0-30V Stabilized Power Supply

[audioguru2]

Please confirm:
- the newest bill of material is rev.3 from page 55
- the newest schemativ is rev.2 from page 55
- the highest voltage of the transformer is about 30V for TLE2141 or MC34071 (as in last posts here) but better is to use slightly lower voltage transformer, to avoide the risk of exceeding oamp's maximum supply voltage.

Yes, yes and yes.

I also have some problem, but I'm not sure if it is a simulation issue or not.
The U2 gain should be about 3x to provide 30V output (11.20 from U2 * 3 - some voltage drop on transistors). But simulation shows that the gain is smaller (about 2.5) if R12 is 56k and R11 is 27k.
I changed values of those resistors to reduce negative feedback and obtain exactly 3x gain on TLE2141. This caused the *simulated* circuit to work better with high load, no ripples at all. What do you think about it? Was is tested by you (the gain on TLE2141)?

 

[jsteve126]

I am going to try this project. I would like some advice about the transformer I intend to use. It is rated at 24V 400VA. Measuring the output, I get: 27.1VAC, rectified (no with caps) to 24VDC. Is this suitable for this project? Thanks

 

[audioguru2]

Your 24V 400VA transformer has poor voltage regulation for such a powerful one. Also its voltage is too low so the max regulated output from this project at 3A will be only about 25V instead of 30.0V.

A much smaller Hammond 28V at 5A (140VA) transformer increases to only 29.5V without a load.

 

[jsteve126]

Thanks for your response audioguru. It is appreciated. I'm surprised to learn that this, what I thought was quite a powerful transformer, is not that suitable.
I have just measured the voltage with a 30,000uF cap across it and it was 35VDC. Does that sound about right for a transformer of this rating?

 

[audioguru2]

The peak voltage of a 25.5V sine-wave is 36.0V. If there is no load then the full-wave rectifier has a drop of slightly more than 1V so makes a filtered 35.0VDC.

 

[Furthermore]

In the name of God
now I have built 0-30v, 2m-3A power supply PCB and have bought some parts,
I want to solder it on the board but there is a problem,
can I use 1n5408 instead of 1n5402 and two parallel 2n3055 transistor instead of one?
??? ???

 

[audioguru2]

In the name of God
now I have built 0-30v, 2m-3A power supply PCB and have bought some parts,
I want to solder it on the board but there is a problem,
can I use 1n5408 instead of 1n5402 and two parallel 2n3055 transistor instead of one?
??? ???

It sounds like you are looking at the original version (and it is a kit) that has many problems.
The latest version has been posted here in these threads many times.

It uses a 6A to 10A rectifier bridge module that can be bolted with heat sink compound to a metal chassis or a heatsink. The original little 1N5402 diodes smoked and burned.
Of course it needs two 2N3055 output transistors each with an emitter resistor and the driver transistor is a BD139 mounted on a heatsink.

Here is the latest schematic and parts list: View attachment 41506

View attachment 41507

 

[zedd]

The voltage drop on the transistors does not affect the gain because they are inside the negative feedback loop. Their voltage drop simply reduces the max output voltage headroom.

Obviously I should have read some docs about operational amps before I asked you My simulation was OK, i just understood it wrong.

You are right about the voltage drops on the transistors.
If I set the gain like you designed then the U2 output is 30V when R11+pot is exactly 34250 ohms. And the voltage drop between U2 output and "+" is 3,13V so the "+" is 26,87V. When set R11+pot = 28840ohm, the U2 output is 33,35V and the "+" output is 30V.
The conclusion is to use a smaller pot, like 5k, but I'm not sure that I should trust simulation results - will check that after assembling the device.

Thank you for your help.

 

[audioguru2]

The reference voltage from U1 is 11.2V. You want the max output to be 30.0V. Then the output amplifier (U2 plus the driver and output transistors) must have a gain of 30.0/11.2= 2.679 times. The gain is not affected by the voltage drop of the transistors because they are inside the negative feedback loop.
Then the ratio of the 56k resistor and the 27k resistor plus trimpot must be 1.679 times.
Then the trimpot must be 6.5k which is close to the center of a 20k trimpot and a 5k trimpot will be wrong.

 

[jsteve126]

Just finished building my SPS. Can anyone point me to the page/s that talk about adjusting the trims and final testing procedures? A lot of pages to search through!

Initial testing;
I get full range of volts (0-30V) and can pull about 4A charging a 12V battery at 13.7V. Current limiting is working, but I haven't touched the trims.
The 10W 0.47Ohm resistor gets very hot (about 60C).  This is normal?

Thanks

 

[audioguru2]

The dissipation in the 0.47 ohm resistor is I squared R. so with a current of 3A it dissipates 3 x 3 x 0.47= 4.23W which makes a 10W resistor very warm. 4A creates a dissipation of 7.52W which is a lot of heat in the small space of a 10W resistor.

One trimpot adjusts the input offset voltage of U2 and adjusts the output for 0.0V when the voltage control pot is zero.
another trimpot adjusts the output to be 30.0V when the voltage control pot is max.
Another trimpot adjusts the max current to be 3.0A when the current control pot is max and there is a high current load (or a shorted output).

 

[jsteve126]

Thanks for that audioguru.
Well, it's done. Seems to be working perfectly. Here are some pics of the finished project.
The top case is bolted to the large transformer on the bottom. The transformer inside the top case is for the 5V panel meter and fan board in the centre. This board uses an Atmega168 to read three LM35 sensors and control the two 12V fans via some MOSFETs. The heavy wire looks a bit over the top because this was initially a 15Amp project using a different board of course.
Many thanks and regards to all in this thread.

View attachment 41512

View attachment 41513

View attachment 41514

 

[redwire]

jssteve126,  Outstanding job!!      Looks like everything is heavy duty.  How many amps have you brought it up to?

 

[jrhodes]

hey guys i built a duel supply the lastest vesion of the picmaster anyhow i had some bad traces and got that straight . i have 34 volts at main power rail to ground but i only get 17 volts max at my output  ive  got 11 volt out of u1 so thats working also before fixing the bad traces my led was coming on and off with current limiter pot now it doesnt come on at all. i havent tryed the second board yet waiting on .33 ohm resister also using 5watt .47 resister at tb2 or (r7)

 

[audioguru2]

Hi J Rhodes,
Since U1 output is almost correct (it should be 11.2V) then with the voltage pot set to max the input to the U2 and transistors amplifier is 11.0V or 11.2V. The feedback resistors R12 (56k) and R11 (27k) in series with the voltage calibration trimpot set the gain of the U2 and transistors amplifier at 2.68 so the output should be 30.0V if your transformer has enough output (it doesn't because the unregulated supply should be +37V to +40V).

 

[arman92]

Hi everybody.

I'm gonna create this power supply. I've bought every pieces!

but, I couldn't find neither TLE2141 nor MC34071  

I tried so hard and looked every single store in my city but no one has it...

Someone suggested me to use the "LM324N" op-amp instead of the original ones,

can you tell me if that's possible or not?
if possible, how can I do that?

thank you very much

 

[audioguru2]

I couldn't find neither TLE2141 nor MC34071  

I tried so hard and looked every single store in my city but no one has it...

Someone suggested me to use the "LM324N" op-amp instead of the original ones,

can you tell me if that's possible or not?

I selected the TLE2141 or MC34071 opamps because their max supply voltage rating is 44V and they are available almost anywhere in North America.

The LM324 has a max supply voltage rating of only 32V which is much too low and it is a quad opamp (it has 4 opamps) not a single opamp.

 

[arman92]

I selected the TLE2141 or MC34071 opamps because their max supply voltage rating is 44V and they are available almost anywhere in North America.

The LM324 has a max supply voltage rating of only 32V which is much too low and it is a quad opamp (it has 4 opamps) not a single opamp.

Thank you for reply.
You said in North America, since I live in Asia!
If I use the LM324, and change the Transformer to another with a lower voltage,
would it be solved?
How much voltage can I get at maximum?
If there is no way to use LM324, would u tell me if there is another suitable power supply? (Max voltage about 30 - 40 , Current 2-4 amps)
Thanks

 

[audioguru2]

If you use LM324 opamps with a max supply of 32V then a power supply project must be re-designed for the lower raw supply voltage of about 30VDC (which rises to about 32VDC when there is no load) and the max output will be about 24VDC at 3A.

Look at www.farnell.com and look for the flag of your country since they are in many countries. They have the TLE2141 and MC34071 opamps stocked in most countries. 

 

[arman92]

Ok, I looked at farnell.com but unfortunately they do not support our country.

24VDC output is a little low for me, I need at least 30VDC at output.

so, what do u say about this project? http://www.electronics-lab.com/projects/power/004/index.html

It has little components inside it, and it has regulated voltage that makes it better!!
But the Max. current is 2.5Amps , can it be higher? (by adding another 2n3055 and changing some resistor, just like you guys do in that power supply to get 5A Max)

Thank you (a lot ;D)