A High Power Factor Forward Flyback Converter with Input Current Waveshaping

A novel power factor correction circuit is proposed as an improvement over a one stage forward converter. This PFC circuit will achieve high power factor by making the circuit operate in a discontinuous conduction mode and changing the duty period after the cross over instant. The switching technique is such that the off time of the PWM generated signal shall always remains equal to or higher than the on-time period by maintaining a minimum off duration related to the peak voltage magnitude. The near sinusoidal input current is achieved by modifying the switching technique so that the duty period is changed over to a new one after the reflected output voltage in the primary of the transformer is smaller than the input voltage. The current drawn is fully sinusoidal without and initial delay as in the case of conventional equal width PWM techniques. A high power factor could be achieved with this simple controller.