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LM350 adjustable voltage Regulator

The lm350 voltage regulator is 3A DC adjustable power supply IC – LM350 that high-performance. It can apply voltage output 1.25V to 35V. so have a few components. If you add two diode series with the output to reduce voltage start with 0-volts.

This circuit looks like in My first Variable DC Power Supply, but this high current higher than 3-Amp. Therefore they cause you can supply more any load circuit. Which we can buy this IC at many stores but expensive than LM317.

How LM350 variable power supply works

In Figure 1 you will see that the circuit form same the My first Variable DC Power Supply.

LM350 adjustable voltage Regulator
Figure1: LM350 adjustable voltage Regulator


When we apply AC220V or AC110V(for the USA) with pressing S1 to turn on this power supply. ACV will flow F1 for protection when the overload or too much voltage input.

Then the ACV will flow into a transformer that has the ability to transform voltage and current to lower levels of AC-18V and next to BD1-bridge diode to convert AC to DC.

Next, they will through C1-4700uF electrolytic capacitor smooth (filter) the pulsating voltage from a transformer into a steady direct current (DC).

Now we have voltage at this point is 22V to 25V

And then, the current will flow to the input lead of IC1-LM350 power supply.
Which it is an adjustable regulator IC that designed to many supplies for 3Amp output and adjustable over 1.2V to 33-volts, and with current limiting, thermal shutdown, full protection.

See LM350 datasheet

This circuit form I see in the LM350 datasheet, which there is a simple detail to do this:
– In normal operation, the LM350 have nominal 1.25V reference voltage (Vref) between the output lead and Adjustable lead (ADJ). This voltage will across R1+R2 (120 ohms+120 ohms = 240 ohms datasheet) and,
– since the voltage is constant, a constant current then flows through the output set resistor VR1. To adjust voltage output.
-C1, C4-0.1uF is input bypass capacitor, it needs if devices (IC1) more than 6 inches from filter capacitors.

-C3-47uF is bypass capacitor prevents 86dB ripple rejection.
-C5- 100uF is used to improves transient response. Output capacitor in the range of 1uF to 1000uF of tantalum electrolytic is commonly used to provide improved output impedance and rejection of transients.

Protection Diodes
When external capacitors are used with any IC regulators, sometimes necessary to add protection diode to prevent the capacitors from discharging through low current point into the regulator.

Although the surge is short, there is enough energy to damage parts of the IC.

When negative voltage or 20A spikes flow backward the output it will be absorbed voltage with D3-diode.

And Then D2 to protect Out and Adj lead.
And D1 is protected voltage spikes to Input and output lead.

Components list
IC1____LM350T___3 terminal positive voltage regulator 3Amp_____= 1 pcs.
C1_____4700uF 35V Electrolytic capacitors______________________ = 1 pcs.
C3_____47uF 35V_________”_________”___________________________ = 1 pcs.
C5____100uF 50V_________”_________”___________________________ = 1 pcs.
C2,C4___0.1uF 50V_ ceramic capacitors__________________________ = 2 pcs.
BD1_____4A 200V brigde diode__________________________________ = 1 pcs.
D1-D3____1N4007___1A 1000V Diode_______________________________ = 3 pcs.
R1,R2____120 ohms 0.5W resistors______________________________ = 2 pcs.
VR1______Variable Resistors___ 5K(B)___________________________ = 1 pcs.
S1______On-Off or SPST switch__________________________________ = 1 pcs.
F1______0.5A Fuse______________________________________________ = 1 set.
T1______3A 18V to 21V transformer_____________________________ = 1 pcs.
Heatsink, PCB, wires, and others

Make LM350 power supply

The circuit has a few parts you can assemble devices on perforated Board and wiring as Figure 2
The IC1-LM350 power supply must be mounted to big size heatsink because at work times it is very hot.

we assemble and wiring parts on perforated board
Figure 2 we assemble and wiring parts on perforated board.


Before check circuit and wiring for error. Then adjust VR1 to a minimum. Next, we test this project with apply voltage output is 1.2V You can watch the video below. Then adjust the voltage to 12V.

And next, I try to use 12Volts 50watt lamp as the load. The voltage will must not lower than 12V and I measure the current of the lamp of 3.5A.
This project is good as we need to. We are happy. Thank for watching.

This Post Has 23 Comments

  1. Good-Morning! First, I would like to express my congratulations and my thanks by your site. Forgive me, but, I think the english that you put in your posts is a little confused. It would be possible, to you, improving this situation? You see, sometimes is very difficult to me, to understand the text; first,due my bad english, secondly, because I´m a electronics begginer.

    Best regards

    José Mota

  2. I Love This Power Supply Circuit!!! I Built A 3 Amp Power Supply Years ago..Instead of a 3 Amp Transformer I Used a 4 Amp Transformer To Allow For A Certain Degree Of Headroom,Anyway This Is Still A Great Design!! Thank You (For more Than 1,000 Times) For A Most Excellent Site For all These Great Circuit Ideas!!! This LM350T is A Handy Dandy Power Supply To Have on any Test Bench!!Happy Building EVERYONE!!

  3. Hi, MR OHM 1970

    Thanks for your feedback.

  4. @admin,,,Thank You For letting me come back to a most Excellent Electronics site!!! I love these Electronics Projects,,So Many Circuits So Little Time!!!

  5. oh.. this circuit is easy weekend we will make it. is circuit work?

  6. @mics.
    It worked please watch in video and you can builds them as circuit diagram.
    Be careful assemble in wrong positions or lead. check error before apply input AC voltage.


  8. Hi,Ali
    Thanks for your feedback.
    You can use both capacitors
    50V will less expensive than 35V.
    But now I have 50V a lot. so use it in this circuit.

    Thanks again for observing.

  9. Can i use LM338 in this circuit

  10. Hi,fahad
    Thanks for your feedback.
    Yes, you can.

  11. hi, im really a beginner in electronics. I am just confused with the polarity of the LM350, you drew that it should be 1-adjust,2-out,3-in, but you used it in your diagram as in-adjust-out?

  12. thank you , About this site

  13. Hi lance,
    the position pins of this ic not same between real body and circuit diagram. I see pin then assemble as circuit.

  14. I done this circuit .But the (C5____100uF 50V) burst .I don’t know .Why?
    I need an answer

  15. Hi Ammar,
    Please polarity of C5 maybe wrong.
    or the output high voltage over 50V.

  16. How we add short circuit protection to this power supply

  17. Hi.
    I did this regulator, but on the outputs gives me only 0 to 4.5v. Where did I go wrong?

  18. I fix the problem. I have bad LM350.

  19. Hi, what i must do to make this 0-16v 2a , in power is 18v 2a , i need this for motor dc

    1. Hi Mateusz,
      Thanks for your question.
      You have many choices.
      1. This circuit but cannot begin with 0V. It begins with 1.25V.
      It begins with 0V. However, an output is lower current in a two series diodes.
      It works well. But it is a difficult circuit, too many parts.

      I hope you can build a circuit that control your motor soon.

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