0-30V Stabilized Power Supply

[audioguru2]

The current regulation simply reduces the output voltage to satisfy Ohm's Law.

 

[GabrielRR]

Hi, I just made circuit, and I have some problems....

The voltage regulation works pretty well, but I cant regulate the current intensity.....
Has anyone had this problem?

Thanks to all,

Best regards

 

[audioguru2]

Opamp U3 is the current regulator.
The 0.47 ohm resistor R7 develops a voltage across it due to the load current in it and this voltage feeds the (-) input of U3. The (+) input of U3 is fed a variable voltage set by the current regulation pot. When the voltage from R7 is higher than the voltage set by the pot then the output voltage at the output of U3 drops which causes D9 to reduce the voltage of the project until the load current is reduced to the setting. When the output voltage at the output of U3 drops then it turns on Q3 that lights the LED to warn that the current regulator is reducing the output voltage.

 

[fgrotti]

I built the old version with TL081 long time ago and I update it without changing the PCB following these instructions, or is it better to redo the PCB with the new version?
Sorry for my imperfect English

View attachment 40941

 

[audioguru2]

I built the old version with TL081 long time ago and I update it without changing the PCB following these instructions, or is it better to redo the PCB with the new version?

The OPA445 high voltage opamps were used about 5 years ago. Today they are available only sometimes (Digikey has some today) and are very expensive (nearly $12.00US each).

The new version has a choice of two inexpensive opamps that are available at many places in North America and maybe in Europe.

 

[matt09]

Hi everyone,

If I used the latest circuit with 5 power transistors can I achieve a 10A constant supply with a verry large heatsink and fan, it works out to about 65W per transistor? I have a 26.3VAC 10A+ transformer with massive 2.5" wide core.

Would anything else need changing other than larger supply caps - guessing about 50000uf or more?

Can I draw 10A at 1V up to 30V 10A theoretically with a massive heatsink?

Thanks

 

[audioguru2]

The BD139 driver transistor Q2 will probably burn up. Also U2 will not be able to drive Q2 hard enough. R7 will need to have much less resistance and be much bigger. T1 and C1 will need to be much bigger.

 

[matt09]

Thanks for the reply guru, would the circuit still work if I replace R7 with a 0.1R power resistor for minimum power dissipation or will this mean further modifications are required?

Regarding the BD139 burning, could I just parallel 2 of them with another 1k resistor?

I wasn't so sure about the best way to resolve the lack of drive?

I have a large transformer and 100000uf cap.

Thanks alot.

 

[redwire]

If matt09 uses several MJ11016G Darlington transistors instead of the 3055's    then the BD139 should be able to drive the output transistors.   Now he may loose one volt of max output.  

And yes R7 would need to be a very low value and large (something like a 0.1 Ohms  25W aluminum housed resistor mounted to the frame)  I would suspect that the current limiting adjustment would be very coarse with low value of R7.

Are you using this for a battery charger or a room heater?

 

[matt09]

Thanks redwire, I'd prefer to use the 3055's as I have a few already but can the problem not simply be solved by paralleling two 139's or using a more powerful substitute such as the D44H11?

I'm guessing I could change the current limiting adjustment by playing around with the value of R18?

I am using this as a powerful test bench supply.

EDIT: Just seen the price of those darlington transistors they're like

 

[redwire]

You don't want to parallel the BD139's  it will become a mess.  YOu would need to add resistors to ensure one doesn't hog all of the current just like what is done for the 3055's.  You are correct in that the easiest solution is to change  the 139.  Audioguru would need to comment on the D44H11 subsitute. 

As for the current limiting issue.  I have a single turn potentimeter so if the original design was based on 3 amps one turn covered 3 amps.  If you move to 10 amps then the single turn would cover 10 amps.    As was suggested you may want a big knob to provide better control. 

 

[fgrotti]

Audioguru Thanks for the advice.
Proceed to build the new project.
Do you know where I can find the PCB in PDF format or JPEG updated?

 

[matt09]

Would this be much better than thhe 3055's, I have loads lying around? http://www.datasheetcatalog.org/datasheet/mospec/2N5683.pdf -- 2N5686
They're massive things with a 50A collector current and 300w handling, could I sub them and get away with just 2 handling 175w each for a 10A output?

I don't suppose the bd139 could drive two of those together if the 3055's weren't used and it would solve the problem?

If not I've also looked around for a BD139 replacement and have a TIP transistor (I'd have to go out and buy the D44 one), would this be a suitable replacement?

http://pdfdata.datasheetsite.com/web/70588/TIP41C.pdf -- TIP41A

http://www.fairchildsemi.com/ds/BD%2FBD135.pdf -- BD139

If guru could check over this I would be eternally grateful, pretty much all the specs match or are better, ie 6A collector current.  

Would the emitter resistor R16 value need changing from 1k or need to be a higher power value also (or both) with the new transistor ?

Regarding the current control I think I'll use two pots in series of different orders in resistance for course and fine control.

I assume this still doesnt solve the problem of U2 not driving this new transistor hard enough?

Sorry there's a hell of alot there!

Thanks so much guys  

 

[audioguru2]

The very powerful transistors will work well at 5A each but you will not be able to cool them unless your heatsink is submeged in liquid nitrogen.
They are spec'd to dissipate 300W when their internal temperature is max and their case is held at 25 degrees C somehow. Of course an ordinary huge heatsink will get hot so the power must be reduced.

 

[matt09]

Thanks guru, the derating graph shows a temperature of 100'C at 175W per transistor so providing they are cooled below this temerature they would work?

You say about cooling them in liquid nitrogen but isnt the total dissipation to the heatsink the same except with the 3055's it's spread across more lower power transistors?

I have a huge heatsink able dissipate 350W with a rise in temperature below 80'C

Thanks

 

[audioguru2]

A heatsink works best when the heat is spread out on it. A single point of heat on a heatsink makes that spot hot but the remainder of the heatsink is much cooler.
There is a loss of cooling whenre the transistor is mounted on the heatsink. Even thermal grease blocks some of the cooling effect.

I never operate transistors at their max allowed temperature.

 

[yafch]

After going through this thread i am confused. I still want to make the version of this power supply with tl081.
So my humble request is for the schematic and parts list of the version with tl081(the one that really works)Please.

 

[audioguru2]

If you use the TL081 then you should use a low voltage transformer then the max output voltage from the project will be about 22V, not 30V.
Many of the parts will still get too hot.

We modified it so that the max output is 30V and it is reliable.

 

[davenz]

If you use the TL081 then you should use a low voltage transformer then the max output voltage from the project will be about 22V, not 30V.
Many of the parts will still get too hot.

We modified it so that the max output is 30V and it is reliable.

Hi there. I have followed this project for some time and while I think it is one of the better power supply circuits around (hence 35 pages of forum discussion on it), I am still confused as to what the actual outcome of all this discussion has been. I built one based on the circuit on the original site and of course it blew the guts out of the op-amps and I threw the rest away in disgust. Months later I found this forum and have read as much as I can of it without my eyes watering. There appear to have been several mods to the original circuit to lower the voltage to the op-amps, therefore saving their lives, and the authors claim the supply works OK, but then there are other rewrites of the circuit to use different op-amps, many of which can't be found locally, so I am at a loss which one to go for. On top of that, so many parts lists and circuits are bandied about here I don't know which goes with what and what version is the one to build. Can someone please summarise for me what the upshot of everything is and, if I was to build one tomorrow, which circuit and parts list would I be best to use. Thanks and sorry for being so lame.

Dave.

 

[Holt]

Hi davenz
At page 30 you will find this.
http://www.electronics-lab.com/forum/index.php?topic=19066.msg91051#msg91051