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LM350 adjustable voltage Regulator

The LM350 voltage regulator is 3A DC adjustable power supply, 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 it works

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

LM350 adjustable voltage Regulator circuit
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 3 Amp output and adjustable over 1.2V to 33-volts, and with current limiting, thermal shutdown, full protection.

LM350 datasheet

How to use LM350? Which there is a simple detail to do this:

The LM350 is best for you. Because it is the adjustable three-terminal positive voltage regulator.

Which it looks like a popular LM317. We can set the output voltage with only two external resistors. But It can supply the output current over 3.0A, on the voltage range of 1.2 V to 33 V. In addition, it uses internal current limiting, thermal shutdown, and safe mode.

We can use the LM350 on a wide variety of applications. For example A simple adjustable switching regulator. A programmable output regulator. A precision current regulator. With connecting a fixed resistor between the adjust and output

LM350 Pinout

LM350 pinout
LM350 pinout

As in the LM350 pinout above. It looks much like the popular LM317. Also, its pin output connects the heatsink surface. Caution!
Since it has high current over 3A, we must mount the LM350 on the large heatsink.


Basic Features

  • 3.0 A Output Current
  • Output Adjustable Voltage from 1.2 V to 33 V
  • Load Regulation Typically 0.1%
  • Line Regulation Typically 0.005%/V
  • Internal Thermal Overload Protection
  • Internal Short Circuit
  • Current Limiting Constant with Temperature
  • Output Transistor Safe Area Compensation
  • Floating Operation for High Voltage Applications

LM350 VOLTAGE REGULATOR CALCULATOR
We love it because easy to use. You see LM350 circuit below. We use only 2 resistors to control the output voltage. The formula is:


Vout = 1.25 x {1+(R2/R1)}

LM350 Basic circuit
LM350 Basic circuit

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.

Capacitor filters

  • Both C1 and C4-0.1uF are 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.
  • Then D2 to protect Out and Adj lead.
  • D1 is protected voltage spikes to Input and output lead.

Components list

IC1_LM350T 3 terminal positive voltage regulator 3Amp
C1_4700uF 35V_Electrolytic
C3_47uF 35V_Electrolytic
C5_100uF 50V_Electrolytic
C2,C4_0.1uF 50V_ ceramic capacitors
BD1_4A 200V brigde diode
D1-D3_1N4007___1A 1000V Diode
R1,R2_120Ω 0.5W resistors
VR1_Variable Resistors_5K(B)
S1_On-Off or SPST switch
F1_0.5A Fuse
T1_3A 18V to 21V transformer
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.

Testing

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 the 12V 50W 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.

Increasing Performance

Also, we can increase the performance of this project as follows.

  • add voltmeter to display a level voltage.
  • add potentiometer for fine adjusting like an LM317 power supply.
  • High current—When actually using, we should use a soldering iron to increase the size of the conductor wire. Because the current flows through input, output and ground are too much.
  • While it is running. It is so hot. We should add a cooling fan.
    add cooling fan

 

Then, We assembled this project on the ABS Plastic Electronic Project Junction Box in Enclosure Case.
Because the drill is easy to install as an electrical insulator And cheap too.

LM350 adjustable voltage Regulator project

Look at! We finished the LM350 adjustable voltage Regulator project.

Buy it here: LM350 Linear Voltage Regulators
LM350 – Voltage Regulators – Linear

Related Posts

  1. 0-12V Variable power supply
  2. 0-50V 3A Variable Power Supply Project
  3. RF power supply circuit with RFI elimination

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.

  7. THANKS.GOOD SITE
    IN TEXT YOU SAY C3 IS 35V BUT IN PICTURE 50 V?
    WHICH ONE IS TRUE?

  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.
      2. https://www.eleccircuit.com/0-12v-variable-power-supply-at-3a/
      It begins with 0V. However, an output is lower current in a two series diodes.
      3. https://www.eleccircuit.com/cheap-adjustable-0-30v-3a-laboratory-dc-power-supply/
      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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