I have a simple circuit question; I need to build a dc-dc amplifier from 5 to12 v and 100mA to .5 A . I played around doing it with just transistors, but failed. I don't really know much about this stuff... any input or literature would be great, thanks!

9/13/2009 2:09:49 AM

What are you trying to do? If you have .5W input, you cannot get 6W output.

9/13/2009 3:45:49 AM

Because this is TWW, I feel obligated to post this...

Quote :

"circut"

9/13/2009 4:00:12 AM

You may want to google DC-DC converter.

However, Nitrocloud is exactly right: you will never be able to turn 0.5 W into 6 W with 'just transistors'.

More information on what you're trying to accomplish would be great.

9/13/2009 8:52:47 AM

^^^ absolutely right. if those current/voltage requirements change, you'll need to look into switched-mode power supply and that would either be a buck converter to step down voltage or a boost converter/charge pump to step up voltage.

9/13/2009 9:26:54 AM

yeah, obviously I cant turn .5w into 6w. I just need the 5v to drive a relay that is connected to my 12v source or something, I thought I could do it with a simple transistor amplifier circuit, guess not. Thanks

9/13/2009 10:54:30 AM

Just wtf are you trying to do? How about you give some more details because it sounds a little like you're out in left field.

9/13/2009 11:32:57 AM

I'm driving something from the parallel port that requires 12v, .5A. The parallel port can't provide this so I need use some other power supply to get there. I can do it easily with some solid state relay, but I thought there would be a cheaper way.

9/13/2009 11:42:53 AM

There's no reason why you can't do that with transistors.

http://www.kpsec.freeuk.com/trancirc.htm

9/13/2009 11:48:24 AM

^^ You're simply not going to get any help unless you say what you're trying to do. I'm guessing you're trying to drive a stepper motor but maybe you're doing something else. Regardless, like someone already mentioned, you aren't going to get more power out of the port than it wants to (or can) supply, so you'll need an external source, in which case you most certainly can get by with just transistors.

[Edited on September 13, 2009 at 5:06 PM. Reason : .]

9/13/2009 5:06:28 PM

http://www.mouser.com/ProductDetail/Coto-Technology/9007-05-00/?qs=sGAEpiMZZMsEIsGLxVc9kHPn0E1S%2fxDs

You can get a reed relay that can switch 1/2 amp from the current available from a parallel port. The problems with them are increased contact wear and shorter life, but will not require an external power supply to handle switching. Use a protection diode in reverse bias on the coil to protect the parallel port driver.

9/13/2009 9:21:26 PM

Logic level conversion circuits... look into them.

ummm Common Drain NMOS Amp anybody?

for $100/hr I'll Draw pictures

[Edited on September 13, 2009 at 9:50 PM. Reason : hourly Rate... I'm an analog design engineer]

9/13/2009 9:49:14 PM

^ yeah, I ended up doing it with an NMOS. Thanks for the help everyone

9/14/2009 12:09:20 AM