0-30 Vdc Stabilized Power Supply

[Alf_Melmok]

You are right, i forgot about  the voltage losses.
In my country mains voltage change from 200 to 240 very often (In rare cases, even is worse (phase is not uniformly loaded)). That's why i want to limit the input voltage.
It's a vicious circle. In my country i can't buy op amp that you recommend. So that i can't use 28VAC transformer. And i can't find 28-30VAC transformer. I can't find another scheme similar PSU. I just want this power supply with 20V transformer. 
Thanks for your help

[audioguru]

Here in Canada my inexpensive mains electricity is 120V. Sometimes it surges very high to 121V and sometimes it drops very low to 119V. It fails maybe every 2 or 3 years for a moment during a thunderstorm.

There are many electronic parts distributors here that have ANYTHING and EVERYTHING at a good price.
If I order a part by phone or online before 8:00PM then it is delivered to me the next morning.

Maybe in your country you should do gardening instead of electronics.

 

[Alf_Melmok]

I envy you. But it's not funny. By our standards in the electrical network there shall be 220V +20 % -20 %. You can calculate how much it turns out (176-264 It's normal ). All of our electronics designed for this.

[asdewq]

hey guys i need some help

i've built this psu project from the first schematic (the original) with the tl081 and everything and it didn't burn up immediately after being switched on as suggested by some

i tried testing the circuit and the current limitation/regulation works fine but voltage regulation does not and im wondering if anyone has had the same problem or if someone has a suggestion as to how to fix this problem

this is a great project and i need this psu for some other projects  and i've spent quite a lot of money on parts (electronics parts are still a bit expensive where i live) and i would hate it this build was a waste of time and money

please help and thank you in advance

[asdewq]

after about two more hours of tinkering with the psu i finally got some kind of reaction on the output of the psu but now i can only get either 0V or 31V nothing in between

any suggestions?

[audioguru]

The input to the output amplifier is 0V to +11.2V from the voltage adjust pot.

The output amplifier is simply opamp U2 with the driver transistor and output transistor as emitter-followers boosting the output current. The output amplifier has R11 (27k) and R12 (56k) for over-all negative feedback which sets the gain too high at (56k/27k) + 1= 3.074. Then the output should be able to go from 0V to (11.2V x 3.074=) 34.4V if the unregulated DC voltage is high enough.

Maybe you have the pins on the driver transistor or output transistor mixed up so that they are on-off switches instead of emitter-followers.

[asdewq]

Solved it. I accidentaly put the wrong transistor in the wrong place.

Just one more thing. I tested one circuit (I built two) by shorting the output to see the max current rating and it put out almost 5 amps. Those 5 amps burned through the rectifier diodes but everything else was fine. Did you get 5 amps as max current on the output?

[audioguru]

Yes, the original project was missing calibration trimpots to reduce the maximum output voltage to 30.0V and the maximum output current to 3.0A.
The modified circuit has the calibration trimpots added and uses a high current rectifier bridge module that can be bolted to a heatsink.

[asdewq]

Would you mind posting a link to the modified circuit?

[audioguru]

Would you mind posting a link to the modified circuit?

I have looked it up on my hard drive and posted it on one of the many threads about the modified circuit hundreds of times.
Here they are again:

[asdewq]

Thx man. Sorry to bother you

[audioguru]

Thx man. Sorry to bother you

You are not bothering me.
I wish that there is a place on this site to post the important modifications and I hope you understand that the original project will not make regulated 30VDC at 3A (it fails to meet its spec's) and that many of its parts were overloaded (then it has poor reliability).

[asdewq]

Yes, sadly

I found out the hard way that the PSU generates around 26 - 27V at 3.5 amps

In the near future I'll make the upgraded version and i will, hopefully, design a pcb (if one is not available) and post it here.

[red baron]

Hi Audioguru
Seems like you have been on this project for some time, and getting a bit frustrated that you have to repeat the same information endlessly - I understand, but I am now new to this project and looking forward to constructing the psu according to the latest version.
I have your bill of materials and latest circuit diagram, what is the status with an appropriate pcb?  Does someone have the masks or can I use the originals and simply change components?