Circuit latches solenoids at a distance

-October 14, 1999

The circuit in Figure 1 controls low-cost, latching solenoid valves over long distances. For example, it can control one valve 1 km away using two wires and a 12V supply. The circuit provides 700 mA at 12V for the 20 msec necessary for latching a solenoid valve. The CD4538 monostable multivibrator provides an output-pulse width of 100 ┬Ásec to 1 sec. The IC consumes 5-nA standby current. The RX1CX1 and RX2CX2 network determines the output-pulse duration and accuracy. When the voltage on CA1 reaches 6V, an input trigger occurs, monostable IC1A delivers an output pulse to Q1's gate, and Q1 sinks the current needed to open the latching solenoid valve. When the voltage on CA1 drops below 6V, monostable IC1B turns on Q2, and Q2 sinks the current needed to close the latching solenoid valve. C1 provides power to the solenoid valve. (DI #2426)

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