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 will remain
at its programmed setting as long as 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 quadrants shows
the output as a source (sourcing power). The area in the shaded quadrants shows 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
setting as long as the output voltage remains within its limit setting. A CC (constant current) status
flag indicates that the output current is being regulated and the output voltage is within its limit
settings.
If the output voltage reaches the voltage limit, the unit no longer operates in constant current mode
and the output current is no longer held constant. Instead, the power supply will now regulate the
output voltage at its voltage limit setting. A LIM+ (positive voltage limit) status flag is set to indicate
that the voltage limit has been reached. This condition is annunciated by VL+ on the front panel.
As shown by the horizontal portion of the load line, when the unit is sinking power, the output current
may continue to increase in the negative direction as more current is forced into the unit. This can
happen when the load is a power source such as a battery, and its output voltage is higher than the
voltage limit setting of the power supply. Once the current exceeds the built-in negative over-current
limit, the output will shut down, the output relays will open, and the OC status bits will be set. In such
a case, it is important to set the voltage limit properly in order prevent this protection shutdown.
Keysight N6900/N7900 Series Operating and Service Guide
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4 Using the Advanced Power System
Summary of Contents for N6900 Series
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