| 摘要 |
A switch selects an inputted direct-current voltage at rising of the inputted direct-current voltage, and selects an outputted voltage after the rising of the outputted voltage, for an input to the constant voltage circuit which supplies power to a control circuit. Therefore, once the step-up operation is carried out in a state where the inputted direct-current voltage is at or greater than the operation voltage of the control circuit, the power source of the control circuit is switched to the side of the outputted voltage which has been increased even when the inputted direct-current voltage decreases. Consequently, the voltage of the power source of the control circuit stays at or greater than the operation voltage of the control circuit, and the stabilized power circuit can carry out a proper operation. This function prevents the operation from being inadequate due to a decrease of the inputted direct-current voltage, and a proper operation can be carried out. Further, a signal of the hysteresis comparator is used for the switching for an input of the constant voltage circuit which supplies the power source to the control section. Thus, the circuit can be simplified.
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