0-30 Vdc Stabilized Power Supply

[subodhthok]

Can somebody give me the principle and working of the circuit mentioning the function of each and every component. I'm a POOR SOUL.

I'll be INDEBTED!

 

[Fluffy]

Please show a new / up-to-date parts list!!

 

[audioguru2]

Subodhthok,
It is a simple circuit with opamps and transistors. When you learn about opamps and transistors then you will understand the function of each and every component.
The Articles section of this website has tutorials on opamps and transistors.

Fluffy,
My recommended parts list for this project has been attached many times and has not changed for more than one year. Here it is again:

0-30V_Mod_parts_list.txt

 

[valorous]

Hi again.
I've build the modified circuit. Everything seems to work. The voltage goes up to 34.5V and the current to 3.8A.
The op-amps U1 and U2 get very hot with no load, especially U1. I measured the voltage at pin7=46V.
Also I used two 2n3055 transistors with 0.33R emitter resistors but one of the transistors gets hotter than the other one. What can I do to fix the problem?
Also when I turn the current potentiometer half way the current increases to 0.5A. So when P2 is half turned the current is not half its maximum value. I'm not sure if this is a problem.
Thank you for the help.

 

[audioguru2]

Hi again.
I've build the modified circuit. Everything seems to work. The voltage goes up to 34.5V and the current to 3.8A.

Good, it works.
Trimpots can be added in series with the voltage and current setting pots to reduce their max outputs to 30.0V and 3.0A. Then the trimpots can be measured and fixed resistors can be installed.

The op-amps U1 and U2 get very hot with no load, especially U1.

The max operating current of the OPA445AP opamp is only 4.7mA x 46V=216mw. Its load is (46V - 11.2V) x 5.6mA= 195mW. The total power dissipation is a max of 411mW and its max is 1000mW. It will be pretty warm but it is fine. 

I measured the voltage at pin7=46V.

It is a little high but it is fine.
A 30VAC/4.3A transformer will be about 31.5VAC without a load. Then its peak voltage is 44.5V and the rectifier bridge drops it to 43V.

Also I used two 2n3055 transistors with 0.33R emitter resistors but one of the transistors gets hotter than the other one. What can I do to fix the problem?

The transistors are all different. That is why the emitter resistors are used to equalize their current gains. Yours must be very different. Use a 0.22 ohms emitter resistor for the coolest one then it will heat more. 8)

Also when I turn the current potentiometer half way the current increases to 0.5A. So when P2 is half turned the current is not half its maximum value. I'm not sure if this is a problem.

I think the action of the current-setting pot is supposed to be linear, so half rotation is 1.5A, but maybe not. Try replacing the pot.

 

[valorous]

Thanks audioguru for your quick response. I will try the tips you suggested.

 

[Steve_hi]

Hi I think I would like to try to make this 0-30Vdc power supply does anyone have a rough idea about how much it might cost

 

[Steve_hi]

I've been reading this thread and I see that there has been a significant amount of problems with this project heating up, with the schematic that is posted in the projects. I also see that audioguru has provided an updated parts list can some tell me why the person who maintains the projects doesnt update the parts list with the scematic  Just curious as to how things work ??? also If i use the new parts list is the schematic still the same
Thank you

 

[audioguru2]

Hi Steve,
The project is a kit. It overheats and does not have 30V/3A output. I don't know what the kit maker does about complaints to them about the kit.

We leave the original project in case somebody has built it and for us to talk about it. If somebody builds the improved version and updates the schematic then it might be made into a new project.

The improved circuit has the same pcb as the original except a few parts values are changed. A few parts are bigger but can be stood up, and Q2 needs to be mounted away from the pcb on a heatsink or its pins will need to be twisted around. A second 2N3055 output transistor was added to share the heat and emitter resistors are used for the output transistors to equalize their different current gains.

 

[akhtar-ece]

how can i modify this circuit to 0 to 50 v dc supply and also for 0 to 30 v 10A

 

[audioguru2]

how can i modify this circuit to 0 to 50 v dc supply

Re-calculate and replace every part in it.

and also for 0 to 30 v 10A

If it is set to 10A and the output voltage is set low or it is shorted then the output transistors must dissipate 420W. Use 6 output transistors on huge heatsinks with fans, use 3 driver transistors, add a pre-driver transistor and make many resistors larger.
A larger transformer, larger main filter capacitor and larger rectifier bridge will be needed.

It will cost a small fortune.

 

[eggy1]

Hi.
I have just built the PSU but surprise-surprise it does not work. Output voltage of the PSU is constantly 33V. Voltage between pin4 and pin6 of u1 is chancing from 0 to 9.9V when turning voltage pot.

I am using UA741 opamps. [+-22V]
Voltage over pins 4 and 7 is 38V on U3 and U2. On U1 it's 33V.
Chanced RV1 to 10k, short circuited R10[Like in the 741's datasheet]

What purpose has D10? Doesn't it just feeds all the output voltage directly to the base of Q2? R15 is heating....voltage on it is ~33V. When I remove all opamps the output voltage stays up. When I remove Q1 or both(!) of it's base resistors then output voltage drops to zero.

-Eggy

 

[audioguru2]

Hi Eggy,
Welcome to our forum. ;D
Q1 is not supposed to make the output voltage high. It is supposed to make the output voltage zero when the project is turned off. Q1 does not have a positive supply.

Maybe the base of Q1 or one of its base resistors is shorted to the positive supply. Then Q1 will turn on Q2 and Q4 through its forward-biased base-collector diode.

D10 is normally reverse-biased. It quickly discharges the output capacitor C7 when the project is turned off to avoid exceeding the max reverse voltage rating (about 6V) of the emitter-base of Q2.

 

[eggy1]

I know that Q1 is for bringing output voltage lo. Base of Q1 is not short circuited to positive supply, only through r13 which is not connected at the moment.
Let's assume that I remove Q1 temporarely, I loose thats protective idea in the circuit, BUT i should be able to chance output voltage, right? What voltage should be on pin6 of U2?

 

[audioguru2]

Hi Eggy,
If you remove Q1 then the circuit should work properly. Q1 quickly reduces the output voltage to zero when the project is tirned off, so that the output voltage doesn't rise.

Pin 6 of U2 should be about 1.4V higher than the output voltage without a load.
U2 and the output transistors have a voltage gain of 3.07 and amplify the voltage from pot P1.

 

[audioguru2]

You said pin 6 of U1 changes from 0V to 9.9V when turning the voltage pot. That is wrong.
Pin 6 of U1 should remain at 11.2V and the slider of the pot should change from 0V to 11.2V.

 

[eggy1]

a little mistake by me: Voltage on pin6 of U1 is 11V...
>>>and the slider of the pot should change from 0V to 11.2V.<<<
Which pin voltage should it change?

 

[audioguru2]

a little mistake by me: Voltage on pin6 of U1 is 11V...

Good. The zener diode and resistors are 5% so it is fine.

>>>and the slider of the pot should change from 0V to 11.2V.<<<
Which pin voltage should it change?

The slider of P1 connects through R8 and R9 to pin 3 of U2 which should change from 0V to 11V when the pot is turned.

Does the output voltage go from 0V to about +32V when the P1 pot is turned?
Did you find out what was wrong with Q1?

 

[eggy1]

The slider of P1 connects through R8 and R9 to pin 3 of U2 which should change from 0V to 11V when the pot is turned.

Yes it does.

Does the output voltage go from 0V to about +32V when the P1 pot is turned?

Nope

 

[audioguru2]

Before you said the output was +33V with Q1, and 0V without Q1.
What is the putput voltage and what is the voltage of pin 6 of U2 when the voltage pot is turned? Also, what is the voltage of pin 6 of U3 when the voltage pot is turned?