Micropower starting circuit of switching power supply

The utility model is applicable to the field of power supply circuits and particularly relates to a micropower starting circuit of a switching power supply. The technical scheme includes that a micropower comparator U1 capable of working under microampere working current is available according to the characteristic that a voltage-regulator tube is capable of working under the microampere working current, so that an under-voltage protection circuit and the starting circuit can be kept under the micropower state when in an under-voltage state and after a circuit works normally, sufficient power is output only when the circuit is started so as to guarantee normal starting of the circuit, and consequently medium-and-low power MOS (metal oxide semiconductor) tubes V20 are available. Therefore, size and power consumption of the starting circuit are reduced, the problem that the starting circuit is high in power consumption and poor in heat radiating performance when high voltage is input into the switching power supply is solved, requirements of low power consumption is met, efficiency of the switching power supply is improved, and the switching power supply is downsized.