Patent ID: 8378634

Claim:
A power management circuit, comprising: a first voltage regulator converting an input voltage to an output voltage; a second voltage regulator coupled between the output voltage and a battery; and a voltage difference control circuit receiving the output voltage and a voltage (Vbat) of the battery, and outputting a voltage difference control signal to control the first voltage regulator so that when the battery voltage (Vbat) does not exceed a minimum output voltage, the output voltage is higher than the minimum output voltage, and when the battery voltage (Vbat) exceeds the minimum output voltage, the output voltage is higher than the battery voltage (Vbat) by a voltage difference; wherein the voltage difference control circuit includes: a battery reference voltage determination circuit generating a battery reference voltage (Vbr) related to the battery voltage (Vbat); and an error amplifier receiving the output voltage and the battery reference voltage and generating the voltage difference control signal.