My low cost, easy to build power supply...

SkinnyBoy · 12-03-2001, 06:15 AM

I wanted a DC-DC power supply able to power my P100 in the car, I didn't need it to be able to power it while starting the car, only while it was running...
I had a budget of less than $5 Australian, and cane up with this idea...
it works quite well, and costs next to nothing to make..

I am using low dropout linear regulators(1084) for the 5 and 12 volts. They are both rated at 5amps... For the negitive voltage I used max774 and max 775, these can supply 1amp at -5volts with a 3-16volt input and 400ma at 12volt with a 3-16volt input...

(all of the above component are available as free samples)

The negitive voltage regulators need an external mosfet, (which I had to buy) and the other component I had to buy was the 4049 for the power good signal, All the other caps and resistors I already had.

The whole thing is housed in a standard AT power supply case from a dead power supply, and the heatsink used is a PII one that I bought for fans for my othe player..

All up, the power supply took less than one day to build, and can quite happily power my P100, HD and CDrom from the cars battery while the car is running...

Yeah, I forgot to add in the point that the circuit board I used also cost nothing, as I didn't use a circuit board as such, I used a piece of MDF wood cut to size, and I just drilled the holes where I needed then, and wired on the bottom as you would with standard matrix board...

Its really simple, and really cheap, and really easy to make...

if you don't care about efficiency or size, and are worried about cost, I suggest you try making one of these supplies, I wall post some pictures soon as possible..

cenwesi · 12-03-2001, 06:38 AM

interesting....post a pic let us all see.

SkinnyBoy · 12-03-2001, 06:43 AM

Sorry, Don't have a picture yet, will get one as soon as possibly, maybe tomorrow..

SkinnyBoy · 12-03-2001, 07:24 AM

Okay, I will have to be honest with you, this supply doesn't exist yet, it half exists, I havn't been able to locate the mosfets, and I haven't bought the 4049 yet, but It will be done in the next few days MAX, thats if I can find the mosfets..

So far though, I have spent nothing on it, the 4049 will cost $1.15, and I HOPE he mosfets aren't too expensive..

[ 12-03-2001: Message edited by: SkinnyBoy ]

Rob Withey · 12-03-2001, 08:37 AM

Linear regulators for the 5V line are not such a good idea, as you'll find when you build the thing. 5V at 5A will have more power dissipated than it actually delivers to the computer. 9V voltage drop (with engine running) times 5A is about 45W...!

Rob

Aaron Cake · 12-03-2001, 09:15 AM

Quote:

Originally posted by Rob Withey:
Linear regulators for the 5V line are not such a good idea, as you'll find when you build the thing. 5V at 5A will have more power dissipated than it actually delivers to the computer. 9V voltage drop (with engine running) times 5A is about 45W...!

We've been through this before with him, he didn't listen. He will find out soon enough though.

magnetik · 12-03-2001, 04:37 PM

i like this thread!

making a claim to fame, then confessing that u aint made it anyway? whats the deal there? just a dead thread im afraid.

and yes we did go over this, like Aaron said... sheesh that thread got heated!!

Fosgate · 12-03-2001, 05:27 PM

HAHAHA

What a bull**** Artist!

moahdib · 12-03-2001, 05:49 PM

LOL i love the way Skinnyboy brings some humor to this board from time to time.

SkinnyBoy · 12-03-2001, 07:46 PM

NO!!!!!!
I have made the positive 12volt and 5volt section, and the supply spins up a HD and the regulators don't even get warm...
I have now finished the power good part of the circuit, and am moving onto the negitive voltages asap..

I am only using linear regulators because it is simpler, and at no time will I be drawing 5volts at 5amps from it..
It should work out fine, I will post some pictures of the power supply (minus the negitive parts) tonight...
STOP COMPLAINING!!!!!!!
you don't have to make this supply, I was just telling you that I was, and I will post how successful it was when I have finished..

okay??

magnetik · 12-03-2001, 09:11 PM

Quote:

Originally posted by SkinnyBoy:
STOP COMPLAINING!!!!!!!
you don't have to make this supply, I was just telling you that I was, and I will post how successful it was when I have finished..

okay??

Fosgate, moahdib and myself ain't complaining, just having a laugh at your expense. We all know that linear regulators are useless for running a computer system in-car, and we dont need to be told otherwise.

We all have the money and the sense not to bother with such pointless efforts.... if u wanna go for it tho.... knock yaself out!

Mastero · 12-04-2001, 03:03 AM

Hey guys give him a break let the guy try ..... he will know himself if its right or wrong...

I dont think this forum is made to laugh on someone here who want advice and is doing some R&D of his own ....

Tell me has anyone here actually built a PSU with those linear chips and and had a feild test?

.....????????

Rob Withey · 12-04-2001, 04:41 AM

Quote:

Originally posted by mastero:
Tell me has anyone here actually built a PSU with those linear chips and and had a feild test?

Erm, I don't need to, I can do the math. Electronics isn't all about trial and error. Lots of it is maths. Switchers are a good deal more efficient, and even my switcher gets pretty hot supplying my setup (my heatsink is my entire aluminium computer case).

Rob

Mastero · 12-04-2001, 04:56 AM

Robby how simple you want me to make this question ..

"DID ANYONE BUILT AND HAD A FEILD TEST DONE"
kindly answer in YES or NO only !

I didnt ask for any theorys....or wise comments.

Mastero

PN: sorry in a very *****ed up mood..

[ 12-04-2001: Message edited by: mastero ]

SkinnyBoy · 12-04-2001, 05:31 AM

Well, I have now sorta made the supply it has the power good line, and it works, but I don't have a power supply able to give high enough current at about 14volts...

any ideas of what I should do???

There is no reason why this wouldn't work, the regulator chips can opperate at upto 125 degrees celcius, and I don't think they will get that hot only powering a P100...

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