| 摘要 |
PROBLEM TO BE SOLVED: To reduce the number of part items of a voltage drop detection circuit. SOLUTION: The voltage drop detection circuit 24 does not have a photocoupler nor a shunt regulator but has a counter to measure the pulse width of a pulse-like voltage at an A point between a secondary coil 4 and a diode 5. A rectifying diode is inserted between the point A and the voltage drop detection circuit 24, with an anode located at the point A. The voltage at the A point is divided by resistances 23 and 24 and inputted to the voltage drop detection circuit 24. The voltage drop detection circuit 24 outputs an /NMI signal when the pulse width of the pulse-like voltage exceeds a predetermined value T0 (S).
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