Patent ID: 7135838

Claim:
A power-on device for a circuit system having a power supply terminal coupled to a battery and a charge input terminal coupled to an adaptor, the power-on device comprising: a voltage detector, having an input terminal and an output terminal, wherein the input terminal is coupled to the battery; a first switch having a first input terminal, a first output terminal, and a first control terminal, wherein the first input terminal is coupled to the adaptor, and the first control terminal receives a first signal from the circuit system; a first diode having a first positive electrode and a first negative electrode, wherein the first positive electrode is coupled to the first output terminal, and the first negative electrode is coupled to the charge input terminal; a second switch having a second input terminal, a second output terminal, and a second control terminal, wherein the second input terminal is coupled to the adaptor, and the second control terminal is coupled to the output terminal of the voltage detector; a second diode having a second positive electrode and a second negative electrode, wherein the second positive electrode is coupled to the second output terminal, and the second negative electrode is coupled to the charge input terminal; a third diode having a third positive electrode and a third negative electrode, wherein the third positive electrode is coupled to the second output terminal, and the third negative electrode is coupled to the battery; an inverter having an input terminal and an output terminal, wherein the input terminal of the inverter is coupled to the output terminal of the voltage detector; and a third switch having a third input terminal, a third output terminal, and a third control terminal, wherein the third input terminal is coupled to the charge input terminal, the third control terminal is coupled to the output terminal of the inverter, and the third output terminal is coupled to the battery, wherein: when a voltage of the input terminal is below a threshold voltage, the output terminal outputs a control signal having a first level such that the adaptor supplies the circuit system through the charge input terminal to start the circuit system and charge the battery; when a voltage of the input terminal is above the threshold voltage, the output terminal outputs the control signal having a second level such that the battery supplies the circuit system; when the first control terminal has the first level, the first switch is turned on; when the first control terminal has the second level, the first switch is turned off, and the first signal is preset at the second level; when the second control terminal has the first level, the second switch is turned on, and when the second control terminal has the second level, the second switch is turned off; and when the third control terminal has the first level, the third switch is turned on, and when the third control terminal has the second level, the third switch is turned off.