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In place of the 150V supplied by the battery, another 12V source (or any lower voltage source) can be used to connect to the HV line. The precharge functions should be tested with a lower voltage first, remember to recalculate the voltage division values to see when precharge stops.
Isolated DC/DC:
Test points:
The first point to test is the capacitor itself. Enable precharge and measure of the change in voltage over the duration of the capacitor's charge. It should follow the expected curve of voltage in an RC circuit. Now unpower the enable pin and check the discharge normally.
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