New PWM converter circuits combining zero switching loss with low conduction loss

A new PWM (pulse width modulation) technique is presented and applied to two DC-DC converters. The new converter topologies completely eliminate switching losses while retaining the low conduction losses typical of PWM circuits. The switches are operated for differing lengths of time, i.e., with unbalanced or asymmetrical duty cycles (for example, one switch at 40% and the other at 60%). The deadtime between switch conduction intervals is made long enough to insure that the switch voltages have commutated naturally from rail to rail, but not so long that the switch voltages have begun their return trip along their oscillatory path between the input rails. Thus, the best features of resonant (zero switching loss) and PWM (low conduction loss) circuits are combined. Design equations and notes are included for a buck type (step-down) and a boost type (step-up) converter.