Ovp Considerations - HP 654 A Series Operating Manual

If you cannot avoid capacitive coupling, it may help to place capacitors from the unused
programming inputs to ground. Especially with auto-paraUel operation, connecting a
capacitor (>4,000 pF) from VP to P Common on the master supply will ensure proper
operation. Also with auto-paraUei operation, do not allow more than about 500 pF capacitive
loading between IM and Common P.
Programming Considerations.
When voltage programming the output, the frequency of the
programming source is limited by the slew rate of the power supply. To keep the power supply
from, slewing its output (going into nonlinear operation), the maximum programming rate is
3750 V/s. The maximum downprogramming rate (when the power supply is sinking current)
is 750 V/s. These restrictions can be expressed as the maximum programming frequency that
can be applied without causing distortion at the output. The following formula can be used to
determine this frequency;
Fmax =_50(voltage rating of supply)
p-p amplitude of desired output sine wave
At frequencies >6 kHz, voltage programming is subject to a 3 dB bandwidth limitation.
Programming Series 657xA Supplies
Wiring Considerations.
The input impedance of the analog input is over 30 kfi. If the output
impedance of your programming source is not negligible with this, programming errors will
result. Larger output impedances result in proportionally greater errors.
Note from Figure 4-3 that you have three options for programming the current. You can use a
voltage source that is positive, negative, or floating with respect to Common P. Do not exceed
±19 V with respect to Common P.
Csution
Make sure that the common connection for your voltage programming source
is isolated from the load. Failure to do this may cause damage to the power
supply.
OVP Considerations
Remote Sensing
The OVP circuit senses the voltage near the output terminals and not at the sense terminals.
Depending on the voltage drop between the output terminals and the load, the voltage sensed
by the OVP circuit can be significantly higher that that actually being regulated at the load.
You must program the OVP trip high enough to compensate for the expected higher voltage
at the output terminals.
Battery Charging
The power supply's OVP circuit contains a circuit that discharges the output of the supply
whenever the OVP trips. If a battery (or other external voltage source) is connected across
the output and the OVP is inadvertently triggered or the output is programmed below the
battery voltage, the power supply will continuously sink a large current from the battery. This
could damage the supply. To avoid this, insert a reverse blocking diode is series with the +
output of the supply. Connect the diode cathode to the + battery terminal and the diode
anode to the supply + output terminal. The diode may require a heat sink.
External Voltage Control
User Connections and Considerations 4-13