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0-30 Vdc Stabilized Power Supply


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Guest 12345678

thank you for the answer.
but i think thats not the problem.
i tryed something and i think its an ofset problem with u3.
the polarity from u3 pin3 against pin2 turns around if i turn p2 to min. at this point when it turns around the output voltage is negativ.
and that should not be.

sorry the last time i learned english was in before 20 years  ;)

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I tried something and I think its an offset problem with u3.
The polarity from u3 pin3 against pin2 turns around if I turn p2 to min. at this point when it turns around the output voltage is negative.
That should not be.

Maybe you have a bad opamp. The typical input offset voltage of an OPA445AP opamp is only 1.5mV and only 5mV is its max. The voltage across R17 when P2 is turned all the way down is 5.6mV.

Connecting a 1N4148 diode across C8 might fix it, cathode to pin 6 of U3.

I still think your negative 5.6V supply is too weak.

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Guest 12345678

with 1n4148 accross c8 it was a little bit better.
not -0,6 at the output but -0,4.

now 1n4148 is not over c8 but i changed r17 to 900 ohm.
now my min current at output is +2 mA and not - 5 mA.
so it works correct but its not perfekt.

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VCC is +-22 have a look at this datasheet.

You are correct. I didn't know the max voltage is different from different manufacturers. It is only 36V max from National Semi and Texas Instruments.

its a 27V AC transformer handmade by me.

27VAC at full load will rise to about 28.5V without a load.
27VAC makes 41.8VDC adding the positive and negative supplies.
28.5VAC makes 44.5VDC adding the positive and negative supplies.

we will see what comes out after i test it.

Other people tested the original project and got a very high ripple at max voltage and max current because it didn't have enough unregulated voltage to regulate. Its max output voltage with good regulation was lower.
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  • 2 weeks later...

To whom it may concern,

I have studied this power supply a bit and found some discrepancies. I can not go along saying that an electronlytic of 3300UF is sufficient for an AC-ripple of 0.01%. 0.1% comes closer according to my experience.

I also have made some changes, e.g. the driver for the power transistor.

Look it up let's discuss.



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Hello Herman,
You will not be able to have a direct conversation with the author of this circuit. The original author is "Smart Kits", but it is a very old kit design and lacks modern principals and newer chips that were offered after the initial design. There are new chips on the market that would do the job much better. However, the point of this area is to discuss what is already here. This thread deals with questions to build this project and questions and answers anyone has regarding it.

Audioguru has suggested a lot of changes, so you might mention which version you are suggesting additional changes. Note that "Smart Kits" are not real elaborate designs. They are simple kits to help beginners learn something about electronics. This thread has turned into a major re-design fiasco instead of simple questions and answers for those who are trying to make the kit. I would have prefferred that those who wanted to discuss a re-design would have taken this subject out of "Projects Q/A" and made a topic in the appropriate area. This approach would have been more beneficial to other members. If I ever see myself having lots of spare time, I might move posts around so that it is more organized in this way. I get lots of emails and PMs grumbling about how this topic is no longer helpful to one trying to build the project and that it is much too long to read through. Perhaps we should open a new forum named "re-design"  ;D  (That was a joke, AG)


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I can not go along saying that an electrolytic of 3300UF is sufficient for an AC-ripple of 0.01%. 0.1% comes closer according to my experience. So I changed C1 to be C1, C1a and C1b with a total capacity of 6600µF.

Hi Herman,
I didn't re-design this project, I just fixed its errors that members complained about.
In addition to the 2N3055, 2N2219 and main rectifier diodes "going up in flames", the opamps with a supply voltage higher than their max ratings and a transformer voltage too low, I have recommended using 12,000uF for C1 so that the bottom voltage of the ripple is high enough at full load.

By the way, is R1 just meant to increase the electric bill? It's just unnecessary!

Hee, hee. ;D I agree.

Using 1N4148 as rectifier diodes for D5 and D6 at peak voltages of 33.9401V they certainly will die soon.
I replaced them by 1N4001.

D5 and D6 have R2 limiting their current and the voltage is much lower than the rating for a little 1N4148. 1N4001 rectifier diodes are also fine.

And finally there is a question concerning life time of semiconductors: How many 2N2219 have you already seen to go up in flames?
The best approach for a combination of a 2N3055 is always using a BD139. They match 100% concerning base current of the 2N3055 and emitter current of the BD139.

The small 2N2219 is in a metal case that doesn't burn but many people said theirs smoked then died. It can't dissipate the heat when the gain of the 2N3055 output transistor is low. I recommended the American TIP31A but a European BD139 is the same.

Here is just a suggestion to you. Why don't you use MOSFETs or TOPFETs (Philips semiconductors)? They have a great advantage over "normal" transistors.

This project works fine with common and cheap 2N3055 output transistors.
Using Mosfets would be a complete re-design. N-channel Mosfets would need a voltage stepup circuit for the gate voltage and P-channel Mosfets have gain and would cause U2 to oscillate without additional frequency compensation.
Two 2N3055 transistors work fine.

Have a look at the layout I made.

Sorry. You zipped a Word-DOC instead of replying and attaching the pics. My pc doesn't do Word properly so I can't see them.
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  • 4 weeks later...

??? ???
Last week I discoverd this site and was really enthousiastic about building this power supply.
But now, I tested it, and it seems to work half, because the Output Voltage is always zero and the Current Limitter LED is always on.
Are there any tricks to see where it went wrong??
does somebody have a clear photo of its schematic, im afraid i connected the ICs in the wrong way (although they're connected like in the schematic, on the photo it seems to be connected otherwise then in the schematic)
PLEASE, help me!
greets from Holland

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Hi Len,
Welcome to our forum. ;D
The schematic in the project is very clear, when you click on it to increase the resolution. It shows where each pin on each IC connects to.
If you mixed up some of the pins then maybe the IC is destroyed.

Did you substitute any parts?

We can help you troubleshoot it if you can give us some voltage measurements of the ICs.
Attach the negative voltmeter lead to the circuit's 0V output labelled "4" on the schematic.
Turn on the power and turn the voltage and current pots to max. Do not load the project.
List the voltage readings on each pin of each IC and post them. Note that pin 4 of U2 and U3 should have a negative voltage.

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