Tektronix PS 505 User manual

Tektronix, Inc.
P.O. Box 500
Beaverton, Oregon 97005
TEKTRONIX®
PS 505
POWER SUPPLY
INSTRUCTION MANUAL
Serial Number
070-1784-00 First Printing JUL 1974

WARRANTY
All TEKTRONIX instruments are warranted against
defective materials and workmanship for one year.
Any questions with respect to the warranty should
be taken up with yourTEKTRONIX Field Engineer or
representative.
All requests for repairs and replacement parts
should be directed to the TEKTRONIX Field Office
or representative in your area. This will assure you
the fastest possible service. Please include the
instrument Type Number or Part Number and Serial
Number with all requests for parts or service.
Specifications and price change privileges reserved.
Copyright 1974 by Tektronix, Inc., Beaverton,
Oregon. Printed in the United States of America. All
rights reserved. Contents of this publication may not
be reproduced in any form without permission of
Tektronix, Inc.
U.S.A. and foreign TEKTRONIX products covered
by U.S. and foreign patents and/or patents pending.
TEKTRONIX is aregistered trademark of Tektronix,
Inc.

PS 505
TABLE
OF CONTENTS
SECTION 1
SECTION 2
SECTION 3
SECTION 4
Page
OPERATING INSTRUCTIONS
INTRODUCTION 1-1
Installation 1-1
OPERATING CONSIDERATIONS 1-2
Overheating 1-2
Load and Monitor Connections 1-2
Grounded and Floating Operation 1-3
Reverse Current Loading 1-3
Overvoltage 1-3
OPERATION 1-4
Setup Information 1-4
Series Operation 1-4
Parallel Operation 1-4
APPLICATIONS 1-5
Differential Voltage Measurements 1-5
FUNCTIONS AVAILABLE AT REAR CONNECTOR 1-6
CHARACTERISTICS 1-6
Table 1-1 Electrical 1-6
Table 1-2 Environmental 1-7
ELECTRICAL REPLACEABLE PARTS LIST 2-1
SERVICE INFORMATION 3-1
Symbols and Reference Designators 3-1
Controls and Connectors &Rear Connector
Pin Assignments
Adjustments
Parts Location Grid &Theory of Operation
(backside of foldout)
Power Supply
MECHANICAL REPLACEABLE PARTS LIST 4-1
Fig. 1Exploded
CHANGE INFORMATION
I

PS 505

Section 1—PS 505
OPERATING
INSTRUCTIONS
INTRODUCTION
The PS 505 is avariable-voltage, variable-current dc
power supply that provides aconvenient way to power
bipolar logic, level shifters, light-emitting diodes, in-
candescent displays, and analog devices. It is designed to
operate in the right-hand (high power) compartment of a
TM 504 or TM 506 Power Module. When operated in the
right-hand compartment of aTM 504 or TM 506, the
PS 505 provides afloating output that is variable between
3.0 and 5.5 volts at amaximum of 4.0 amperes.
NOTE
If the PS 505 is operated in acompartment other than
the right-hand (high power) compartment of aTM 504
or TM 506, the output current drawn from the PS 505
must be limited to 1.0 amperes maximum. However, the
negative output terminal should be grounded at the
front panel since there is apossible ground path of
uncertain characteristics through the rear connector
when the PS 505 is operated in anyplace other than in
the right-hand compartment.
Afront panel lamp, marked VOLTS, indicates the
presence of voltage at the output terminals. The light
intensity varies with the output voltage and verifies that the
output is indeed variable. Afront-panel, light-emitting
diode indicates when the PS 505 goes into current
limiting. Hard limiting causes the light emitting diode to
glow brightly and causes the VOLTS lamp to dim. Acheck
of the limiting circuitry and the operation of these lights
can be made by momentarily shorting the output ter-
minals.
Asecond front-panel mounted light-emitting diode
indicates that the PS 505 is being operated in acompart-
ment other than the right-hand (high power) compartment
of the Power Module and that the output current must be
limited to 1ampere or less. It also Indicates that the
PS 505 is to have its negative output terminal grounded
and operated in anon-floating mode.
Installation
The PS 505 is calibrated and ready to use as received.
Referring to Fig. 1-1, install the Power Supply and turn on
the Power Module. Press the OUTPUT button to apply
power to the PS 505. Check that the VOLTS indicator light
on the front panel comes on (the light will be very dim at
low voltages).
NOTE
Because of the high current drawn by the PS 505, it is
recommended that the Power Module be turned off
before inserting or removing the PS 505. Arcing at the
connector terminals can reduce connector life.
However, no internal damage will result if the monitor is
inserted into alive Power Module.
1-1

operating Instructions—PS 505
Fig. 1-1. Plug-In Intlallallon and ramoval.
OPERATING CONSIDERATIONS
Overheating
The PS 505 is designed to operate at an ambient
temperature from 0°C to +50® C. However, when
operating several power supplies in amulti-plug-in Power
Module, especially at low output voltages, or when
operating close to other heat-producing equipment, inter-
nal temperature may exceed safe limits and actuate a
thermal cutout in the Power Module. Refer to the Power
Module Instruction Manual for more complete informa-
tion.
Load and Monitor Connections
Improper connections between the power supply out-
put and the load(s) and/or monitoring device(s) are a
common cause of errors. Multiple loads or monitoring
devices must be connected directly to the output terminals
with separate pairs of leads as shown in Fig. 1-2. Avoid
using clip leads, since their contact resistance can exceed
the output impedance of the PS 505 and cause significant
measurement error. Fig. 1-2. Monitor artd load connacilona.
1-2

Operating Instructions—PS 505
Grounded and Floating Operation
The PS 505 is a"floating" suppiy (when instaiied in the
high power compartment of the Power Module) since no
internal connections are made to either the chassis or
ground. The supply can thus be used as apositive or
negative supply by simply connecting between the com-
mon and the negative or positive output terminal.
However, there may be undesirable effects caused by
grounding the supply to the chassis while the load is
grounded at some point removed from the supply chassis.
For example, if aremote load is connected as shown in Fig.
1-3, ground currents containing the power line frequency
could result and create excessive noise and ripple in series
with the load. Thus, floating operation is recommended to
insure against problems caused by undesirable ground
currents. \
Reverse Current Loading
In some applications as when driving an inductive load,
the load might behave as acurrent source for part of its
operating cycle. Since the output circuit of aseries
regulated siipply is unidirectional, reverse current will not
normally pass through the regulator. The internal reverse-
current diode (CR75) conducts only when the PS 505
terminal voltage reverses and therefore protects the series
regulator against reverse currents. However, when
operating aswitching or inductive load, connecting a
shunt resistor (Rs) of about 12 nas shown in Fig. 1-4
provides an external reverse current path so the power
supply sources or delivers current only.
Fig. 1-3. Ground loop created by grounded remote load.
If the power supply is operated into aswitching load
where the current demand changes abruptly, it is
recommended that a12 0shunting resistor be placed
across the output terminals. This will ensure that the
supply always sees aminimum load and improves regula-
tion.
NOTE
The PS 505 is ground referenced negative when
installed in any other compartment of aPower Module
except the high power compartment. If the PS 505 is
installed in any compartmentother than the high power
compartment, operate it with astrap between the minus
and ground terminals.
Fig. 1-4. Reverse current shunt (Rs) with active load.
Overvoltage
The PS 505 is protected from overvoltage conditions by
an overvoltage protection circuit which blows the fuse at
about? Vdc. Component failure In the PS 505 could result
in load damage if external protection is not provided. Like
wise, if the load (or other instruments connected to the
load) produce avoltage across the PS 505 terminals which
is the same polarity but of greater amplitude, damage to
the PS 505 may result, depending on the amount of
overvoltage and the impedance of the load.
1-3

Operating Instructions—PS 505
OPERATION
Setup Information
The following steps demonstrate the use of the PS 505
controls and connectors.
1.
Install the PS 505 into (preferably) the right hand
compartment of the Power Module.
2.
Press the OUTPUT button to apply power to the
PS 505. Observe that the VOLTS indicator light comes on
(the light will be very dim at low voltages).
3.
Set the VOLTS controls for approximately 3.5 V.
4.
Turn the CURRENT LIMIT control fully ccw (to
protect the ammeter). Connect an ammeter between the +
and —terminals and adjust the CURRENT LIMIT control
for the maximum desired current output.
5.
Remove the ammeter. Connect the load between the
+and —terminals. Adjust the VOLTS control for the
desired output.
Series Operation
The outputs of two or more supplies can be connected
in series as shown in Fig. 1-5 to obtain an output voltage
equal to the sum of the output voltages from each supply.
The maximum output is limited to 350 Vdc +peak ac (i.e..
the isolation voltage rating between the output terminals
and ground). Each supply must be adjusted individually to
obtain the desired output voltage.
NOTE
The PS 505 has internal diodes connected across
the output to protect any of the series-connected
supplies against reverse polarity if the load is
shorted, or one of the supplies is not on.
Fig. 1-5. Series-connected supplies.
Paraiiei Operation
Parallel operation is not recommended unless a
forward biased diode capable of handling the re-
quired current and voltage is inserted between each
power supply and the load. Failure to do this may
cause power supply damage.
The outputs of two or more current-limiting, automatic-
crossover supplies can be connected in parallel as shown
in Fig. 1-6 to obtain an output current equal to the sum of
the output currents from each supply. Each supply must
be adjusted individually to obtain the desired output
current.

Operating Instructions—PS 505
One supply should be set forthe desired output voltage
and the other should be set for aslightly higher voltage.
The supply set for the desired voltage will then become a
constant voltage source, while the supply with the higher
voltage output becomes acuri;pnt-limited source (due to
automatic crossover) which results in their output voltage
decreasing to that of the supply with the lowest output
voltage.
APPLICATIONS
Differential Voltage Measurements
Very small dc voltage changes or unknown voltages
can be measured by connecting the PS 505, anull
detector, and the source under test in adifferential
configuration as shown in Fig. 1-7. Comparison
measurements at nearly the accuracy and sensitivity of
costly differential voltmeters can be made with the
inexpensive PS 505. The ultimate accuracy and sensitivity
of the measurement depends on the PS 505 and the type
of null detector used. Acalibrated DC amplifier in ahigh-
gain oscilloscope such as the Tektronix 5100-Series
Oscilloscope with a 5A20N Differential Amplifier plug-in
will serve as aconvenient null detector, or a sensitive
milliameter with aseries resistor is also satisfactory.
NOTE
Examine the circuit for ground loops when using a
null detector with one input terminal grounded (see
Grounded and Floating Operation).
Fig. 1-6. Parallel-connected supplies.

Operating Instructions—PS 505
FUNCTIONS AVAILABLE
AT REAR CONNECTOR
Unassigned pins are available at the rear connector for
routing signals to and from the PS 505 for specialized
applications (see Rear Interface connector assignments at
the rear of this manual). One or more compartments of a
multi-plug-in Power Module can be wired with barriers
installed to provide specific functions between com-
partments. See Power Module instruction manual for
additional information.
CHARACTERISTICS
Performance Conditions
Unless otherwise noted, the electrical characteristics
are valid only if the instrument has been calibrated at an
ambient temperature between -(-20° Cand -f30°C and is
operated at an ambient temperature between 0°C and
-1-50° C.
TABLE 1-1
Electrical
Characteristics Performance Requirements Supplemental Information
Line Regulation
!
Within 10 mV for a±10% line
voltage change
Load Regulation Within 5mV for a0.5 to 4.0 Aload
change
Transient recovery <20 /js for a
constant voltage to recover within
20 mV of nominal output voltage
after a3.5 Achange in output cur-
rent
Ripple and Noise 3mV peak-to-peak or less Power supply output voltage set to
5Vwith asupply load of 4.0 A
Temperature Coefficient 0.01 %/°C or less
Stability 0.1% +5 mV of drift in 8hours Line voltage, load and temperature
held constant
Folcjback Current When output current exceeds 4.1 A,
current folds back to less than 1.5 A
and latches
To restore to normal operation, turn
PS 505 power off. Reduce current
load to <4.0 A, then turn PS 505
power on
1-6