Redesigning My Broken PSU

A

Thread Starter

AndrewStenson

Hello,

My old PSU quit on me. I've decided, rather than fixing it - I'd like to design a new one. Here is what I'm looking to do:

- I want to keep the original carbon fiber case I built for the old board. It has 5 switches and LEDs so I would need it to stay that way, unfortunately (but what are you gonna do about it).

- I need it to have 3.5v,5v,9,12v,15v, and 24v. It must fit in a 2.5" by 7" area with 4 inches of height.

- The original broke down with less than 300ma of draw. I'm hoping the new PSU could be at least 2a.

- I have quite a few random parts just laying around in my storage unit. I see a lot of schematics that use the lm317 as the voltage regulator but the datasheet says it's only good up to 1.5a. I have a few of these so can I use 2 of them to get the current up or is there a better solution? I also have a bunch of transformers from small to pretty big. But most of them have no writing at all on them.

How would I find the primary and secondary coils in them and find out what the voltages, ampere of them are? So this is where I'm at with my project. I'd like to stay at a beginner skill level. So anyone who is a good teacher over forum chat would be helpful, but I'm open to all ideas.
 
I have to ask — do you think you have enough training to build a new one? These can get tricky. Maybe get a friend to help out.


I'd rethink the idea. Older computer-bsaed PSUs are basically free these days. I love recycling old electronics and there are many places that will help you find something. Why spend hours building something new?
 
S

Scott Ranger

You know, you could use the LM317. In series with a 0.2Ω/5W resistor of the output. Connect all the resistors together to be the last output, it will be double or triple the current, I = 1.5A*n.

It would look like so —

Vin─┬─LM317─0.2Ω/5W─┬─○ Vout
......└─LM317─0.2Ω/5W─┘

Vin─┬─LM317─0.2Ω/5W─┬─○ Vout
......├─LM317─0.2Ω/5W─┤
......└─LM317─0.2Ω/5W─┘
 
Everybody wants 2 amp supplies from 3.3 to 24 volts using the easy LM317.

The problem is that when you have it set for 3.3 volts and draw 2 amps the power in the 317 is about 50 watts. That is a lot of heat.

I would look for something on Ebay or Amazon.
 
A

AndrewStenson

The only schematics I could find had the lm317. And that is why I ask.

I guess I don't necessarily need one. I know I could just use a PSU from a pc but I want to build one of my own so that I can better learn for the future.
 
A

AndrewStenson

@ScottRanger

So, will I have to double up the lm317's and double the current?


Definitely having a hard time making sense of this subject for some reason. It's not computing. haha
 
You should build a PSU that has all these bells and whistles. Or, you could repair the one you've got just like you said above. I guess you could say I've changed my mind on what is probably best in this situation.

After all this, you're definitely going to want something that is simply more reliable.
 
Make sure you decide on the specs before you start building.

Right now there is a conflict between the size of your box and the heatsink and circuitry required for an analog supply. As you probably know, there's nothing worse than thinking you have a 4 amp 3 to 24 volt supply and finding out you really only have a .5 amp supply.
 
Well, I am using 3 317's to make 4a.

I think I've finally found the right transformer for my PSU. I'm using an old tube amp power transformer. it has an H.V.

The bridge rectifier I chose is an mb354-w, 40-100v 35a.

I'm really thinking I have solid basics to put together a pretty good PSU. I will most likely have to build another case for it. The old case is just too small. Wish I could save it.
 
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