Undervoltage locking circuit

The invention relates to the technical field of power supply circuits, in particular to an under-voltage locking circuit which comprises a reference voltage establishing module, a main switching tube and a starting circuit. When the under-voltage locking circuit is started, the starting circuit applies a first voltage to the grid electrode of the main switch tube so that the main switch tube is conducted; the reference voltage establishing module establishes a reference voltage according to a power supply voltage of the power supply circuit and an output signal of the under-voltage locking circuit and outputs the reference voltage to a grid electrode of the main switching tube, and then the starting circuit is closed. The under-voltage locking circuit has the beneficial effects that aiming at the problem that a resistance voltage dividing network in the prior art is easy to operate mistakenly in the starting process, the resistance voltage dividing network is omitted in the under-voltage locking circuit, the