Patent ID: 8508902

Claim:
An electric circuit for electrically connecting a constant-current power supply and a detachable functional element to each other, the constant-current power supply having a capacitance between an output terminal and a reference potential terminal, and the detachable functional element being configured to exhibit a predetermined function based on electric power from the constant-current power supply, comprising: an element breakdown prevention circuit having a first circuit terminal connected to the output terminal of the constant-current power supply via the functional element and a second circuit terminal connected to the reference potential terminal of the constant-current power supply, the electric circuit being characterized in that: the electric circuit has a disconnected state in which the first circuit terminal and the output terminal of the constant-current power supply are electrically disconnected by demounting of the functional element and a connected state in which the first circuit terminal and the output terminal are electrically connected to each other by mounting of the functional element; the element breakdown prevention circuit increases an impedance between the first circuit terminal and the second circuit terminal self-adjustingly to a disconnected state impedance in response to a state transition from the connected state to the disconnected state; and the element breakdown prevention circuit decreases the impedance between the first circuit terminal and the second circuit terminal self-adjustingly to a connected-state impedance that is lower than the disconnected-state impedance in response to a state transition from the disconnected state to the connected state.