Charging device and power transmission method

A power transmission method, comprising:

• receiving a first supply power from an electric vehicle when a charging device is connected to the electric vehicle through a first detection resistor;
• utilizing the first supply power to drive a control circuit of the charging device;
• determining, by the control circuit, a voltage across a second detection resistor of the charging device;
• and
• selectively utilizing the first supply power to supply power to an external device, or obtaining a second supply power from the electric vehicle, according to the voltage across a second detection resistor, wherein the first supply power is different from the second supply power.

A charging device, comprising:

• a first connector having a first detection resistor, wherein when the first connector is connected to an electric vehicle through the first detection resistor, the first connector receives a supply power from the electric vehicle;
• and
• a control circuit is electrically connected to the first connector, and configured to be driven by the supply power;
• wherein when the charging device is connected to an external device and obtains a sensing signal, the control circuit is configured to utilize the supply power to supply power to the external device, and is configured to selectively provide a communication signal to the electric vehicle, so that the electric vehicle changes a voltage of the supply power.