Home     Contact     Projects     Experiments     Circuits     Theory     BLOG     PIC Tutorials     Time for Science     RSS     Terms of services     Privacy policy  
 Home      Projects     Experiments     Circuits     Theory     BLOG     PIC Tutorials     Time for Science   

This project is not completed yet - Last update: June 19, 2014
Lab Power Supply 0-20V 10mA-2AAuthor
Zoran Petkovic
June 5, 2012

PAGE 4 of 4 - Lets Strart Building


I tried to draw this schematic into recognizable blocks so lets go trough those blocks see what they do in circuit build them and test each block and its the order we build each block.

Block 1:


this block couldn't get any simpler 220VAC comes into primary of transformer and on the secondary we get 24VAC this is rectified by bridge rectifier consisting of 4 diodes then its fed to the high value capacitors for smoothing once we build this part time to turn it on and measure DC voltage across capacitors without load it should read ~32.44v �6v .

Now you might ask how come we get 33v on the output when we had 24VAC this is because on the AC scale of your multimeter multimeter takes only effective value of the AC voltage or RMS value real peak of the AC is increased by √2 or 1.41 so you take effective value in our case 24VAC and multiply it with 1.41 and we get 33.84 now we need to reduce this further for the amount of 2 diodes voltage drop, now in school i was taught that this voltage drop for silicon diode is about 0.7v but later you will find out that this value varies with temperature but lets just call it 0.7 for now, so 33.84-2x0.7=33.44v but in reality it should be close to that you will never get exact value calculated �6v for our application is fine. If it works proceed to next block.

Block 2:

Again simple block this block is just stable supply for the op-amps and voltage inverter it takes any higher voltage and spits out voltage set by the resistors. it consists of 3-Terminal Positive Adjustable Regulator chip LM317T 2 resistors which will set our output voltage and smoothing capacitors.

On schematic it is labeled that in that node we should get 22v but in reality i measured 23.5v which is totally fine. but here is how to calculate the output voltage, in datasheet we can find that Vout=Vref*(1+R2/R1) Vref is chips internal voltage reference which is 1.25v in case of LM317T now to calculate for our case Vout=1.25*(1+5100/300)=22.5v but again resistors aren't perfect and in this application they don't need to be precise they will also vary with temperature its why they are somewhat higher power there is no other reason, and again couple of capacitors to keep things smooth as possible

Block 3:

This block is voltage inverter it means that it takes voltage that is more positive then the GND and on its output gives voltage that is more negative in respect to the GND.

But why do we need such a contraption? Well its due to a fact that op-amps cant go to supply rails let me explain that if you supply op-amp with 22v on its output you will never get 22v or 0v it will always be close to those 2 extremes but in our application we need 0-20 volts on the output of the op-amp 22v is high enough to get 20v out but if we want to go to 0 volts output we would have to go lower then the GND thats why we need negative voltage anything lower then -2 and within a limit of what op-amp can handle is fine in schmatic is -6.6v which is fine

Continue reading. Click here to go back to the first page <<<.
 OR click here to view the presentation.



  Email (shall not be published)


Notify me of new posts via email

Write your comments below:
BEFORE you post a comment:You are welcome to comment for corrections and suggestions on this page. But if you have questions please use the forum instead to post it. Thank you.


  • At 12 June 2015, 17:27:05 user Wiki wrote:   [reply @ Wiki]
    • This power supply can be used to power amplifiers or lab, because the LM723 is a very good voltage regulator, with good specifications, like noise figure. It has sense voltage, feedback, overall protection. It is a way good comparing to LM317 series. It can be used for a final year project at university, if it has a documentation. I've seen at my university, final year projects like power supply with digital view of voltage.

  • At 26 February 2015, 7:23:46 user Zoran Petkovic wrote:   [reply @ Zoran Petkovic]
    • I uploaded PDF with my second populated unit pictures ( On presentation page click download file) it should be easy to build in one go but if you have questions ask them in comments ill spare some time to answer.

  • At 25 February 2015, 17:47:39 user Gamini wrote:   [reply @ Gamini]
    • Dear Zoran,
      Oh, Very sorry to here this. Now you're paying for some others mistake, But appreciate your courage. Wish you good luck and Gods; Blessings.

      Bes regards


  • At 22 February 2015, 14:00:42 user Zoran Petkovic wrote:   [reply @ Zoran Petkovic]
    • 3 months ago my house caught fire from neighbours burning house resulting in my house burning down to along with the computer with files for this build, my prototype burned down also but i redone schematic and even built a new unit i can post schematic PCB files and silk screen files AS IS. for now i cant write any text for it, at the moment im working 2 jobs to rebuild my home. anyway ill post files in PDF and they will be on first page

  • At 22 February 2015, 12:46:57 user Gamini Patabendige wrote:   [reply @ Gamini Patabendige]
    • Dear Sir,
      This is a very interesting and usefull project. When can you post the balance content?
      Best regards

  • At 12 December 2014, 22:01:51 user electronics-student-from-spain wrote:   [reply @ electronics-student-from-spain]
    • Any news? I'm a newbie electronics student at an electronics vocational trainingschool, I can get most parts cheaply or for free at the lab. I have zero incomes, so I must get smart and do my equipment in the DIY way.

  • At 12 September 2014, 20:03:01 user Zoran Petkovic wrote:   [reply @ Zoran Petkovic]
    • @george schematic have some mistakes also the pcb, once i get time to fix the files will write complete text im sorry i couldn't do this in one go but work i do demands a lot of my time stay tuned the prototype works really well will be worth waiting

  • At 12 September 2014, 18:15:00 user Giorgos Lazaridis wrote:   [reply @ Giorgos Lazaridis]
    • @george click on the worklog tab, you will find everything there

  • At 11 September 2014, 20:03:09 user george wrote:   [reply @ george]
    • Did you finish it? Where are the plans? How does it work?

    reddit this Reddit this

     HOT in heaven!

    NEW in heaven!

    New Theory: AC electric motor working principle

     Contact     Forum     Projects     Experiments     Circuits     Theory     BLOG     PIC Tutorials     Time for Science     RSS   

    Site design: Giorgos Lazaridis
    © Copyright 2008
    Please read the Terms of services and the Privacy policy