0-30V Stabilized Power Supply

[audioguru]

The output of U2 reads 28.5V when in input of U2 above 0.5V and output U2 reads zero at input is zero

Then either the output transistors or driver transistor are not working or both 0.33 ohm emitter resistors at the emitters of the output transistors are missing.

[karthikeid]

both the the resistance are available .33ohms 2watts....
how do i test the transistor 2n3055... pls help me

[audioguru]

The 2N3055 transistor is an NPN. Measure the base-emitter diode then measure the collector base diode with the "diode test" of your multimeter.
Maybe you have the pins mixed up. Look at the pins on the datasheet.

[karthikeid]

everything is perfect, the voltage across the base emitter and collector are constant ie 32.2V

can i also try with TIP3055

[audioguru]

Hi Karthikeid,
The output voltage of your U2 opamp goes from 0V then suddenly switches to +28.5V.
Do you have inputs pin 2 and pin 3 swapped?

When the output of U2 is +28.5V then the base of the driver transistor is also +28.5V. Then the emitter of the driver transistor should be +28.0V which is the base voltage of the output transistors and their emitters should be +27.5V when there is no load.

The output transistors were supposed to be tested with a "diode test" of your multimeter when they have no power and are out of the circuit.

[karthikeid]

finally i have completed my circuit and it is working fine.... ;D :D
there was a small problem with pcb track and i have rectified it...
audioguru thanks for ur valuable help.....
ill post my photos as soon as possible....
how to measure the max load current ??? 

[audioguru]

finally i have completed my circuit and it is working fine.... ;D :D

Good!

how to measure the max load current ???

Your little transformer will be at its maximum rating when the output current from the project is 2.1A.
The max voltage at 2.1A will be about 26VDC. So use a resistor that is 26V/2.1A= 12.4 ohms. It will dissipate 26V x 2.1A= 54.6W. Maybe you can find a heater that is the resistance needed.

[karthikeid]

some of the pictures of my psu...

[Hero999]

No offence intended but it's not very neatly assembled.

If you put a bit more time into getting the PCB right you wouldn't have to solder some of those components so crookedly.

If you made more of an effort to form the components properly then it would have made it easier to test and get working.

If the soldering is a good as the component forming and placement then it won't be very reliable; making sure you solder neatly is important for reliability.

A poorly assembled board can introduce many errors you wouldn't expect due to bad solder joints, bridges and shorting between badly formed component leads.

I'm just saying this to help you so you make a more reliable project next time.

[audioguru]

The heatsinks look very small. When the current is set to max and the output is set to a low voltage with a heavy load or is shorted then the driver transistor and output transistors will get very hot.

[karthikeid]

thanks for ur valuable comments and ill change the heatsink into bigger one....

[audioguru]

Both heatsinks are too small. The driver transistor has a tiny little heatsink.

[Hero999]

There doesn't appear to be anything insulating the components from the heatsink which will need to be isolated from the metal chassis when it is cased unless the case is going to be non-conductive.

[effenberg0x0]

Hi guys, I am beginning a 1-year course in electronics right now. The course strategy is that every student has to find a working (correctly) project, we will study this project for 6 months (as well as the theory behind all components used). Then the project will be built and tested / modified for 6 more months. Selecting the project for a variable power supply was recommended by instructors.

I found the project at http://www.electronics-lab.com/projects/power/003/index.html. Further investigation brought me to the threads at http://www.electronics-lab.com/forum/index.php?topic=19047.0 and http://www.electronics-lab.com/forum/index.php?topic=19066.0. I understand the original complete thread over this project was lost. I also understand the original project was wrong and the version using OPA445, which Audioguru posted part lists at http://www.electronics-lab.com/forum/index.php?topic=19066.msg87812#msg87812 was also not correct.

Audioguru posted the latest schematics ans parts list for the correct version at http://www.electronics-lab.com/forum/index.php?topic=19047.msg87749#msg87749 at Aug 19, 2009. Schematics show the new opamps, so I believe those are really the latest files. However, Redwire posted a parts list at http://www.electronics-lab.com/forum/index.php?topic=19066.msg88462#msg88462 at Oct 11, 2009 that has some differences to Audioguru's.

I must make sure the project I select works to its specifications before I submit it as my project for the entire year. So I would like you to please help me with a couple questions before I begin:

- Which are the right files?
- Are the parts lists posted by Redwire targeted at a 5A PS? If so, which schematics to use?
- Are these really the latest schematics and parts lists or I am missing another version at another thread?
- Audioguru mentions at http://www.electronics-lab.com/forum/index.php?topic=19066.msg87814#msg87814 the schematics is missing a 10V Zenner diode. Is it?
- If so, are there other parts missing?
- If built according to the correct schematics and parts list, which you're hopefully pointing me to, will this project supply 0-30V at 3A with low ripple, no overheating and, of course, safety for use in students workbench? Or is it still a faulty project?
- We were supposed to deliver PCB design along with schematics. I see at http://www.electronics-lab.com/forum/index.php?topic=19066.msg88538#msg88538 that Hero999 mentions the PCB was lost. Redwire posted a PCB file at http://www.electronics-lab.com/forum/index.php?topic=19066.msg89170#msg89170. Is it the right one?

Sorry for bothering you with so many stupid questions, but I need to make sure I am starting the right way. A wrong project would make it all more difficult to learn.

Thank you

[karthikeid]

hi effenberg

ill the post the complete components list and the schematic with the pcb i made on monday...

[audioguru]

I also understand the original project was wrong and the version using OPA445, which Audioguru posted part lists at http://www.electronics-lab.com/forum/index.php?topic=19066.msg87812#msg87812 was also not correct.

No.
I simply fixed all the errors in the original project so the modified circuit worked perfectly and reliably. But the OPA445 opamps were expensive and frequently not available.

The latest version uses common inexpensive opamps from either of two manufacturers.

Audioguru posted the latest schematics ans parts list for the correct version at http://www.electronics-lab.com/forum/index.php?topic=19047.msg87749#msg87749 at Aug 19, 2009. Schematics show the new opamps, so I believe those are really the latest files. However, Redwire posted a parts list at http://www.electronics-lab.com/forum/index.php?topic=19066.msg88462#msg88462 at Oct 11, 2009 that has some differences to Audioguru's.

It is the same circuit but maybe the calibration trimpots are in different locations. I did not compare the parts lists. It will be simple for you to post the differences.

I must make sure the project I select works to its specifications before I submit it as my project for the entire year.

It works perfectly when built by an experienced electronics person. most Noobies had problems with it.

- Are the parts lists posted by Redwire targeted at a 5A PS?

Redwire made a 5A power supply. Everybody else made the latest 3A power supply.
The differences are very small.

- Are these really the latest schematics and parts lists or I am missing another version at another thread?

My schematic and parts list are the latest.

- Audioguru mentions at http://www.electronics-lab.com/forum/index.php?topic=19066.msg87814#msg87814 the schematics is missing a 10V Zenner diode. Is it?

Yes it is missing a 10V/1W zener diode that is shown on the schematic.

- If built according to the correct schematics and parts list, which you're hopefully pointing me to, will this project supply 0-30V at 3A with low ripple, no overheating and, of course, safety for use in students workbench?

Yes if you use large enough heatsinks that are mounted correctly.

- We were supposed to deliver PCB design along with schematics. I see at http://www.electronics-lab.com/forum/index.php?topic=19066.msg88538#msg88538 that Hero999 mentions the PCB was lost. Redwire posted a PCB file at http://www.electronics-lab.com/forum/index.php?topic=19066.msg89170#msg89170. Is it the right one?

Make Redwire's pcb if you want. Then use his schematic and parts list.

[redwire]

Hi effenberg0x0.              There are insignificant differences between audioguru's part list and mine.  Mine reflect preferences rather than errors.  I wanted to have a little more range so I used a 0.27ohm power resister instead of the 0.49 ohm in the original.  Some of the calibration pots may have different values to fully utilize the increased amperage range but both work.      After adding the 10V Zener, I reduced the value of R22 because it no longer see the output of the transformer.  R2 got pretty hot so I increased the resistance a bit.  The sketch attached to my post is Audioguru's so there should be no difference in the pcb.

[corsa]

Hi redwire, good afternoon, i will make your pcb and i have some questions about down traces, on left side of pcb. The trace descontinued should be continuos? And they be intesect D1 of bridge, right?
And R7 are conected to C1 ground, right?
I make this changes, please, can you tell me if i right?

Regards

PS-6_Changed.rar

[effenberg0x0]

Thank you Audioguru and Redwire. This is the info I needed.
Karthikeid: I'd appreciate that. Thanks!

Hopefully I'll be able to contribute to this forum in the near future.

Regards,
Effenberg

[redwire]

corsa     The area contained  in the blue shape on the left hand side of the pcb should all be a solid blue ground plane.    I used an earlier version of EAGLE  to create the pcb and I had to down load the latest version to open your copy.   You need to take the original version I posted,  and hit the Ratsnest button and it will fill.   The copy you posted looks like you altered something because it does not fill properly.      

[corsa]

Thanks redwire, i'm learning to work with eagle, sorry my mistakes  ???
I used the Ratsnest button like you said, and created this solid ground and i think its more logical!

PS-6_Original1.pdf

[redwire]

corsa,  That looks correct.    If you notice a few extra holes or pins it's because I added a few to connect the LCD display and one led connection for your front ase.  It will work with or without the pins installed.

[effenberg0x0]

Hi guys,  

In order to understand the differences between the original project and the two versions (updated 3A and 5A) I have built a table comparing parts, according to Redwire's and Audioguru's parts lists. I thought of posting it here, so that maybe it might help other newbies. There are in fact many differences (about 60% for 5A project and 40% for fixed 3A). I'd appreciate if you could have a look at it. I am gonna go for the 5A project.  

The ZIP file holds the original XLS file that generated the PNG, in case anyone wants to make changes.

Regards,
Effenberg

EDIT: Attached file was updated at December 11th, 2009. Reason: Correct transformer specs for Redwire's parts list.

[audioguru]

Hi Effenburg,
thanks for the comparison that shows both almost the same.

[karthikeid]

here is the circuit, the parts list are the same as such in the above post.....
no change...
u can start doing the circuit...