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Before applying power to the supply, check the label on the
heat sink to make certain that the supply's line voltage option
agrees with the line voltage to be used. If the option does not
correspond to your line voltage, refer to paragraph "LINE
VOLTAGE OPTION CONVERSION" in the service section
before applying power.
TURN -ON CHECKOUT PROCEDURE
a. Connect line cord to power source and turn LINE
switch
on.
b. Push +6V METER switch
nected, vary +6V VOLTAGE control
and check that the voltmeter responds to the control
setting and the ammeter indicates zero.
c. Set the +6V VOLTAGE control to 6 volts and short the
+6V output terminal
with an insulated test lead. The ammeter should
indicate a short-circuit output current of approximately
1.0 A. Remove the short from the output terminals.
d. Push the +20V METER switch
Ratio control
fully clockwise to the Fixed position.
With no load connected, vary ±20V VOLTAGE control
over its range and check that the voltmeter
responds to the control setting and the ammeter indi-
cates zero.
e. Set the ±20V VOLTAGE control
short the +20V output terminal
with an insulated test lead. The ammeter should
indicate a short-circuit output current of 0.55 A ± 5%.
Remove the short from the output terminals.
f.
Repeat steps (d) and (e) for -20 V output.
g. Adjust the +20V output to 20 volts. Then push -20V
METER switch and check the effect of the Tracking
Ratio control on the voltage of the -20V output. The -
20V output should be adjustable from less than 0.5
volts to a maximum of 19 to 21 volts.
If this brief checkout procedure or later use of the supply
reveals a possible malfunction, see the service information
section for detailed test, troubleshooting, and adjustment pro-
cedures.
OPERATION
This power supply can be operated individually or in parallel
or series with another supply (see Parallel and Series Opera-
tion paragraphs). All output terminals are isolated from
ground. The ±20V and +6V outputs use a single common out-
put terminal. This common (COM) terminal or any one of the
other output terminals may be grounded to the chassis at the
front panel ground terminal (
be left floating. Loads can be connected separately between
each of the 0 to ±20V output terminals and the COM terminal,
or between the -20V and the +20V terminals for a 0 to 40V
output. Each output voltage or current can be quickly selected
for monitoring with the push-button meter switches. To moni-
and, with no load con-
over its range
to COM (common) terminal
and turn Tracking
to 20 volts and
to the COM terminal
in Figure 2), or all outputs may
tor the 0 to 40V output voltage, add the voltmeter readings of
the +20V and -20V output and use either the +20V or the -
20V meter to measure the current.
Tracking Ratio Control
With the Tracking Ratio control in the Fixed position, the volt-
age of the -20V supply tracks that of the +20V supply within
1% for convenience in varying the symmetrical voltages
needed by operational amplifiers and other circuits using bal-
anced positive and negative inputs.
Turn the Tracking Ratio control counter clockwise out of the
Fixed position to set the voltage of the -20V supply lower than
that of the +20V supply. The negative supply can be set from
a minimum of less than 0.5 volts to a maximum within 5% of
the +20V supply's output. Once this is done, the ±20V voltage
control still controls both outputs and maintains a constant
ratio between their voltages.
Overload Protection Circuits
±20-Volt Current Limit. The +20V and -20V outputs are indi-
vidually protected against overload or short circuit damage by
separate current limit circuits to limit the output current to 0.55
A ± 5%. (This is 110% of the maximum rated output.) If a sin-
gle load is connected between the +20V and -20V outputs,
the circuit set for the lesser current limit will limit the output.
No deterioration of supply performance occurs if the output
current remains below the current limit setting.
+6V Current Foldback. The overload and short-circuit pro-
tection circuit for the +6V output 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
4.) The maximum rated output current is 2.5 A and the current
limit is factory-adjusted to operate at 2.75 A ± 5% when the
output is 6 volts. At lower output voltages, the circuit reduces
the maximum obtainable output current linearly until 1 A ±
15% flows when the output is shorted. The short-circuit cur-
rent can not be adjusted.
During the actual operation of the ±20V and +6V outputs, if a
load change causes the current limit to be exceeded, the OL
LED is lighted. If overload conditions occur, the ±20V supplies
will protect the load by limiting the current to 0.55 A and the
+6V supply will protect the load by reducing both voltage and
current simultaneously along the foldback locus as shown in
Figure 4. The ±20V and +6V supplies are self restoring; that
is, when the overload is removed or corrected, the output
voltage is automatically restored to the previously set value.
Operation Beyond Rated Output
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 be extended up to
5% over the rated output without damage to the supply, but
performance can not be guaranteed to meet specifications in
1-7
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