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0-30 Vdc Stabilized Power Supply


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Hi Maksar,
That heatsink extrusion mentioned a length of 87 inches so I thought it is sold that long.
I don't know the calculation for a different length than 3 inches, when you double it then the thermal resistance certainly doesn't become half.

A thermal resistance of 0.2 would be great with a fan and you can add 0.7 for a transistor insulator. Then at 57W in a transistor and a 30 degrees C ambient its junction temp would be 167 degrees C.
Without a transistor insulator and without a fan, the junction temp would be 144 degrees C.
You'll have to calculate the 5A version separately but the temp will be only a little higher.
There isn't a requirement to limit the metal transistor's junction temp to only 100 degrees C because its max rating is 200 degrees C.
2 heatsinks are required for the 3A project, and 3 for the 5A project.

I think the fins on the heatsink must be vertical to allow for convection cooling.

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Hi Zeppelin,
Common opamps are designed for a 30V supply, 36V absolute max. I posted some with 44V absolute max.
If you want this project to produce a well-regulated 30V at full load then its positive supply will be more than 38V at full load and about 44V without a load and when the transformer's voltage increases without a load. Add some more voltage when your AC or refrigerator shuts off. Then add the 5.6V negative supply and look for another opamp with a 54V supply rating. The OPA445AP is the only one I could find. It is $9.50US today at Newarkinone and Digikey if you buy only a few, less cost if you buy 25 or more.  ;D

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Hi Zeppelin,
The original circuit supplies up to 41V (with no load) to its opamps that have an absolute max supply voltage of 36V. If you use cheap opamps with a 44V supply rating like the MC34071 or TLE2141 then they will be happy.
Then the project might be able to supply 2.5A at up to about 25V, if its little Q2 and its single Q4 don't melt.
Replace the original 2N2219 for Q2 with a cheap but powerful TIP31A and the project will be a bargain. ;D

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Hi everybody...

I have a little question, can I replace the 2N2219 (Q2) by a 2N2222A ?

Or is there anyone transistor who can work in this list (list of my shop)

2N1613 (=2N1711) 0,40 € 16,14 FB 2,62 FF
2N2222A 0,30 € 12,10 FB 1,97 FF
2N2646 1,20 € 48,41 FB 7,87 FF
2N2904 0,40 € 16,14 FB 2,62 FF
2N2905 1,00 € 40,34 FB 6,56 FF
2N2907 0,30 € 12,10 FB 1,97 FF
2N2907AP 0,30 € 12,10 FB 1,97 FF
2N3055 1,50 € 60,51 FB 9,84 FF
2N3773 6,50 € 262,21 FB 42,64 FF
2N3819  0,70 € 28,24 FB 4,59 FF
2N3904 0,25 € 10,08 FB 1,64 FF
2N3906 0,25 € 10,08 FB 1,64 FF
2N4403 0,30 € 12,10 FB 1,97 FF

Big thanx in advance ;)

See you soon :)


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I have old transformer with a secondary winding rated at 24 V / 1.2 A, or you can say 20VA.

Can I use this one with this project with no changes in parts values?


I can also buy from my friend transformer 2x12 V that can handle 8,33A...
Maybe i should put this one. I think this one will heat less and buzz less than smaller one??

What do you think?

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Hi Vedran,
The transformer will be seriously overloaded unless you change the value of R7 to 2.2 ohms/2W to limit the project's max output current to about 0.6A.
Change R11 to 39k to limit the max output voltage to about 27V because the output will have a high ripple when it is set to voltages above about 25V with its full 0.6A current.

The project's original little 2N2219 can be used for Q2 and a single 2N3055 can be used for Q4 because they won't overheat.

I think the transformer will produce 28VAC or more when the project has a low load current with your transformer. Therefore the opamps will have a total supply of about 44V or more and I recommend using OPA445AP high-supply-voltage opamps. ;D

With the 8.33A transformer, you can build the 5A option for this supply and change R11 to 39k to limit its output voltage to about 27V.

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Hi Vedran,
We discussed the necessary changes to make this project produce 5A in this topic:

It needs three 2N3055 output transistors with emitter resistors and each transistor needs its own pretty big heatsink. The project also needs a powerful heatsinked rectifier bridge module, and a huge filter cap.
A few resistors have their power rating increased and R7 must be 0.27 ohms.

With your lower voltage from the transformer you should keep the value of R14 at 1.5k.
Yes, also change R11 to 39k.

Kain made a schematic and pcb for the 3A version here:


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Hi Ta,
Welcome back. I hope you had a nice vacation.
Now that I am retired, every day is a holiday and sometimes I have a nice vacation too. ;D

Sure, use 3 or 4 2N3055 transistors to divide the heat dissipation among them. Use a separate heatsink for each one.
One member had trouble matching them even though he used 0.1 ohm emitter resistors.
For a 3A supply, maybe 1 ohm/2W or 5W emitter resistors should be used for a better match.

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Yes,i had a wonderfull vacation thank you!I envy you audioguru.I am still a student and i have 50 years in order to become retired.
I finally used 3 of them with  0.1ohm emmiter resistor at 2 of them and 0.2ohm at the third one  in order to match them.What i did is ok?With a fan blowing them they dont become hot at all.Another discovery: I have 4A max output :o

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Hi TA,
It's good to hear that your vacation was wonderful. ;D
It is fine to change the emitter resistors to balance the output transistors.
If you want to feel some heat, turn up the current regulator and short the output. That will be when the output transistors should be matched. Almost the same thing will happen if you turn up the current regulator and turn down the voltage regulator to drive a low-voltage high-current load. ;D

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I tried with a 2.7ohm 200W dummy load.I set 3A output.All transistors were quite cool.I am afraid to short the output.Another discovery: From one transistor passed 1.3A,from the other 1,1A and from the third(with 0.2ohm emmiter resistor) 0.6A.My mistake is that i measured the third transistor's  resistor and found the voltage drop almost the same with the other 2,forgeting that it was not 0.1 ohm. :-\ :-\ :-\ .
How much current can pass from one transistor without damage?

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How much current can pass from one transistor without damage?

If the output is shorted of your project with its low unregulated supply voltage of only 31V, the internal chip of a 2N3055 transistor will operate with no margin for safety at its absolute max temperature of 200 degrees C, with an enormous heatsink of infinite size, with a very high velocity fan blowing away all heat so its case doesn't exceed 25 degrees C, at a current of  only 3.7A (115W of heat with your 31V supply).
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Audioguru, give us some hints about this, please :) :


I like your web site.
I'm interrested about 0-30 VDC STABILIZED POWER SUPPLY WITH CURRENT CONTROL 0.002-3 A and have couple of questions.
Is it possible to increase output current to 5 Amps ? (adding 2N3055 and changinging some component values)
Can I built 2 similary power supply and use it in serial mode 0-60 V or in parallel mode to get more current 0-10 Amps or use it like dual power supply +/-
30 V ?

Thank you



Hi all, I'm new to the EL forums, but not new to the website, nice stuff here  :D

As Tom said, I'd be interested on building a bipolar PSU unit with the capabilities of this project. I still have to read all the threads, I have read something about fixing the original design among the posts(so many!)...

Right now, I have a 3-wire trafo, 28+28 (really 28+0+28) over my table... but it's just 1A...
I was wondering: If I found a 28+0+28 (or with a little higher voltage), what current should it be: 3A or 6A?

What changes should it have to operate bipolarity?

You know, many experiments requires bipolar feeds...

I would be interested in adding parallel LM7(8/9)0(5/6/9/12/whatever)s or LM3(1/3)7s for extra fixed voltages...

I still have much left to learn indeed... but for now, my knowledge allows me to provide good shcematics/pcb design, maybe we could open another topic: "[glow=red,2,300]30-0-30 VDC BIPOLAR STABILIZED PSU[/glow]" ??? Then we could adapt the changes of the 5A topic to the bipolar one to become a bipolar 5A PSU ???

All that is left for my improvement idea is a button to make it speak the current and voltage instead of displaying with the digital meter presented ;D (Just joking!)

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