A little help with my university project please... - Electronic Circuits Projects Diagrams Free

morrissey · 28th August 2006, 01:47 PM

Hello!
I was assigned a project at my university to build a power supply that gives output +6V , -6V and 5V. I have attached it to show it to you and if you could tell my what's wrong...
I would apreciate if i could get an answer by the end of the day because i have to make the corrections and prepare it for printing it on a board.

Thank you.

**Nigel Goodwin** · 28th August 2006, 02:03 PM

First thing, don't post diagrams af JPG's, they are poor quality and much too large - use GIF or PNG.

As for your circuit, use only ONE bridge rectifier, across the outside two of the transformer pins, the centre pin connects to 0V. Also, you have a 100nF in series with the positive output, so it can't possibly work, and you don't have a large electrolytic on the positive supply.

Hero999 · 28th August 2006, 02:23 PM

You only need one bridge rectifier with two large electrolytics both conected from the positive and negitive to the centre tap.

HiTech · 28th August 2006, 02:34 PM

Go easy on him Hero--- at least he's trying and learning in the process. We all made mistakes at once (and I still do). His attempt to design and then inquire for advice on improvements is certainly alot more admirable and constructive than the many jokers who march in here asking for us to provide them with an idea, diagram, parts list, etc.

I remember when I was a kid tinkering with a drycell, a lamp, and hookup wire to make a working light. I was so proud of my (simple) accomplishment, but my father wasn't impressed and even placed it aside from me, telling me to pay attention to other things in life. That action of his only served to further fuel the flames of my interest in electronics, eventually leading to a career in it. My mother on the otherhand recognized my interest in it and did things to cultivate me.

Hero999 · 28th August 2006, 02:38 PM

Quote:

Originally Posted by HiTech

Go easy on him Hero--- at least he's trying and learning in the process. We all made mistakes at once (and I still do). His attempt to design and then inquire for advice on improvements is certainly alot more admirable and constructive than the many jokers who march in here asking for us to provide them with an idea, diagram, parts list, etc.

Fair enough, post edited. I suppose universities aren't very good at teaching the pratical side of electronics.

JimB · 28th August 2006, 03:36 PM

Try this.

I have redrawn the rectifier part of your circuit, in the way that others have also suggested.
You need to be aware of the pin-outs of the voltage regulators, the 78xx and 79xx are different.

JimB

Hero999 · 28th August 2006, 03:57 PM

One more thing for safety's sake the fuse an switch are always connected to the phase conductor, never the neutral.

morrissey
I don't think you have enough experiance to build mains powered circuits. I recommend you should by an AC adaptor with an AC output or a torroidal halogen lighting transformer to power your project with.

morrissey · 28th August 2006, 03:58 PM

Thank you very much for your help and your quick respond!
I will try it right on and as soon as i get it fixed i'll tell you the results..
As for the universities , and especially for the greek technological university
i study, the things are very bad...It's quite difficult to "survive" in there if you
don't try to learn things by yourself and not wait for the university to learn things to you and help you...I believe in England and the U.S. the things are far more better!
Thanks again for your help!
I'll let you know how it went

**Nigel Goodwin** · 28th August 2006, 04:21 PM

Quote:

Originally Posted by Hero999

One more thing for safety's sake the fuse an switch are always connected to the phase conductor, never the neutral.

Actually that's not entirely true!, there are many commercial units where the fuse is in the neutral lead, and many more (using figure 8 mains leads, or non-UK two pin leads) where it depends which way you insert the mains lead.

However, I agree that I MUCH prefer to see the fuse in the live lead, and not the neutral - and anything I build has a fuse in the live.

morrissey · 29th August 2006, 02:56 PM

hello again,
I printed the board and i tested it and the results are:instead of 6V i got 2,4V , instead of 5V i got -5V and instead of -6V i got 6V
The weird thing is that lm7806(down) gets really really hot.
I downloaded multisim 7.0 so i can simulate it there.But i can't find in its librady lm7805 and 7806. Is anything else similar so i can use?
And also i can't find the bridge rectifier.
thnx

morrissey · 29th August 2006, 02:58 PM

Oh and someone mentioned, as i was reading your replies again, about lm79xx.
Maybe i should use them instead of the ones i have?

JimB · 29th August 2006, 03:48 PM

Quote:

Originally Posted by morrissey

instead of 6V i got 2,4V , instead of 5V i got -5V and instead of -6V i got 6V
The weird thing is that lm7806(down) gets really really hot.

Never mind simulators, you will never learn electronics that way.

OK, -5 and -6v instead of +5 and +6v, did you have the meterconnections the correct way round?

2.4v instead of 6v, and a regulator that get hot. Is this the -6v output?
You have used a 7806, you should use a 7906. In that circuit the 7806 will get hot and is now probably in silicon heaven.
I did not notice that you had 7806 for the -6v supply, which is why I made the comment to beware of the pin-out difference between 78xx and 79xx.

JimB

audioguru · 29th August 2006, 03:53 PM

Hee, hee.

The JPG schematic is so fuzzy that nobody noticed the wrong 7806 instead of a correct 7906.

Are the pins connected the correct way around as on the datasheets for the regulators?

morrissey · 29th August 2006, 04:09 PM

Yes that must be it!
I tested it again, i didn't tell you the results right!
The top LM7806 gave me 6V! correct!
The middle LM7805 gave me 5V! Correct!
The bottom LM7806 gave -2.5V. False!
So that must be it!
Tommorrow i'm going to buy an LM7906 and place it on the circuit
and tell you how it went!
thnx again! I'll write your names on the project

muki55 · 30th August 2006, 07:46 AM

try this one i edit your diagram

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28th August 2006, 02:03 PM	(permalink)
Nigel Goodwin	First thing, don't post diagrams af JPG's, they are poor quality and much too large - use GIF or PNG. As for your circuit, use only ONE bridge rectifier, across the outside two of the transformer pins, the centre pin connects to 0V. Also, you have a 100nF in series with the positive output, so it can't possibly work, and you don't have a large electrolytic on the positive supply. __________________ PIC programmer software, and PIC Tutorials at: http://www.winpicprog.co.uk

28th August 2006, 02:23 PM	(permalink)
Hero999	You only need one bridge rectifier with two large electrolytics both conected from the positive and negitive to the centre tap. __________________ I also post at the following sites: http://www.stop-microsoft.org http://www.heated-debates.com Screen name: Aloone_Jonez And http://www.silicontronics.com, same screen name as here. Last edited by Hero999; 28th August 2006 at 02:36 PM.

28th August 2006, 02:34 PM	(permalink)
HiTech	Go easy on him Hero--- at least he's trying and learning in the process. We all made mistakes at once (and I still do). His attempt to design and then inquire for advice on improvements is certainly alot more admirable and constructive than the many jokers who march in here asking for us to provide them with an idea, diagram, parts list, etc. I remember when I was a kid tinkering with a drycell, a lamp, and hookup wire to make a working light. I was so proud of my (simple) accomplishment, but my father wasn't impressed and even placed it aside from me, telling me to pay attention to other things in life. That action of his only served to further fuel the flames of my interest in electronics, eventually leading to a career in it. My mother on the otherhand recognized my interest in it and did things to cultivate me. __________________ Don't make me reach through this monitor to slap you a good one!

28th August 2006, 03:58 PM	(permalink)
morrissey	Thank you very much for your help and your quick respond! I will try it right on and as soon as i get it fixed i'll tell you the results.. As for the universities , and especially for the greek technological university i study, the things are very bad...It's quite difficult to "survive" in there if you don't try to learn things by yourself and not wait for the university to learn things to you and help you...I believe in England and the U.S. the things are far more better! Thanks again for your help! I'll let you know how it went

29th August 2006, 02:56 PM	(permalink)
morrissey	hello again, I printed the board and i tested it and the results are:instead of 6V i got 2,4V , instead of 5V i got -5V and instead of -6V i got 6V The weird thing is that lm7806(down) gets really really hot. I downloaded multisim 7.0 so i can simulate it there.But i can't find in its librady lm7805 and 7806. Is anything else similar so i can use? And also i can't find the bridge rectifier. thnx

29th August 2006, 02:58 PM	(permalink)
morrissey	Oh and someone mentioned, as i was reading your replies again, about lm79xx. Maybe i should use them instead of the ones i have?

29th August 2006, 03:53 PM	(permalink)
audioguru	Hee, hee. The JPG schematic is so fuzzy that nobody noticed the wrong 7806 instead of a correct 7906. Are the pins connected the correct way around as on the datasheets for the regulators? __________________ Uncle $crooge

29th August 2006, 04:09 PM	(permalink)
morrissey	Yes that must be it! I tested it again, i didn't tell you the results right! The top LM7806 gave me 6V! correct! The middle LM7805 gave me 5V! Correct! The bottom LM7806 gave -2.5V. False! So that must be it! Tommorrow i'm going to buy an LM7906 and place it on the circuit and tell you how it went! thnx again! I'll write your names on the project