A protection circuit includes a control unit, a switch unit, a storage unit, and a delay unit, and the protection circuit is used for protecting a processing unit. The control unit is used for receiving a control signal from the processing unit when the processing unit has completed initialization, and generating a pulse voltage. The switch unit is respectively turned on and cut off when the pulse voltage is at a first and second voltage level. The storage unit receives a second supply voltage from the power source and stores energy when the switch unit is turned on, and releases energy to generate a third supply voltage when the switch unit is cut off. The delay unit delays the pulse voltage for a predetermined time period, wherein the third supply voltage is provided to the primary module.