Current Sinking OperationPower Dissipator OperationQuerying the Power DissipatorCurrent SinkingCurrent sinking, also referred to as down-programming, is the ability to pull current into the positiveterminal of the DC power supply. For example, the power supply pulls or sinks current into the positiveterminal whenever a lower output voltage is programmed. This is necessary because stored energyfrom the power supply's output capacitor and external capacitance from the load including the wiringmust 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 thepower 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 itsrated current for an indefinite time. This is adequate for rapidly down-programming the majority ofloads connected to the output.With the addition of Keysight N7909A Power Dissipator Units, the DC power supply can sink up to100% of it rated current. This allows for the possibility of sinking the power supply’s full rated outputcurrent for an indefinite time. This capability is useful with large capacitive loads, or with batterycharging/discharging applications.Note that this two-quadrant sourcing and sinking capability of the DC power supply allows forseamless transitions between sourcing and sinking current without changing the power supply’soutput characteristics or introducing any disruptive behavior. The following controls are provided tofully utilize the two-quadrant output capability of the supply.Current Limit control in voltage priority modeWhen operating in voltage priority mode, you can program a negative or positive current limit. This willlimit any current overshoots that may occur during rapid down-programming or up-programming.Current setting control in current priority modeWhen operating in current priority mode, you can program the output current to seamlessly cross thezero point when transitioning from positive to negative or negative to positive. Additionally, whenoperating in the negative current quadrant, you can program a negative current setting that will holdthe sink current at the specified value. This is useful, for example, for discharging a battery at aconstant current rate.If your application requires precise control of the source and sink currents, current slew controls areavailable to specify a current slew rate when sourcing and sinking current.4 Using the Advanced Power System174 Keysight N6900/N7900 Series Operating and Service Guide
