Latching with a momentary switch

Hi All,

I have a project for which I have found the perfect power on / off switch.  Unfortunately the switch is momentary and not latching, so it won't work as is.  The switch will be used to switch the mains power to a switching PSU (12Voutput) on and off.

A quick hunt on the internet has come up with a circuit to make this latching, but I have a couple of questions as I have a feeling this circuit won't help me in its standard form.

Here is the switch (781842):

http://www.rapidonline.com/Electronic-Components/Switches/Push-Button-Switches/IP67-Miniature-sealed-push-button-switches/81475/kw/781842

And here is the circuit:

http://www.daycounter.com/Circuits/Latching-Momentary-Switch/Latching-Momentary-Switch.phtml

But!

The question is, can I get a power transistor for Q4 which will A: switch a 240V supply to the switching PSU on and off and B: work in the circuit I linked to?  I get the impression that the circuit is designed for switching on and off loads which operate at smaller volatges than mains voltage.

And secondly, even if I could do this ^^^, would I need a separate 'always on' power supply to power the circuit so that when I pressed the switch, the latch latches and the 240V flows?

Thanks,

Rob

And secondly, even if I could do this ^^^, would I need a separate 'always on' power supply to power the circuit so that when I pressed the switch, the latch latches and the 240V flows?

Click to expand...

Unfortunately, I would think that's true

I have a momentary push button switch on my pc computer front panel that switches the PSU on and off, but if I power off the PSU with the rocker switch PSU on the rear of PC chassis, the front panel push button doesn't power on the computer anymore

[edit]
On second thought, you don't need to play with the 240V mains directly, you could use a latching circuit that powers on and off a relay
http://www.amb.org/audio/epsilon24/

Cool thank you

I will try and breadboard this and see how it works for my application.