Patent ID: 7285991
Filing Date: 2007-10-23
Classification: H02M,Y02B

Abstract:
1. A semiconductor device comprising a switching element for controlling a switching power supply, said switching element for receiving a DC input voltage via a primary winding of a transformer, wherein a switching operation of said switching element for controlling the DC voltage is obtained by rectifying and smoothing an alternating current generated in a secondary winding of such transformer, the semiconductor device controlling the switching operation of the switching element, said semiconductor device comprising a control circuit, which further comprises: a transformer reset detection circuit for detecting a reset state of such transformer from an alternating voltage generated in a tertiary winding of such transformer and for outputting a transformer reset detection signal indicating the reset state, the reset state being generated by the switching operation of said switching element, an IV converter for converting into a voltage a current value of a control current indicating a change of the DC voltage based on the alternating current generated in the secondary winding of such transformer, and a light load detection circuit for outputting a control signal for controlling an intermittent switching operation of said switching element when detecting a light load according to a change of an output voltage from said IV converter, wherein said switching element comprises a control electrode for receiving a signal for controlling the intermittent operation, based on the transformer reset detection signal from the transformer reset detection circuit and the control signal from the light load detection circuit, the control signal from the light load detection circuit outputs the control signal for controlling the intermittent operation and stops the switching operation of said switching element when the output voltage from the IV converter is lower than a lower limit voltage, and restarts the switching operation of said switching element when the output voltage from the IV converter is higher than an upper limit voltage, said control circuit further comprises: when the control signal indicating the restart of the switching operation is outputted from the light load detection circuit within the transformer reset detection setting time, the switching-on control unit restarts the switching operation in response to the transformer reset detection signal.