A circuit for controlling the duty cycle of a two-stage electrostatic precipitator power supply. The circuit includes a switching device connected in series with the primary winding of the power supply transformer and a circuit operable for controlling the switching device. A capacitive network, adapted to monitor the current in the primary winding of the power supply transformer, is provided for operating the control circuit. Under normal operating conditions, i.e., when the current in the primary winding of the power supply transformer is within normal limits, the capacitive network operates the control circuit to allow current flow through the power supply transformer primary winding in a normal manner. However, upon sensing the increased primary current level associated with a high voltage transient generated by arcing between components of the precipitator and reflected from the secondary winding of the power supply transformer to the primary winding thereof, the capacitive network operates the control circuit for causing the switching device to inhibit current flow through the primary winding substantially until the arcing condition associated with the high voltage transient is suppressed. Following an interval after termination of the high voltage transient, the switching device is automatically caused to re-establish primary winding current flow thereby re-establishing normal operation of the electrostatic precipitator power supply.

 
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