Patent ID: 8203857

Claim:
A booster device for increasing a voltage at a voltage supply point of a power supply circuit for supplying a driving voltage to an electronic control circuit, the power supply circuit including a first series-connected circuit having a diode, a resistor, and a capacitor which is connected to a DC power supply, wherein one end of the capacitor is connected to a ground and a connection point of the resistor and the capacitor serves as the voltage supply point, the booster device comprising: a clamp circuit that outputs a drive disabling signal when the voltage at the voltage supply point is equal to or greater than a predetermined threshold voltage, and outputs a drive enabling signal, which is generated by inverting the drive disabling signal, when the voltage at the voltage supply point is smaller than the threshold voltage; an oscillation circuit that outputs a pulse signal when the drive enabling signal is output from the clamp circuit; and a booster circuit that increases the voltage at the voltage supply point by supplying electric charges, which are accumulated by a voltage output from the DC power supply, to the voltage supply point when the pulse signal is output from the oscillation circuit, wherein the clamp circuit includes: a second series-connected circuit having a Zener diode (ZD 1 ), a first resistor (R 21 ), and a second resistor (R 22 ), and provided between the voltage supply point and the ground; and a first switching element (Q 10 ) having a control electrode which is connected to a connection point of the first resistor and the second resistor, and the first switching element is switched to ON/OFF in response to a voltage generated in the second resistor; and wherein the clamp circuit outputs the drive disabling signal when the first switching element is in an ON state, and outputs the drive enabling signal when the first switching element is in an OFF state.