An over current protection circuit, comprising: a current transformer, having a primary winding connected in series with a primary winding of a power supply transformer and a secondary winding, of which one end is grounded and the other end is coupled to a diode anode; a first resistor, having one end coupled to a diode cathode and the other end grounded; a second resistor, having one end coupled to the diode cathode and the other end coupled to a zener diode cathode; a triode, having a base coupled to a zener diode anode, an emitter grounded and a collector coupled to a light emitter cathode; wherein a light emitter anode is coupled to a LLC chip and a first voltage output end in the power supply; an output end of a light receiver is ground, an input end is coupled to a second voltage output end and a PFC chip.