0-30V Stabilized Power Supply

[karthikeid]

when the U2 will measure zero... what should i check it is not working...

 

[audioguru2]

Check that the voltage adjust pot gives from 0V to +11.4V to the input of U2.

 

[karthikeid]

yes the input voltage at U2 varies from 0 to +11.4V....
then what should i do...

 

[audioguru2]

U2 is an opamp that drives two emitter-followers. They have a voltage gain of slightly more than 3.

What does the output of U2 do when you vary the voltage pot?

 

[karthikeid]

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

 

[redwire]

Hi karthikeid    I posted my pcb file a few pages up but here is the link:

    http://www.electronics-lab.com/forum/index.php?topic=19066.msg89170#msg89170

 

[audioguru2]

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

 

[audioguru2]

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

 

[audioguru2]

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
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 ??? 

 

[audioguru2]

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

View attachment 40730

View attachment 40731

View attachment 40732

 

[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.

 

[audioguru2]

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....

 

[audioguru2]

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