NCP1351 pdf,detasheetVariable Off Time PWM ControllerThe NCP1351 is a current-mode controller targeting low poweroff-line flyback Switched Mode Power Supplies (SMPS) where costis of utmost importance. Based on a fixed peak current technique(quasi-fixed TON), the controller decreases its switching frequency asthe load becomes lighter. As a result, a power supply using theNCP1351 naturally offers excellent no-load power consumption,while optimizing the efficiency in other loading conditions. When thefrequency decreases, the peak current is gradually reduced down toapproximately 30% of the maximum peak current to preventtransformer mechanical resonance.