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.

Figure 1 The My first Variable DC Power Supply.

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 the 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 than ICs.

LM317T the ever popularBut 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.

Figure 2 The LM317T, I love it.

Note: be careful Out pin is connected to metal body.

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 to D4 there is dc voltage into the filter capacitor C1 equal to DC35V

Figure 3 circuit diagram

Note: See large circuit at: 3-circuit diagram of variable power supply 125-30v_1a_by_lm317t.jpg

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 data sheet. I use 220 ohms.

- Normally as data sheet I see them use VR= 5K (Potentiometer) 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 are the protector from external voltage to reverse to makes the damage to the IC1.

Parts you need

IC1_____LM317T

D1-D6___1N4007 Diode 1000V 1A

R1_____220 ohms Resistor 1/4W

R2_____12K Resistor 1/4W

VR1____10K__Potentiometer

C1_____1,000uF 50V___Electrolytic Capacitor

C2_____0.1uF 50V_____Polyester Capacitor

C3_____470uF 50V___Electrolytic Capacitor

C4_____10uF 50V___Electrolytic Capacitor

T1____Transformer secondary coil 24V 1A (use 2A better) ***Read text below.

The PCB of this projects and layout diagram.

How to builds

Firstly you need to builds the PCB as Figure 4 .

Figure 4 the PCB layout.

(This image is 300px per inch for printer.)

and then soldered components on the PCB as shown Figure 5 correctly completed.

Figure 5 the components layout

And The LM317 should be installed on the heat

sink that fits.

And a the terminals device. Be careful with the terminals, especially Electrolytic Capacitor,Diode.

***The transformer to set output voltage.As show in circuit we use 24V transformer making have voltage output is 30V(about 32Vdc)

– But you use 18V transformer will have output is 22V maximum.I like this way because I have this transformer a lot.

OR

If you output near 30V we can modify transformer connecting is 21V. It cause output is about 30V maximum.

I select this way when some project required 25V up.

CautionI 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.

Video: over-voltage-transformer.mov

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

as Figure 6

This circuit perfectly works, as video below. I can adjust voltage output is 1.25V to 27V since I use the 21V output transformer.

Figure 6 Modify the transformer into 21V

Video: how to modify the transformerModify-transformer-21v.mov

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.

As video: 1-25v-to-27v-variable-regulator-1a-using-lm317.mov

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

Adding fine adjustable voltage.

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 7 and Figure 8

Figure 7 adding function thoroughly adjust voltage output.

Figure 8 connecting two potentiometers

You will see that we can adjust voltage at VR2 (new) is 4 volts since resistance sum of 500 ohms approximately.

As Figure 9 the wiring inside this projects.

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.

add function thoroughly adjust voltage output.mov

I assemble in universal box to use easily.

In addition, you may modify these circuits work as well a lot.

Thanks for read.

By Momename

www.eleccircuit.com