A device for precise vernier control of the net charge on the high-voltage filter capacitor in a high voltage, high energy power supply through control of the charge on a low-voltage capacitor in series with the grounded end of the main high-voltage filter/storage capacitor of a power supply. Current in this series capacitor arrangement is detected bidirectionally by a current transformer, the output of which is time-integrated. An error signal is detected by a reference amplifier through comparison of the instantaneous low-voltage (bootstrap) capacitor with the integrated value, the latter being a precise analog of the high voltage across the filter capacitor. The bootstrap signal in current amplified form is fed back (in the proper sense) from the output of this comparison to the low-voltage capacitor. Since the net high voltage is the algebraic sum of the voltages on the main filter capacitor and this bootstrap capacitor, the high voltage is thereby controlled or regulated on a pulse-to-pulse basis.
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