DAC-Controlled Soft-Start Circuit for AC/DC Converters

A soft-start circuit for pulse-width modulation (PWM) AC/DC controller is presented in this paper. The soft-start strategy is based on a stepped reference which is generated by a 5-bit counter-controlled current-steering digital-to-analog converter (DAC). A monolithic PWM AC/DC controller with proposed soft-start circuit has been fabricated with a 40-V 0.8-μm one-poly two-metal (1P2M) CMOS process. The measurement result shows that the soft-start period of 8 ms is good performance and agrees well with the designed high-power application.