Study on Mode Transition Instability in PFM/PWM Dual-mode Circuit

Study on Mode Transition Instability in

PFM/PWM Dual-mode Circuit

Study on Mode Transition Instability in PFM/PWM Dual-mode Circuit Zhang Fan Dept. of Electronic Systems Graduate School, Hanyang University Abstract To obtain higher efficiency PFM/PWM dual-mode control is widely used for DC-DC converters. Pulse width modulation (PWM) control shows high conversion efficiency for heavy load range in DC-DC converter. On the other hand, pulse frequency modulation (PFM), according to its effective switching frequency variation proportion to the load, is adopted for high efficiency in light load condition. But some serious jitter in switch control signal is brought out during the mode transition in PFM/PWM dual-mode control. The jitter can cause system instability. In this thesis, a stable mode transition circuit based on Schmitt trigger is designed to solve the problem.