Patent ID: 7888926

Claim:
A control circuit for controlling a synchronous rectifier step-down switching regulator comprising: an output stage which includes a switching transistor and a synchronous rectifier transistor connected in series, and which supplies a switching voltage at a connection node between said two transistors to a switching regulator output circuit connected as an external component to said control circuit; a pulse modulator which generates a pulse signal; a driver circuit which generates first and second gate voltages, which are to be applied to the gates of said switching transistor and said synchronous rectifier transistor, based upon the pulse signal in an enabled state, and which stops the switching operation of said switching transistor and said synchronous rectifier transistor in a disabled state; and a comparator which compares an output voltage from the switching regulator with a threshold value determined by a predetermined reference voltage, and which switches between the enabled state and the disabled state of the driver circuit in accordance with a result of comparison; a light-load detection circuit which compares the switching voltage with a threshold voltage that is synchronous with the second gate voltage, and that is in the high-level state in a period when said synchronous rectifier transistor is to be turned off and in the low-level state in a period when said synchronous rectifier transistor is to be turned on, and which is configured such that, when the switching voltage is greater than the threshold voltage, said light-load detection circuit outputs a light-load detection signal at a predetermined level, wherein, upon reception of the light-load detection signal at the aforementioned predetermined level from said light-load detection circuit, said driver circuit controls the second gate voltage so as to forcibly turn off said synchronous rectifier transistor.