Patent ID: 8760223

Claim:
A switching circuit comprising at least one semiconductor switch element having an input terminal, an output terminal, and a common terminal, a pulse-like signal being applied between the input terminal and the common terminal to switch a current between the output terminal and the common terminal, further comprising a capacitance suppression element section connected at least one of between the input terminal and the output terminal, between the input terminal and the common terminal, and between the output terminal and the common terminal, wherein the capacitance suppression element section reduces a parasitic capacitance between the terminals of the semiconductor switch element, where the capacitance suppression element section is connected, to less than that obtained when the capacitance suppression element section is not connected, at a frequency N times (N is an integer of 1 or more) as high as a clock frequency of the pulse-like signal, wherein the pulse-like signal is a PWM signal, and wherein the capacitance suppression element section is configured to satisfy expressions (1) and (2) when a reactance of the capacitance suppression element section is a function X(ω) of an angular frequency: [ Expression ⁢ ⁢ 1 ] j ⁢ ⁢ X ⁡ ( n ⁢ ⁢ ϖ 0 ) = - 1 j ⁢ ⁢ n ⁢ ⁢ ϖ 0 ⁢ C X ⁢ ( n = 1 , 2 , … ⁢ , N ) ( 1 ) [ Expression ⁢ ⁢ 2 ]  1 j ⁢ ⁢ n ⁢ ⁢ ϖ 0 ⁢ C X + 1 j ⁢ ⁢ X ⁡ ( ϖ M )  = α ⁢ ⁢ R CO ⁡ ( α >> 1 ) ( 2 ) (in the expressions (1) and (2), j represents an imaginary unit, ω 0 represents a product of a clock frequency of the PWM signal and 2π, ω M represents a product of a modulation frequency of the PWM signal and 2π, C X represents a parasitic capacitance between the terminals of the semiconductor switch element as the parasitic capacitance between the terminals of the semiconductor switch element where the capacitance suppression element section is connected, R CO represents an output impedance of a drive circuit that is connected to the input terminal of the semiconductor switch element where the capacitance suppression element section is connected and supplies the PWM signal).