Parallel Operation; Special Operating Considerations - HP 6236B Operating And Service Manual

them to reduce noise pick-up. If shielded wire is used,
connect one end of the shield to the power supply
ground terminal and leave the other end unconnected.
3-18 If load considerations require locating output
power distribution terminals at a distance from the power
supply, then the power supply output terminals should be
connected to the remote distribution terminals by a pair of
twisted or shielded wires and each load should be
connected to the remote distribution terminals separately.

3-19 Parallel Operation

3-20 Two or more power supplies can be connected in
parallel to obtain a total output current greater than that
available from one supply. The total output current is the
sum of the output currents of the individual supplies. The
output voltage controls of one power supply should be set
to the desired output voltage, and the other supply set for
a slightly larger output voltage. The supply set to the
lower output voltage will act as a constant voltage source,
while the supply set to the higher output will act as a
current-limited source, dropping its output voltage until it
equals that of the other supply. The constant voltage
source will deliver only that fraction of its rated output
current necessary to fulfill the total current demand.
3-21

Special Operating Considerations

3-22 Pulse Loading. The power supply will automatically
cross over from constant-voltage to current-limit operation
in response to an increase in the output current over the
preset limit. Although the preset limit may be set higher
than the average output current, high peak currents as
occur in pulse loading may exceed the preset current limit
and cause crossover to occur and degrade performance.
3-23 Output Capacitance. An internal capacitor across
the output terminals of the power supply helps to supply
high-current pulses of short duration during constant-volt-
age operation. Any capacitance added externally will im-
prove the pulse current capability, but will decrease the
load protection provided by the current limiting circuit. A
high-current output pulse may damage load components
before the average output current is large enough to cause
the current limiting circuit to operate.
3-24 Reverse Current Loading. An active load connected
to the power supply may actually deliver a reverse current to
the supply during a portion of its operating cycle. An external
source cannot be allowed to pump current into the supply
without risking loss of regulation and possible damage to the
output capacitor. To avoid these effects, it is necessary to
preload the supply with a dummy load resistor so that the
power supply delivers current through the entire operating
cycle of the load device.
3-25 Reverse Voltage Protection. Internal diodes con-
nected with reverse polarity across the output terminals
protect the output electrolytic capacitors and the driver
transistors from the effects of a reverse voltage applied
across a supply output. Since series regulator transistors
cannot withstand reverse voltage either, diodes are also
connected across them. When operating supplies in
parallel, these diodes protect an unenergized supply that is
in parallel with an energized supply.
Figure 3-3. Current Limit Characteristics of the 6V Supply
3-3
(Model 6236B)