Patent ID: 7120036

Claim:
A switching-mode power supply for DC-to-DC conversion, comprising: (a) DC input means for inputting a DC voltage; (b) DC output means for outputting a DC voltage; (c) a converter circuit connected between the DC input means and the DC output means, the converter circuit including an active switch for switching the input DC voltage on and off; (d) a switch control circuit connected to the active switch of the converter circuit for on/off control thereof; (e) a synchronous rectifier switch connected between the converter circuit and the DC output means; (f) a diode connected in parallel with the synchronous rectifier switch; (g) conduction period detect means for providing a conduction period detect signal indicative of periods of time during which the active switch is held conductive by the switch control circuit; (h) a capacitor for determination of conducting periods of the synchronous rectifier switch; (i) a charge/discharge circuit connected to the converter circuit and the capacitor for causing the latter to be charged and discharged according to whether the active switch is conductive or nonconductive; and (j) a logic network having an input connected to the conduction period detect means, another input connected to the capacitor, and an output connected to the synchronous rectifier switch, for making on/off control of the synchronous rectifier switch according to whether the active switch is conducting or nonconducting and whether the voltage across the capacitor is higher than a predefined voltage or not.