Patent ID: 7498791

Claim:
A reverse current preventing circuit, applied in a synchronous switching voltage converter having a first switch, a second switch, and an inductor, three of which are coupled together to a switch node, such that an inductor current flowing through the inductor increases when the first switch is turned ON and the second switch is turned OFF, and the inductor current decreases when the first switch is turned OFF and the second switch is turned ON, the reverse current preventing circuit comprising: a current detecting circuit for detecting the inductor current such that the current detecting circuit generates an original prevention signal when the inductor current reduces to reach a predetermined threshold current; a voltage detecting circuit for detecting a switch voltage at the switch node, wherein the voltage detecting circuit is implemented by a first comparator and an enabling circuit, and the enabling circuit is used to control the first comparator such that the first comparator is disabled when the first switch is turned ON but is enabled when the first switch is turned OFF; a delay time adjusting circuit for generating a corrected prevention signal in response to the original prevention signal, such that the corrected prevention signal is output after an adjustable delay time with respect to the original prevention signal, the adjustable delay time being adjusted on a basis of the switch voltage at the switch node; and a blocking circuit for turning OFF the second switch of the synchronous switching voltage converter in response to the corrected prevention signal.