0-30 Vdc Stabilized Power Supply

[audioguru2]

MonSSter,
Greetings, and welcome to our community.
We have discussed this project and have discovered some problems. We have another post that discusses how correct the problems and to increase its output to 5A. I have recently recommended changes that should allow this. There is a revised PCB layout there for my changes.The other post is here:
http://www.electronics-lab.com/forum/index.php?board=13;action=display;threadid=196

The circuit doesn't use a LM317 nor LM338 because they would not easily allow the circuit to do important functions:
1) Automatic change between voltage and current regulation.
2) 5A output at low output voltage. The LM317 and LM338 automatically fold-back their current limiting to protect themselves for their Safe Operating Area. The LM317 is guaranteed to give only 75mA, and the LM338 doesn't even have a guarantee, but is expected to give no more than 1A.
3) Voltage regulation down to 0V, and current regulation down to 2mA.

You have a good idea for a dual supply. With 2 separate transformer windings, the circuits will be completely independant.

 

[MP1]

MonSSter, if you want to build a bipolar supply using LM317, LM337 with 5A, you can use the output of the 317 or 337 to control the base of power transistors.
The following post might give you some ideas:

http://www.electronics-lab.com/forum/index.php?board=22;action=display;threadid=815;start=0

MP

 

[MonSSter]

Thank u for quick answers

 

[mav]

Hi! I have built this psu, but when I connect some load to it and I set voltage to some value and then I decerase current (by setting current limit), voltage decerases too. Has it to be so?

 

[Xenobius1]

If the LED starts to light, then yes the voltage decreases.

 

[mixos1]

Hi! I have built this psu, but when I connect some load to it and I set voltage to some value and then I decerase current (by setting current limit), voltage decerases too. Has it to be so?

Yes, it's normal... if the current limiter (led is on) is working. Current limiter limits the current to a certain value and the voltage drops across the load, so Ohms law always stands.

 

[NightHawk_099]

I need help solving the most unusual problem for the 0-30 Vdc Stabilized Power Supply With Current Control 0.002-3 A power supply. The voltage control and current limiter work correctly, they respond to changes in the potentiometers, the led lights, etc. There is no problem while the power is on, but once the power is off, the problem starts.

First off all, this problem is encountered only when the voltage output is less than 8 volts
When I power off the power supply, the voltage remains stable at the output value for about 2 seconds, then QUICKLY GOES UP, exceeding 16 volts and the starts going back down until it goes to 0 volts, all in about 1 second. The measurments were made with a digital multimeter in perfect condition.
I have added a switch to this project. It connects/disconnects both AC line cables from the transformer. I dont have a clue as to what may be causing this problem, and I greatly need your help. I have invested a lot of time and money into this project and would hate to see it all go to waste because of a strange problem like this.

 

[audioguru2]

NightHawk,
It sounds like transistor Q1 is not working. When you shut off the power, the negative supply voltage across D7 is supposed to disappear very quickly, since it has a small filter capacitor. Q1's base is biased by the voltage divider of R13 from the positive supply voltage of about 36V (no load), and R14 from the 5.6V negative supply. With both supply voltages present, the voltage divider keeps Q1 turned off. When the negative supply disappears, Q1 is turned on by R13 and the project's output should quickly go to zero volts.
Check that Q1 is installed the right way around.
Is it possible that you sustituted an American transistor, such as a 2N3904? Its collector and emitter are in the reverse positions compared to a BC548.

Can your project supply 30V at 3A?

 

[Capricious]

Can anyone please list all the parts should be changed to be safe?
Perhaps with a short description why it should be changed.
I am a newbie and after reading the 8 pages of this thread I am a bit confused.

I've read something about exploding C7... Is it only a problem of one guy doing something wrong or must I take glasses if I switch on my PSU?

I can not find the specified 50V 3300uF C1.
I have the choice between a 40V 3300uF and 50V 4700uF.
Would it be a problem using more capacity for C1?
Can a 24V trafo has more than 28V output?
My trafo is on the way so I can not check the max. output voltage.
If the maximum is 28 V the 40V C1 should be enough, shouldn't it?

Then the 200nF C5. Is 200nF a usual capacity? I can only find 220nF capacitors.

Thanks.

 

[MP1]

Capricious, The owner of the list has built this supply. He has not noted anything dnagerous. In fact, he started a thread on how to make it better and capable of more current. I suggest you contact 'mixos' directly through e-mail or with the private message to ask him about his experience. All of those making comments on this forum have not necessarily built the project and therefore, I point you in the direction of one who has.

MP

 

[audioguru2]

We have discussed this project and have discovered some problems. We have another post that discusses how correct the problems and to increase its output to 5A. I have recently recommended changes that should allow this. There is a revised PCB layout there for my changes.The other post is here:
http://www.electronics-lab.com/forum/index.php?board=13;action=display;threadid=196

Hi Capricious,
Welcome to our forum.
You are right, this project has created much confusion since its specified parts don't seem to do the job unless you are very lucky and don't use it at its limits. Shown above is a link to the other forum where boosting its output to 5A is discussed. I recommend that you follow those modifications since the original article has parts operating at and beyond their ratings.
Don't worry about C7 exploding. One member was using this project to power a switching power supply that was malfunctioning. Its high current pulses gave his C7 a real workout. Just use a 50V cap that has a good ESR rating.
Use 10,000uF for C1 rated at 50V. If it doesn't fit the PCB then strap it nearby to the case, using heavy connecting wire.
I don't know the ratings of your transformer, but 24VAC, 3A is too small to get 30VDC at 3A out of this project. It will be fine at a lower voltage output.
220nF is fine for C5.
Good luck.

 

[Kain]

Hello, I'm new in this forum but I built this PS with no real headache. Actually I built 2 separated boards (2 PS) for my project is to build dual lab PS. They both worked right away. The only thing I noticed is that R2 heats way too much for it's rating so I changed it to .5W of the same value and now everything is fine (seems fine ). Now to my question. I want to put a voltmeter and Ampermeter - analog ones, but i noticed they are expensive. I checked few stores as well as online ones but same result - they are expensive. However, I saw AC ones that were fairly cheap and in the exact range I need, so my question is is there some way to compensate those AC ones in order to make them work (acurately) for DC? Of course if you know some store where I can buy the DC ones for cheap it will be even better ;D

 

[ante1]

Kain,

Welcome to this community.
The analog meters are more expensive than the digital these days, are you sure you don

 

[Kain]

Well I wouldn't mind digital either I guess. However, digital V meter is not a problem to get - I found them in a local electronics store for 5$ each. The problem comes with A meter for the ones I found actually can be used for this by changing the pin configuration (I think I saw this modules actually discussed in this forum), but it will work only for mA, and as we all know this PS goes all the way to 3A... I haven't really payed attention too much on how digital A meters work (besides I know it analogic/digital converter). However I have broken quite few cheap multimeters in the past ;D and I saw one common thing in them all - there is a power bridge which is some resistor with small value but high power rating to handle 10A if the multimiter supports it. I might be wront though - as I said I haven't dig in too much onto measuring devices. If I'm correct though those units will need something additional to measure A. Any ideas?

 

[ante1]

Kain,

You can use a V meter as an A meter you just need a shunt.

Ante :

 

[Kain]

Well I'll need to dig a bit more into this I guess... Ante, can you recommend a good article on digital V and A meters? Reference scheme of some type will be good too if possible :. Thanks btw

 

[ante1]

Kain,

Try to find the datasheet from your suppliers panel meters and study it.
Most of the LCD & LED panel Volt meters have 199,9 mV, 1,999 V, 19,99 V, 199,9 V ranges. On the 199,9 mV range just shunt with a 0.01 Ohm resistor and your meter will show 0

 

[Kain]

Good thing. I'm going to buy one today and see what it can do. Costs only 5$ - one meal (i need to loose 5kg anyways ;D). The only thing that bugs me is that it's made in korea, so hopefully I won't have to decrypt hangul :

 

[ante1]

Kain,

There is one more thing to consider, these meters can usually not be powered from the same supply as you measure on. This is not a big problem, there are several ways to fix this.

Ante :

 

[Kain]

Well, I am aware of this fact anyways. I was thinking to add one more transformer with simple zenner stabilizator and filtering capacitor with high enough value. I saw low power transformers that are small in size and cost no more than 2$. Good option?