Wouldl like to make a benctop varible power supply

[Marks256]

I have found a nice transformer that puts out a little over 40 volts. The center tap puts out about 21 volts. The transformer is rated at something like 2.4 amps. It came out of an equipment monitor from IBM...

I would like to make a variable power supply with it. 0-30v would be sufficient. I would be fine with something around 2 amps (the more the better). Anyone have any ideas? I was going to go off on my own and design something, but i figured it would be safer to ask first...

Variable current would be nice, but it isn't mandatory.

Meters would be nice, too... (ok, i am done asking for features... )

thanks.

 

[BeeBop]

Hero has a power supply project posted in the projects forum, and it seems very well developed:
https://www.electro-tech-online.com/threads/variable-bipolar-power-supply.24291/

Take a look at that one, it should give you ideas.

 

[Marks256]

I was thinking something more or less like this

**broken link removed**

Hero's looks pretty good, too.

 

[audioguru]

There is a 0V to 30V/2mA to 3A regulated lab power supply project at Electronics-Lab. It doesn't meet its spec's and many of its parts operate beyond their max allowed ratings.
It is a kit.

We fixed and improved it and have a reliable version that meets its specs very well and there is a 5A version too.

 

[Marks256]

Yeah, i saw the one at electronics lab... But after reading the thread about Electronics-lab, i am wondering whether or not not i should trust it...

Could i have a link to the "improved" one? The one that won't kill me, please.

This is the one i saw. https://www.electronics-lab.com/projects/power/003/index.html

But i just found this one, as well. https://www.electronics-lab.com/projects/power/032/index.html


Would my 21volts from the center tap work?

 

[audioguru]

Project #003 is the original faulty project that we fixed and improved.
The moderator didn't bother sorting troubleshooting, parts substitutions, adding meters, fixes and improvements etc. from the 153 pages in the forum. Many people posted their own pcb but the original one can be used with a couple of small changes. It uses a 30VAC/4.2A transformer.

I have never heard from anybody who made project #032 but it should be the same as in the datasheet for the LM723. Its minimum voltage is 3.0V and its max current is fixed at 2.5A but can be reduced to 1.7A for your transformer.

Your 21V center-tapped transformer can make an unregulated supply of 57.4V or 27.7V. No electronics parts distributor has an OPA445AP high voltage opamp in stock so you won't be able to make a 50V/1.7A project. You could make a 20V or 21V/1.7A project.

 

[Marks256]

I think i may have a 30VAC transformer from an old printer. I don't know if it works yet or not...

Would a 2n3054 work instead of a 2n3055? I found a 3054 while i was trying to search for a 3055...

EDIT: Would it be possible to drop the ~40vac to 30vac?

 

[audioguru]

The 30V/3A power supply needs two 2N3055 transistors. 10 little 2N3054 transistors might work.
If you drop 10V at 3A then the power wasted is 30W. I have seen 25W resistors in an aluminum heatsinked case. Maybe somebody makes a 50W one.

 

[Marks256]

Well then i am going to need to find some 2n3055s...

 

[audioguru]

The project uses a lot more than just two very common power transistors.
I recently made a separate thread about replacement opamps for it:
https://www.electronics-lab.com/forum/index.php?topic=14259.0

 

[Marks256]

Ok. Thanks audio. When i get a few more parts around, i will try to make something.

 

[chemelec]

I have found a nice transformer that puts out a little over 40 volts. The center tap puts out about 21 volts. The transformer is rated at something like 2.4 amps. It came out of an equipment monitor from IBM...

I would like to make a variable power supply with it. 0-30v would be sufficient. I would be fine with something around 2 amps (the more the better). Anyone have any ideas? I was going to go off on my own and design something, but i figured it would be safer to ask first...

Variable current would be nice, but it isn't mandatory.

Meters would be nice, too... (ok, i am done asking for features... )

thanks.

That transformer is probably rated at 2.4 amps, Using two diodes and the center tap as common negative.
Not the 40 volts at 2.4 amps.

With good filtering, you might possibly get 1.5 amps DC output.

And if your building a power supply, find one with both Voltage and Current limiting.

There is one on my website that fairly good.

 

[jpanhalt]

Have you seen the supply here:

http://mondo-technology.com/

Click on bench power supply. John

 

[Hero999]

I'd recommend building a bipolar trqacking supply similar to mine.

A 20V centre tapped trqansformer should pretty comfortably give a DC voltage of +-22VDC. The LM317 probaly isn't a good idea as the output current will drop at lower voltages so you're probably better off using a uA723 and a beefy transistor.

 

[Brian218]

Hey Mark,

I'm also in the process of making a power supply. A few of the "must-have" features include the following:
Fixed voltage outputs of 5, 9, 12 and 15 Volts
Adjustable positive and negative outputs (-18__0__+18)
A cooling fan that goes on when a certain temperature is reached, and then turns off when the temp goes below a certain level.
LCD display

Here's a link for an inexpensive ($9.00) 3 1/2 LCD. I bought a few of these, and the work great.
https://www.allelectronics.com/cgi-bin/category.cgi

Good luck

 

[Marks256]

That transformer is probably rated at 2.4 amps, Using two diodes and the center tap as common negative.
Not the 40 volts at 2.4 amps.

With good filtering, you might possibly get 1.5 amps DC output.

And if your building a power supply, find one with both Voltage and Current limiting.

There is one on my website that fairly good.

No, the 40 volts is rated at 2.4 amps. The transformer was in a case (along with an EMF filter), and on the side it said "output: 40VAC @ 2.4A" Also, the module that the transformer provided power for required something around 2 amps.

 

[MRCecil]

I would like to make a variable power supply with it. 0-30v would be sufficient. I would be fine with something around 2 amps (the more the better). Anyone have any ideas? I was going to go off on my own and design something, but i figured it would be safer to ask first...

Variable current would be nice, but it isn't mandatory.

Meters would be nice, too... (ok, i am done asking for features... )

thanks.

Last year I got around to building a replacement for my 20+ yr old noisy bench supply that lacked current limiting. The one I replaced it with is a hundred fold better in every respect; % of regulation, thermal stability, noise, etc. The schematic is attached. As configured, it is 0-24V (changing ratio of R20 & 21 to 4:1 will take it to 0-30V with the 6.0V reference), current limited and metered (LCD PM's); both voltage and current. If you have any questions, I'll be happy to answer them.

Edit: Marks256, I screwed up and posted an early, non-validated rev of the PS. If AudioGuru hadn't have posted a question regarding the efficacy of the design, you or perhaps others could have been led in the wrong direction. My apologies. The as-built that went to the board house is attached.

 

[Marks256]

Thanks, MRCecil.

 

[audioguru]

Hi MR Cecil,
What is the current rating of your power supply?
What is its transformer voltage and current rating?

I notice that the power transistor Q1 has a very low max base current of only about 30mA so if its gain is low then the max output current will be less than 1A.
Doesn't R4 get extremely hot when the load current is high?

 

[chemelec]

Although a bit more complex, I like this Analogue power supply.
It is Based on the MC1466L IC, which was discontinued Years ago. But this is an All Transistor Equivalant of it.

**broken link removed**

I have a Dual version of it, Each one is 0 to 8 amps and 0 to 36 volts. And I can Series for a slit supply or parallel them for Higher current.