| 摘要 |
PURPOSE:To prevent troubles due to heating of a plunger by detecting such an accident that a transistor adapted to attract the plunger has been broken. CONSTITUTION:If a drive transistor 2 or a first transistor 3 is broken by some reason, the connection point between the first transistor 3 and the plunger 4 becomes high potential with first source voltage V1 and transistors 8, 9 of a detection circuit 7 are turned off, whereby base potential of a transistor 10 is raised in accordance with a time constant determined by a resistor R7 and a capacitor C1. When the raised potential conducts between base and emitter of the transistor 10, the transistor 10 is turned ON so that the output voltage of its collector drives a control circuit 1 and a second transistor 5 for holding is turned ON. Thus, the subsequent power supply to the plunger 4 is interrupted to prevent damages of the second transistor 5 and the printed circuit board. |
