A Novel Ladder Control Assisted Startup for Primary Side Regulated Flyback Converter

A novel ladder control assisted startup for primary side regulated flyback converter without off-chip capacitors is proposed in this paper to reduce the overshoot voltage and optimize the startup time under different loads and input voltages. Large peak current in traditional soft-startup process may damage devices, and the detail reasons are illustrated in this work. To overcome the problems caused by the slow callback process of the error amplifier, sample information relative to the input voltage and load current is used by the ladder control circuit to generate a series of voltages to assist the startup. The proposed controller chip is fabricated in 0.18pm BCD process. The experiment results show that the overshoot voltage can be reduced from 20V to less than 0.3V and startup time can be reduced from 105ms to 42ms with the ladder control.