A constant power limit feedforward control circuit for flyback converters

A new feedforward pulse width modulator (FF-PWM) control circuit for AC-DC flyback converters is proposed in this paper. By using the proposed circuit, the DC converter input voltage with the AC line voltage is proportional to the reference voltage. In addition, the proposed FF-PWM can be easily implemented on chip by using a transconductance amplifier, Wilson current source and current mirror. Simulation and experimental results show that the maximum power change ratio of the flyback converter adopting the proposed feedforward PWM modulator is within 20% at the universal input voltage ranging from 85VAC to 265VAC.