TM 11-6625-2965-14&P
3-35 AUTO-TRACKING OPERATION (See Figure 3-10)
3-36 The Auto-Tracking configuration is used
when it is necessary that several different voltages
referred to a common bus, vary in proportion to the
setting of a particular instrument (the control or
master).
A fraction of the master’s output voltage
is fed to the comparison amplifier of the slave sup-
ply, thus controlling the slave’s output. The mas-
ter must have the largest output voltage of any
power supply in the group (must be the most posi-
tive supply in the example shown on Figure 3-10).
3-37 The output voltage of the slave is a percent-
age of the master’s output voltage, and is deter-
mined by the voltage divider consisting of R
X (or
Rx and R
Y) and the voltage control of the slave
supply, R
p
, where:
E
MRP
E
=
Rx+Rp
Turn-on and turn-off of the power supplies is con-
trolled by the master.
Remote sensing and pro-
gramming can be used; although the strapping pat-
terns for these modes show only local sensing and
programming.
In order to maintain the temperature
coefficient and stability specifications of the pow-
er supply, the external resistors should be stable,
low noise, low temperature (less than 30ppm per
O
C) resistors.
3-38
SPECIAL OPERATING CONSIDERATIONS
3-39 PULSE LOADING
3-40 The power supply will automatically cross
over from constant voltage to constant current op-
eration in response to an increase (over the preset
limit) in the output current, Although the
preset
limit may be set higher than the average output
current high peak currents (as occur in pulse load-
ing) may exceed the preset current limit and cause
crossover to occur.
If this crossover limiting is
not desired, set the preset limit for the peak re-
quirement and not the average.
3-41 OUTPUT CAPACITANCE
3-42 An internal capacitor, acress the output ter-
minals of the power supply, helps to supply high-
current pulses of short duration during constant
voltage operation.
Any capacitance added exter-
nally will improve the pulse current capability, but
will decrease the safety provided by the current
limiting circuit.
A high-current pulse may damage
load components before the average output current
is large enough to cause the current limiting cir-
cuit to operate.
3-43 REVERSE VOLTAGE LOADING
3-44 A diode is connected across the output ter-
minals.
Under normal operating conditions, the
diode is reverse biased (anode connected to neg-
ative terminal).
If a reverse voltage is applied to
the output terminals (positive voltage applied to
negative terminal), the diode will conduct, shunt-
ing current across the output terminals and limit-
ing the voltage to the forward voltage drop of the
diode.
This diode protects the series transistors
and the output electrolytic capacitors.
3-45 REVERSE CURRENT LOADING
3-46 Active loads connected to the power supply
may actually deliver a reverse current to the power
supply during a portion of its operating cycle. An
external source cannot be allowed to pump current
into the supply without loss of regulation and pos-
sible damage to the output capacitor.
To avoid
these effects, it is necessary to preload the sup-
ply with a dummy load resistor so that the power
supply delivers current through the entire operat-
ing cycle of the load device.
3-6
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