Tektronix PS 503A, Instruction Manual

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Operating Instructions—PS 503A
Fig. 1-2. Plug-in module installatlon/removal.
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OPERATING CONSIDERATIONS
Overheating
The PS 503A is designed to operate at an ambient
temperature from 0°C to +50" C. However, when
operating several power supplies in a multi-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.
Grounded and Floating Operation
The PS 503A is a + and —20 V "floating" supply since
no internal connections are made to either the chassis or
ground. The supply can thus be used as a positive 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 a remote load is connected as shown in Fig.
1-5, 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
ensure against problems caused by undersirable ground
currents.
Load and Monitor Connections
Improper connections between the power-supply out­
put and the load (s) 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. 1-4. Avoid using
clip leads, since their contact resistance can exceed the
output impedance of the PS 503A and cause significant
measurement error.
Reverse Current Loading
In some bias supply and digital circuitry applications
the load might behave as a current source for part of its
operating cycle. Since the output circuit of a series-
regulated supply is unidirectional, current will not pass in
the opposite direction except through undesirable paths.
The internal reverse-current diodes conduct only when
the PS 503A terminal voltage reverses and therefore will
not work when the voltage is correctly polarized. Connec-
1-2
REV. A MAR 1977