12 February 2010

Momentary latching circuit

Here is a little circuit I made that will allow a momentary switch to turn on/off a load.

Q1 can be any NPN transistor, and Q2 is any N-channel MOSFET capable of handling the current being switched. It should be fine with a range of ~5-12V but I've only tested it at 7.4V.

It somewhat mimics the action of a newer console's power button. I made it so I could switch a relatively large amount of power with a small tactile switch, press for on, press again for off.


  1. Howdy daftmike !!!

    Ive made one of these also awesome momentary to latching switch circuits as i had stocked up on momentary switches over the last few weeks but i made a pcb from the exact schematic you have shared here, i used a free software called "Yenka" which uses "realPCB" (another free software) to make the pcb but once all the components were soldered, i cheacked, tripple & quadruple-cheack all the solder joints for defects, but have a problem...

    I used all the stated components that your circuit used, NO Exceptions, as i wanted it to mirror your circuit to avoid problems!

    Anyhoo, i connect a 9v battery to the input power of the circuit and the output power to a simple heart-flasher circuit (using 555 timer & 4017 decade counter IC's) but strange behavior is being shown... This is what happens...

    When i push the momentary switch, the circuit lights up with a 10 second delay, i push the momentary button again and circuit switches off ! (sweet so far!)

    But when i leave it alone and not touch either circuit, the heart flasher starts working again without me pushing the 'on' button... I press the button again to switch off the circuit but then it starts up again every 10 seconds.

    ***! HELP !***

    Have you had this problem or would you know whats gone wrong here ?

    I could send you a short video to show you whats going on but i have no idea how to contact you !!

    Please help because i really love the usefulness of this circuit and ive already bought 30 tactile momentary switches to be able to add this circuit to mostly all of my projects!! !!!! !

    Many thanks in advance,

    Kind & Best regards,

    Anil Sethi Jnr

  2. i built the circuit above. one problem, i used a remote rf with relay to close the switch contact. it goes high, but will not open when i close the relay (momentatry) on the rf board. any ideas on how to fix this?
    thanks to all