Patent ID: 7259973
Filing Date: 2007-08-21
Classification: H02M,Y02B

Abstract:
1. A semiconductor apparatus for controlling a switching power supply in which a direct-current input voltage is applied to a transformer via a switching element, a direct-current voltage obtained by rectifying and smoothing an alternating current generated in the transformer is controlled by a switching operation of the switching element, and power is supplied to a load, the switching element performing the switching operation controlled by a control signal supplied from a control circuit to a control electrode of the switching element, wherein the control circuit comprises: a transformer reset detection circuit for detecting a reset state of the transformer by means of a transformer reset detection signal indicating the state; an I-V converter for converting into a voltage a current value of the control signal indicating a change of a direct-current voltage based on the alternating current generated on a secondary winding of the transformer; and a standby detection circuit for detecting a standby state during power supply to the load based on the detection signal of the transformer reset detection circuit and a change of an output voltage from the I-V converter, and outputting a control signal for controlling an intermittent operation of switching performed by the switching element, wherein the standby detection circuit outputs the control signal for controlling the switching operation of the switching element as the control signal for controlling the switching of the switching element in such a way that the switching operation of the switching element is stopped when the output voltage from the I-V converter is lower than a standby detection lower limit voltage for detecting a standby state of power supply to the load based on the detection signal of the transformer reset detection circuit, and the switching operation of the switching element is restarted when the output voltage from the I-V converter is higher than a standby detection upper limit voltage for detecting a standby state of power supply to the load.