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A single-stage high power factor bridgeless forward converter with an improved constant on-time control

A new isolated single-stage power factor correction (PFC) bridgeless forward converter is proposed in this paper. The proposed converter consists of two forward loops with a four-winding transformer. By eliminating the input bridge diodes, conduction losses can be decreased. An improved constant on-time control (COT) is applied to the proposed converter to achieve high power factor and then the input current harmonics can meet the IEC61000-3-2 Class C standard. The proposed converter operates in either discontinuous current mode (DCM) or boundary continuous current mode (BCM) according to the input voltage value. Detailed analysis and circuit operation stages are provided. An 80-W prototype is built up to verify the theoretical analysis of the proposed converter.