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i-1
INTRODUCTION
5-2
Upon receipt of the power supply, the performance
test (paragraph 5-5) can be made, This test is suitable for in¬
coming inspection. If a fault is detected in the power supply
while making the performance test or during normal opera¬
tion, proceed to the troubleshooting procedures. After
troubleshooting and repair (paragraph 5-53) perform any
necessary adjustments and calibration (paragraph 5-121), Before
returning the power supply to normal operation, repeat the ap¬
plicable portions of the performance test to ensure that the
fault has been properly corrected and that no other faults
exist,
5-4
Table 5-1 lists the test equipment required to perform
the various procedures described in this section,
5-6
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. The tests are performed using the specified
nominal input voltage for the unit. If the correct result is not
obtained for a particular check, proceed to troubleshooting
(paragraph 5-53).
7
Measurement Techniques
5-8
All specifications are measured at the rear terminals of
the power supply. Also, ail tests are performed with the supply
strapped for local programming and sensing, as shown in
Figure 3-3. The wires used to connect the load to the supply
should be heavy enough to ensure that they will drop less than
0.5 V. The procedures are written for use of local (front-panel)
controls. However, output voltage and current can be set
via HP IB.
5-9
Selecting a Load Resistor. Specifications are check ¬
ed with varying amounts of load resistance connected across
the supply. For most of the constant-voltage tests, the value of
load resistance must be 20 to permit operation of the supply at
20 V and its maximum-output-power rating current of 10 A.
For the constant current tests, the load resistance must be
approximately
18 0 to permit operation at 3.3 A and its
maximum output-power rating voltage of 60 V, The power
rating of the load resistance must, be at least equal to the max¬
imum output power of the supply: 230 watts.
5 10
Either fixed or variable (rheostat type) load resistors
can be used. However, a rheostat is very convenient when
changing values and for accurately setting the output current
of the supply. Table 5-1 lists a rheostat that is adequate for this
supply. For clarity, illustrations in this section show the
rheostat as a single resistor, although the recommended unit
is a twin resistor model to provide adequate current capacity.
If fixed resistors are used, their tolerance must be accounted
for when evaluating the test results.
5-11
Connecting a Current-Monitoring Resistor. To
allow precise measurement of output current, a current
monitoring resistor is inserted between the output of the
power supply and the load resistance. This resistor must be
connected as a four-terminal device in the same manner as a
meter shunt would be (see Figure 5~1). The load current is fed
to the extremes of the wire leading to the resistor, while the
monitoring terminals are located as close as possible to the
resistance element itself. A current-monitoring resistor should
have low noise, a low temperature coefficient (less than 30
pprn/°C), and should be used at no more than 5% of its rated
power so that its temperature rise will be minimized.
CURRENT MONITORING
TERMINALS
TO NEGATIVE
TERMINAL OF
POWER SUPPLY
\
/
/
CURRENT -MONITORING
RESISTOR
LOAD TERMINALS
TO POSITIVE
TERMINAL OF
POWER SUPPLY
Figure 5-1. Current-Monitoring Resistor Terminals
5-13
Connect all of the measuring devices used in the
constant-voltage performance tests directly to the power sup
ply sensing terminals i t S, .S), For best accuracy, the sens¬
ing terminals must be used rather than the output terminals,
since the measuring instruments must be connected to the
same pair of terminals to which the feedback amplifier within
the power supply is connected. This is particularly important
when measuring the regulation or ripple of the power supply.
A measurement made across the load includes the impedance
of the leads to the load, and such lead lengths can easily have
an impedance several orders of magnitude greater than the
supply impedance typically < 1 milliohm at dc), thus in¬
validating the measurement.
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