0-30V Stabilized Power Supply

[MAntunes]

So what would I get?
I don't mind getting a little bit less than 30V!

 

[audioguru2]

So what would I get?
I don't mind getting a little bit less than 30V!

The original project could not produce 30VDC at 3A and when it was tried, its little 72VA transformer and many other parts were overloaded and they overheated. Maybe its maximum output was 25V at 3A or 20V at 3.75A.

The improved project uses a 28V transformer rated at 118VA and many parts are stronger. It is reliable.

We do not know which circuit you are making.

 

[liquibyte]

I'm using these 130VA transformers from Digikey.  At $25 each they are fairly economical and will produce the voltage and amperage required.  I searched high and low for 118VA 28V transformers and these were as close as I could get that were a stock item.

 

[MAntunes]

Sorry for that.
I am making the newer one (3A), I got the parts and the schematic from the first post of this topic, but I only got a 24VAC transformer i think, it may be a little bit more.
I wanted to know what voltage would I get with that tranformer!
Thank you for the help so far

 

[audioguru2]

Sorry for that.
I am making the newer one (3A), I got the parts and the schematic from the first post of this topic, but I only got a 24VAC transformer i think, it may be a little bit more.
I wanted to know what voltage would I get with that tranformer!
Thank you for the help so far

The main filter capacitor, R7, the output transistors, the driver transistor and opamp U2 all reduce the maximum output voltage when the project has a load. With a 24V/102VA transformer the improved project will make a maximum of 24VDC at 3A.

 

[MAntunes]

Thank you very much audioguru.
I will give feedback here when my power supply is ready!

Another two questions, the BD139 is the only transistor thay should have a heatsink or should all of them have one?
About the opamp, there are 4 references (TLE2141CP, TLE2141CPE4, TLE2141IP and TLE2141IPE4) which one should I get?
Regards and thank you for the help

 

[audioguru2]

...the BD139 is the only transistor thay should have a heatsink or should all of them have one?

Heat in a transistor is caused by the voltage across it times the current in it. The result is in Watts.
Each of the two output transistors has a voltage across it of 36V and a current of 1.5A when the current from the project is set to 3A and the output voltage is low or is shorted. Then the heating is 54W in each transistor so a pretty big heatsink is needed. The bridge rectifier can be bolted to this heatsink. 
The BD139 will have a max voltage of 35V and a max current of 75mA so its max heating is 2.6W and a medium heatsink is needed.

About the opamp, there are 4 references (TLE2141CP, TLE2141CPE4, TLE2141IP and TLE2141IPE4) which one should I get?

Get the CP. The I and M have slightly better spec`s that you do not need and a much higher price.

 

[redwire]

I finished with working on power supply and made a test yesterday but just one think is not working properly, i can adjust the current only up to 3A then current blocking turning on.
I use elements for 5A project (Redwire) as i mentoined couple of times above but i have not idea where is the problem, i hope that i didn't overlook some element value, i will make a review of all elements in circuit once again.

What is the value of R7?  if it is 0.47 Ohms,  you need to use  0.27 Ohms.  Did you adjust the 100k pot to allow a higher current?

 

[electroguy]

Is KBL406 able to handle 24V 3A transformer ?By the way, I have four 1N5402.

 

[audioguru2]

Is KBL406 able to handle 24V 3A transformer ?By the way, I have four 1N5402.

I do not recommend them because they are cooled through their leads which will get VERY HOT.
Instead use a bridge rectifier that is bolted to a heatsink like this: View attachment 42021

 

[electroguy]

Do you think four 1N5402, a good choice ?

 

[audioguru2]

The 1N5402 gets extremely hot at continuous 3A. It cools itself through its leads.
Is the copper on your pcb thick enough and is its area large enough?
Is the pcb enclosed where it can get hotter and hotter and will heat all the other components?

 

[electroguy]

The 1N5402 gets extremely hot at continuous 3A. It cools itself through its leads.
Is the copper on your pcb thick enough and is its area large enough?
Is the pcb enclosed where it can get hotter and hotter and will heat all the other components?

The copper is thick but not the professional quality as it for college project use.
I will drill the pcb below the 1N5402s to keep air flow and also will be using a PC brush-less exhaust fan to cool the power transistors.

 

[audioguru2]

I like to be safe, not sorry.
I worked for a company that began to sell and install business telephone systems. A new system was all digital and had many features. The first company to buy this system had the owner worried about the heat from the ring generator. The manufacturer said it will be fine. It failed the next week and re-design was needed for it to be cooler.

We also sold many high power high quality power amplifiers. None ever failed. I was asked to test a competitor's amplifier and it did not produce its rated output and it smoked.

 

[electroguy]

I like to be safe, not sorry.

I definitely take your advice, thanks Man.

 

[liquibyte]

I started asking about hooking up the TO-3's over at EEVBlog because it's a much more active site and I was looking for an immediate answer to my question.  I am getting a bit of negative feedback regarding the fact that someone thinks that this design isn't sustainable due to the fact that with a 28V transformer after rectification and smoothing that the voltage into the opamps is going to be around 50V.  Has anyone that's built the 3 amp version run into issues with this?  If so, what sort of solution did you use to fix the issue to get the voltage to less than 44V so as to not overload the max limits on the TLE2141's?.

Edit:  Nevermind.  I hooked up the filter cap and measured 45.1 VDC.  It's a little over the 44V max of the op amps which worries me a bit.  So I guess a new question would be, is there a recommended way to drop that to the 44V?  Voltage divider to ground?

 

[audioguru2]

The peak of 28V RMS is 28V x 1.414= 39.6V. The bridge rectifier drops 1.2V when the current is very low so the positive voltage is 39.6V - 1.2V= 38.4V. The opamp U2 is the only one using the full 38.4V which is not near the maximum allowed voltage of 44V.

I selected a Hammond high quality torroid transformer that has good voltage regulation. its voltage is 29.5V with no load. Then its peak is 41.7V and the bridge rectifier drops it to 40.5V which is still less than the maximum allowed 44V.

Maybe you used a cheap transformer with poor voltage regulation and maybe your AC electricity voltage is too high.

 

[liquibyte]

I typically get 122.4 VAC out of the wall.

The transformers I'm using are Triad Magnetics VPS28-4600's with the following ratings wired parallel input and serial output:

1. Maximum Power: 130.0VA
2. Primary – Series: 230VAC, 50/60Hz; Parallel: 115VAC, 50/60Hz
3. Secondary: Series: 28.0V CT@ 4.6A; Parallel: 14.0V @ 9.2A
4. Voltage Regulation: 25% TYP @ full load to no load
5. Temperature Rise: 30C TYP (45C MAX allowed)
6. Insulation Resistance: 100MΩ

When I measure the output of each transformer I get 35.5 VAC and 35.4 VAC (building two units).  After rectification I get 28.5-28.6 VDC (it fluctuates a bit) and after I hook up the smoothing caps I get right around 45 VDC for each transformer.

I'm not sure what I should do now.  I don't want to exceed the op amp ratings and I'm not sure whether I should work on a limiting circuit or try and find a higher rated op amp to replace these.  Any suggestions?

 

[audioguru2]

Years ago I selected an opamp with a 90V maximum power supply rating but it was not available frequently and was not common in distant countries.

Connect the + supply pin of all the opamps to the 10V zener diode, and feel if it gets hot.

 

[redwire]

liquidbyte   I have the Triad Magnetics VPS28-6250 (175VA) transformer and I am getting approx 41VDC rectified.   Add another 2V for the negative rail on U2 results  in 43V across U2.   The TLE2141's are rugged devices.    In my first unit, I used a home built transformer that puts out nearly 60VDC rectified.   I was concerned about the TLE2141's operating well outside of their specifications so I put them on sockets in case I smoked one.  I did blow one when I had wires crossed during fabrication but once corrected I never had a problem.    I don't use the high voltage unit much but its been working for several years.  I am fairly confident that operating the TLE2141's at 44-45Volts will not be a problem.  

I just built a smd version of this board using smd TLE2141's using the same 175va,28V transformer. I haven't had any issues  or temperature problems.  JUST BUILD IT!