NCP1361: Low Power Offline Constant Current PWM Current-Mode Controller

The NCP1361 offers a new solution targeting output power levels from a few watts up to 20 W in a universal-mains flyback application. Thanks to a novel method this new controller saves the secondary feedback circuitry for constant current regulation while achieving excellent line and load regulation with traditional opto coupler and TL431 voltage reference. The NCP1361 operates in valley lockout quasi-resonant peak current mode control mode at high load to provide high efficiency. When the power on the secondary side starts to diminish, the controller automatically adjusts the duty-cycle then at lower load the controller enters in pulse frequency modulation at fixed peak current with a valley switching detection. This technique allows keeping the output regulation with tiny dummy load. Valley lockout at the first 4 valleys prevent valley jumping operation and then a valley switching at lower load provides high efficiency.