Full-range high-frequency high-efficiency class D2 resonant power supply

A full-range offline power supplies based on a class D² DC-DC parallel resonant power converter is presented in this paper. The class D inverter is operated above the resonant frequency to produce zero voltage turn-on of the MOSFETs. Turn-off losses are drastically reduced by using only one capacitor connected in parallel to one of the two MOSFETs of the inverter. As a result, switching losses are nearly zero and a full-load, low line high-efficiency h=86% is achieved at an operating frequency of about 500 kHz including the front-end rectifier. The output voltage V₀=12 V is regulated over the entire load range, that is, for an output current I₀ ranging from 0.25 A to 2.5 A and for both American and European standard input voltages in a narrow frequency range, from f_min=290 kHz to f_max=490 kHz. Other advantages of the power supply are its inherently short-circuit protected operation, the low di/dt at the MOSFET turn-off that allows the parasitic MOSFET diodes to be used, and the low conduction losses in ESR of the rectifier filter capacitor