Patent ID: 8912777

Claim:
A control circuit for a boost, buck or buck-boost switching power supply comprising a switching element, wherein the switching element comprises a first switching transistor and a second switching transistor smaller than the first switching transistor whose respective control terminals are independent of each other and which are disposed side by side; the control circuit is configured to repeat a driving duration enabling the switching element to be switched and a stop duration stopping the switching element from being switched in a light load state; the control circuit comprises: a pulse signal generating portion generating a driving pulse signal, wherein the driving pulse signal comprises at least one pulse in the driving duration, and wherein during the light load state, a number of pulses in the driving duration is less, and the pulse signal generating portion comprising: a first oscillator generating a first period signal of a first frequency; a second oscillator generating a second period signal of a second frequency lower than the first frequency and having a slope portion; an error amplifier generating an error signal, wherein the error signal is corresponding to an error between a feedback signal denoting an electric state of the switching power supply and a predetermined reference voltage; and a first pulse modulator generating a first pulse signal having the first frequency and having a pulse width corresponding to the error signal and the first period signal, and clamping the pulse width of the first pulse signal at a predetermined first minimum pulse width; a first driver driving the first switching transistor according to the at least one pulse in the driving pulse signal other than a predetermined K pulses (K is a natural number); and a second driver driving the second switching transistor according to at least the predetermined K pulses in the driving pulse signal, wherein the driving pulse signal is generated based on the first pulse signal.