Voltage-reduction-type switch power supply and control circuit thereof

The utility model discloses a voltage-reduction-type switch power supply and a control circuit thereof. The voltage-reduction-type switch power supply comprises a voltage-reduction-type basic circuit with an inductor. The basic circuit has a constant-voltage working mode and a constant-current working mode. Under the constant-voltage working mode, when the inductor is discharging, a conducting state of a power switch tube is controlled according to output voltage sampling values of the voltage-reduction-type basic circuit, and output voltages of the voltage-reduction-type basic circuit are enabled to remain constant in a first load range. Under the constant-current working mode, after the discharging current of the inductor crossing zero, the conducting state of the power switch tube is controlled, and when the inductor is charging, the inductor charging current is detected, and the turn-off state of the power switch tube is controlled, so that the peak current of the inductor is enabled to be a constant whic