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A New Primary PWM Control Strategy for CCM Synchronous Rectification Flyback Converter

A new primary PWM (pulsewidth modulation) control strategy for continuous conduction mode (CCM) synchronous rectification (SR) flyback converter is proposed in this letter. The PWM signal for the primary switch has been divided into two pulses in a switching period (dual-pulse PWM, DP-PWM). The first pulse is a fixed narrow pulse, which is used to turn off the SR, whereas the second pulse is a regulated pulse for output voltage regulation. With the proposed DP-PWM control scheme, the shoot-through currents exist on both the primary side and secondary side of the CCM SR flyback converter can be effectively reduced. Meanwhile, the efficiency has been improved obviously. Detailed theoretical analysis has been presented and verified by a 12 V/2.5 A CCM flyback experimental prototype.