0-30 Vdc Stabilized Power Supply

[audioguru]

A few people designed pcbs for this project but I did not save them.

[KevinIV]

The PCB consruction for both high frequency and low frequency circuits is more complicated than that of the average use for this power supply. I would say to use a simple solder and wire circuit. Most often the problems will be the rest of the circuit. If you can fabricate a PCB, use larger conductors that will handle the current.

[tdx]

I have built this power supply some time ago and used the PCB in the PDF attached for it. From the PCB's posted it is by far the best I found with proper trace sizes and probably the best layout you can do for a single sided board with this circuit. The PDF includes a redrawn schematic and parts list but the part names DO NOT MATCH the ones posted by audioguru and others, so pay close attention when assembling.

The attached PDF is not mine, I forget the username of the person who created it but all credit goes to them.

[audioguru]

I forget the username of the person who created it but all credit goes to them.

The 6th page shows the username Picmaster who did it.

[Qwicol]

Hi, it's my first post here

 I've just finished soldering of this http://www.electronics-lab.com/projects/power/001/index.html  power supply and I've encountered following issue:

In max position of potentiometer responsible for maximum current and in short circuit with amp meter my max output current is only about 40mA and current limiter is working.
What should I check in the first place?

I've checked op amps and voltage regulation and they're ok.

I'm counting on Your help.

And sorry for possible gramatic errors, i'm rather bad at writing in english [I'm from Poland]

[audioguru]

The original project has many errors and does not work properly and is not reliable. That is why this thread and another thread recommends modifications.

R7 senses the output current. It is 0.47 ohms and with 3A it produces 1.41V across it which is fed to the inverting input pin 2 of opamp U3. The positive non-inverting input pin 3 of U3 has the voltage from the current-setting pot P2. U3 in the original circuit needs the negative supply of -5.6V on its pin 4. when the sensed voltage exceeds the set voltage then the output of U3 goes low enough for D9 to reduce the output voltage until the output current is reduced to the set current.

U2 drives the driver transistor Q2. Q2 drives the high current output transistor Q4. There should be much more than 3A of output current when the output is shorted.

[fly3rman]

Hey guys,
as my power supply is finished and actually working, i was testing very heavy loads (2x12volt halogen lamps) with it.
But something is gone wrong, my voltage regulation doesnt work anymore and i get fully 40 volts on my output. Also U2 is getting very hot, so i replaced it, still same problem.
The current limiting is still working, i can turn current to zero and led is also showing that.
Any idea where to start and which parts to check?

[audioguru]

U2 gets very hot if the pins on the driver transistor are connected backwards because then the transistor operates like a simple series diode.

Maybe you built the defective original version that used the old 2N2219 driver transistor that fails when it gets too hot and it is difficult to keep cool.

Maybe the output transistors had a heatsink too small so they melted and are now shorted.

[fly3rman]

You were right, it was a output transistor  has died (2n3055). But they are on a huge cooler. I replaced them now, hooked up my multimeter for amper-measurement and ... one died again.
So it seems only one of them route the power, and dies. They were from the same charge, so resistance and hfe shouldnt be that different. Ideas why they dont share the power not symmetrical.

[audioguru]

Transistors with the same part number are not the same. Their hFE and base-emitter voltage are different so one transistor hogs the current and gets hotter which makes it hog more current and get hotter which... (Thermal Runaway).

The emitter resistor added in series with each output transistor's emitter makes them properly share the current.

Calculate how much heating a low output voltage and a high output current makes and you will see that a huge heatsink is needed maybe with a fan.

[KevinIV]

There is nothing wrong this stabilized 30Vdc power supply. Having not tested the orginal circuit, it must be a good design, or it would not be posted. Since it's a good design, but doesn't meet your requirements, a totally new design is needed. The engineering principle behind this design is found in many different power supplies. Can't you just buy this power supply from the website?

[audioguru]

There is nothing wrong this stabilized 30Vdc power supply. Having not tested the orginal circuit, it must be a good design, or it would not be posted. Since it's a good design, but doesn't meet your requirements, a totally new design is needed. The engineering principle behind this design is found in many different power supplies. Can't you just buy this power supply from the website?

Kevin,
This power supply project is defective which is why I fixed it:
1) It is not reliable since many parts (the transformer, the rectifiers, the transistors and many resistors) are overloaded and burn out.
2) The opamps operate with a total supply voltage that is more than their maximum allowed supply voltage.
3) It does not provide 30V at 3A because the transformer voltage is too low.

This project is a kit sold by a company in Greece. I don't know what they do about people complaining about its problems.

Many defective projects have been posted here. I fixed a few of them. 

[rosana]

i don΄t know how i have to put the "legs" of the trimpot in wich number the mc4071 (U2)...

[audioguru]

i don΄t know how i have to put the "legs" of the trimpot in wich number the mc4071 (U2)...

U2 is an MC34071. Its RV1 input offset voltage trimpot is 10k and is wired as shown on the schematic. Its voltage calibration trimpot RV2 is 20k and is wired as shown on the schematic.

The middle leg on a trimpot is its slider which is the middle pin with the arrow of the trimpot on the schematic.