0-30V Stabilized Power Supply

[effenberg0x0]

Why is your schematic a hard to see negative? I changed it to a positive (white background) so i could see it like most other schematics.

Sorry, I'm new to Eagle. It was setup like this and I didn't know I could put a white background. Now I know, thanks. I have attached the new image.

1) Some of your opamps have the  pin numbers on the inputs backwards. Some of your opamps have the + and - input symbols backwards. Pin 3 is supposed to be + and pin 2 is supposed to be -.

Thank God you saw it. I couldn't find TLE2141 or MC34071 in Eagle libs, so I used another opamp that has the pins inverted. Its fixed now.

2) U1 has R5 connected to pin 1 instead of to pin 2.

Yes, I was wrong to use pin1, but schematics I found in the thread show it at pin3. Is it 3 or 2?

3) For C1 you have 3 capacitors in series instead of parallel.

Fixed Lame mistake...

Questions:
1)I have attached the list of Potentiometers and Trimmers in the parts lists of the three versions (Original, 5A, 3A). I'm confused to be honest. I'm building my version with two 30V/5A transformers in parallel and MC34071 opamps. In this case, I guess I should use 10K for RV1, 50K for RV2, 200K for RV3?

2)About the third Potentiometer (1K), I placed it in series with P1. Can you tell me if it is correct?

3)A serious problem: All schematics show an unnamed capacitor (0.1uf) between R19 and U3. I named it CX. I cannot understand why it would be there. Can you give me a hint? I have highlighted it in the attached schematics.

Thanks


View attachment 40754

View attachment 40755

 

[audioguru2]

I can't find Redwire's schematic. Maybe because it is an Eagle-only file type but i don't use Eagle.

I found a few mistakes when compared to my schematic.

View attachment 40756

 

[redwire]

2)About the third Potentiometer (1K), I placed it in series with P1. Can you tell me if it is correct?

When you asked me earlier about P3,  I thought you were referring to point 3 from the original sketch instead of Potentiometer 3.  I don't think I ever labeled it P3, so it was throwing me off.    I don't have the coarse and fine Potentiometers shown on the Eagle PCB file I posted because no additional connections on  the PCB are necessary to use the coarse/fine controls.

Yes you intall P3 in series with P1 but you do not have it installed correctly in your sketch.  On P3  you need to cut the connection between  ground and point 2.  Then connect  pins 1 and 2 together.      I think.

 

[besarmatis]

If only I saw this conversation a few days earlier...
Last night I built the PS using schematics and part list from the original version...
I tried to test it: connected voltmeter to the output, then turned it on, led blinked and I saw a voltage on the voltmeter.
But it doesn't matter anymore
Now I will make a new project from the latest schematics...
And now I want to ask a lame question about potentiometer. Let's say I use the original version of PS. I'm confused about how to connect the potentiometer (ie. Voltage adj. one) correctly. Pot has 3 pins: ground, the one we take + from pot, and the one we give + to pot.
So is that right to connect the ground one to 5th, middle one to 12th, and the one where we give plus to pot - to 10th?

 

[effenberg0x0]

Is it possible to modify the link in the original project that points to the lost thread so that it points to this thread?

Besarmatis: I have posted a table comparing parts lists for the original, fixed and 5A versions some days ago in this thread.

 

[Hero999]

Is it possible to modify the link in the original project that points to the lost thread so that it points to this thread?

It is possible to do that but we can't do it, only the administrator can.

 

[besarmatis]

effenberg0x0, I saw that table and I appreciate for you comparing parts
The only thing left for me is to buy some new parts and the transformer (which is the worst thing, because it costs much).

Someone, please answer my question which i posted before about the pot connection. I need to know if my thoughts are right.

And one more question. I want to build two of these projects to have  2 separate power supplies and if I need, I have a dual polarity one. So the question: Do I need 2 transformers or it is enough to have one but with dual second winding (like 2x30V 2x4A)?

 

[audioguru2]

Hi Besarmatis,
It is easy to see how to connect a pot when you look to see that it is a semi-circular resistance track and a rotating wiper along it. The resistance connects to the end pins and you can see which end is connected to the wiper pin (the middle pin) when the control is turned clockwise then counter-clockwise.

The original version of this project does not have an output of 30VDC at 3A. Its output might go as high as 25V at 3A but might reach 30V at much lower current.
At full power its output is full of ripple.
At full power many parts are overloaded.
Its voltage and current controls try to go too high.
Without a load its opamps have a total supply voltage that is higher than their max allowed voltage.

You can use your transformer if you allow the new version to have reduced max output voltage and current.

If you want to connect two of these power supplies so that one supplies a negative voltage then they need to be completely separate with separate transformers or two separate windings on one transformer.

 

[besarmatis]

Thanks for reply, audioguru,

So were I right saying that one is ground pin and two others are adjustable resistance? And were I right saying which pin should be connected to looking at the original project?

I know that it has to be completely separate power supplies, and the question is: which one is better, to use two transformers or one with double second winding? Or it is doesn't matter?

One more question, maybe someone could suggest some e-shop, where I could buy transformer (230V first winding) with lower price, because in my country (Lithuania), for example, transformer 2x24V 2x3.12A (sec. wind.) costs 50$. So I already bought one, but now I need to buy new one which has more power and I don't have bags of money, so I need to find cheaper ones

 

[effenberg0x0]

Besarmatis, I couldn't find transformers at reasonable prices in the market here too. My solution was to have them built in a small shop that does it on demand. I managed to get two units for half the average price of a single unit in the market. They were built exactly to my specs (core, wire, windings, etc). Mine are 115V/230V - 30V 5A. Maybe you can find a shop like this there?

Also, if you're putting them in parallel, its important that they don't differ much. I have posted some links that explain why.

I would go for two separate transformers, simply because I may want to reuse one of them in a new project in the future (considering trafos are expensive).

 

[besarmatis]

effenberg0x0, if it's not a secret, what was the price of you transformer?

And to be correct, if I want to build the version of the project 0-30V 0-3A, then I need secondary winding 30V and at least 4A?

 

[effenberg0x0]

effenberg0x0, if it's not a secret, what was the price of you transformer?

And to be correct, if I want to build the version of the project 0-30V 0-3A, then I need secondary winding 30V and at least 4A?

Any transformer up to 2A is common here and costs an average of US$8.
3A transformers are a little harder to find and were priced at an average of US$15.
4A are WAY hard to find. They were priced at US$30.
5A units were simply nowhere to be found. After searching for an entire week I found only four stores that had them, but prices were beginning at US$100.

I had my 30V/5A units made for US$21 each.

In the latest parts list, a 28V 4.3A, 118VA transformer is mentioned. So if you go for 30V 4.5 or 5A it will be enough.

 

[besarmatis]

OMG how cheap  :'(
I've been searching for shop to make the transformer for me for a few hours, but no luck.
I tried to search for already made trafos and found such: Toroidal mains transformer 160VA 230/30V for 40$.
So for 2 it would be 80$...
It would be perfect, but the price for the student...
Well, I'll have to choose whether to eat food or to make a dual polarity power supply...

 

[effenberg0x0]

Redwire said in a previous post that me made his unit using a microwave oven transformer. The unit was 7A or more I think. Actually I almost cried when I read this: If I had searched at repair shops, electronics dump places or even sites like eBay, I would be able to buy a broken microwave oven almost for free. Consider this option. Also think of other appliances that may have a suitable transformer.

Another option would be to buy 2A transformers, if they're cheaper, and put them in parallel.

 

[audioguru2]

So were I right saying that one is ground pin and two others are adjustable resistance?

No.
The voltage and current setting pots are voltage dividers, not adjustable resistors. The calibration trimpots are adjustable resistors.

 

[besarmatis]

So it the only matter how to connect the end pins of pot is how you want to adjust voltage.
First way: turning clockwise increasing voltage.
Second way: turning clockwise lowering voltage.
Now I understand
The middle one stays the same in both ways.

 

[effenberg0x0]

Earlier today I had requested the admin of the website to update the wrong link at the original project page (it was ponting to a thread that was lost and not to here). It is done now. Maybe other users will read this thread before building the wrong project.

Regards,
Effenberg

 

[besarmatis]

I think that link should be put on the top of the project page, moreover, someone should make new tutorial for building this project. For example you, effenberg0x0, when you done your project
Maybe I could make some tutorial after 2 months with pictures and schematics and pcb and periphery like lcd vmeter ameter and automatic cooling system with fans (avr).

 

[audioguru2]

So it the only matter how to connect the end pins of pot is how you want to adjust voltage.
First way: turning clockwise increasing voltage.
Second way: turning clockwise lowering voltage.
Now I understand
The middle one stays the same in both ways.

Yes.
Trimpots have an arrow marked "CW" that points to the pin that the slider goes toward when the shaft is turned clockwize.

 

[effenberg0x0]

I think that link should be put on the top of the project page, moreover, someone should make new tutorial for building this project. For example you, effenberg0x0, when you done your project
Maybe I could make some tutorial after 2 months with pictures and schematics and pcb and periphery like lcd vmeter ameter and automatic cooling system with fans (avr).

It will take a while for me besamartis. I have one month to write an essay describing the operation and importance of each component in this circuit, the main individual circuits, possible changes/updates, etc. A lot of it is still not clear to me and I have to study more to get it done. I have it assembled on breadboard and am using multimeter/oscilloscope to analise it. I'll go for the PCB and assembly only by the end of January...

By then, I'll be happy to post all my material here for whoever may benefit from it.