Patent ID: 8471546

Claim:
A switch circuit, comprising: a time constant circuit comprising: a serial-parallel circuit that is formed by serially connecting a plurality of parallel circuits each structured with a resistance element and a capacitance element between a first terminal and a second terminal; and a voltage-dividing resistance element connected between a third terminal that is connected to the second terminal and a fourth terminal, wherein the first terminal and the second terminal are input terminals, and the third terminal and the fourth terminal are output terminals; wherein when a DC (direct current) voltage is applied between the input terminals, an output voltage acquired between the output terminals changes according to a sum of a plurality of exponential functions of a different time constants; and wherein: the serial-parallel circuit is formed with a first parallel circuit and a second parallel circuit; a first exponential function and a second exponential function are derived approximately from the sum of the plurality of exponential functions; and the output voltage changes according to the first exponential function from a point immediately after the DC current is applied until a specific time, and changes according to the second exponential function after the specific time; a control terminal, and a semiconductor switch element having a first conductive terminal and a second conductive terminal, wherein: when a specific voltage is applied to the control terminal, between the first conductive terminal and the second conductive terminal of the semiconductor switch element becomes conductive; the first terminal is connected to the first conductive terminal, and the third terminal is connected to the control terminal; and the output voltage reaches the specific voltage after the specific time.