Variable power supply using LM317 circuit

If you are beginner in electronics and you want to have good variable power supply using LM317. This is best project that design for you. It can supply voltage 1.2V to 30V at all range is 1A.

New update Please read below this article.

Variable power supply using LM317, 1.2V to 30V at 1A

This is the First DC power supply in my life that made to use in many projects. It is ideal for those who want to adjust voltage from 1.25V to 30V and currents up to 1A. Which is sufficient for normal use Such as is power supply instead of an one 1.5V AA battery or when you want to listen to music from a 30-watt amplifier that required voltage of 24V 1A, it can be done easily.

In the days before that we commonly used the transistor that is very difficult, large, and probably more expensive ICs. But this circuit can be created with a single IC is lm317 based variable power supply.

The LM317 or LM117 series of adjustable 3-terminal positive voltage regulators is capable of supplying in excess of 1.5A over a 1.2V to 37V output range,
And has many special features that I like are :
• Output Voltage Tolerance 1%
• Line Regulation 0.01%
• Load Regulation 0.3%
• Prevent the deposition temperature.
• Short-circuit protection.
• Ripple is eliminated with ratio of 80dB
• Maximum input voltage 40V

The working of circuits
Followed circuits below, the transformer T1 is changed a AC 220V down as AC 24V to the bridge diode rectifier D1(1N4001) to D4(1N4001) there is dc voltage into the filter capacitor C1 equal to DC35V
The output voltage from IC1 Depending on the Voltage Adj pin of the IC. Or to adjust the VR1.
The VR1 is control output dc voltage 0V(1.25V) to 30V(32V) or 37V maximum voltage at 1.5A max all range.

Circuit Diagram of My First Variable DC Power Supply 1.25V to 30V at 1A using LM317

Calculate the LM317 output voltage

And we can calculate output voltage equal to:
Vout = 1.25 x {1+ (Rp/R1)
– Vref = 1.25V
– Typically R1 is 220 ohms or 240 ohms as datasheet. I use 220 ohms.
– Normally as datasheet I see them use VR= 5K (Pontentiometer) But I have VR-10K only since it easy to use.
Rp = {(VR1 x R2) / (VR1 + R2)}

Then we test it,Suppose, rotate VR1 to lowest resistance cause Rp = 0 hms. put it in formula above:
Vout = 1.25 x {1+(0/220)}
= 1.25V
But when adjust VR1 to maximum resistance VR1 and R2 are parallel together. Rp = 5.46K = 5460 ohms. test it in formula above:
Vout = 1.25 x {1+(5460/220)}
= 32.2V

Then the capacitor C3 is Better performance filter of IC1.
The diode D5 and D6 ( both is 1N4007) is the protector from external voltage to reverse to makes the damage to the IC1.

How to builds

If you want to see PCB layout and component layout and fully content.
This is first ebook.

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Many begin friends tell me this project difficult to adjust voltage output. so I add potentiometer 1K and parallel 1K-resistor together. then connects them to VR1 as Figure below.

add function thoroughly adjust voltage output

connecting two potentiomers

You will see that we can adjust the voltage at VR2 (new) is 4volts since resistance sum of 500 ohms approximately.
For example, I set voltage is 9V with rotate VR1 is 8.00V and rotate VR2 easily to control the output voltage of 9.00V.
View in video below.

I assemble in the universal box to use easily.



I have old a transformer 12V CT 12V output, but I measure it as 30.9V too much voltage.
It may cause overvoltage DCV as 30.9V x 1.414 = 43.7V. Which can be damaged to IC1 by too much current.

So I modify another transformer 12V CT 12V and 0V 6V 9V 12V output into 21-volts.
as Figure below

This circuit perfectly works, as the video below. I can adjust voltage output is 1.25V to 27V since I use the 21V output transformer.
If you can adjust 24V or 12V CT 12V it causes output up to 30V but IC overheat when a short circuit or overload.

I test circuit with the 12V 8W lamp as a load. A steady (DC) Voltage will not be transferred from 12V.

Add LED Voltmeter display

DC 0-30V 3 Wire Green LED Display Digital Voltage Voltmeter Panel
We can add LED voltmeter to show a voltage level of output.
Mr. Ali Mohammed, ask me how to use 3 wires voltmeter, red, black, and yellow.

It is a good idea. It’s accurate and more convenient.
Block diagram of adding a voltmeter to the first power supply-min

Block diagram of adding a voltmeter to the first power supply

In the circuit diagram, it needs an External DC power supply. We have to build a 9V DC regulator for it.
Please read this idea: Diy digital voltmeter panel meter

We connect a bridge diode (D1 through D4) to SEC (0 and 12V) of a transformer. Then we connect the measure voltage wire in yellow (+) to the output LM317 power supply. And Ground to (-).
Just this we can already read voltage output.

If you use other AC voltage such as 24 volts. You must change:

  • C1 = 1,000uF 50V Electrolytic capacitor
  • R1 = 1K 0.5W resistor

This so saves and easy circuit.

and then…

Low noise LM317 adjustable voltage regulator circuit

This is also LM317 based variable power supply and Low noise, adjustable voltage output: 1.25V to 10VDC (0-12V) from 12V battery source, so simple circuit

If you have a 12V battery. But you have load to use the voltage 1.5V to 9V at 0.75Amp And should reduce the noise as well. Search-based circuits. We use IC LM317K main equipment.

This circuit is DC converter low voltage , 12V from be 1.25V to 10Vdc by can give current topmost get about 1.5A. You should use IC number LM317K because have electric many power more the number LM317K. By should hold heat sink. That have large-sized with. The R4 use for fine decorate voltage output. The C1-470uF 25V(electrolytic capacitors) , C3-0.1uF 63V (Ceramic Capacitor or Mylar Capacitor) , and , C2-22uF 25V , for decrease all noise well. The detail is other , see in the circuit.
circuit source by joe (aircraftdesigner)
Low noise variable power supply using LM317,1.25V to 10VDC

Adjustment DC power supply 1.25-15V Max current 0.5A

This is LM317 based variable power supply that have Voltage output fine the value has 1.25-15V. From by Output current that be valuable about 0.5 amp that 12V and 0.2 amp that 15V. When Volt , from 220V houses reach transformer. It will modify Volt 220V to be 18VAC already to change rectifier circuit. Which D1, D2, C1 and R1 wasp be Full wave rectifier circuit.

For modify DCV to ACV to a signal DCV. It make get a signal DCV that have voltage at pin 3 of IC1 be 20V. From that time DCV signal this reach fight DC Regulator circuit. Which use IC number LM317. This circuit will perform to maintain one’s position Voltage smoothly. Which level output voltage at get this will go out the way pin 2 of IC1. By have capacitors C2 be voltage filter in order that voltage output level of the circuit is will high class modify to follow fining. The performing fee withstands VR1 there.

Adjustment DC power supply 1.25-15V Max current 0.5 amp

Related: Power supply using LM317 Circuits

In addition, You may be not like this. But you may modify these circuits work well too.below.

LM317 Linear power supply Regulator selector 1.5V,3V,4.5V,5V,6V,9V 1.5A

It’s easy to selects voltage output.

0-60 volt DC variable power supply using LM317&LM337

It’s high volt and start voltage at zero! good job.

Best Adjustable DC power supply 3A; 1.2V-20V, 3V-6V-9V-12V

High current for all circuit easy to use.

Dual power supply 3V,5V,6V,9V,12,15V using LM317,LM337

There positive and negative voltage output for all circuit easy to use.
And now you can see

3A Adjustable Regulators using LM350T


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