DATA TRANSMISSION SYSTEM, POWER SUPPLY APPARATUS, AND EXTERNAL DEVICE

This application relates to the technical field of electric tools, and particularly discloses a data transmission system, a power supply apparatus and an external device. The system includes a battery pack and an external device. A first level shifter module in the battery pack carries out data transmission with a first processing module at a first transmission voltage, and a second level shifter module in the external device carries out data transmission with a second processing module at a second transmission voltage. When the first level shifter module sends data to the second level shifter module, the first level shifter module switches the first transmission voltage of the data to a preset voltage, and the second level shifter module switches the preset voltage to the second transmission voltage after receiving the data; or when the second level shifter module sends data to the first level shifter module, the second level shifter module switches a transmission voltage of the data to the preset voltage, and the first level shifter module switches the preset voltage to the first transmission voltage after receiving the data. The preset voltage is greater than the first transmission voltage and the second transmission voltage.