LM317T 12v 8amp power supply help!! / General Science and Electronics / Forums

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LM317T 12v 8amp power supply help!!

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LAN_403

HVLOVER!!

Thu Dec 24 2009, 12:33AM

Registered Member #2567 Joined: Wed Dec 23 2009, 11:56PM
Location:
Posts: 11

ok i've had some problems with making a powersupply using a LM317T regulator. I've gotten the whole thing to work without using pass transistors but i can't seem to find a schematic that works with pass transistors for me. what i'm saying is that i need to know how to connect 2n3055's to the LM317T to obtain about 8 amps max on the output instead of a measly 1.5 amps. if the circuit/schematic you give me involves a pnp transistor, i only have one pnp that is rated for 8 amps at 400v so keep that in mind. can anybody help me?

Mattski

Thu Dec 24 2009, 02:25AM

Registered Member #1792 Joined: Fri Oct 31 2008, 08:12PM
Location: University of California
Posts: 527

Have you tried the one given in the datasheet?

For the high current you want I would tend to recommend a switching regulator. Or if you only want 12V then it's easiest to just use an old ATX power supply which will do plenty of current.

Conundrum

Thu Dec 24 2009, 12:15PM

Registered Member #96 Joined: Thu Feb 09 2006, 05:37PM
Location: CI, Earth
Posts: 4062

get one from a demised flat panel, those are usually around 5-8A.

there's normally a pile of them in the WEEE bins and if you ask nicely they let you take 'em.
regards, -A

HVLOVER!!

Thu Dec 24 2009, 02:57PM

Registered Member #2567 Joined: Wed Dec 23 2009, 11:56PM
Location:
Posts: 11

yeah i have tried the datasheet one, it unfortunately didn't work for me. i'm not exactly sure why. i built it everything exactly as it said except with a TIP42G PNP transistor in place of the 2n2905 and 2n3055's in place for the LM195's. that one would be a great regulator since i have the parts for it (somewhat) but when i hook all of it up like the diagram says, it only lets my regulate a voltage between 11.58-12.48vdc...when i take out the transistors i can once again regulate a full 1.2-12vdc again. i'm not exactly sure what's going wrong here.
what do you mean by a switching regulator? could you explain please??? i sorta know what it is but i'm a bit fuzzy

teravolt

Thu Dec 24 2009, 04:31PM

Registered Member #195 Joined: Fri Feb 17 2006, 08:27PM
Location: Berkeley, ca.
Posts: 1111

there are two ways to do this one way is to use 2 lm338k to-3 regulators the information for gangeing them up is in the national PDF. the other way you are talking about is called with 2n3055's is called a emiter follower. I just entered 2n3055 regulator in google and came up with this

this site has less more powerfull regulators if you don't want to build this or fixed regulators. they also have a cuple of other circuits if you go to there home.

HVLOVER!!

Thu Dec 24 2009, 05:32PM

Registered Member #2567 Joined: Wed Dec 23 2009, 11:56PM
Location:
Posts: 11

ah ok, i see. i just tried constructing a much simpler version without even realizing it was in the emitter follower configuration and it seemed to work very well....one of my resistors started smoking on the output lol so plenty of current! anyways i will try and build this one and see how it goes! thanks for the site!

teravolt

Thu Dec 24 2009, 06:34PM

Registered Member #195 Joined: Fri Feb 17 2006, 08:27PM
Location: Berkeley, ca.
Posts: 1111

there are formes of this schematic that have foldback current limiting witch alow you to control the maximum current.

MinorityCarrier

Thu Dec 24 2009, 07:51PM

Registered Member #2123 Joined: Sat May 16 2009, 03:10AM
Location: Bend, Oregon
Posts: 312

I would not expect that circuit to have good load regulation.

2N3055 is a rather wimpy transistor, try a transistor with huevos, a couple of 2N3771's will kick four '3055's sorry butts.

teravolt

Thu Dec 24 2009, 08:07PM

Registered Member #195 Joined: Fri Feb 17 2006, 08:27PM
Location: Berkeley, ca.
Posts: 1111

true but if he doesn't have any 2n3055 kick but today

HVLOVER!!

Thu Dec 24 2009, 08:49PM

Registered Member #2567 Joined: Wed Dec 23 2009, 11:56PM
Location:
Posts: 11

well unfortunately i cannot regulate my voltage on that circuit you gave me! i don't know what is wrong with it! oh well...i'm just gonna build it from scratch, designing it as i go! i'v already connected a "wimpy" 3055 to the output of a second regulator i built kinda like in the circuit you gave me and it works just fine...nothing is different yet one works and the other doesn't. really weird. so now i'm designing one for around 10 amps output at 24 volts regulated. it just seems that the most simplest circuits seem to work the best!

oh and the 3055 i have to admit is wimpy but the highest i own right now is the 2n5885....atleast for transistors....mosfets i have go into the 50A range but even still that's nothin compared to some. anybody have ideas for power supplies using mosfets?? got plenty of those!

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