B&K 1794 instruction manual Output Capacitance, Reverse Voltage Loading, Reverse Current Loading

4.6OUTPUT CAPACITANCE :

Internal capacitor C3 ( L1791-FP-CNT-0603 PCB ) connected across the output terminals of the power supply, helps to supply high current pulses of short duration during constant voltage operation. Any capacitance added externally will improve the pulse current capability, but will decrease the safety provided by the constant current circuit. A high current pulse may damage load components before the average output current is large enough to cause the constant current circuit to operate.

The effects of the output capacitor during constant current operation are as follows: a.The output impedance of the power supply decreases with increasing frequency

b.The recovery time of the output voltage is longer for load resistance changes.

c.A large surge current causing a high power dissipation in the load occurs when the load resistance is reduced rapidly.

4.7REVERSE VOLTAGE LOADING :

A diode CR1 is connected across the output terminals. Under normal operation, the diode is reverse biased (anode connected to the negative terminal ). If a reverse voltage is applied to the output terminals ( positive voltage applied to the negative terminal), the diode will conduct, shunting current across the output terminals to the forward voltage drop of the diode. This diode protects the series transistor and the output electrolytic capacitors.

4.8REVERSE CURRENT LOADING :

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 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 operation cycle of the load device.

4.9EXTERNAL PROGRAMMING :

Remote external programming can be achieved changing the external program link on rear panel and connecting a variable resistor of 5K across the terminals as shown on the rear panel.

7