Abstract: A power supply system, for example, for use with a portable personal computer, includes a smart battery pack and a charging system. The smart battery pack is provided with a dedicated microcontroller for controlling the charging level of the battery charger system. In particular, the status of the battery including the voltage and temperature of the battery is applied to the microcontroller along with a signal representative of the current load demand of the computer system. The micro controller, in turn, provides a control signal in the form of fixed frequency, variable duty cycle pulse width modulated (PWM) signal for controlling the charging level of the battery charger system. The duty cycle of the PWM signal is used to regulate the charging current supplied by the battery charger. In particular, the DC value of the PWM signal is used as a reference to control the charging current of the regulator to provide a variable output charging current with a relatively wide current range.

Abstract: Since means (control terminal a 16, control terminal b 17, control terminal c 18 and voltage detection terminal 22) for controlling portable electronic apparatus charger 2 directly from CPU 13 in the inside of portable electronic apparatus body 1 is provided, the circuit scale is reduced. Further, since means (power supply detection circuit 6, switch a 7, switch b 8 and regulator a 9) for supplying an electric current to CPU 13 to allow CPU 13 to operate with a signal from sub clock 11 even when the power supply to portable electronic apparatus body 1 is in an off state is provided, if portable electronic apparatus body 1 is connected to portable electronic apparatus charger 2, then CPU 13 and only a limited number of the other circuits in the inside of portable electronic apparatus body 1 are allowed to operate as a control circuit for portable electronic apparatus charger 2.