Power supply mod to change output

Thread Starter

be80be

Joined Jul 5, 2008
2,073
I started this and was wanting to change output the transformer is 120 volts the output is 32 volts.
16 volts to ground plus and minus.

I'd like to modified the output to go plus and minus 15 volts but that would be like 5 volt up to 15.
I can live with that but I would like to go lower right now i only have lm7805 and lm7905.

I seen a lm317 doing both sides is there a way to do that and then go lower then 5 volts.

power.png
 

Thread Starter

be80be

Joined Jul 5, 2008
2,073
Some thing like this but with the lm317
power1.png

Forget that idea i found lm337
 
Last edited:

dendad

Joined Feb 20, 2016
4,503
Just remember to check the reg pin outs. They are not the same as the others. And the tabs will have to be insulated.
 

Thread Starter

be80be

Joined Jul 5, 2008
2,073
I have a board made that had the 7805 and 7905 on it.
I found a transformer that powered a clock on a old stove with center tap but the output for current was low
maybe 300 mA .

I found a new one rated at 2 amps 32 volt output so I was going to make a better board but I couldn't find a 337 i found them.

I tested power is nice and clean using my old board now to build a new regulator.
I want to add current control to it.

And add some meter to it as well. Going to work on that tonight.
 

Thread Starter

be80be

Joined Jul 5, 2008
2,073
This is my plan I want add voltage and current meter using a uC pic or avr.

I'm going to use the stunt out o 2 cheap dvm that are broke and read the current across them on both sides of the supply.

I can't figure out tho say I use a 317 and 337 to set current how could I add a meter to show setting of output
wouldn't I need to load the power supply to get the reading.
Im sure I would what's the best idea on this a light load of say 10k from -5 to ground a ns +5 to ground.

I have some old opamp's that scale it up for the uC .
Any one want post ideas that be great.

lm337.png

How do I add that looks backward

lm3371.png
Do i feed where I show in the drawing.
 
Last edited:

dendad

Joined Feb 20, 2016
4,503
Remove thr ground connection. Only 2 connections are needed for the current limit. Also, the current sense resistor will be carrying the full load current so a standard pot won't do. And it must not go to zero I think.
LM317_Current.jpg
But there looks to be a better way...
LM317LabSupply.jpg
Have you got the data sheet?
https://www.onsemi.com/pub/Collateral/LM317-D.PDF

I would imagine you can just mirror that circuit with the LM337 and reverse all the diodes and caps for the -ve side if you want.
 

Thread Starter

be80be

Joined Jul 5, 2008
2,073
I got both datasheets one for the lm337 looks wrong.
The lm317 shows the output for current on the output pin
the lm337 has it on the input pin.
 

Thread Starter

be80be

Joined Jul 5, 2008
2,073
I understand that the picture in post #6 is out of the texas instrument data sheet for a lm337
and is shown as is with the current coming out the in pin and part labal lm137
I just changed R1 to a pot.
But Is that right the output is on th Vin not the Vout
 

AlbertHall

Joined Jun 4, 2014
12,397
The circuit in post #6 will draw a fixed current from a negative supply.
The first circuit in post #7 is that same circuit rearranged as a current limiter for a negative supply, but see the second circuit in that post for an improved way of doing it without needing the entire current to go through the pot.
 

Thread Starter

be80be

Joined Jul 5, 2008
2,073
second circuit in that post
Would I mirror for the 337 I tried the lm337 it got hot with no load but I think I hooked the dang thing up like the lm317.

So I just made it 10 volt supply but this time im using the 337 and 317 so i can make a better one.

So I feed at the ground from my negative side and it powers out Vin
likethis.png
 
Last edited:

AlbertHall

Joined Jun 4, 2014
12,397
Sort of. In the first circuit only the polarities and current direction changes.
In the second circuit the same applies but also diodes, capacitors, FETs are the other way round.
 
Top