Convert 0-30V 3A PSU to 5A or more

[ginji]

ginji, thanks for the update on the project. I would also be interested in an easy method of building transformers if your dad would not mind sharing. There is a post and an article on this website but it is very difficult. If you could do this, please add as a new post so that the subject is easily found by others.
Thanks!
MP

it's been a while since he's actually built a transformer (last time was at least 16 years ago if not more) so i think what ever he can actually remember is a bit out of date. The article in articles section explains the process quite well (from my understanding of it) although i can understand that people get confused by i

the printed circuit board i'm using was made by my uni (yay for my uni) using protel and some CAM stuff (CAM is computer aided manufacturing) so it isn't etched but has the copper round the tracks cut away.

 

[bigpetespc]

Hello all,
I have been following this discussion with interest as I wish to build this power supply as my first 'home brew' PSU project.
I have a transformer rated at around the suggested 'upgrade' level, but I dont want to start collecting other parts until I am sure there is nothing else to change.
I would like to make mine the 'upgraded' version with a 5A output, so I need to get to the bottom of the changed components list.
Im a beginner to electronics, so if anyone has a finalised upgrade list I would love to have a copy. Im not too worried about keeping the costs down on this one as I want this to be the only bench supply I build for a while, so it has to be good.
Does anyone have the suggested component list yet? Hope you can help and thanks for a really good forum.
Ian (bigpetespc)

 

[ginji]

C1 upgrades to 4700uF or higher, 10 000uF is suggested i believe

The rectifer bridge as a single 10A or higher part, this way it can be attached to the side of the case

I'm changing Q2 from the 2n2219 to a BD139 (you can use a BD137)
WARNING! the pins on the BD139 is different to the 2n2219

Feed back resistors (R4/5/6) to metal film type for the lower tolerance

Other suggestions (not made in this thread, but the other one)
Replace R2 and R3 with 1/2W resitors
R7 with 10W resistor
R1 with 2-3W
P1 is a many-turns wire-potentiometer (10 turns), and P2 is a "cermet" single-turn

 

[bigpetespc]

Thanks Ginji,
I was a little lost to be honest with all of the suggestions that had been made in the two forum topics.
Youve saved me a bit of head scratching with the components youve listed.
I will now start to get some parts together and hopefully I will have a working PSU in the not to distant future.
Ian

 

[ginji]

another suggestion that has been made is to wire 2 pots in series, one the recomended resistance, and the other 10% for fine tuning

 

[bigpetespc]

Hi Jingi,
Now that souds like a really good idea. Ive seen it mentioned in the threads, so If I understand it correctly, it would allow a super fine tuning of the output voltage.
Would this second pot be 10% of the original value? and is it easy to wire the two pots together?
Thanks for the answers by the way.
Ian

 

[ante1]

Hi all,

This project is a long one; does anybody have an updated schematics which agrees to the project so far?

Ante :

 

[MP1]

Ante, this subject was started by mixos and I think he and staigen have a list of changes that they have made. You might contact him direct. He has been very busy with keeping up the site.

MP

 

[ante1]

MP, thanks!

OK, I

 

[MP1]

No, I have not heard from Staigen for some time.
Staigen, are you still dropping in?

MP

 

[mastrila]

I have isolated the VARIAC from the PSU with an isolation transformer (it has taken sometime to find a suitable one) but this has had no effect on my problem with the output.
Any fresh idea?
Mastrila

 

[ante1]

Hi, mastrila

Earlier you said

 

[mastrila]

Hi Ante,
thank you for the response.
I certainly do not expect to be able to have 3.5A with a 75R load.
But I cannot understand why I should not be able to obtain at least
2A (@30V) with 15R, or 1.5A with 20R.
Ohm's law is linear.
This is my problem.
Mastrila.

 

[ante1]

mastrila,

Have you measured the voltage at Q4 collector when doing these tests? Is here enough voltage to supply the output or are the transformer and rectifier dropping too much? If there is plenty of slack here the problem is in the controlling part. Measure the base to emitter voltage under these load conditions. This is where I would start the troubleshooting. Please let me know.

Ante :

 

[tuzvihar]

Hy,

Im new in this forum, and just wanted to make a good power supply for my projects. I already made the PCB for this supply. I dont really understad that the U2 and U3 opamps are good, or not? In this or the other thread somebody said, that it has a voltage of 38V instead of the maximum 36V. Is it true, or do i really need to get some other high voltage amplifier?

thx

 

[MP1]

tuzvihar,
That comment is still in debate. The person who made the comment has not built the project. Those who have already built this project have not given me a reason to believe there is a problem with it as yet.
Welcome to the forum. I am glad to see someone who is actually building a project instead of redesigning it in their head. Please keep us posted on how it performs for you.

MP

 

[tuzvihar]

I'm going to build the circuit as soon as possible, but i'm very busy bcause of my exams. I think , the diodes will be replaced by 6A types, because i have them at home, and the input capacitor will be a bit bigger, 4700uF or so because i have some in stock

As soon , as it will be complete, i'll do some measurements.

 

[ante1]

Hi, tuzvihar

About the changes of caps and diodes I can only say: Bigger is better!!
I am looking forward to hearing about the measurements. Good Luck.

Ante :

 

[ginji]

Hey MP, i've built the power supply, and it works, and i should be able to take it up to the uni for testing with a cro later... will let you know what happens

 

[MP1]

ginji, thank you for the update on your progress. Good work!

MP