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While I am waiting on some parts I made this circuit in a simulator. When S1 is pressed it should toggle the relay K1 and latch in that state, turning on the other LED. When I press the switch, though, it does not change the relay state. Before I assume an issue with the simulation software, is the circuit itself correct?

S1 open:

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S2 closed:

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So just looking at the LED when S1 is toggled it does turn on, but the state does not latch. It turns off when S1 is released.

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  • \$\begingroup\$ Where did the circuit come from? Can't you look at the various node voltages and see if the circuit is doing what it is supposed to do? \$\endgroup\$ Aug 27, 2021 at 15:52
  • \$\begingroup\$ How quickly are you pressing S1? That circuit won't work if you press it faster than about once per second. \$\endgroup\$ Aug 27, 2021 at 15:53
  • \$\begingroup\$ It also won't work with a one ohm relay - it needs at least several hundred ohms \$\endgroup\$ Aug 27, 2021 at 15:55
  • \$\begingroup\$ I found it here:edn.com/latching-power-switch-uses-momentary-pushbutton \$\endgroup\$
    – justin4fun
    Aug 27, 2021 at 16:24
  • \$\begingroup\$ How much current is the LED using? Could need a current-limiting resistor. Might have to take the output node and further buffer that, with an NMOSFET perhaps (to drive something with lots of current without affecting the rest of the circuit.) \$\endgroup\$
    – rdtsc
    Aug 27, 2021 at 17:06

1 Answer 1

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A standard 'impulse relay' alone would suffice for your application. It's also known as a 'ratchet relay'.

The relay is set and reset with alternate pulses to the coil.

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