I've built a power supply 0-30V 0-5A with a lm723 and a ca3140. but it doesn't work. it should be regulated with a transistor controled with Vz from the lm723 only the voltage is to low so the zener diode in the lm723 wont let anything trough. it should be regulated from the diference from pin 4 and 5 only it doesn't do anything. does anyone have a idea what the problem could be?


here is the link for the schematic :
http://bp1.blogger.com/_oH9cuSJx7ZY/SHHxdZs56lI/AAAAAAAAA90/6cIP5ymoJKg/s1600-h/PS+Schematic.jpg

 

Do you see the switch at the out put of the supply.
Did you have it installed ?
Is it normally closed switch?

Come to think of it, why do you need a switch wired like that.
I don't think that diagram will even work.
You can find better ones with in this forum.
Try searching for it first.

 

no don't have it installed because it seemed useless. it actualy works if I connect Vz to the output of the lm723. it will give an output only it cant be regulated.

 

Is ur IC LM723 OK.
Did u try using Vout Pin.
Are you sure you do not have any problem in ur soldering

 

Yes replaced it and rebuilt the entire circuit on a circuit building board(don't know the exact name) and have the same results. V out doesnt work the voltage is to high.

 

Before you start making a circuit you should make sure the schematic u are referring to is legit and that it works.
You won't get any where by just referring to a circuit u find on the net, it should have reference and building details as well and the person who post the circuit should give help. Other wise it is very difficult.
There may be plenty of reasons ur cct does not work.
If we were to tell you that circuit will work we have to draw it and simulate and see the results with our own eyes if we were to tell you what to do.

Besides that circuit is somewhat new to me, and is totally different from my design with the same ship, and my one works pretty well though.
My one is also variable from 0 to 30V, and adjustable current from 0 to 10amps.

I am still making changes to it and the current regulator stage is yet to be designed.
For now the voltage regulator is working.

But let's see if any other member is familiar with ur circuit.
If you like you can check my post and from that you can learn very well.
And if you like I can explain what I am doing to make the PSU better.

 

Well you have a point there that would be a very good idea before I started building it But it is a school project and have only two weeks left so I will try getting this to work rather than starting over again. it actualy worked today when I connected pin 5 with a potentiometer 100k to the 18V + (by accident but hey it worksxD). it could be regulated. havent tested what it does when I hook anything up to it though. will test this tomorrow hope it works

 

Here is what I am working on.. just follow through the post and you will understand these things are not easy .
http://forum.allaboutcircuits.com/showthread.php?t=35039

 

ow I know it is not easy I've been working on the problem for a few weeks now even my teacher doesn't understand it that's why I tried at this forum maby somebody has an idea that i haven't tried if you want further information I can give it so you can get an better idea of the situation

 

You are confusing ur teacher....now tht's how you do it keep it up.
May be Ur feedback is creating problem, I had a problem with mine due to poor feedback.
I cannot say any thing without studying ur diagram.
And studying means simulating it and it takes a lot of time.
We members are not always available, since this is a free forum, we are volunteers and we have our lives to live too.
So what I am trying to say is, that you might not get an answer soon, you must have patience and If no body replies it probably is that they have no clue on ur problem cause they might not have deal with those type of situation them selves. I know this cause I was the same as you are when I began. So I know what you are going through.
A word of advice is not to give up, just relax and think it through step by step.
A better solution is to have the IC data sheet with you always, It will help you a lot, cause I know this by experience.
I only replied to u when I saw ur post was not getting any reply and I just want to keep ur hopes up. As I once was like that, and it some times is frustrating

 

well that's one thing what's true studying it takes loads of timexD I steadely found out what is suposed to happen now to fix it I have both ic's datasheets lying next to me(Y) I will look into the feedback. and I surely understand that it will take time and that reply's won't happen in an instand I just hoped that somewere in this world somebody has experience with a problem like this posted an hoped for a reply thanks in any case for the help anything is welcome and besides as long as I keep my teacher puzzeld it's fun