Zero-voltage transition PWM converters

Claim 1

A pulse-width-modulated, d.c. to d.c. converter comprising in combination: a d.c. voltage input means; a d.c. voltage output means; a pulse-width-modulating switch connected between said d.c. voltage input means and said d.c. voltage output means; a resonant circuit comprised of a capacitance connected in parallel across said pulse-width-modulating switch and an inductor connected to a node that is common to said capacitance and to a terminal of said pulse-width-modulating switch; an auxiliary switch connected in parallel with said inductor to provide low impedance path across said inductor in the on state of said auxiliary switch; a pulse-width-modulating signal source with means connecting said signal source to said pulse-width-modulating switch, and means connecting said signal source to said auxiliary switch; said pulse-width-modulating signal source switching said pulse-width-modulating switch between an on state and an off state at a fixed frequency and a varying duty cycle; said pulse-width-modulating signal source switching said auxiliary switch between an on state and an off state; said auxiliary switch being switched to an off state prior to said pulse-width-modulating switch being switched to an on state so that said auxiliary switch is in said off state a sufficient interval that said resonant circuit establishes a substantially zero voltage across said pulse-width-modulating switch when said pulse-width-modulating switch switches to an on state and said auxiliary switch being switched back to an on state for an interval after said pulse-width-modulating switch switches to an on state in order to control the resonance of said inductor, whereby the pulse-width-modulating switch operates at a constant frequency and zero voltage switching over wide load range.