How can I get -5 volts?

jeffslot · Post by **jeffslot** » Mon Dec 04, 2006 7:24 am

HI,

I might need to generate -5v for a portable. Is this possible, and how can I accomplish this? Thanks.

Jeff S

timmeh87 · Post by **timmeh87** » Mon Dec 04, 2006 10:17 am

TI saves the day again

PT5022

Post by **marshallh** » Tue Dec 05, 2006 3:01 pm

Or, you can get a 7905 regulator from Digikey. Works the same as the standard-issue 7805, but outputs -5v.

jeffslot · Post by **jeffslot** » Tue Dec 05, 2006 3:09 pm

marshallh,

Do you think this might have an effect on the auido on my jamma board I've been portabalizing. Right now everything is working fine, except audio. My audio is just producing a staticy buzz. Most Jamma's don't require the -5, but it is the only thing that I'm not doing for sure? Thanks.

Jeff S

Post by **marshallh** » Tue Dec 05, 2006 3:13 pm

I'd guess the audio is generated using the -5v. It's common for older PC sound cards to use the -12v input, so I think that may be your problem.
Or, am I misinterpreting something and you already have a -5v power source available?

jeffslot · Post by **jeffslot** » Tue Dec 05, 2006 3:15 pm

Nope, I'm hoping it's the -5 also. That is the only input that I don't have now. But I was worried, where as my neo geo board didn't require the -5, only a +12 for audio. I guess I should go shopping for a 7905, then. Thanks Marshallh.

Post by **marshallh** » Tue Dec 05, 2006 3:18 pm

Here's a part on Digikey that should work:
497-1472-5-ND

jeffslot · Post by **jeffslot** » Tue Dec 05, 2006 3:19 pm

Thanks Marshall.

Turbo Tax 1.0 · Post by **Turbo Tax 1.0** » Tue Dec 05, 2006 4:48 pm

whats the difference between -5 volts and a normal 5 volts that a 7805 gives outputs?

vskid · Post by **vskid** » Tue Dec 05, 2006 4:52 pm

Turbo Tax 1.0 wrote:whats the difference between -5 volts and a normal 5 volts that a 7805 gives outputs?

Its negative.

Like with computer PSUs, if you connect a fan's positive wire to the +12v and the negative to the -12v, its like its 24v, so it spins really fast.

Post by **gannon** » Tue Dec 05, 2006 5:40 pm

vskid wrote:its like its 24v, so it spins really fast.

Or it burns out

vskid · Post by **vskid** » Tue Dec 05, 2006 5:42 pm

gannon wrote:
vskid wrote:its like its 24v, so it spins really fast.
Or it burns out

Hopefully after it spins really fast.