0-30 Vdc Stabilized Power Supply

[Mayhem]

Hello Mayhem!
I did make test to my unit and result is next: Output voltage is set to 1.50V and then when I put a 1.5A load voltage falls to 1.37V!!!
Accordingly, there is a voltage drop of about 0.13V!!! How much is Your voltage drop under this conditions?
P.s. My project is not entirely original. I did make a small changes in rectifier.

Hey Kvakva, thanks for doing the tests. My voltage drop is much higher. When i put a load of 1.5A the voltage drops nearly to 0V. I did what audioguru suggested concerning the voltage in the output of U1. I have a steady voltage of 11V, even under load conditions. I'm almost giving up this project, i measured everything that i thought could cause the problem and i found nothing that seems to be wrong. Kvakva, can you tell me what were the modifications that you did in the original project? What transistors did you use for Q1 and Q3? The only thing that i can't understand is the voltage between base and emitter of Q2 and Q4. I measure none voltage drop. I believe i should be measuring 0,7V but i can find the problem. Can you measure also these voltages on your ckt?

Thanks for helping me Kvakva and congratulations for your success!!!!!

Is this the project that you build?View attachment 40513

 

[audioguru2]

Hi Mayhem,
Of course Q2 and Q4 should have a base-emitter voltage drop of 0.7V to 1.2V when there is a load. They are emitter-followers. Yours must be shorted from base to emitter.

Opamp U2 has an open-loop voltage gain of about 200,000 so it should amplify the small error to keep the output voltage from dropping when there is a load.

 

[noworries2004]

Cheers for that Audio Guru.
Also just wondering for C1. I got a 6800uF 63V Cap instead of 12,000 V63V. Would this work as well or will i have to order another cap?

 

[audioguru2]

Hi No Worries,
At a DC current of 3A, a 6800uF filter capacitor of a 60Hz mains that is full-wave rectified produces a ripple voltage of 1.85V peak which is a fluctuating loss of voltage which might cause hum at the output.
If the mains frequency is 50Hz then the peak ripple voltage is 2.2V.
Use two 6800uF capacitors in parallel.

 

[Mayhem]

Hi Mayhem,
Of course Q2 and Q4 should have a base-emitter voltage drop of 0.7V to 1.2V when there is a load. They are emitter-followers. Yours must be shorted from base to emitter.

Opamp U2 has an open-loop voltage gain of about 200,000 so it should amplify the small error to keep the output voltage from dropping when there is a load.

Hey Audioguru. I allready replaced both Q2 and Q4. Before the replacement i did a diode test with a multimeter on both transistors to verify if they had any problems. They had none. No shorts and only two voltage drops. I believe my problem is in this area because the output (pin6) of U2 varies according to the load, but i don't know where. Is there any other component (or problem in the pcb) that could cause this problem?  What is the function of R1?

 

[audioguru2]

with the voltage adjusted to 1,5V and connecting a load of 3,7 ohms i get the following table:
                         with load                   without a load
pin 3 of U2            0,5V                             0,5V
pin 2 of U2            0,49V                           30mV
pin 6 of U2            1,52V                           25,4V

I measured Vbe of Q2 and Q3 and i have always 0V, with and withoud the load connected. The only voltage drop i have is 66mV in Q2 when the load is connected.

1) Pin 3's voltages are normal because U2 and the output transistors have a voltage gain of 3.07.
2) Pin 2's voltage without a load is way too low. If the output transistors are working properly then the output voltage would be pinned as high as it can go. When the output voltage is 1.5V without a load then pin2 and pin3 voltages should be almost the same. If the output voltage tries to go a little too high then the negative feedback through voltage divider R11 and R12 increases the pin2 voltage slightly that causes U2 to reduce the output voltage. If the output voltage tries to be too low then the negative feedback reduces the pin2 voltage slightly that causes U2 to increase the output voltage.
3) The pin6 voltages are both wrong.
a) With a 405mA load the voltage should be 1.5V plus 0.7V for the base-emitter for Q4 plus 0.6V for the base-emitter voltage for Q2 plus a little voltage for R15. Then the pin6 voltage should be about  2.9V, not 1.52V.
b) Without a load the output voltage is way too high. It should be 1.5V plus 0.4V for Q4 plus 0.3V for Q2. Then the pin6 voltage should be about 2.2V, not 25.4V.

Check the transistor datasheets to see which pin is which.

 

[rcakto]

hey ppl!!
i buyed today some commponents but i have some problems... the zener diodes is bzx55c5v6 and bzx55c10, is it the same of bzx79c5v6 and bzx79c10???

and the diodes 1N4148 is all like zener diodes.. is correct or i buyed the wrong diode??

ty all XD now if all is correct i just have to buy trimpots, ics, bridge and capactors

 

[redwire]

rcakto    For the large cap you have lots of options to use,  one, two  or parallel several.  On one build I used 3  of these  661-EKMH630VNN562MR (mouser part #)    It doesn't need to be exactly 12,000uf.

 

[karthikeid]

hi

i am having only 10000uf/63V capacitor can i use it instead of 12000uf  ???

 

[audioguru2]

hi

i am having only 10000uf/63V capacitor can i use it instead of 12000uf  ???

It will be fine. The tolerance of a big electrolytic capacitor is wide so a 10000uf capacitor could be 8000uF to 15000uF.

 

[_TwisT_]

Hi all! Can anyone help me?

I've built this power supply. All worked fine. But when I try to load it (15-20 V, 1.5-2 A), C7 explodes. The load itself is a flyback (its primary winding, 5 turns of 1mm wire), which is driven by a power MOSFET. Could this be because of self-induction impulses?

View attachment 40535

 

[audioguru2]

Another member also had C7 explode in his power supply. He used the power supply to power a high power high frequency switching circuit.

Your flyback circuit also has high power and high frequency which exercises C7 too much.

Your flyback circuit should have its own pretty big main filter capacitor then the ripple current in C7 of this power supply project will be much lower.

 

[_TwisT_]

Thanks audioguru, I've added a capacitor (10000uF, 63V) in parallel with flyback, C7 no longer explodes (and even does not warms up).  8)

 

[fabio1]

I was wondering whether someone had a PCB layout file (Eagle or analogous) and would be willing to share it.  :

Thank you so much,
Fabio

 

[josko]

Hi, great design... but I need even more powerful one  ;D
How to modify this circuit to by usable for 2x 0-35 V DC at  0-12A ?
Because I have unused 1000VA transformer with output 2x 30V AC so it is about 42V DC on caps so I think that it would be sin not to use it.
I think that using more powerful transistors should be enough (do you know some more powerful sort usable in this circuit?), but what about that OPAMPs, do I have to use some sort for higher voltage?

 

[audioguru2]

The 30VAC transformer is needed because of the voltage loss of the main filter capacitor, output opamp, output transistors and current-sensing resistor. Then the output is regulated at 30VDC.

Two 2N3055 transistors can dissipate a total of about 140W when the heatsink is pretty big.
When the unregulated positive supply is +40V, the output is set to a low voltage or is shorted and the output current is set to 3A then they dissipate 120W.
For the 5A version we decided that three output transistors can dissipate a total of 210W.

You want 35V at 12A. Then the output transistors must dissipate 420W!!
You want two of them to heat your home.

In the long thread about this power supply, we discussed 80V opamps then finally 44V opamps that do not need the negative supply.

 

[Ich Will]

Hallo everybody!
That an output transistor did not warm up, offer here such regulator. He supports the difference of tension between an entrance and output of stabilizator equal 6v. Works, it is tested!
It is taken with http://radiokot.ru/circuit/power/supply/02/
You will forgive me my bad English  

View attachment 40549

View attachment 40550

 

[josko]

To audioguru:
Thanks for answer!

So is it possible to do something like this? To use it as symmetric power supply...

I don't want to have 2x 12A now, 2x 5A is enough for me, but transformer is capable of deliver such power so I want only know that there is such possibility with this circuit.
And also is there PCB design for this last version?

 

[audioguru2]

Hi Josko,
You are shorting the transformer.
The two power supply circuits must be fed from completely separate windings or separate transformers for the negative output of one to be connected to the positive output of the other.

Your kind of transformer could be used if one power supply regulates its positive voltage like our project, then the other power supply must regulate its negative output.

 

[josko]

Thats OK... actually, my transformer have separate windings. I draw it wrong on schematic.
This is photo of my monster transformer (it has 12 kg), that 9V battery is just for comparison sake.

And what about that PCB design?