Series resonant inverter with integrating feedback control loop

Claim 1

A power supply comprising: a resonant tank circuit including a series-connected capacitor and inductor through which current can flow, the tank circuit having a resonant frequency; a transformer having a primary winding and a secondary winding, the primary winding being connected in series with the resonant tank circuit; switching means for alternately applying a predetermined positive voltage and a predetermined negative voltage to the series-connected tank circuit and transformer primary winding, each such voltage application being for a duration substantially equal to one-half the inverse of the tank circuit's resonant frequency; means for returning excess energy from the tank circuit to the source of the predetermined positive and negative voltages; output voltage means connected to the transformer secondary winding, for providing an output voltage that varies in accordance with the frequency at which the switching means alternately applies the predetermined positive and negative voltages to the series-connected tank circuit and transformer primary winding; means for comparing the output voltage with a predetermined reference voltage and for producing an error signal indicative of the time-averaged difference therebetween; voltage-to-frequency converter means for producing a control signal having a frequency that varies in accordance with the error signal; and pulse generator means responsive to each cycle of the control signal, for generating pulse signals that condition the switching means to alternately apply the predetermined positive and negative voltages to the series-connected tank circuit and transformer primary winding.