A synchronous switching voltage converter has a first switch, a second switch, and an inductor, which are all coupled together to a switch node. A reverse current preventing circuit has a current detecting circuit, a voltage detecting circuit, a delay time adjusting circuit, and a blocking circuit. When an inductor current reduces to reach a predetermined threshold current, the current detecting circuit generates an original preventing signal. The voltage detecting circuit detects a switch voltage at the switch node. In response to the original preventing signal, the delay time adjusting circuit generates a corrected preventing signal after an adjustable delay time with respect to the original preventing signal. The adjustable delay time is adjusted on a basis of the switch voltage. In response to the corrected preventing signal, the blocking circuit turns OFF the second switch.