A mother board including a controller, a rapid charging initiation unit, a connection port, and a switching unit is provided. The rapid charging initiation unit provides a first voltage ranging from 3.2 V to 11 V and a second voltage ranging from 2.7 V to 0.6 V. A voltage difference between the first voltage and the second voltage ranges from 0.5 V to 0.8 V. The connection port is coupled to a smartphone. The switching unit is coupled to the controller, the rapid charging initiation unit, and the connection port for determining whether the connection port is coupled to the controller or the rapid charging initiation unit according to a switching signal. When the connection port is coupled to the rapid charging initiation unit, the first voltage and the second voltage are sent to the smartphone through the connection port for activating the rapid charging function of the smartphone.