US Patent 7166932 Power circuit

A power circuit for generating a standard voltage based on an input voltage, includes a step-down circuit, a step-up circuit, a voltage determiner, a voltage output unit, and a circuit actuator. The step-down circuit steps down the input voltage to the standard voltage, when the input voltage is larger than the standard voltage. The step-up circuit steps up the input voltage to the standard voltage, when the input voltage is smaller than the standard voltage. The voltage determiner determines whether the input voltage is larger than or smaller than the standard voltage. The voltage output unit receives the input voltage, and outputs the input voltage as a supply voltage when the voltage determiner determines that the input voltage is larger than the standard voltage, and outputs no voltage when the voltage determiner determines that the input voltage is smaller than the standard voltage. And the circuit actuator can detect the supply voltage, actuate the step-down circuit when the supply voltage is detected, and actuate the step-up circuit, when the supply voltage is not detected.