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0-30 Vdc Stabilized Power Supply


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Hi all. I am new to electronics and I have built this power supply. Everything worked great except for the panel meters, it seems I'm not the only one. I tried everything I could think of which wasn't much. ended up adding to extra transformers, so at least now I have A power supply that I can use. I built the whole thing in an old stereo case and use the transformer from it. It doesn't look quite as bad as it sounds but there is enough room inside to swing a cat. If someone could help me with detailed information on solving the panel meter problem. so I can get rid of the two transformers would be very much appreciated. I can then put it into a proper case. Thanks in advance.


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Thanks for your reply. The panel meters work very well. I would just prefer to make it more compact, and I want to incorporate a previous project I made from electronic lads(3-30 V/2.5 A Stabilized power supply). this is probably going to be one of my most used piece of equipment. So I would like to make it as good as a can.

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Dazza, what kind of panel metters do you use on first place? Can you upload the schematic that you use to wire them up - I mean their power supply - dipolar +-5V or single 9V, or whatever it is? I use panel meters too, and I power up everything from the same transformer that I use for the PSU itself - probably what you want to do too since this will automatically kill the reason to have extra trasformer in the case :).

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Thanks for your reply. I used one transformer a + voltage regulator, rectifier bridge and two capacitors. that is the only way I know how to supply the 9v. I then tried another separate voltage regulator set up, on the same transformer. The voltage panel meter still went haywire. I have searched the net for a circuit to allow me to connect these two panel meter to the same power supply, but couldn't find anything. This problem is probably very trivial to most electronic enthusiasts. I am very much a beginner in electronics and I have no problem of constructing a detailed project with, schematics, PCB, overlay, circuit operation. Simple schematics to connect the panel meter to my main transformer would be very much appreciated. I'm reluctant to experiment in fear of damaging than.

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I had similar problem, but mine was with fluctuation of the panel all over. My solution was to power up the pannel on bipolar, i.e. +-5V with midpoint. I suppose your panels allow you to connect them this way, or hopefully they do. The good thing is that you only need few miliampers to power up the thingy. What I did is I used two zeners at 5.1V with resistors, and built basically the analogue scheme of voltage devider, but instead of 4 resistors, I used 2 resistors and 2 zeners. Zeners are connected together in series the resistors are connected again in series - one attached to each zenner. The midpoint between the zenners you can take as zero - it will be relative zero, so between the midpoint and the other pin of the zeners you will have relatively +5.1 and -5.1. The good thing is that you can take the power to power up the zener stabilizators from the rectifier bridge of the PSU, meaning no more transformers in the case. Resistor values will depend on the potential input - use ohm's law. This worked for me and hopefully it will work for you :)

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I have never disassembled a toroid ;D and often there is an airgap on the old types that is enough to put on a few turns. The wire needed for this kind of low current is only a very thin insulated one and not many turns are required. The PCB transformers that are moulded are of curse out of the question.

Ante ::)

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AUDIOGORU!!!!....I need your help......i have a problem with my project....(0--30 Power Spuply)....

the symptoms ar:

1- the outpu is always constant at 32 VDC, when i move the pots it doesn't change.
2- the U2 gets hot when i get the Supply on for a few minutes.

i have read that the Q1 emitter is wrong, that it shoud we at 0V, but where are 0V, because the circuit is no earthed. So where I hve to connect it in the PCB.
then i read that the Q2 2N2219 COULD BE REPLACED BY TIP 31, can you confirm that.......thank you very much!!!......

DJZERO......may e-mail adress is [email protected].....

sorry for my very bad english!!1 :'(

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Welcome to our forum.
I'm sorry to hear that your project doesn't work.
1) What are the ratings of your power transformer?
a) AC voltage at full load.
b) AC current at full load, or VA rating.
c) AC voltage with no load.
2) What is the DC voltage at the base of the 2N3055 (PCB terminal 8)?
3) What opamp are you using?
4) What is the DC voltage at the pin 6 output of U2?
5) What is the DC voltage at pin 2 of U2?
6) What is the DC voltage at U2's input pin 3?
7) Q1's emitter should connect to 0V, which is the negative output terminal of the project, and PCB terminal 4.
8) A 2N2219 is much too small for Q2. Instead, use a TIP31A mounted on a medium heatsink. Its pinout is different.
9) Q1 should also be a TIP31A, but a heatsink is not needed.
10) Change R15 to 100 ohms.

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Thanks to everyone for your help. I think I will use the method mentioned of adding turns of wire to the transformer. As I want to incorporate a second power supply I will have to try to find a transformer that I am able to add the wire to as my existing one won't allow me to. As for the Q2 2N22219 I use a TIP37 and managed to carefully bend the legs to suit the PCB.

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Hi Oz,
Welcome to our forum.
I am sorry to hear that your power supply project has failed.
U2 has overheated because:
1) Maybe the supply voltage is too high for it.
Which opamp did you use?
What are the ratings of the power transformer?
2) Q1 is connected directly to the output of U2 to shut down the project's output voltage quickly when you turn it off. Maybe Q1 is shorted because it is too small to do that job.
Which transistor did you use for Q1?
Maybe the value of R14 needs adjustment to match your
transformer's voltage, to keep Q1 turned off when the project
is operating.
3) Maybe D7 has shorted, causing Q1 to be turned on all the time.
Which zener diode part number did you use for D7?
4) Maybe Q2 has shorted base to emitter because it is too small to
do its job.
Which transistor did you use for Q2?
What resistance value did you use for R15?
Did R15 also overheat?

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  • 3 weeks later...

hello.I'm MOH and have a question pleas help me .
the max Vcc for TL081 is 18 volts (data sheet) . how in this circuit the opamp supplied by the voltage that come from bridge and has about 35 volts . it must be damaged .isn't it
its very important for me pleas answer to me ???

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Hi Moh,
Welcome to our forum.
The absolute maximum supply voltage for a TL081 and most other opamps is +, - 18V which totals 36V.
If you use a 24VAC (which is too low) transformer in this project, then it will produce about 27VAC or more when lightly loaded. Therefore the positive rectified and filtered supply will be about 37V. But U2 and U3 in this project also have a negative supply of -5.6V, so their total supply voltage is about 42.6V which is much too high for the TL081s. That is why I recommended using an opamp with a higher supply voltage rating in this thread, the MC34071AP or TLE2141CP which have supply ratings of 44V. But even their high supply ratings are not enough if you use a 30VAC transformer that I recommended so that this project can produce a regulated output voltage of 30V with a 3A load.
I have posted in this thread a revised list of parts for this project. The PCB will need to be changed a bit for the different pinout of Q1 and Q2, and changing the connection of Q1's emitter to the "ground" output terminal. Q2 and the rectifier bridge module will need heatsinks. My revised list of parts is here:


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audiogoru!!...i need your help....i built this PSU...and he led voltmeter with the 7107.....but when i connect it with that PSU..it turns off.....i think that it could be because :

1- I have a 70 VAC at the output when i have 30 VDC..

to make the dual polariti supply I took 24VAC from the transformer and I rectifier and filtered, and there i connected the two regalutaros with some resistors...


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Hi Emiliano,
Where do you have 70VAC?

The 7107 voltmeter needs its own power supply that is separate from what it is measuring. See its own thread.

If you made 2 power supplies so that they can be in series for up to 60V, or so the output is positive and negative 30V, then each power supply must have its own transformer, or separate windings on a common transformer.

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