How do I convert SPDT to DPDT with a few components.

[brett]

Hi
I feel that someone must have done this before, but I can't find anything on the web.  I've got a circuit that uses two indpendant power supplies that I want to switch on and off with a single SPDT.
Is there a simple circuit for doing this (without bulky relays)?
thanks

[deathbravo]

i think u can use 2 FETs and some resistors ,4 cap , maybe 2 diodes to make a switch,

[Peter Snowberg]

I know the answer is on GEO.

[brett]

Thanks Peter
...Oh!  It's where so many good answers are!

[brett]

Just a final comment:
I'm looking at two systems: the one that RG uses in his pancake pedals (2 micro-relays), and another using a dual opto-isolator to drive 2 power trannies.

[R.G.]

Try using the switch to turn on a bipolar transistor so it's fully saturated. Saturate the transistor to a gain of maybe 20, and use one with a good high current rating. 2N3904 and 3906 are actually pretty good at this. If it's high current, use higher current transistors.

To turn on a positive supply, pull down in the base of a PNP through a resistor. To turn on a negative supply pull up on the base through a resistor. To turn on both a positive and a negative at the same time, put the PNP in the positive, NPN in the negative, and pull both to ground through resistors with another NPN/PNP set up in CE/CB around ground.

... or just use the SPDT to switch a relay...