Thread: Sanity Check

Cheater2k - that is easy, just get a different chip that regulates 12V out instead of 5V.

What about this?

http://www.national.com/ds/LM/LM123.pdf

The 1084 is not like the 7805 .. PINS not compatable.

pin 1 gnd , pin 2 out, pin3 In

So your connections looks a little like a 4th of july fireworks setup.

Mastero

LOL - Yeah - Fortunately I read the specs Prior to soldering! Didn't end up with much of a show other than blowing the 10mF cap on the way out!

Looks like good work. I'd like to make one myself instead of buying expensive voltage adapters from radio shack.

I've experimented with this before for a pda adapter. I wired a couple .5 amp 5v reg chips in parrallel to provide 1 amp for my old iPaq. No caps or resistors attached, and no regard for heat transfer. It only worked intermittently and eventually died. Is it safe to say this schematic will actually work? I need to power my dvd drive, my audigy NX2, and a 6v usb hub.

Where's a good place to find a 6volt chip?

Thanks, Rob.

Originally Posted by Mastero

ok to make the long story small,

Lm1084 is a linear chip with 5amp capability....(HEAT IS THe ISSUE HERE)

Use a 220UF/ 25v cap on both side input and output... wont blow then ..


Mastero

Resurrecting a 6 month old thread here. Maestro I want to build this using the original schematic. According to your suggestions, the only changes to the original schematic would be to use an LM1084 (as opposed to an LT1084 that the OP used) and 220UF/25V caps.

My local radio shack doesn't have 220UF/25V caps, they have 220UF/35V - would this work? Also, they don't have the 2 resistors listed in the original diagram, would 100 & 330ohm .5 watt resistors work as replacements?

Lastly, if I paste on one of those RAM heatsinks to the LM1084, would that be enough to dissipate the heat? Thanks!

-HD

The power dissapated by a linear device is equal to the voltage drop across the regulator times the load current. If you are going to supply 5 volts at 6 amps, your equation is (12.6-5)*6, or roughly 45 Watts with the engine off. That's quite a lot of power. If you put a fan on an old socket 7 heatsink, you might get by. The caps you listed should be fine, but Mastero may have more to say about that, he's the master. The positive end of the cap should go to the regulator in/out, and the negative should go to ground.

Hope that helps
Walt

Those caps should be fine .. on the 5 v section try to use like 10 - 16 v

I dont know your actual use of the device so judging the heat sink shall be hard the best way is to get practical and check how hot the heat sink gets with hours of use ... increase size accordingly.

BE CAREFULL these are not pin compatable with 7805.

As for the resistor you will have to do the calculation. The formula is on national site ... i dont have it now ..if i have the time shall post it here. you can also use a 1084- 5 that is a 5v version so you dont require the resistors.


Hope it helps

Cheers
Mastero

Originally Posted by hd54321

Resurrecting a 6 month old thread here. Maestro I want to build this using the original schematic. According to your suggestions, the only changes to the original schematic would be to use an LM1084 (as opposed to an LT1084 that the OP used) and 220UF/25V caps.

My local radio shack doesn't have 220UF/25V caps, they have 220UF/35V - would this work? Also, they don't have the 2 resistors listed in the original diagram, would 100 & 330ohm .5 watt resistors work as replacements?

Lastly, if I paste on one of those RAM heatsinks to the LM1084, would that be enough to dissipate the heat? Thanks!

-HD