Current Sinking Operation
Power Dissipator Operation
Querying the Power Dissipator
Current Sinking
Current sinking, also referred to as down-programming, is the ability to pull current into the positive
terminal of the DC power supply. For example, the power supply pulls or sinks current into the positive
terminal whenever a lower output voltage is programmed. This is necessary because stored energy
from the power supply's output capacitor and external capacitance from the load including the wiring
must be discharged to lower the voltage at the output terminals.
The ability to rapidly transition from a higher to a lower constant voltage level greatly improves the
power supply’s output response time. This is the most commonly used function of the built in down-
programmer, which is automatic and completely transparent to the user.
When operated as a stand-alone unit, the DC power supply can continuously sink up to 10% of its
rated current for an indefinite time. This is adequate for rapidly down-programming the majority of
loads connected to the output.
With the addition of Keysight N7909A Power Dissipator Units, the DC power supply can sink up to
100% of it rated current. This allows for the possibility of sinking the power supply’s full rated output
current for an indefinite time. This capability is useful with large capacitive loads, or with battery
charging/discharging applications.
Note that this two-quadrant sourcing and sinking capability of the DC power supply allows for
seamless transitions between sourcing and sinking current without changing the power supply’s
output characteristics or introducing any disruptive behavior. The following controls are provided to
fully utilize the two-quadrant output capability of the supply.
Current Limit control in voltage priority mode
When operating in voltage priority mode, you can program a negative or positive current limit. This will
limit any current overshoots that may occur during rapid down-programming or up-programming.
Current setting control in current priority mode
When operating in current priority mode, you can program the output current to seamlessly cross the
zero point when transitioning from positive to negative or negative to positive. Additionally, when
operating in the negative current quadrant, you can program a negative current setting that will hold
the sink current at the specified value. This is useful, for example, for discharging a battery at a
constant current rate.
If your application requires precise control of the source and sink currents, current slew controls are
available to specify a current slew rate when sourcing and sinking current.
4 Using the Advanced Power System
174 Keysight N6900/N7900 Series Operating and Service Guide
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