Stylus, Circuit System, Control Circuit and Method Thereof for Power Saving

The present invention provides a circuit system for saving power, including: a battery for supplying power; a boost converter circuit, coupled to the battery, for increasing voltage of direct current outputted from the battery; a switch circuit including a first end and a second end, the first end coupled to the boost converter circuit; a load circuit, coupled to the second end; a capacitor, coupled to the second end, for storing and discharging electric power for solely supplying the load circuit; and a control circuit, coupled to the boost converter circuit and the switch circuit, for implementing the following steps: if the voltage of the second end is less than a first voltage, enabling the boost converter circuit and having the switch circuit connect the first and the second ends; and if the voltage of the second end is larger than a second voltage, disabling the boost converter circuit and having the switch circuit disconnect the first and the second ends, wherein the second voltage is larger than the first voltage.