| 摘要 |
A solenoid drive circuit includes two output transistors in parallel paths of relatively high and low resistance respectively. The low resistance path transistor is controlled by a voltage comparator arranged to compare the voltage across a common current sensing resistor with a reference voltage. When the input to the circuit is low, the high resistance path transistor is biased on, but where the current is below a set level, only the low resistance path transistor conducts. Only when the comparator changes state as the solenoid current exceeds its set level does switching off of the low resistance path transistor permit the other transistor to turn on. A delay circuit is included which operates to prevent the low resistance path transistor turning on if there is a short circuit across the solenoid.
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