A charge control circuit supplies power from an external power source to a first common node and charges a second common node. A regulator circuit is coupled between the external power source and the first common node, and a transistor is coupled between the first common node and the second common node. A current sensing and control device senses the current from the first common node to the second common node and generates a first control signal. A first voltage sensing and control device senses a voltage at the first common node, and generates a conduction control signal to control the transistor. A second voltage sensing and control device senses a voltage at the second common node, and generates a second control signal. The regulator circuit provides system power to the first common node according to the first control signal and the second control signal.