A power supply circuit for a vehicle control device of an AC charging electric vehicle, wherein the power supply circuit comprises a charging connection confirmation, CC, signal detection and amplification circuit configured to be connected with a CC terminal of a vehicle charging plug and the vehicle control device, a relay and a relay control circuit for controlling the relay; wherein the relay coil is connected in series with the relay control circuit; wherein said CC signal detection and amplification circuit comprises a triode Q 1, the base of the triode Q1 is configured to be connected with the CC terminal of the vehicle charging plug and the vehicle control device, the emitter is connected with a first contact of the relay; the relay comprises three power terminals: a power input terminal, the first contact and a second contact as two output terminals, wherein the first contact is a normally closed contact and the second contact is a normally open contact, the relay is configured to switch a low voltage on-board power supply received on the power input terminal between the two output terminals; the second contact is connected with a first terminal of the relay coil and a power supply terminal (Vpw) of the vehicle control device; the first terminal of the relay coil is connected with the collector of the triode Q1, the other terminal of the relay coil is grounded through triode Q2, the base of the triode Q2 is configured to be connected with a control terminal of the vehicle control device; the power supply circuit being configured such that when a vehicle charging plug is inserted, a signal on the CC terminal pulls down the base of the triode Q1, the triode Q 1 is turned on, the relay coil is energized through the first contact, the relay is controlled to switch the low voltage on-board power supply to the second contact, the power supply terminal (Vpw) and the relay coil is energized through the second contact, the relay is self-locked; when the vehicle charging plug is pulled off, the vehicle control device detects that the CC terminal is disconnected, and controls the triode Q2 to turn off by outputting a signal to the base of the triode Q2, then the relay coil is de-energized, the relay switches to the first contact, and the vehicle control device is de-energized. wherein said CC signal detection and amplification circuit comprises a triode Q 1, the base of the triode Q1 is configured to be connected with the CC terminal of the vehicle charging plug and the vehicle control device, the emitter is connected with a first contact of the relay; the relay comprises three power terminals: a power input terminal, the first contact and a second contact as two output terminals, wherein the first contact is a normally closed contact and the second contact is a normally open contact, the relay is configured to switch a low voltage on-board power supply received on the power input terminal between the two output terminals; the second contact is connected with a first terminal of the relay coil and a power supply terminal (Vpw) of the vehicle control device; the first terminal of the relay coil is connected with the collector of the triode Q1, the other terminal of the relay coil is grounded through triode Q2, the base of the triode Q2 is configured to be connected with a control terminal of the vehicle control device; the power supply circuit being configured such that when a vehicle charging plug is inserted, a signal on the CC terminal pulls down the base of the triode Q1, the triode Q 1 is turned on, the relay coil is energized through the first contact, the relay is controlled to switch the low voltage on-board power supply to the second contact, the power supply terminal (Vpw) and the relay coil is energized through the second contact, the relay is self-locked; when the vehicle charging plug is pulled off, the vehicle control device detects that the CC terminal is disconnected, and controls the triode Q2 to turn off by outputting a signal to the base of the triode Q2, then the relay coil is de-energized, the relay switches to the first contact, and the vehicle control device is de-energized.