| 摘要 |
PURPOSE:To prevent abnormal heating due to abnormal energization by primary current running through an ignition coil so as to enhance the safety of an ignition device, by detecting damage of a power switching element by short- circuiting, and by isolating the ignition device from a power source terminal in accordance with the above-mentioned detection. CONSTITUTION:A control unit 1 applies a predetermined control signal to the base terminal of a power transistor 2 connected in series to the primary winding of an ignition coil 3. Then the ignition coil 3 produces arcs at a spark plug 4. In this arrangement, when the power transistor 2 is damaged by short- circuiting, this condition is detected by a short-circuiting detecting circuit 5. Further, the output level of the circuit 5 is made to be high so that the output levels of a latch circuit 6 and a current cut-off and drive circuit 7 are also made to be high, thereby a circuit breaker 8 is opened. With this arrangement, primary current running through the power transistor 2 damaged by short- circuiting and the primary winding of the ignition coil 3 is cut-off.
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