dc-ac inverter alternative

[wsladaritz]

I have a in-dash dvd player with a audio/video input. Just for shits and giggles I'm on a little project to get my snes put in there somehow. The power requirements are 10V, 850mA, 17W DC. Now I know the aux power output is 12V... and I have a power inverter that puts out 200W, 120V AC. So I was thinking, instead of converting the 12V DC aux to 120V AC and then using the snes power cord to step down to 10V is there way that anyone knows of to possibly fabricate a step down transformer for this application. I have a little knowledge on these electronics involved from recent college classes. But the young teacher... well, she wasn't all that great at teaching :wink:

Any help or ideas would be awesome! Or this might be a fool's idea that shouldn't be messed with... let me know please

[CTScott]

Use an LM2940T-10.0 voltage regulator (which is a 10V fixed output regulator). It's a three pin device (input, ground, and output). That, a 0.47uF capacitor on the input to ground, and a 22uF (or higher) capacitor on the output to ground and you are good to go.

http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=LM2940T-10.0-ND

The datasheet shows the application example on the first page:
http://www.national.com/ds/LM/LM2940.pdf

[jdinrc]

Try a DC-DC adapter from Radio Shack
http://www.radioshack.com/product/index.jsp?productId=2103679

[talnlnky]

Use an LM2940T-10.0 voltage regulator (which is a 10V fixed output regulator). It's a three pin device (input, ground, and output). That, a 0.47uF capacitor on the input to ground, and a 22uF (or higher) capacitor on the output to ground and you are good to go.

http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=LM2940T-10.0-ND

The datasheet shows the application example on the first page:
http://www.national.com/ds/LM/LM2940.pdf

Scotts post above would probably be a good option. I like the idea of you skipping the 120v transformer because that will help keep efficiency up, and heat generation from electronics down. It will be more work however.

[wsladaritz]

DUDE!!! CTScott, thanks so much!!! now to get to work...

[wsladaritz]

so one more question... where would be the best place to find these things? Or is that site my best bet? Cause I went searching for the capacitors and there are lots of options...

just thought of another question... how would be the best way to wire this up? I don't really have a circuit board lying around. Obviously I need to solder these connections. But I've never done anything like this outside of class on my breadboard.

Thanks again for the info you've already given!!

[CTScott]

so one more question... where would be the best place to find these things? Or is that site my best bet? Cause I went searching for the capacitors and there are lots of options...

just thought of another question... how would be the best way to wire this up? I don't really have a circuit board lying around. Obviously I need to solder these connections. But I've never done anything like this outside of class on my breadboard.

Thanks again for the info you've already given!!

I like Digikey for one-stop-shopping for this kind of a project. Newark.com is also good and can be a bit cheaper for shipping.

For the caps you could use any type of film or ceramic for the .47uf and an electrolytic for the 22uF.

Try this for the .47uF
http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=399-4309-ND

And this for the 22uF
http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=P918-ND

A heatsink for the regulator:
http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=HS111-ND


And to build it on, I would go to radioshack and grab a little plastic project box that comes with a small piece of perf board. You could probably fit it into a 2"x2"x1" box without a problem.

[wsladaritz]

ur amazing....

[talnlnky]

if you ever need to find electrical parts... and are having problems finding them...
www.mouser.com has millions of parts. The catalog is like a phone book. I've ordered from them multiple times for resistor networks for active crossovers. There's no minimum purchase either which is nice if you only need single resistor or cap, etc.

[CTScott]

I always forget about Mouser - Their shipping tends to be very reasonable. We have a significant corporate discount with Digikey, so I tend to always use them.

[talnlnky]

I always forget about Mouser - Their shipping tends to be very reasonable. We have a significant corporate discount with Digikey, so I tend to always use them.

i've never dealt with digikey, but i've also never heard anything bad about them. I remember a few years back I bought like 3 resistor networks... price was $2.xx and after shipping it was only $5. And from that point on I got a huge catalog every 6 months... the catalog prolly costs them $5 to produce and ship to me... I can't imagine how much money they've lost to me considering I've only made about $10 in purchases (before shipping) total in 5 years.

[wsladaritz]

Got the plastic project box today, ordered the reg and caps, heatsink is on backorder, gonna check mouser tomorrow for that. Got the project box at radio shack. It is just a black plastic box, no perf board.... I didn't think to look on the wall and see if it is just a seperate item or something. I'll go back tomorrow.

Just want to check on some stuff before I go wiring and soldering when I get the stuff in. The input on the reg goes straight to the + battery? cap on input side goes to chassis ground? middle lead goes to chassis ground? cap on output goes to chassis ground? output goes to load (snes).

Now I was planning on cutting my existing power cord (I can get a new one ebay if I need to) and getting some kind of plug for a quick setup. Not planning on keeping it in their permanently. Just want a quick and easy setup for a trip without all the wires.

[CTScott]

Got the plastic project box today, ordered the reg and caps, heatsink is on backorder, gonna check mouser tomorrow for that. Got the project box at radio shack. It is just a black plastic box, no perf board.... I didn't think to look on the wall and see if it is just a seperate item or something. I'll go back tomorrow.

Just want to check on some stuff before I go wiring and soldering when I get the stuff in. The input on the reg goes straight to the + battery? cap on input side goes to chassis ground? middle lead goes to chassis ground? cap on output goes to chassis ground? output goes to load (snes).

Now I was planning on cutting my existing power cord (I can get a new one ebay if I need to) and getting some kind of plug for a quick setup. Not planning on keeping it in their permanently. Just want a quick and easy setup for a trip without all the wires.


For the project box, some come with perf, some do not. They sell perf separately as well.

For the heat sink, any that fits a TO-220 package is fine. You should be able to grab one at radio shack.

Correct on the regulator wiring. Just note that the cap on the output side is polarized. It will have a stripe on one side, typically with (-). Make sure that the negative side goes to ground and the positive to the output leg.

When you cut the power cord, make sure to check polarity.

[wsladaritz]

On the polarized cap the positive lead is longer than the negative isn't it? I'll make sure I get that on right.

The power cord will have a positive and negative lead right? The negative lead of power cord I need to run to chassis ground as well correct?

[wsladaritz]

Thanks for all the help guys...

IT WORKS!!!!!

[CTScott]

Cool! You'll have to post a pic of it up and running.