The control circuit and power switch

The utility model discloses a control circuit and a switch power supply. The switch power supply comprises a first switch tube and a control circuit. The control circuit comprises a mode selection unit which outputs mode control signals according to load states, a frequency-hopping mode control unit which produces a low-frequency pulse signal with a first frequency according to the value of loads of the switch power supply, and produces a first pulse signal with the first frequency and a second frequency according to the low-frequency pulse signal, wherein the second frequency is greater than the first frequency, and the duty ratio of the low-frequency pulse signal changes along with changes of the loads; a normal mode control unit which produces a second pulse signal with a third frequency; and a driving-signal-producing unit which selects the first pulse signal or the second pulse signal to drive the first switch tube according to the mode control signal, thereby adjusting output signals of the switch power supply.