Patent ID: 7208985
Filing Date: 2007-04-24
Classification: H02M

Abstract:
1. A semiconductor device comprising a switching element for controlling a switching power supply comprising the switching element and a transformer, wherein a DC input voltage is applied to said switching element through primary windings of said transformer, a switching operation of said switching element for controlling the DC voltage by rectifying and smoothing an alternating current across secondary windings of said transformer, said semiconductor device comprising a control circuit, said control circuit, comprising: a transformer reset detection circuit for detecting a reset state of said transformer due to a switching operation of said switching element from an AC voltage across tertiary windings of said transformer, and for outputting a transformer reset detection signal indicating the reset state; an I-V converter for converting into a voltage a current value of a control current indicating a change in said DC voltage based on the alternating current across the secondary windings of said transformer; and, a current detection signal output device for detecting a value of a current flowing in said switching element based on an output voltage from said I-V converter, and for outputting a current detection signal for controlling a switching turn-on action of said switching element according to the detected value, wherein a control electrode of said switching element is driven by said control circuit based on a transformer reset detection signal from said transformer reset detection circuit and a current detection signal from said current detection signal output device, said control electrode for controlling operation of said switching element, said semiconductor device further comprising a delay circuit for applying a prescribed delay time to the current detection signal outputted from said current detection signal output device, the delay circuit for applying a prescribed mask time to delay the transformer reset detection signal until said current detection signal is outputted to halt switching operation of said switching element.