A charging circuit for a capacitor includes a current mirror module including a first branch circuit, a second branch circuit and a third branch circuit for supplying a plurality of output currents respectively, a switching module coupled to the first branch circuit and the second branch circuit for determining a conducting condition of the switching module according to the plurality of output currents from the first branch circuit and the second branch circuit, and an active loading circuit coupled to the third branch circuit and the switching module for adjusting a current passing through the active loading circuit according to the conducting condition of the switching module. The capacitor has one end coupled to the first branch circuit and the switching module to process a charging operation according to the output current of the first branch circuit.