 1
O.OIuf
— d).
V
<—
% ^
>n
VERTICAL
INPUT
V„
VERTICAL
INPUT
AC
ACC
-GND
T-CONNECTOR
son
TERMINATION
Figure 5-7. Noise Spike Test Setup
power supply would be zero at all fre
quencies, while the output impedance
for an ideal constant current power
supply would be infinite at all fre-
quenc ies.
The output impedance of a power supply is normal
ly not measured, since the measurement of tran
sient recovery time reveals both the static and
dynamic output characteristics with just one meas
urement. The output impedance of a power supply
is commonly measured only in those cases where
the exact value at a particular frequency is of
engineering importance.
5-36 To check the output impedance, proceed as
follows:
a. Connect test setup shown in Figure 5-8.
cables, must be substituted for the shielded two-
wire cable.
2. Impedance matching resistors must be
included to eliminate standing waves and cable
ringing, and the capacitors must be connected to
block the DC current path.
3. The length of the test leads outside the
coax is critical and must be kept as short as pos
sible; the blocking capacitor and the Impedance
matching resistor should be connected directly
from the inner conductor of the cable to the power
supply terminals.
4. Notice that the shields of the power sup
ply end of the two coax cables are not connected
to the power supply ground, since such a connec
tion would give rise to a ground current path
through the coax shield, resulting in an erroneous
measurement.
5. The measured noise spike values must
be doubled, since the impedance matching resis
tors constitute a 2-to-l attenuator.
6. The noise spikes observed on the oscil
loscope should be less than 0. 5mV p-p.
5-34 The circuit of Figure 5-7 can also be used
for the normal measurement of low frequency ripple
and noise; simply remove the four terminating re
sistors and the blocking capacitors and substitute
a higher gain vertical plug-in in place of the wide
band plug-in required for spike measurements.
Notice that with these changes, Figure 5-7 be
comes a two-cable version of Figure 5-6C.
5-35 OUTPUT IMPEDANCE
Definition: At any given frequency of
load change, AEqut/ AIqUT- Strictly
speaking the definition applies only for
a sinusoidal load disturbance, unless,
of course, the measurement is made at
zero frequency (DC). The output im
pedance of an ideal constant voltage
VOLTMETER
hp403B
INDICATES Eo
POWER SUPPLY
UNDER TEST
VOLTMETER
hp403e
INDICATES Ein
OSCILLATOR
hp 200 CD
IK
IVWVJ
100 OHM
Figure 5-8. Output Impedance, Test Setup
b. Set METER SELECTION switch to VOLTS
position.
c. Turn on supply and adjust VOLTAGE con
trols until front panel meter reads 20 volts.
d. Set AMPLITUDE control on Oscillator to
10 volts (Ein), and FREQUENCY control to 100 Hz.
e. Record voltage across output terminals of
the power supply (Eq) as indicated on AC voltmeter.
f. Calculate the output impedance by the
following formula:
Zout = g.
t-in - tiO
Eq = rms voltage across power supply output
terminals.
R = 1000
Ein =10 volts
g. The output impedance (Zout) should be
less than 0. 030 ohms.
5-6