# My first Variable DC Power Supply 1.2V to 30V 1A by LM317

If you are beginner in electronics and you want to have a great power supply. This project is design for you. It can supply voltage 1.2V to 30V at all range is 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 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%
• 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.

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.

You like my sites want to support me by buy this E-book.

Update:
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.

You will see that we can adjust voltage at VR2 (new) is 4volts since resistance sum of 500 ohms approximately.
For example I set volage 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 universal box to use easily.

### Note:

I have old a transformer 12V CT 12V output, but I measure it as 30.9V too much voltage.
It may cause over voltage 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 video below. I can adjust voltage output is 1.25V to 27V since I use the 21V output transformer.
If you can fine 24V or 12V CT 12V it cause output up to 30V but IC over heat when short circuit or over load.

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

and then…

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