Charging circuit and an application system thereof

The present invention provides a charging circuit and an application system thereof. An error amplifier is used to control a transistor gate for charging a battery with a charging power. While the voltage difference between source and load terminals of the transistor gate lowered due to the transistor gate is turned on, the output voltage of error amplifier is changed and the resistance of turning-on transistor gate is rose to keep the voltage difference between source and load terminals of the transistor gate above a level. Therefore, an unstable state of turning on-off constantly in charging circuit can be prevented.