Patent ID: 8415928

Claim:
A power circuit, comprising: an input transistor coupled to a voltage source; a first transistor connected in series with the input transistor to provide a supply voltage; an input detection circuit coupled to the voltage source to generate a control signal in response to the voltage level of the voltage source; a second transistor coupled to the input detection circuit, the input transistor and the first transistor to turn off the input transistor and the first transistor in response to the control signal when the voltage level of the voltage source is higher than a threshold voltage; an output detection circuit coupled to the supply voltage to generate a first enable signal and a second enable signal in response to the voltage level of the supply voltage; and a resistive device coupled to the input transistor and the first transistor to provide a bias voltage to turn on the input transistor and the first transistor; wherein the first enable signal is coupled to the input transistor and the first transistor to switch off the input transistor and the first transistor when the voltage level of the supply voltage is higher than an output-over-voltage threshold, the second enable signal is utilized to turn off the output of the power circuit when the voltage level of the supply voltage is lower than an output-under-voltage threshold.