Seamless Mode-Switch Control Scheme for Primary Side Regulation Flyback With Capacitorless Self-Adaptive Startup

A seamless mode-switch control scheme for primary side regulation flyback with capacitorless self-adaptive startup is presented in this article to increase the system stability for full-load range and reduce the area cost. Instead of traditional soft-startup, a peak current of primary side (PCPS) control scheme without off-chip capacitor is adapted during the startup process and a homologous startup modeling is built. Including the traditional pulsewidth modulation (PWM), the pulse frequency modulation (PFM), and deep pulsewidth modulation (DPWM) are adapted to reduce the standby power at utralight load. Meanwhile, a seamless control scheme is proposed to assure the continuity among the PCPS, PWM, PFM, and DPWM mode switch. The controller chip is fabricated in 0.18 μm BCD process. The experiment results show that the startup time and overshoot voltage are, respectively, 35 ms and 4 V at 0.8 A load current, 48 ms, and 0.2 V at 0.008 A load current. The accuracy of output voltage is within ±0.98% under different input voltages and loads while the peak power efficiency of 88.52% is achieved.