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output voltage.
b. Short output terminals and adjust CURRENT
control for maximum output current allowable (cur¬
rent limit) as determined by load conditions and
voltage range selected in step (a).
If a load change
attempts to cause the output current to exceed this
setting, the power supply will automatically cross¬
over to constant current mode and output current
will be constant at the level set by the CURRENT
control.
The CURRENT MODE indicator will come
on and output voltage will drop proportionately to
maintain constant current.
In setting the CURRENT
control, allowance must be made for high peak cur¬
rent which can cause unwanted cross-over (refer to
paragraph 3-56).
As discussed above, however,
if voltage is set too high with respect to current,
the supply will gross current limit and "override the
VOLTAGE setting, see paragraph 3-65.
3-10 CONSTANT CURRENT
3-11 To select a constant current output, within
the normal range ratings of the supply, proceed as
follows:
a.
Short output terminals and adjust CUR¬
RENT control for desired output current.
b.
Open output terminals and adjust VOLT¬
AGE controls for maximum output voltage allowable
(voltage limit) as determined by load conditions
and current selected in step (a). .If a load change
causes the voltage setting to be exceeded, the
power supply will automatically crossover to con¬
stant voltage output at the voltage setting and out¬
put current will drop proportionately.
As discussed
above, however, if voltage is set too high with re¬
spect to current, the supply will gross current lim¬
it and override the VOLTAGE setting, see paragraph
3-65.
In setting the voltage limit, allowance
must be made for high peak voltages which can
cause unwanted crossover (refer to paragraph 3-56).
3-12 OVERVOLTAGE CROWBAR OPERATION
3-13 Trip Point Adjustment,
The crowbar trip vol¬
tage can be adjusted using the OVERVOLTAGE screw¬
driver control on the front panel.
The trip voltage
range of the crowbar is approximately 0. 5 to 45Vdc
for the 6104A and 6114A supplies and 0. 5 to llOVdc
for the 6105A and 6115A supplies.
To set the crow¬
bar trip voltage, perform the following procedures:
NOTE
Do not connect a load to the power
supply when setting the crowbar trip
voltage.
a.
Turn OVERVOLTAGE control fully clock¬
wise and turn-on supply.
b.
Set output voltage to desired trip voltage.
If the desired trip voltage is above 40 volts for the
6114A or 100 volts for the 6115A, perform the next
step.
If the desired trip setting is within the max¬
imum voltage rating of the 6114A or 6115A supplies
or in order to set the trip voltage for the 6104A and
6105A supplies, go on to step (d).
c. If the output of the 6114A or 6115A can¬
not be set to the desired crowbar trip voltage:
1.
Turn off the supply.
2... Disconnect the voltage programming
pushbutton switch assembly (two wires connect
the switch assembly to Main Power Supply Board
Al).
3.
Temporarily connect an external re¬
sistor (5%, 1/2W) in place of the voltage program¬
ming resistor according to the following formula:
Equt ~ * 5mA X R
Where: Eout is the desired output voltage;
. 5mA is the voltage programming current; &
R is the external resistor.
For example, connect a 90Kn, 5%, 1/2W resistor if
the 6114A is to be set to 45V or a 220Kn., 5%,. 1/2W
resistor if the 6115A is to be set to 110V,
4.
Turn on the supply, the output will be
the desired output voltage.
NOTE
The output voltage can be set above the
recommended ranges but the crowbar trip
voltage may not be adjustable above the
recommended ranges.
d.
Slowly turn the OVERVOLTAGE control
counterclockwise until the crgwbar trips: output
falls towards 0 volt and OVERVOLTAGE indicator
comes on.
e.
The crowbar remains activated and the
output shorted until the supply is turned off.
To
reset the crowbar, turn the supply off.
If neces¬
sary, before turning the supply back on, remove
the external resistor installed in step (c) and re¬
place the voltage programming pushbutton switch
assembly connections to the Al board.
Next, set
output voltage to zero.
Turn supply back on and
set it to desired output voltage (see next paragraph-
for an. important operating consideration).
3-14 False crowbar tripping must be considered
when adjusting the trip point.
If the trip voltage
is set too close to the operating output voltage, a
transient in the output or load can falsely trip the
crowbar.
It is recommended that the crowbar trip
voltage be set higher than the operating output
voltage by 2% + 0.' 5V.
For example, the crowbar
should be set to trip at a minimum of 31. lVdc if
the output voltage is set to 30Vdc.
This operating
margin, of course, is not possible if the crowbar
is set to trip at or near its lower limit.
3-15 Resetting Crowbar.
If the crowbar trips dur¬
ing normal operation (supply output goes to near
3-3
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