HP 654 A Series Operating Manual page 45

Series 654xA and 655xA Load Capacitance
For Series 654xA and 655xA power supplies, the OVP circuit has been designed to discharge
fully-charged capacitances up to a specified limit for each model. These limits are as follows:
C541A 6542A 6543A 6544A 6545A 6551A 6552A 6553A C554A 6555A
700,000 35,00 mF 13,000 7,000 ^iF 3,000 jiF 1.6 F 100,000 mF 50,000 wF 18,000 mF 8,000 jiF
If a load capacitance approaches the specified limit, it is recommended that you do not make
it a normal practice of tripping the OVP circuit and discharging the load capacitance through
that circuit. This could cause long-term fatigue in some circuit components.
Caution
Because of its high output voltage, the HP 6555A generates very high currents
when discharging the load capacitor under overvoltage conditions. Excessive
currents can damage the supply. The peak discharge current is limited by
the sum of the external capacitor's ESR (equivalent series resistance) and
the series resistance of the external circuit. For the HP 6555A external
capacitance limit of 8,000 /iF, this total resistance must be not less than 56
milliohms. For smaller values of external capacitance, this resistance may be
derated linearly.
External Voltage Control