Quasi-resonant switching power supply

摘要

A quasi-resonance switching power supply quickly determines the number of bottom skips corresponding to the load condition even in abrupt load change. The quasi-resonance switching power supply is provided with a bottom skipping control function and a capacitor to hold a voltage corresponding to the load condition of the switching element over one switching period of the switching element. The quasi-resonance switching power supply comprises a bottom skipping number determining circuit that compares the voltage held on the capacitor with comparison reference voltages selected from a plurality of reference voltages for determining the number of bottom skips, and revises the comparison reference voltage according to the comparison result. The processing of comparison and revision is executed multiple times in one switching period of the switching element. Thus, the bottom skipping number determining circuit determines the number of bottom skips corresponding to the voltage held on the capacitor.

主权项

1. A quasi-resonance switching power supply that utilizes resonance phenomenon in a resonance circuit including an inductance and a resonance capacitor connected to an ON-OFF driven switching element of the quasi-resonance switching power supply, and that turns ON the switching element at a timing of a bottom of a resonant voltage, the quasi-resonance switching power supply comprising:
a bottom detecting circuit that detects a bottom of the resonant voltage developed upon turning OFF of the switching element; a bottom skipping number determining circuit that determines a number of bottom skips corresponding to a load of the switching element; and a turn ON control circuit that turns ON the switching element when a number of bottoms detected by the bottom detecting circuit reaches the number of bottom skips determined by the bottom skipping number determining circuit; wherein the bottom skipping number determining circuit comprises a capacitor that holds a voltage corresponding to the load of the switching element over one switching period of the switching element, and sequentially compares the voltage held on the capacitor with a plurality of reference voltages for determining the number of bottom skips in one switching period of the switching element to determine the number of bottom skips corresponding to the voltage held on the capacitor.