I want to make a circuit that at the touch of a button turns on a 12V circuit controlling LED lights, powered from 240VAC.

So I need a latch/unlatched relay circuit after a 12V converter, and I've done some searching and found this link.

My thoughts are to put the 12V DC converter in the circuit before the controlling circuitry, so I don't have to use 240V switches (they need to be small). (This may be wrong or unwise or unnecessary, please inform me if it is).

Would the circuitry in the link be wise (the one with the MOSFETS or relays), or is there a significantly better solution? I only need 10W of power.

  • \$\begingroup\$ Why not use a latching relay in the first place? \$\endgroup\$ – Ignacio Vazquez-Abrams Jul 26 '15 at 18:31
  • \$\begingroup\$ I'm not very good at this kind of thing, but I need something that ideally is one trigger to turn it on and off, as well as the 240V question. \$\endgroup\$ – David Boshton Jul 26 '15 at 19:04

If I'm reading this question correctly all you need is a very simple relay latch such as

enter image description here

Top push button (push to make type) sets the relay ON by connecting the coil to the 12V rail. Once the relay contacts close this supply will be maintained through the relay contats.

The bottom switch (push to break) will break the coil circuit and the relay switches OFF. D1 is there to reduce the back emf spike (on turn off) and prevent arcing across the switch.

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