A novel constant current control circuit for a primary-side controlled AC-DC LED driver

A novel constant current control circuit for a primary-side controlled universal-input AC-DC LED driver is proposed in this paper. The proposed control circuit employs minimum voltage detection circuit to monitor the zero crossing information of secondary winding current. The ideal demagnetization time signal is generated by demagnetization time detection circuit. In addition, the ratio between the secondary winding demagnetization time T_Demag and switching period T_S is maintained constant by adopting the intelligent charging and discharging circuit, finally achieving high-precision constant output current. A control IC has been fabricated in TSMC 0.35μm 5V/600V CMOS/LDMOS process. Experimental results of a 3-W circuit prototype show that the constant current precision is within ±1% in a wide range of universal-input ac voltage from 85V to 264 V, and that above 80% efficiency is obtained by driving 3 1-W LEDs. The start-up time is only 46 mS under 90V-input, and the standby power is tested to be lower than 142 mW under 220V-input.