Negative LM7805

[computer]

Call me stupid if you want, but I can't for the life of me work out how to make a 'negative' LM7805. IE, I have a 9v input and an LM7805 giving me a +5v output.

I want to also have a -5v Supply derived from that +9v input. Any ideas? I think there was an LM337 that does this but it has all sorts of extra components and adjusters in the example circuits I can find. All I want is a simple regulator with a few caps either side

Thanks

 

[EdwardM]

Hi

nope, don't want to call you stupid

Use a negative LM7805, it's called a 7905, just turn things upside down.

If you want -5v from a 9v supply there are at least two ways that I know of, use a DC-DC converter or consider a charge pump IC, it all depends on how much current you need.

Additionally, if you have a centre-tapped transformer as part of your power supply - take the centre-tap to 0v and AC input to the the bridge rectifier, you will then have + and - supplies available for regulation

Hope this helps

Ed

 

[absolution]

another way is just change ur reference to ground its much easier. as long as ur not doing anything with really sensitive equipment it should be fine.

 

[Dean Huster]

Just be careful, for the input and ground pins are interchanged on the 7905 vs. the 7805. As you look at the 7905 laying on its back with the leads pointing at you, you should have, from left to right: ground, input, output.

Dean