I've been searching for a similar circuit and only found latching relays with two momentary switches for on and off. I don't know if this circuit has a specific name or not, and since I am a complete begginer I'm sorry if I missed it somehow. Here's my case.

I have a circuit that runs off a 12V DC power supply with one main switch. I need the circuit to be active when the power supply goes on. Simple enough. What I would need now is a switch that cuts the power to the circuit and keeps it off until the power supply is turned off and on again. So just one switch, no turning the circuit on after it's been pressed.


1 Answer 1


This is pretty straightforward. What you need is a single pole, double throw relay with a 12 volt coil and contacts which will handle your load current. Connect it like


simulate this circuit – Schematic created using CircuitLab

When the circuit turns on, there is no power applied to the relay, so it connects the 12V to the load through the NC (normally closed) contact.

When you connect the switch, the relay activates, and the load is disconnected. 12V is applied to the coil, so when the switch is released the relay stays activated, and it will remain so until power is removed.

  • \$\begingroup\$ The relay coil negative failed to connect to the supply '-'. Minor edit required. \$\endgroup\$
    – Transistor
    May 1, 2016 at 21:04
  • \$\begingroup\$ @transistor - Thanks. Fixed. I'd also misidentified the load contact in the text. \$\endgroup\$ May 1, 2016 at 21:30
  • \$\begingroup\$ What a curious little circuit. A self-latching in reverse circuit lol. \$\endgroup\$
    – Passerby
    May 1, 2016 at 21:34
  • \$\begingroup\$ @Passerby - Hey, I had the schematic right. \$\endgroup\$ May 1, 2016 at 23:21

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