The NCP1377 combines a true current mode modulator and ademagnetization detector which ensures full borderline/criticalConduction Mode in any load/line conditions together withminimum drain voltage switching (Quasi−Resonant operation). Dueto its inherent skip cycle capability, the controller enters burst modeas soon as the power demand falls below a predetermined level. Asthis happens at low peak current, no audible noise can be heard. ForNCP1377, an internal 8.0 s timer prevents the free−run frequency toexceed 100 kHz (therefore below the 150 kHz CISPR−22 EMIstarting limit), while the skip adjustment capability lets the userselect the frequency at which the burst foldback takes place. ForNC1377B, the internal timer duration is reduced to 3.0 s to allowoperation at higher frequencies (up to 300 kHz).The transformer core reset detection is done through an auxiliarywinding which, brought via a dedicated pin, also enables fastOver Voltage Protection (OVP). Once an OVP has been detected, theIC permanently latches off. The 1377 features a sampling time of4.5 s whereas it is 1.5 s for the B version.The NCP1377 also features an efficient protective circuitrieswhich, in presence of an overcurrent condition, disables the outputpulses and enters a safe burst mode, trying to restart. Once the defaulthas gone, the device auto−recovers. Finally an internal 1.0 msSoft−Start eliminates the traditional startup stress.