0-30 Vdc Stabilized Power Supply

[halen]

Hello

Iam new there. I have problem with this PSU. I designed it in the Multisim simulation, but doesn't work. Used modified partlist, 24VAC TR, BZX83C5V6, I have troubles with - 5.6V D7. I using TLE2141CP OP amps in simulation and if I connect U2 to the -5.6V, then voltage drop to 800mV. If I connect U2 pin 4 to GND, then PSU work, but LED slow flashing :-D. It seems that RV1 don't work. It is possible to test this PSU in simulation or PSU in simulation don't work? I mean that it must work. I have 100% correct wiring and parts. Please help.

 

[audioguru2]

is anything wrong with this circuit?

People who made it reported that some parts overheated and failed.
Its output doesn't reach 30V at 3A so I investigated and made parts change recommendations to fix it.
The revised parts list and reasons for the changes are in this thread.

 

[audioguru2]

I designed it in the Multisim simulation, but doesn't work.
It is possible to test this PSU in simulation or PSU in simulation don't work?

Multisim might not understand how the negative 5.6V supply works.

 

[jhanus]

audioguru, thanks.

When you said that they are in this thread, did you mean scattered, or in one place, if they are in one place(plz link) or if anybody is willing to put them in one place?, I can remake the circuit, list all the changes and upload for future viewers.

If the answer is no, then I'm off to read,and I'll post as soon as possible my result.

greeting

 

[audioguru2]

Hi Jhanus,
Others recommend adding trimpots in series with the voltage and current adjustment pots for calibration of 30.0V and 3.0A. A few pcb designs have also been posted in this thread.
Here is my recommended list of parts for this project:

View attachment 40396

 

[jhanus]

;D thanks! audioguru  ;D

I can't buy:- TIP31A, but I can TIP33C, and (BC548,2N2219).

                  - OPA445AP, but I can TL081CN (C=operating temperature 0=>+70,
                                                                    N=DIP8 package).
Are they good substitution? 

Under two paralleled 2N3055, just to connect B-B, E-E, C-C or something else.

Thanks a lot.

 

[audioguru2]

I can't buy:- TIP31A, but I can TIP33C, and (BC548,2N2219).

A huge difference.
The BC548 has a max current rating of only 100mA and max power rating of only 625mW.
A 2N2219 has a max current rating of only 800mA and a max power rating with a clip-on heatsink of only 1.6W.
The recommended TIP31A has a max current rating of 3A, a max power rating of 40W and a max voltage rating of 60V.
A TIP33C has a max current rating of 10A, a max power rating of 80W and a max voltage rating of 100V. It can replace the TIP31A but it costs more.

A TIP31A costs $.68US each and a TIP33C costs $1.80US at Digikey.
There are many BDxxx european transistors that are the same as a TIP31A.

I can't buy - OPA445AP, but I can TL081CN.

The TL081 has a max supply voltage rating of 36V. The OPA445 has a max voltage rating of 90V.

With a 30VAC transformer, with no load current on the project the positive supply will be 43VDC and the negative supply will be 5.6V. Therefore the total supply voltage for the opamps is 48.6V and even opamps rated for a 44V supply won't be good enough.

Under two paralleled 2N3055, just to connect B-B, E-E, C-C or something else

No. The transistors are not exactly the same. One will have more current gain.

Each 2N3055 transistor has its own 0.33 ohm resistor in series with its emitter to equalize their current gains so they share the current better.

 

[jhanus]

Again, audioguru thank you.

I found OPA445, and with yours recommended list I'm ready to go!

And I must say that people like you make this world a better place!  ;D

 

[halen]

Multisim might not understand how the negative 5.6V supply works.

I replaced TLE2141CP with OPA445 (I try many others OP amp but 100% work only OPA445) and replace 24VAC TR with 30VAC to get max voltage 30V and now, in simulation PSU work. Both V and I regulation work perfect.  But I have next problem. If I measure output with osciloscope I get 20kHz oscilating about 200mV AC. Where can be problem? If I replace output 10uF capacitator with 100uF, oscilating is now pretty low in uV. But this is not right way.... Can somebody help please?

 

[audioguru2]

C5. C6 and C9 keep the output from oscillating.

 

[Tinny]

Hi,

I have made the standard PSU from the projects page, and am after some help with troubleshooting.

the few changes in parts

-TL081 for HA17741, which seem similar.
-C1 is a 4700uF / 63V
-C4 i used two 53nF
-Q2 is a TIP31C, with bent legs to fit the original PCB design
-Resistors are half watt, R1 1W, R7 5W
-D7, D8 is a 5v6 zener tho im not sure the power rating, i can check if the problem seems to point to this
-transfo is 72VA, 24VAC output
-RV1 . ther is some confustion about this, 100ohm trimmer resistor, not a 100k trimpot? still not really sure what the difference is.

The problem seems to be the current regulation.

I can't seem to get more then 50mA out of the PSU.

I can run a LED at 2V draws about 40mA.

25V bulb that is spose to run at 750mA  i think, measures 33ohm, i donno if you can measure the expected current like that ? Draws about the same at 50mA if i set the voltage at 25V before load it goes to 8V with this bulb on it. There is a faint light.

Also a 3A load, voltage drops to 0.1V or so

Current pot at full off . volts measures -0.06 and the LED is on. if i turn (current pot) it up 10% or so the voltage goes up to 0 which is when the LED turns off. This is with no load.

volt pot at 100%
Voltage at the output is 32.00V
C1 33.8V
D8 5.7V

I have read both this thread and the 5A+ mod thread and i did find a few things around page 20 and some interesting things around page 76 but not really anything the same as the problem i have

Im just after it to actually work right before i change a few things which i do plan on.

Thankx for any help.

 

[audioguru2]

Hi Tinny,
Welcome to our forum. ;D
Your project has a few problems:
1) the 741 opamps have a positive supply of 33.8V as you measured plus a negative supply of 5.6V for a total of 39.4V. Their absolute maximum voltage allowed is only 36V so maybe they are broken.
2) Your transformer has only a 72VA output rating. Then it is overloaded if the output current is more than only about 2.1ADC.
3) The TL081 needed a value for RV1 of 100k in series with 270k to the negative supply.
Your 741 opamp needs 10k for RV1 in series with a wire to the negative supply. Look at its datasheet.
RV1 is a trimmer pot that is small and is adjusted with a small screwdriver. 100 ohms is much too low.

You said that you cannot get more than 50mA from the project. When you try more than 50mA for a load is the current pot set to max and does the LED light to show that it is regulating the current?

The current regulation depends on U3, D9 and the values of  R7, R17, R18, R21 and P2.
R7 is supposed to be 0.47 ohms which is less than half of one ohm. If it is 30 ohms instead then the current regulation will be about 50mA max.

Measure the voltage at pin 4 of U2 and U3. It is supposed to be -5.6V.

 

[halen]

C5. C6 and C9 keep the output from oscillating.

Ok thank you. I have one more question  It is impossible to buy OPA445 in my country and TI dont send free samples for me. I can buy LM143 (SG143) OP amp.  Will those op amps work or I must change some parts?   

 

[audioguru2]

The old LM143 and SG143 are very slow and their output voltage swing is limited. Their offset voltage adjustment is different. The circuit would need many changes for them to be used.

 

[halen]

The old LM143 and SG143 are very slow and their output voltage swing is limited. Their offset voltage adjustment is different. The circuit would need many changes for them to be used.

Thank you for super-quick answer! So what now? I find next Ha7-2645-5 OP, but best is OPA445 isnt it?

 

[audioguru2]

Where are you where common parts are not available?

Come over to this part of the world where everything is available.

 

[halen]

Where are you where common parts are not available?

Come over to this part of the world where everything is available.

Czech Republic - Europe, Alll distributors of electronics parts doesnt have OPA445, and if I want to buy them, i  must buy 100+ pieces... :-( Iam not crazy.

 

[audioguru2]

It is too bad that you can't get stuff in your country.

I just order parts from a neighbor country (USA) online and they are delivered to me the next morning.

 

[Tinny]

Thx for the info audioguru,

it seems the PSU works better with the correct value at R7 0.47 and not 47ohm

now that i can run it over 50mA, looks like i will have to find some better cooling for this power transistor 15V at 2A for a few mins and the whole heatsink is pritty hot. small heatsink tho

 

[audioguru2]

That is why I recommend using two output transistors on two separate heatsinks to share the heat.
A 24V transformer is used like in the original project. Then it is set to a low output voltage and set to 3A or its output is shorted. Then the 2N3055 output transistor must dissipate 32V x 3A= 96W. It can dissipate 115W if its case id held at 25 degrees C somehow, but a huge heatsink isn't good enough without also having a fan or liquid nitrogen.