Patent ID: 8110944

Claim:
A switching circuit comprising: a main power source having a first power source terminal and a second power source terminal; a power source capacitor rechargeable with the main power source, the power source capacitor having a first terminal and a second terminal, the first terminal being connected with the first power source terminal, the second terminal being connected with the second power source terminal; a switching device, which has normally-on characteristics, having a conduction control terminal to which a voltage is applied with the power source capacitor, the switching device having a low voltage terminal; a first changeover switch for connecting the first terminal of the power source capacitor to the conduction control terminal if the connection to the conduction control terminal is selected in the first changeover switch; and a second changeover switch for connecting the second terminal of the power source capacitor to the low voltage terminal if the connection to the low voltage terminal is selected in the second changeover switch; and a diode connected between the second terminal of the power source capacitor and the low voltage terminal, wherein the power source capacitor is rechargeable by disconnecting the first terminal of the power source capacitor and by connecting the second terminal of the power source capacitor to the main power source, and wherein the power source capacitor applies a voltage to the conduction control terminal by connecting the first terminal of the power source capacitor to the conduction control terminal and by connecting the second terminal of the power source capacitor to the low voltage terminal.