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4 Using the Regenerative Power System
Note that when the output current reaches the positive or negative current limit, the unit no longer
operates in constant voltage mode and the output voltage is no longer held constant. Instead, the
power supply will now regulate the output current at its current limit setting. A LIM+ (positive current
limit), or LIM– (negative current limit) status is set to indicate that a current limit has been reached.
These conditions are annunciated by CL+ or CL- on the front panel.
As shown by the vertical portions of the load line, the output voltage may continue to increase in the
positive direction or decrease in the negative direction as current is forced into or pulled out of the
unit. When the output voltage exceeds the over-voltage protection setting, the output will shut down,
the output relays will open, and the OV status bit will be set.
Current Priority
In current priority mode, the output is controlled by a bi-polar constant current feedback loop, which
maintains the output source or sink current at its programmed setting. The output current remains at
its programmed setting, provided the load voltage remains within the voltage limit setting. Current
priority mode is best suited for use with batteries, power supplies, large charged capacitors, and loads
that are sensitive to current overshoots. It minimizes current overshoots during programming, turn-on,
and turn-off transitions and seamlessly transitions between positive and negative currents.
In current priority mode, the output current should be programmed to the desired positive or negative
value. A positive voltage limit value should also be set. The voltage limit should always be set to a value
that is greater than the actual output voltage requirement of the external load. The following figure
shows the current priority operating locus of the output. The area in the white quadrant shows the
output as a source (sourcing power). The shaded quadrant show the output as a load (sinking power).
The heavy solid line illustrates the locus of possible operating points as a function of the output load.
As shown by the vertical portion of the line, the output current remains regulated at its programmed
Keysight RP7970 & RP7980 Series Operating and Service Guide
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