The NCP1337 combines a true current mode modulator and a demagnetization detector which ensures full Borderline/Critical Conduction Mode in any load/line conditions together with minimum drain voltage switching (Quasi-Resonant operation). The transformer core reset detection is done internally, without using any external signal, due to the Soxyless concept. The frequency is internally limited to 130 kHz, preventing the controller to operate above the 150 kHz CISPR-22 EMI starting limit. By monitoring the feedback pin activity, the controller enters ripple mode as soon as the power demand falls below a predetermined level. As each restart is softened by an internal soft-start, and as the frequency cannot go below 25 kHz, no audible noise can be heard.