0-30 Vdc Stabilized Power Supply

[audioguru2]

Hi Tom,
Welcome to our forum.
It is wonderful that your projects work well with outputs up to 25V. Did you connect them as positive and negative supplies?

Their output voltages will probably reach a volt or two higher if you replace R15 (1K) with 100 ohms. You can increase the value of C1 to increase the voltage even more and reduce ripple at high output current.
Your single 2N3055 must be well beyond its thermal limit if the supply is shorted or set to a low voltage with its output current set to 3.2A. How is the temperature of the little 2N2219 driver transistor?

 

[Zwieke]

And yet another question from me

I'm designing a PCB for the PSU at the moment, but there's something in the schematic that's not entirely clear to me.

On U2 there are 2 pins that do not have a number next to them. I figured that it shoud be pins 1 and 8, but i just wanted to double check...

So can anyone confirm this?

View attachment 36358

 

[ante1]

That

 

[naldo]

Hi!!
Sorry for my english is only technic
My PSU is original circuit.
The PSU not start Led is ligh permanetly
Volt across C1 (33.2V)
Volt pin 6 (U3) and point 4(ground) (-5.8V)
Volt pin 6 (U1) and point 4(ground) (11.5V)
Volt pin 6 (U2) and point 4(ground) (-5.3V)
Volt across R15 (3.9V)
Volt across Base-emitter Q4 (0V)
Volt across Base-emitter Q2 (0.7V)

Thank in advance

 

[audioguru2]

Hi Naldo,
Welcome to our forum.
It sounds like R7 is open or a wrong value. It should be 0.47 ohm (a little less than 1/2 of 1 ohm).

 

[naldo]

Thanks, Thanks, Thanks....
R7 is open the PSU start
I was very upset because my PSU didn't work
What change do You suggest to make in the PSU??.
The device TLE2141CP and MC34071AP is not able in my country
but TIP31A and the other component is available

Best regards AUDIOGURU

 

[audioguru2]

Hi Naldo,
Good, I'm glad you fixed it. Suggested changes:

1) Your max output voltage with a 3A load is probably only 25V, you can get a couple more volts by changing R15 to 100 ohms.
2) You can also get more output if you change the rectifiers D1 to D4 to a 10A rectifier bridge module.
3) Even better, change C1 to 10,000uF or more.
4) Q2 will probably get too hot with a shorted or low voltage output when it is set for 3A. Use a heatsinked TIP31A for Q2.

 

[naldo]

Hi Audioguru
Ok this change I'cant make.
R7 is 5W suggest more??
Q1 is BC548 You suggest change??
What dimension heatsink for Q2??

Thank's

 

[audioguru2]

Hi Naldo,
With 3A going through the 0.47 ohm R7, the continuous power dissipation is 4.23W, so a 5W resistor will be extremely hot. I suggest using a 10W resistor.
A BC548 for Q1 is OK with your low transformer voltage.
A TIP31A for Q2 will need a fairly small heatsink, about 4cm L by 2.5cm W with 1.5cm fins. You could also use a thermally conductive insulator and bolt it to a metal chassis.

 

[naldo]

Hi my friend:

I make the changes
Full-Bridge rectifier 8A 200V
C1 10000uF 50V
Q2 TIP31C with heatsink
R15 100 ohms
R7 10W

The measurment are:

Not RLoad (not charge) 27V

RLoad 100 ohms 10W 25V 0.25A
RLoad 50 ohms 10W 23.8V
Rload 25 ohms 10W 23.4V 0.55A
RLoad 10 ohms 10W 19,8V 1.7A

One Car Bulb (Lamp) 12V 20W 12V 1.66A
Two Car Bulb in // parallel 12V 3.47A
Two Car Bulb in series (10V across each lamp) 20V 1.55A

What is your appreciation???
Sorry my english is horrible

Thank's AudioGuru

 

[audioguru2]

Hi Naldo,
As Mixos and others have discovered, your project has very poor voltage regulation at higher output voltages and currents.
That is why this thread is so long.

When you measured its output with resistors for a load, did you set its voltage output pot to maximum?

Your circuit has a high voltage drop somewhere.
1) Did you use a 2N3055 transistor for Q4?
2) Did you use only a 24VAC/3A (72VA) transformer as wrongly spec'd in the original project?
For this circuit to provide regulated 30VDC at 3A, the voltage across C1 must be at least 37V at full load. Plus a 2.5V loss in the rectifier bridge is a voltage requirement of 39.5V. Therefore the load to the transformer is 118.5W. That is much more power than a little 72VA transformer can deliver.
The required peak voltage from the transformer of 39.5V is nearly 28VRMS. So a 24V transformer's voltage is also much too low. With a higher transformer voltage, high-voltage IC's must be used and another 2N3055 must be added.

 

[naldo]

This text is posted for me to http://www.electronics-lab.com/forum/index.php?board=13;action=display;threadid=196;start=165
*****************************************************
I don't understand like they where carried out the calculations of this original PSU from Mixos.
I have carried out the following changes:

D1 D2 D3 D4 for component brige S4VB (8A 200V) with heatsink
C1 3300uF x 50V for 10000uF x 50V
R7 0.47 ohms 5W for 0.47 ohms 10W
Q2 2N2219 for TIP31A with heatsink
R15 1K 1/4W for 100 ohms 1/2W
Q4 2N3055 with heatsink and fan
The correccion suggest AUDIOGURU, thank's!!!

Working with 1V 3A
the brige burn not hot
R7 burn
2N3055 very hot

He wanted to know that you probe I carry out. Since the values of the original components are very below those that I have changed.
I was very silly of not seeing that the difference of Voltage,
24 V to 1v it represent 23V * 3A = 69W this is the heat to dissipate
for 2N3055 is to much for one device, the heatsink is to big. The power dissipation at 25 grade centigrade is 115W but TC case 75 grade is only ~60 grade.
I request them they excuse me but it was very delighted with this PSU thinking that it had already bean proven (testeada).
In any way the idea is very good but there would be that dimension most of the components ones and therefore the printed circuit.
Until soon and thank you.
*************************************************
I am very happy of being able to speak with you.

C1 across Voltage is 31V

I am a doctor in medicine but I like the electronics for that reason I am studying ,my I finish exam it was regrettably on feeding sources (PSU) when I began this project it doesn't revise my notes.
For example for an output of 30V 3A the VA to transformer it should be 207W. The value for rectifiers it is of three times the half current n this case 9A and the voltage for each diode 200V. The C1 = (40 * 10000) / RLoad
For 30V 3A RLoad = 10 ohms
C1 = 40000uF insulation is output to filter more 50% in this case around 150V.(it is loaded to the pick tension 60V minimum). I can be mistaken but it is what you/they taught me .

I thank you your attention
By AudioGuru

 

[audioguru2]

Hi Doctor Naldo,
Hola, como estas. (My wifey is from Spain, but please don't talk to me in Spanish)
1) Your 10W resistor for R7 shouldn't burn when it dissipates only 4.2W, but it will get hot.
2) Sure the 2N3055 gets very hot when it dissipates 69W, but it is possible with a big heatsink (like in the picure of the project) and maybe a fan.
3) Your 31V across C1 is much too low for this circuit to produce 30V with some current.
4) The transformer must provide the power for the load (max 90W), plus extra power that is lost in Q2, R7, the rest of the circuit and the rectifiers. I think your 207W calculation is much too high, I figure 118.5W.
5) When the project is powering a 3A load, I think the peak rectifier current is about 30A, not just 9A. Rectifiers are made to conduct very high momentary current.
It isn't necessary to use 200V rectifiers in this max 40V circuit.
6) With a 3A load, I think a 10,000uF value for C1 will be OK and keep the ripple less than 1V p-p. In the case of your transformer voltage being too low, the more capacitance the higher the output voltage. It gets a max voltage of only 40V, so a 63V rating is OK.

It looks like the low ratings of your transformer limit your project's max output to 24V at 2,1A, and up to 3A with less output voltage.

 

[giova]

Hi to all!
I built this project but something goes wrong.
I can regulate the voltage from 0 - 30 BUT I can't
regulate the current.Also when I turn the current's pot all the way
then the volts drop to -00.6 !!
Can someone help me?
I use a 24v - 5A Transformer.
I also use the TL081 IC.
And finally i use the tip131 transisors for q1 q2.

 

[audioguru2]

Hi Giova,
Welcome to our forum.
Did you use the original project's schematic?
Check R7, R21, R17, R18, P2 and U3. They regulate the output current.

 

[Dex555]

Hy!!!!! ;D ;D
First of all I must say that my english isn`t very good so forgive me if I make some mistakes. ;D ;D
I am new in electronic, and I am also new here.I choose this projects for my first serious work.So i will need some help from you.I make complete scheme of this circuit with some repairs which I had read here.I would like that someone look this schematic and say if there is some mistakes,so i can repair it on time.Is the emiter of Q1(T1) connected right???? ???
I also have some questions.
Someone write that RV1 is connected between 1 and 8 (of U2) but before also someone write that connections is 1 and 5.Please could someone check this!I look pbc and I think that is 1 and 5.
Also i can`t find TIP31(A-F) for replace 2N2219 and BC 547 so I plan to put two of BD 135(139)

View attachment 36476

 

[audioguru2]

Hi Dex,
Welcome to our forum.
Your schematic looks fine.
1) Using TL081 opamps, you shouldn't use a 30VAC transformer so the project's output voltage won't reach 30VDC with a load.
2) You are correct, the emitter of T1 should connect to the negative side of C1.
3) You are also correct, RV1 connects to pins 1 and 5 of U2.
4) BD135 transistors are fine for T1 and T2. Use a heatsink for T2 or bolt it to a metal chassis with an insulator.
5) Separate rectifiers for D1-D4 will be very hot at full load. Use a 6A to 12A rectifier bridge module that is bolted to a metal chassis. A 100V or more rating is fine.

With this project being your 1st serious work, double check IC and transistor pins and diode and capacitor polarities before powering it. ;D

 

[giova]

Hello audioguru and thank you for your quick answer!
First yes I use the original project's schematic.
I also checked the things you said and they seem to be ok.
The problem is tha i can;t go more than 0,08 amperes and when i regulate amperes to minimum the voltages drop to zero is this correct?
I would also like to ask if theproblem may be to pot.The pots I have they write: 1

 

[audioguru2]

Hi Giova,
With the current pot turned up and the output voltage set to about 22V or less, the output should be able to provide 3A to a load that draws 3A at that voltage. Is the transformer rated for 3A? The current regulation indicator LED should not light. Maybe your load draws only 0.08A at the voltage you have set. Try a load with less resistance.

It is normal for the output voltage to fall during current regulation. How do you reduce the current through a load? Just reduce the voltage across it, that's what the current regulator does. The current regulation indicator should light to warn you that the output voltage is being reduced from your setting.

The pots are supposed to be 10K ohms linear. Usually a pot marked "10KA" is not linear but instead has an audio logarithmic taper for a volume control. Linear is usually marked "10KB". Disconnect the pot from the circuit, turn it to halfway and measure the resistance from its center slider to both ends. You should measure about 5K to each end. An audio taper will measure about 1K or 2K to one end and about 8K or 9K to the other end.

 

[giova]

Hi Audioguru,
I really appreciate the help you try to give me.
Well I checked the pots and they give 5.4k when they are at the middle.
My transformer is 24v 5A.So I think that i can have 3A and more regulation.
When i regulate voltages works perfect from 0 to 30V.
However when i regulate the current It doesn't go more than 0.08A no matters where i put the pot of the volatges.One more thing is that when i put the current pot to one end then the voltages drop to
-0.06, the led lights then, and the current is zero.When i turn a little the current just to show me 0.01A or 0.02A then the led turn off and the voltages work normal.
One more thing that i tried is that i changed the current 10k linear pot with a 100k pot not linear and i managed to regulate the current from 0 to almost 1A.But this is also no right.The led turns on ONLY when i regulate the current to zero and the voltages drop
to -0.06 only then.
I don't have much experience at electronics and i really can't figure out why this happens.I have checked my project with the original schematic thousand of times and i can't find any mistake.I also bought some new tlo81 and changed them but the same problem persist!