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An ignition device for an internal combustion engine includes a control circuit that generates an ignition signal for allowing or interrupting the supply of a primary current of an ignition coil under control, a waveform shaping circuit that waveform-shapes the ignition signal, a switching element t

An ignition device for an internal combustion engine includes a control circuit that generates an ignition signal for allowing or interrupting the supply of a primary current of an ignition coil under control, a waveform shaping circuit that waveform-shapes the ignition signal, a switching element that allows and interrupts the supply of the primary current on the basis of the ignition signal that is waveform-shaped to generate a high voltage on a secondary side of the ignition coil, and an over-current protection circuit that forcedly interrupts the supply of the primary current and holds an interrupt state until the ignition signal turns off when the primary current of the ignition coil exceeds a given value.

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1. An ignition device for an internal combustion engine, comprising:a waveform shaping circuit that waveform-shapes an ignition signal for controlling the supply/interruption of a primary current of an ignition coil; a switching element that allows and interrupts the supply of the primary current on

1. An ignition device for an internal combustion engine, comprising:a waveform shaping circuit that waveform-shapes an ignition signal for controlling the supply/interruption of a primary current of an ignition coil; a switching element that allows and interrupts the supply of the primary current on the basis of the ignition signal that is waveform-shaped to generate a high voltage on a secondary side of the ignition coil; and an over-current protection circuit that forcedly interrupts the supply of the primary current and holds an interrupt state until the ignition signal turns off when the primary current of the ignition coil has a given value larger than a maximum value of the primary current in a normal state. 2. An ignition device for an internal combustion engine according to claim 1, wherein the over-current protection circuit comprises:a detection resistor which is connected in series to the switching element; a comparator that compares a terminal voltage of the detection resistor with a given voltage of a reference power supply; and a latch circuit that controls the energization/disenergization of the switching element on the basis of the output of the comparator and the ignition signal. 3. An ignition device for an internal combustion engine according to claim 1, wherein the given value in the over-current protection circuit is 1.6 times or more of the maximum value at the time when the primary current is normal.4. An ignition device for an internal combustion engine according to claim 1, wherein the switching element is an insulated gate bipolar power transistor.5. An ignition device for an internal combustion engine, comprising:a waveform shaping circuit that waveform-shapes an ignition signal for controlling the supply/interruption of a primary current of an ignition coil; a switching element that allows and interrupts the supply of the primary current on the basis of the ignition signal that is waveform-shaped to generate a high voltage on a secondary side of the ignition coil; an over-current protection circuit that forcedly interrupts the supply of the primary current and holds an interrupt state until the ignition signal turns off when the primary current of the ignition coil has a given value larger than a maximum value of the primary current in a normal state; and an energization time abnormality protection circuit that forcedly interrupts the supply of the primary current of the ignition coil and holds an interrupt state until the ignition signal turns off when the ignition signal exceeds a given energization time.6. An ignition device for an internal combustion engine according to claim 5, wherein the energization time abnormality protection circuit comprises:an integrating circuit that integrates a constant current on the basis of the ignition signal; and a comparator that compares an integrated voltage of the integrating circuit with a given voltage of a reference power supply and controls the energization/disenergization of the switching element on the basis of the comparison result.7. An ignition device for an internal combustion engine according to claim 6, wherein the over-current protection circuit comprises:a detection resistor which is connected in series to the switching element; a comparator that compares a terminal voltage of the detection resistor with a given voltage of a reference power supply; and a latch circuit that controls the energization/disenergization of the switching element on the basis of the output of the comparator and the ignition signal.8. An ignition device for an internal combustion engine according to claim 5, wherein the over-current protection circuit comprises:a detection resistor which is connected in series to the switching element; a comparator that compares a terminal voltage of the detection resistor with a given voltage of a reference power supply; and a latch circuit that controls the energization/disenergization of the switching element on the basis of the output of the comparator and the ignition signal.9. An ignition device for an internal combustion engine, comprising:a waveform shaping circuit that waveform-shapes an ignition signal for controlling the supply/interruption of a primary current of an ignition coil; a switching element that allows and interrupts the supply of the primary current on the basis of the ignition signal that is waveform-shaped to generate a high voltage on a secondary side of the ignition coil; an over-current protection circuit that outputs a given signal when the primary current of the ignition coil has a given value larger than a maximum value of the primary current in a normal state; and an energization time abnormality protection circuit that forcedly interrupts the supply of the primary current of the ignition coil and holds an interrupt state until the ignition signal turns off when the primary current of the ignition coil exceeds a given value or the ignition signal exceeds a given energization time on the basis of the given signal.10. An ignition device for an internal combustion engine according to claim 9, wherein:the over-current protection circuit includes a detection resistor which is connected in series to the switching element, and a comparator that compares a terminal voltage of the detection resistor with a given voltage of a reference power supply and outputs a comparison result; and the energization time abnormality protection circuit includes an integrating circuit that integrates a constant current on the basis of the ignition signal and the comparison result, and a comparator that compares the integrated voltage of the integrating circuit with a given voltage of the reference power supply and controls the energization/disenergization of the switching element on the basis of the comparison result.11. An ignition device for an internal combustion engine, comprising:an over-current protection circuit that forcedly interrupts a supply of a primary current of an ignition coil when the primary current of the ignition coil has a given value larger than a maximum value of the primary current in a normal state, wherein the interruption of the supply of the primary current is held until an ignition signal turns off. 12. The ignition device for an internal combustion engine according to claim 11, further comprising:a waveform shaping circuit, that waveform-shapes the ignition signal, for controlling the supply and interruption of the primary current of the ignition coil; and a switching element that allows and interrupts the supply of the primary current, on the basis of the wave-shaped ignition signal, to generate a high voltage on a secondary side of the ignition coil. 13. The ignition device for an internal combustion engine according to claim 12, further comprising an energization time abnormality protection circuit that forcedly interrupts the supply of the primary current of the ignition coil when the ignition signal exceeds a given energization time, and holds an interrupt state until the ignition signal turns off.