Help building a Variable Hi amp power supply

Thread Starter

sparkfishes

Joined Oct 19, 2009
16

I have been looking at this "need" for several weeks and - like most things I do I wanted not just to build the supply but learn more .
I want about 15 Amps out of the supply 20A would be better
I have read about the various Higher amperage regulators and about putting regulators in parallel but I really wanted to make this circuit




There are several similar ( PNP) circuits on the net and they all have the same values

I don't understand how the LM317 t controls the voltage of the by-pass transistors
The input of the transistors is Supply voltage ( 29.6) The out put is straight to the out put terminal and the base is at 29V and 296mA

Any way I can not get the circuit below ( or the six other I have built) to vary . The LM317 side works OK but as soon as I add the 2955's the output goes to 32.6V


 

Attachments

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Thread Starter

sparkfishes

Joined Oct 19, 2009
16
I can't see any of your schematics?
That is because I can not find out how to upload them I have read the instructions but I still can not do it
I have up loaded the circuit but it will not display it
The circuit is a jpg file and only 18mB
Time zone BST
 

Thread Starter

sparkfishes

Joined Oct 19, 2009
16
Hello,

Did you thing of the big brother of the LM317, the LM338?
Here is a schematic for a 15A regulator using 3 X the LM338 (from the datasheet):



I also have attached the full datasheet for the LM138/LM338.

Bertus
Thanks for the circuit but is not really what I want to do
I want to get my circuit working and understand why it does not work - where I am making my mistakes
The Lm 388 are expensive and I would need to get theop amp when I have theother componet here.
I don't want to appear ungrateful, but I want to learn, not just make A power supply
 

Thread Starter

sparkfishes

Joined Oct 19, 2009
16
If you could explain HOW iget them to display I would be very grateful- YES i have read the instruction but I can not get te SMALL JPG file to diplay
They upload - I think
 

Wendy

Joined Mar 24, 2008
22,690
How to upload an attachment.

To attach a document or picture to a post

Click "Go Advanced" at the bottom of your post,

One of several options will pop up,

Click "Manage Attachments" much further at the bottom of your post,

To upload a file from your computer click "Browse", then select the file.

Schematics should be .gif or .png format, pictures should be .jpg. .jpg formats will fuzz out schematics, and should not be used for that purpose.

---------------

If you want to display this file there is an old thread I made,

How to Display Attachments Full Size
 

Thread Starter

sparkfishes

Joined Oct 19, 2009
16
The circuit is not from the LM317 data sheet although the p[art that is just for the voltage regulation is as per data sheet and that side works OK.
It is only when I put the TRS in the circuit it does not regulate the voltage
Thanks to Bill MarstonI have now uploaded the circuit- I swear I did the same instruction before I asked for help and it did not show up!
 

evilclem

Joined Dec 20, 2011
118
High amp variable.png

Try using the 317 to drive the base of the transistors.

At the moment you have no control on the transistors and the 317 is doing nothing (as it's output is saturated by the transistors bypassing it).
 

Thread Starter

sparkfishes

Joined Oct 19, 2009
16
That is exactly what I thought but there are at least TWO circuits on the web that have the same configuration
I have been doing this almost constantly for 5 day I am going to ak a break and come back to it - thanks
 

bertus

Joined Apr 5, 2008
21,755
Hello,

The link I gave in post #8 also contains the explanation of the circuit.
Driving the PNP transistors with the output of the LM317 will not work.

Bertus
 

t06afre

Joined May 11, 2009
5,934
Would not a LM723 approach be better in this case? The circuit posted by Bertus look quite complicated. Compared to using 1 LM723 and some support circuits
 
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