Reverse Current Loading; Output Capacitance; Reverse Voltage Protection - HP E3620A Operating Manual

Dual output power supply

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peak currents (as occur in pulse loading) may exceed the

preset current limit and cause crossover to occur and

degrade performance.

REVERSE CURRENT LOADING

An active load connected to the supply may actually deliver a

reverse current to the supply during a portion of its operating

cycle. An external source can not be allowed to pump current

into the supply without risking loss of regulation and possible

damage to the output capacitor of the supply. To avoid these

effects, it is necessary to preload the supply with a dummy

load resistor so that the supply delivers current through the

entire operating cycle of the load devices.

Figure 3. Reverse Current Loading Solution

An internal capacitor across the output terminals of the 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 load protection 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 circuit to operate.

A diode is connected across the output terminals with reverse

polarity. This diode protects the output electrolytic capacitors

and the series regulator transistors from the effects of a

reverse voltage applied across the output terminals. Since

series regulator transistors can not withstand reverse voltage

either, diodes are also connected across them. When operat-

ing supplies in parallel, these diodes protect an unenergized

supply that is in parallel with an energized supply.

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