| 摘要 |
There is provided a misfire detecting circuit for an internal combustion engine for detecting a misfire on the basis of the presence or absence of an ion current caused by combustion by applying a voltage to an ignition plug of the internal combustion engine, which circuit prevents malfunction caused by stray capacitance generated in the line up to the ignition plug and by the input impedance of the circuit. The misfire detecting circuit includes an ion current detection section which is formed of a diode for causing electric current to flow out from a capacitor, which diode is connected between the ground and the electrode on the low potential side of the capacitor which is charged by electric current at the time of ignition and charged to a predetermined voltage for detecting the ion current, and a current/voltage conversion section which is formed of a diode for causing electric current to flow out and of an operational amplifier whose inverting input is connected to the electrode on the low potential side of the capacitor and whose non-inverting input is connected to the ground.
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