Advantages of using a two-switch forward in single-stage power factor corrected power supplies

A single-stage power factor corrected power supply using a two-switch forward is proposed to increase efficiency. The converter is operated in the DCM (discontinues conduction mode) and it is shown that this operation mode ensures the intermediate DC-bus to be controlled only by means of circuit parameters and therefore independent of load variations. The DCM operation often has a diminishing effect on the efficiency but by use of the two-switch topology high efficiency with minimum circuit complexity can be achieved in this mode. A 500 W 70 V prototype of the two-switch boost-forward PFC power supply has been implemented. The measured efficiency is between 85% and 88.5% in the range 30 W-500 W and the measured power factor at full load is 0.95