Many electronics circuits and projects for learning in simple ways.

0-50v variable power supply circuit, at 3A using LM723

This regulator is 0-50v variable power supply circuit. It can adjust output voltage wide range between 0V to 50 volts, and current at least 3A.  The important is the overload protection. It will immediately cut off when a load short circuit.

The output is a voltage regulation circuit. Because they use IC-LM723 ICs to provide better performance. So it is suitable as a power supply circuits for various experiments.

Now we have this project that covers almost all applications.

0-50V 3A Variable power supply

Because it can adjust the output voltage between 0V to 50V. Because we use 2SC5200 transistor to replace the 2N3055 old transistor.  2N3055, though very ancient but it still has many uses we like it.

And also apply current to 3A which better than DC Variable Supply 0-50V, 2A. Hope you will like it.

Technical information

  • Uses the transformer, size voltage: 24V – 18V – CT – 18V – 24V , at current : 3A  to 4A
  • There is an overcurrent protection to prevent damage to the circuit
  • Adjustable Voltage between 0V to 50 VDC (Depending upon  the AC supply voltage of Input)
  • Can apply maximum current to 3A

Working of 0-50v variable power supply circuit

Figure 1 is the circuit diagram of this project.

First of all, the AC-voltage from the transformer-T1 flows through diode D1-D4 to the rectifier to DC voltage.

Second, capacitor-C1  filters that pulsed DC voltage to smooth, before sent through R1, R2 into TR5.

The circuit diagram of 0-50V 3A Variable DC power supply
0-50V 3A variable power supply circuit

And there are IC1 is used to control a voltage at OUT point by adjusting VR1 can adjust voltage between 0-50 volts.

0-30V Variable Power Supply at 3A’ »

Two resistors R1 and R2 limit the overload current. They work together with two transistors TR1, TR2.

When the current exceeded, TR1 and TR2 will work. Then, there is an output voltage at lead E  of TR2 through LED1 into 2 pins of IC1.  LED1 is an alarm display.

Thus the circuit stops to provide voltage to the output.

We need to use normal load current that under lower than 3A.
After that, press the switch-SW1 to reset the system to restart working circuit again.

How to make the variable power supply circuit

This project has quite many components. You should experience a modest electronic. You can use the perforated PCB. As components layouts in Figure 2
The components layout and wiring
Figure 2 The components layout and wiring

If you want to build this circuit. I have designed this with

First, Schematic diagram of 0-50V, 3A variable power supply circuit
Schematic of 0-50V, 3A variable DC power supply

Second, Actual-size of Single-sided Copper PCB layout in this project.
Actual-size of Single-sided Copper PCB layout
Print it on 300dpi.

Component-layout of 0-50V 3A variable DC power supply
Third, the components layout of the variable power supply circuit

Components lists of LM723 power supply


  1. IC1 = LM723—High precision voltage regulator  = 1 pcs.
  2. TR1 = BF423—PNP transistor = 1 pcs.
  3. TR2,TR3 = BF422—NPN transistor = 2 pcs.
  4. TR4 = BD140—PNP transistors = 1 pcs.
  5. TR5 = 2SC5200—NPN transistors = 1 pcs.
  6. ZD1 = 36V 0.5W Zener diode = 1 pcs.
  7. D1-D4 1N5401—3A 100V Diode = 4 pcs.
  8. LED1,LED2—LED 3 mm as you want = 2 pcs.


  1. R1,R2 = 0.1 ohms 2W = 2 pcs.
  2. R3 = 56 ohms 0.5W = 1 pcs.
  3. R4,R10 = 100K 0.25W = 2 pcs.
  4. R5,R8,R20 = 10K 0.25W = 3 pcs.
  5. R6,R22,R23 = 1K 0.25W = 3 pcs.
  6. R7 = 15K 0.25W = 1 pcs.
  7. R9 = 2.7K 0.25W  = 1 pcs.
  8. R11,R12 = 5.6K 0.5W = 2 pcs.
  9. R13,R17 = 8.2K 0.5W = 2 pcs.
  10. R14,R15,R16 = 10K 0.5W = 3 pcs.
  11. R19 = 330 ohms = 1 pcs.
  12. VR1 = 10K potentiometer  = 1 pcs.

Ceramic capacitors
C6 = 470pF 50V = 1pcs.

Mylar Capacitors
C2,C7 = 0.1uF 100V = 2 pcs.

Electrolytic capacitor

  1. C1 = 2200uF 63V  = 1 pcs.
  2. C3 = 47uF 50V = 1 pcs.
  3. C4,C5 = 10uF 50V  = 2 pcs.
  4. C8 = 100uF 63V = 1 pcs.
    SW1_____Reset switch normally open pushbutton_____= 1 pcs. PCB,wires,heatsink,nut,screw,and other.

Note: You can buy this KIT here:

Keep reading: ‘0-70V,2A DC variable power supply’ »

Mounting transistor to the heatsink
When load uses too much current, 2SC5200 is also too heat.
Thus, we must mount the large size heatsink to save 2SC5200.  We can install 2SC5200 transistor to the heatsink as Figure 3.  It is a proper way of mounting the transistor in a heatsink. Using hex nut and metal screw to mount them together by use mica insulator to protect the short circuit.

The mounting the transistor on the heatsink
Figure 3 The mounting the transistor on the heatsink

Connecting the transformer
We see in Figure 2. If you want to use output voltage are 0-50VDC, can connect 18,24 terminal. The output 0-30VDC can connect 0,24 terminal and The output 0-20VDC can connect 0,18 terminal.

connecting wrong polarity voltage is low

But I cannot buy the transformer as Figure 2. So, use 2 transformers to connected with 0-18V and 0-24V in series.  18V+24V = 42V AC
If connecting is the wrong polarity, the output voltage will be low. As Figure 6, the output is 5VAC only.

It means that you connect the transformer wrong. Must return a new polarity wire. We will read voltage about 43V.

Eventually, we will have a successful circuit

Simple Testing and Repair

Connect the transformer as shown in Figure 2. Use a coil of a transformer to match our needing. Then measure the voltage at OUT.

Be careful!! Check and Check again!
Check for error before power on the circuit.

Then, use a voltmeter to measure the voltage at the output. hold it!
Next, supply the AC main to the transformer. While we read voltage the output 0-50V, begin to adjust the VR1.

As Video below.


The repairing
If this project is not working. Please check and check it again. Often, caused by wearing the wrong device position and soldering. Make sure that all the various solder points.

Answer the Question
Mr balasaheb desai: You can use 15V 0 15V transformer, you not use CT or 0 terminal. I think you will have the maximum output voltage of about 40V. Yes, you can use 20K pot, But you should add 20K resistor in parallel with this 20K pot.

See in the picture below, the total resistance is 10K the same in the circuit.

Keep reading: ‘0-30V 0-5A regulated variable power supply’ »

This Post Has 52 Comments

  1. Thank you it useful for us.

  2. hi can we power electromagnets with this circuit

  3. hi can we power electromagnets with this circuit & is it possible to vary output current

  4. Hi, where did you buy the KIT?

  5. pls i need the component to build this power supply circuit for my school projec
    i am in abia state Nigeria
    tnks for a prompt reply

    I cannot send the parts to you. 🙁
    Please visit the store near your house.
    They are cheap and easy to buy.

  7. hii yr ckt is useful but the transistor 2sc5200 is not available everywere so ., tell me another transistor insted of this , i can use in this ckt thank u

  8. Hi, is possible to modify the schematic for current control as well? I use this regulator for 0-50V, 0,3A. I would like to build regulator with voltage and current control (0-50V and 0-4A). Thanks

  9. I thank you

  10. Hi MOMENAME, Thanks for the scheme. But, i only have transformer with 15v and 18v 2A. On the scheme shown above, 18v + 24 v= 50v max.. How about 15v + 18v?? How many volt and ampher i’ve got from 15v and 18v??

    Greetings from indonesia 😀

  11. I think pin no 11 and 10 of IC LM723 are interchanged by mistake….Hope you correct it.


  12. it’s really a interesting design but i suggest to put a 470 pF capacitor between pin 5 and pin 13 to get less ripple on the ouput.
    @Tania the pins are the right ones because he is using the lm723 to drive first the pnp transistor than the npn power transistor.
    @Adrian Bondan the maximum output voltage it’s pretty close to the DC input voltage so you can find it with the formula Vdc=(Vac-1.4)*1.41, (this circuit should be able to regulate every voltage with some little changes) but be careful because when you change the input voltage you have to change the electrolytic capacitor voltage rating and capacitance.
    @prashant (even if it’s a bit late but i hope that it can also help other people) you can use every transistor with a Vceo and Vcbo higher than the circuit V output and a Ic higher than the maximum current output of your circuit

  13. i ve tested this circuit … but why i just got 5Volt as lowest voltage and not zero … .. there’s someting wrong ? i ve interchanged pin 11 and 10 but the voltage wont changed when i turn the VR , still at 42V .. the input voltage ac was 18v and 12Vac .. and the output from capacitor filter was 41VDC …

  14. Please how can i get the PCB design of the circuit?

  15. Please mail me the PCB lay out

  16. Please, can You sand me PCB layout.
    Thank you

  17. Please, can I get PCB layout.
    Thank you

  18. Hi Goran,
    Please look in post again.

  19. Dear sir can i very the above mentioned power supply with single 20k pot. means i have done dual (15-0-15) power supply and i have to very both power supply with single 20k pot.
    Please provide some solutions. thanks

    1. Hi balasaheb desai,
      Thanks for your Question please see the post. It may be your the solution.

  20. I feel this is one of the sᥙch a lot vital information for me.
    And i’m satisfied reading your articlе. However should
    obsеrvation on few normal issues, The website style is perfect,
    the articles is actually grеat : D. Good job, сheers

  21. hello dear sir
    i would love to know if you could possibly inform me of pcb sizes .
    it is very important
    thank you

  22. What is the word on how to series these safely with a single control to push 5ish amps?


    1. Sorry…obviously I mean how would one parallel these? Would it be possible to get two to provide 5A at 50V with minor modification. I would want a single pot to control voltage.

  23. hai sir
    i created the circuit as per circuit diagram but,i got 26v to 35v when i connet a 36vtransformer,its output potection is not working, when out put is short the TR4 will damaged,&how can i receive below 26v on the output?pls Help Mail me your comments.

  24. Hello,
    I have build serveral times power supplies like this one with the lm723 for different output voltages.
    But the problem is always I cannot control the output voltage to 0 volt.
    I exchange the lm723 and the transistors nothing helps.
    Any idea

  25. Do not waste your time. This circuit is not working.

    1. Hi Ericson,
      Thanks your feedback.
      This circuit is working surely. It is Kit.
      Please check your project again. The wires or components may be error!
      Good luck.

  26. 10 cherywood ave. wahroonga 2076 NSW Australia

    1. Hello WALDIR ROLDAO,

      Thanks you comment. But I don’t understand.
      What are you mean?

  27. Hi,
    I need one pcb of power supply 50v-3A in Tehran-IRAN.
    where can i get this pcb in tehran
    please help me!

  28. Hello, can you send me the PCB layout pretty of power supply 50v-3A please?
    its:[email protected]
    Thank you.

    1. Hello falcon,
      Thanks for your feedback.
      I will send you next Tuesday.

  29. Good evening admin, my name is Sakis your procect is amazing and I have a issue about protect of circuit, it does not work, may you help me?
    Thanks a lot!

    1. Hello Sakis,
      I am sorry to hear that. This circuit should work as its function.
      You do not worry, you can check it slowly.
      First, check the component as a circuit diagram.
      Second, test it by adjusting at low voltage like 3V.
      Third, short circuit the output, suddenly LED alarm light up and the output is zero.
      Fourth, we reset it, press SW1.

      I hope this helps you, If it still does not work, please tell me.

  30. Buenas tardes, una consulta, es posible que en la placa de circuito impreso haya que cambiar la ubicación de las patas de TR2, base por colector al montarlo?, agradezco sú respuesta. Muy buen artículo. Gracias
    José Luis de Aza
    email: [email protected]

  31. Hola buenas tardes, una consulta, es posible que el TR2 en la placa deba ir montado con sus patas cruzadas, base por colector, con respecto al circuito esquemático?, agradezco sú respuesta.Muy bueno el artículo.

  32. Thank for sharing. People like you make the electronic world. First,please send me by email your PCB layout. Secondly, what do you think if I add a couple of bypass transistors to increase the current capacity?


  33. Please , I need Help . lm723 gets hot and there is no output voltage , it’s zero volt and protection led is turned on when increase the potentiometer . there is no any short circuit ,I tested it ,

    1. Hello, Kirollos
      Thanks, you are interested in this circuit.
      If IC-723 is hot. You need to check it again. Somethings may be short circuit. Or the pins is wrong. When LED alarm show. the output is OV, no load. Then, you press the reset Switch. To restart circuit. I hope your project will finish. Have a good day.

  34. hy its Athar here
    can you send me the PCB layout of power supply 50v-3A please?
    [email protected]

    1. Hi, Athar Ashraf
      Yes, you can. You may click in PCB layout photo in this article.

  35. i click on that pcb photo…but it spreads all over the page..means it loooses its original size and became very big…i tried many ways to get real size but failed…plz help me…..

    1. Hello, Athar Ashraf
      You should it on a laser printer. Important, you should set it 300 dpi per inch.

  36. why is it that in the diagram, you have only 1 LED? but in the video you have 2? im sorry i saw the difference because i also did this as my school project and im almost done with it. why is it that above and below the 5401 diode you have a resistor and top and LED at the buttom but its not in the diagram? i hope you reply asap. thanks

    1. Hello,
      In circuit has 2 LED, check again. I am sorry I not clear you said to me. My English is poor.

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