Series Diode Considerations
The series diode protects the power supplies by isolating the potentially harmful external energy
source from the power supply outputs, thereby completely eliminating the risk of instrument damage
due to reverse currents. The use of the protection diode will not allow current-sinking operation. The
power supplies will not be able to down-program the voltage at the load, nor can they act as a load.
The series diode needs to have a reverse voltage rating of at least the sum of the voltage ratings of all
the series-connected units. Allow an appropriate margin for voltage overshoots and for the maximum
current rating of the series-connected units.
As shown in the figure, the + sense lead of the end unit must be connected to the anode (the power
supply side) of the diode, and not to the cathode (the load side) to protect the sense leads from
possible damage. Note that this will degrade the voltage regulation and programming accuracy at the
load.
To improve programming accuracy, use a DMM to measure the voltage at the load and
programmatically compensate for the voltage drop across the diode by adjusting the output voltage of
the power supplies. The diode drop will vary depending on output current and temperature.
If using the series diode is not acceptable in your application, please contact
Keysight Technologies to speak to a power product support engineer for assistance.
Keysight N6900/N7900 Series Operating and Service Guide 81
2 Installing the Instrument
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