Jump to content
Electronics-Lab.com Community

0-30 Vdc Stabilized Power Supply


Sallala
 Share

Recommended Posts

Hi Esil,
Welcome to our forum. ;D
People have made the original project and report that the max output is only about 25VDC at about 2.5A. I made a list of the circuit's voltage losses to show why.
The transformer's voltage rating is too low for the project to have a well regulated output of 30VDC at 3A. Even with a 24VAC transformer, when the load current is low then two of the opamps have a total supply voltage that is much higher than their absolute max rating of 36VDC. Therefore opamps with a higher supply voltage rating are needed anyway.

Transformer manufacturers make transformers with many different output voltages and the 30VAC that I recommend for this project is one. 

Link to comment
Share on other sites

  • 2 weeks later...

r21 is in correct place.
Short history of my problem :
When i start power supply first time everything was ok. current limiter worked etc... but when i short circuit output then q4 burned, i replace q4 with new 2n3055 and q2 with bd243. Now when i short output curent limiter  work v out = 0v but led dont light. In normal operation current limit is work "too good" :) when i turn P2 only little led light and v =0v

Link to comment
Share on other sites

U3 is supposed to compare the voltage across R7 caused by the load's current, with the voltage from P2 which is from nearly nothing to 1.7V.
With P2 at max and the voltage from P2 at 1.7V then U3 does nothing until the voltage across R7 is slightly more than 1.7V which would be caused by a load current of 1.7V/0.47= 3.6A. If P2 is set to half then the load current must exceed 1.8A for U3 to begin reducing the output voltage.
Q3 conducts and turns on the LED whenever the output of U3 drops to begin reducing the output voltage.

Maybe your R7 has also burned and is now a much higher value.

Link to comment
Share on other sites

  • 3 weeks later...

Hi Rufinus,
Welcome to our forum. ;D

It must be a big transformer. Use one of the 24V/5A windings, it is probably 48V with a center-tap. Insulate the other 24V wire.

The voltage adjustment for your project will try to make the output exceed 24V and then settings higher will be full of ripple. Maybe you should add a resistor in series with the voltage adjustment pot to limit the max output voltage to a little lower than where the ripple becomes noticeable with full load.

Link to comment
Share on other sites


Now, i remember few pages ago you posted new version of mod with 2 trimpots for V/C limiting, i guess i should use that one?

Adding both trimpots is a good idea. I forgot that the current adjustment pot will try to make a max current of 4A which is way too high.

Parts list stays the same ( 0-30V Mod parts list)?
Link to comment
Share on other sites

Went for a walk and had an idea. Surely i want to have an volt/ammeter built in.
Digital one. One way is to buy standard models such as 7021 based. I thought of making one myself. I have spare PIC16F870 which has four 10 bit A/D converters on board. And i just bougt two 2x16 LCD screens on ebay. The question is, how to make multimeter out of this. Software for conversion i can write, but how to interface 0-24 volts to 0-5 volts of PIC? Hardware is my weak point :(
Besides simple multimeter it is possible to output other info on screen too, such as how mant watt load is consuming, temperatures of power transistors, control of the cooling fan... Any ideas will be appreciated. In the case of success i could share a firmware for PIC here on forum. If anyone interested....

Link to comment
Share on other sites

Yes, thank you, audioguru, but i already saw it. It is based on a chip from Atmel plus it is a surface mount version of chip, which will be difficult to mount for beginners. I work with PICs and program in PicBasic.
There is no sourse code for development and in general schematics and project are not very clear, at least for me.

Link to comment
Share on other sites

Guys

You have been awesome supporting this project. I have built this PSU (see attached) but need some help!

I have a step-down transformer with 2x75VA secondary windings. If I connect them in series I get 34.0v AC and 52.0v rectified. This I think is too much for the OPA445s, in fact I know it is because 2 of them blew up after I connected it  ;D

As a test for the circuit, I disconnected one of the secondary windings and replaced my dead OPA445s with 60p TL081s. With P1 cranked up, I measured [email protected] across pins 3 and 4  8)

With the 2 windings connected, the reference voltage is ok - 5.6v appearing across D8 - and 11.v at pin 6 of U1. U2 is not happy though, he gets an input voltage at pin 3 proportional to P1's setting but nothing at pin 6.

What's my best bet? Upgrade R1? If so, what to?

Thanks fellas
spy

post-20144-1427914309026_thumb.jpg

Link to comment
Share on other sites

Hello All.
I am new to electronics, can anybody help me about some questions?!
First i want to know how the voltage in output of U1 gradually increases till D8 turn on?
And my second question is about the current limiter; in fact i read the explanations but i wonder if some body explain more about how it work...
I'm sorry for my stupidily questions...

Many thanks,

Link to comment
Share on other sites


I have a step-down transformer with 2x75VA secondary windings. If I connect them in series I get 34.0v AC and 52.0v rectified.

52VDC is much too high for many parts of the circuit.

This I think is too much for the OPA445s, in fact I know it is because 2 of them blew up after I connected it

The OPA445 has an absolute max supply voltage of 100V. The factory tests them at 80V. Your circuit gave them a total supply of only 52V + 5.6V= 57.6V but had them dissipate too much heat and they melted. The heat is caused by the supply voltage times their output current.

U2 is not happy though, he gets an input voltage at pin 3 proportional to P1's setting but nothing at pin 6.

Then either U2 is broken or its output is shorted. With a 52V positive supply, maybe Q1 is turned on which would short the output of U2 to ground. Q1 is turned off by R14. The vaue of R14 was 1.5k for a 35VDC positive supply, then was changed to 1.2k for a 43VDC positive supply. R14 should be about 1k for your 52VDC positive supply to make sure Q1 is off during operation of the circuit.

What's my best bet?

Get a 30V/4.3A 130VA transformer.
Get a much bigger heatsink and mount it on the outside of the case.
Link to comment
Share on other sites


First i want to know how the voltage in output of U1 gradually increases till D8 turn on?

U1 doesn't have a negative supply so its output can go only positive.
R5 and R6 provide positive feedback so that the output voltage is double the voltage at pin 2.
The output voltage begins a little positive and the positive feedback increases it until the zener diode conducts at 5.6V, making pin 2 also 5.6V and then U1 makes its output double at 11.2V.

And my second question is about the current limiter; in fact i read the explanations but i wonder if some body explain more about how it work...

U3 is used as a comparator. It compares the voltage across R7 due to load current, with the voltage setting of the current-setting pot.
When the voltage across R7 exceeds the voltage from the pot, then the output of U3 goes low which causes D9 to conduct and pull down the voltage at the input of U2. Then the output voltage decreases, reducing the load current until the voltage across R7 equals the voltage at the current-setting pot.

post-1706-14279143090779_thumb.gif

Link to comment
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

Loading...
 Share

×
  • Create New...