A charging circuit applied to a post-stage circuit includes a power converting circuit, a power storage circuit, a switching circuit and a processing circuit. The power converting circuit receives an external voltage and converts the external voltage to a charging voltage. The power storage circuit is coupled to the power converting circuit and receives the charging voltage to store the power. The switching circuit is coupled to the power converting circuit and the power storage circuit. The processing circuit is coupled to the switching circuit and controls the charging circuit operated in a first mode or a second mode. When operated in the first mode, the external voltage supplies power to the post-stage circuit. When operated in the second mode, the charging voltage supplies power to the post-stage circuit.