In the event, we need to build a variable DC power supply that output of 1A and can adjust up to about 30V.

Most people will use LM317 because of high-efficiency, easy to apply, and cheaper.

Is it really? You find out below.

**Table of Contents**Show All

**LM317 Datasheet**

It has an adjustable 3-terminal positive voltage regulator designed to supply more than 1.5 A of load current with an output voltage adjustable over a 1.2V to 37V range.

It has an internal current limiting, temperature detects shutdown and safe area compensation.

### LM317 pinout

**Figure 1: LM317 pinout on TO-220**

Look:

**Connection Diagram various LM317 Pinout**

LM317T on TO-220: output 1.5A

LM317L on TO-92: output 100mA

LM317K on TO-3: output 1.5A

LM317 on DPARK: output 1.5A

### Basic Features

- Output current in excess of 1.5A
- Output-Adjustable between 1.2V and 37V
- Internal Short-Circuit Current Limiting or Output is short-circuit protected
- Internal Thermal Overload Protection or Current limit constant with temperature
- Output-Transistor Safe Operating Area Compensation
- TO-220 Package like 2SC1061 transistors.
- There are 1% output voltage Durability
- There are max. 0.01%/V line regulation(LM317), and 0.3% load regulation (LM117)
- There are 80 dB ripple rejection

**Figure 2 the basic circuit diagram**

**Basic circuit diagram**

If the power supply filter has distance from IC-regulator too much. Tt should insert Ci to lower noise before IC-input.

Next in the figure circuit. The Co is not needs if you do not high-efficiency, but we put it better. It will keep lower an output ripple.

As Iadj is controlled to less than 100uA, the little error Unimportant in most applications.

The input voltage to the LM317 must be at least 1.5v greater than the output voltage.

## LM317 calculator

This **calculator** will work for most DC Voltage Regulators with a reference voltage (VREF) of 1.25. Typically, the program resistor (R1) is 240 ohms for the LM117, LM317, LM138, and LM150.

Some said Iadj is very low current.

So, we may reduce it down. To be shorter and easy.

Vout = 1.25V x {1+R2/R1}

Which is better?

For example:

You use R1 = 270 ohms and R2= 390 ohms. It causes output is 3.06V

Is it easy? If you have voltages choice with most resistors. In local stores near you.

look at the list:

### Output Voltage with R1 and R2 List

1.43V : R1 = 470Ω, R2 = 68Ω

1.47V : R1 = 470Ω, R2 = 82Ω

1.47V : R1 = 390Ω, R2 = 68Ω

1.51V : R1 = 330Ω, R2 = 68Ω

1.51V : R1 = 390Ω, R2 = 82Ω

1.52V : R1 = 470Ω, R2 = 100Ω

1.53V : R1 = 390Ω, R2 = 82Ω

1.56V : R1 = 330Ω, R2 = 82Ω

1.57V : R1 = 270Ω, R2 = 68Ω

1.57V : R1 = 470Ω, R2 = 120Ω

1.57V : R1 = 390Ω, R2 = 100Ω

1.59V : R1 = 390Ω, R2 = 100Ω

1.60V : R1 = 240Ω, R2 = 68Ω

1.63V : R1 = 330Ω, R2 = 100Ω

1.63V : R1 = 270Ω, R2 = 82Ω

1.64V : R1 = 390Ω, R2 = 120Ω

1.64V : R1 = 220Ω, R2 = 68Ω

1.65V : R1 = 470Ω, R2 = 150Ω

1.66V : R1 = 390Ω, R2 = 120Ω

1.68V : R1 = 240Ω, R2 = 82Ω

1.71V : R1 = 330Ω, R2 = 120Ω

1.71V : R1 = 270Ω, R2 = 100Ω

1.72V : R1 = 220Ω, R2 = 82Ω

1.72V : R1 = 180Ω, R2 = 68Ω

1.73V : R1 = 470Ω, R2 = 180Ω

1.73V : R1 = 390Ω, R2 = 150Ω

1.76V : R1 = 390Ω, R2 = 150Ω

1.77V : R1 = 240Ω, R2 = 100Ω

1.81V : R1 = 270Ω, R2 = 120Ω

1.82V : R1 = 150Ω, R2 = 68Ω

1.82V : R1 = 330Ω, R2 = 150Ω

1.82V : R1 = 180Ω, R2 = 82Ω

1.83V : R1 = 390Ω, R2 = 180Ω

1.84V : R1 = 470Ω, R2 = 220Ω

1.86V : R1 = 390Ω, R2 = 180Ω

1.88V : R1 = 240Ω, R2 = 120Ω

1.89V : R1 = 470Ω, R2 = 240Ω

1.93V : R1 = 330Ω, R2 = 180Ω

1.93V : R1 = 150Ω, R2 = 82Ω

1.94V : R1 = 270Ω, R2 = 150Ω

1.96V : R1 = 390Ω, R2 = 220Ω

1.97V : R1 = 470Ω, R2 = 270Ω

1.99V : R1 = 390Ω, R2 = 220Ω

2.02V : R1 = 390Ω, R2 = 240Ω

2.03V : R1 = 240Ω, R2 = 150Ω

2.06V : R1 = 390Ω, R2 = 240Ω

2.08V : R1 = 330Ω, R2 = 220Ω

2.10V : R1 = 220Ω, R2 = 150Ω

2.12V : R1 = 390Ω, R2 = 270Ω

2.13V : R1 = 470Ω, R2 = 330Ω

2.16V : R1 = 330Ω, R2 = 240Ω

2.16V : R1 = 390Ω, R2 = 270Ω

2.19V : R1 = 240Ω, R2 = 180Ω

2.23V : R1 = 470Ω, R2 = 390Ω

2.25V : R1 = 150Ω, R2 = 120Ω

2.27V : R1 = 270Ω, R2 = 220Ω

2.27V : R1 = 330Ω, R2 = 270Ω

2.29V : R1 = 470Ω, R2 = 390Ω

2.29V : R1 = 180Ω, R2 = 150Ω

2.31V : R1 = 390Ω, R2 = 330Ω

2.36V : R1 = 270Ω, R2 = 240Ω

2.37V : R1 = 390Ω, R2 = 330Ω

2.40V : R1 = 240Ω, R2 = 220Ω

2.44V : R1 = 390Ω, R2 = 390Ω

2.50V : R1 = 470Ω, R2 = 470Ω

2.57V : R1 = 390Ω, R2 = 390Ω

2.61V : R1 = 220Ω, R2 = 240Ω

2.65V : R1 = 330Ω, R2 = 390Ω

2.66V : R1 = 240Ω, R2 = 270Ω

2.73V : R1 = 330Ω, R2 = 390Ω

2.74V : R1 = 470Ω, R2 = 560Ω

2.75V : R1 = 150Ω, R2 = 180Ω

2.76V : R1 = 390Ω, R2 = 470Ω

2.78V : R1 = 270Ω, R2 = 330Ω

2.78V : R1 = 220Ω, R2 = 270Ω

2.84V : R1 = 390Ω, R2 = 470Ω

2.92V : R1 = 180Ω, R2 = 240Ω

2.96V : R1 = 270Ω, R2 = 390Ω

2.97V : R1 = 240Ω, R2 = 330Ω

3.03V : R1 = 330Ω, R2 = 470Ω

3.05V : R1 = 390Ω, R2 = 560Ω

3.06V : R1 = 270Ω, R2 = 390Ω

3.06V : R1 = 470Ω, R2 = 680Ω

3.08V : R1 = 150Ω, R2 = 220Ω

3.13V : R1 = 220Ω, R2 = 330Ω

3.14V : R1 = 390Ω, R2 = 560Ω

3.18V : R1 = 240Ω, R2 = 390Ω

3.25V : R1 = 150Ω, R2 = 240Ω

3.28V : R1 = 240Ω, R2 = 390Ω

3.35V : R1 = 220Ω, R2 = 390Ω

3.37V : R1 = 330Ω, R2 = 560Ω

3.43V : R1 = 270Ω, R2 = 470Ω

3.43V : R1 = 390Ω, R2 = 680Ω

3.43V : R1 = 470Ω, R2 = 820Ω

3.47V : R1 = 220Ω, R2 = 390Ω

3.50V : R1 = 150Ω, R2 = 270Ω

3.54V : R1 = 180Ω, R2 = 330Ω

3.55V : R1 = 390Ω, R2 = 680Ω

3.70V : R1 = 240Ω, R2 = 470Ω

3.82V : R1 = 180Ω, R2 = 390Ω

3.83V : R1 = 330Ω, R2 = 680Ω

3.84V : R1 = 270Ω, R2 = 560Ω

3.88V : R1 = 390Ω, R2 = 820Ω

3.91V : R1 = 470Ω, R2 = 1K

3.92V : R1 = 220Ω, R2 = 470Ω

3.96V : R1 = 180Ω, R2 = 390Ω

4.00V : R1 = 150Ω, R2 = 330Ω

4.02V : R1 = 390Ω, R2 = 820Ω

4.17V : R1 = 240Ω, R2 = 560Ω

4.33V : R1 = 150Ω, R2 = 390Ω

4.36V : R1 = 330Ω, R2 = 820Ω

4.40V : R1 = 270Ω, R2 = 680Ω

4.43V : R1 = 220Ω, R2 = 560Ω

4.44V : R1 = 470Ω, R2 = 1.2K

4.46V : R1 = 390Ω, R2 = 1K

4.50V : R1 = 150Ω, R2 = 390Ω

4.51V : R1 = 180Ω, R2 = 470Ω

4.63V : R1 = 390Ω, R2 = 1K

4.79V : R1 = 240Ω, R2 = 680Ω

5.04V : R1 = 330Ω, R2 = 1K

5.05V : R1 = 270Ω, R2 = 820Ω

5.10V : R1 = 390Ω, R2 = 1.2K

5.11V : R1 = 220Ω, R2 = 680Ω

5.14V : R1 = 180Ω, R2 = 560Ω

5.17V : R1 = 150Ω, R2 = 470Ω

5.24V : R1 = 470Ω, R2 = 1.5K

5.30V : R1 = 390Ω, R2 = 1.2K

5.52V : R1 = 240Ω, R2 = 820Ω

5.80V : R1 = 330Ω, R2 = 1.2K

5.88V : R1 = 270Ω, R2 = 1K

5.91V : R1 = 220Ω, R2 = 820Ω

5.92V : R1 = 150Ω, R2 = 560Ω

5.97V : R1 = 180Ω, R2 = 680Ω

6.04V : R1 = 470Ω, R2 = 1.8K

6.06V : R1 = 390Ω, R2 = 1.5K

6.32V : R1 = 390Ω, R2 = 1.5K

6.46V : R1 = 240Ω, R2 = 1K

6.81V : R1 = 270Ω, R2 = 1.2K

6.92V : R1 = 150Ω, R2 = 680Ω

6.93V : R1 = 330Ω, R2 = 1.5K

6.94V : R1 = 180Ω, R2 = 820Ω

7.02V : R1 = 390Ω, R2 = 1.8K

7.10V : R1 = 470Ω, R2 = 2.2K

7.33V : R1 = 390Ω, R2 = 1.8K

7.50V : R1 = 240Ω, R2 = 1.2K

8.07V : R1 = 330Ω, R2 = 1.8K

8.08V : R1 = 150Ω, R2 = 820Ω

8.19V : R1 = 270Ω, R2 = 1.5K

8.30V : R1 = 390Ω, R2 = 2.2K

8.43V : R1 = 470Ω, R2 = 2.7K

8.68V : R1 = 390Ω, R2 = 2.2K

9.06V : R1 = 240Ω, R2 = 1.5K

9.58V : R1 = 330Ω, R2 = 2.2K

9.77V : R1 = 220Ω, R2 = 1.5K

9.90V : R1 = 390Ω, R2 = 2.7K

10.03V : R1 = 470Ω, R2 = 3.3K

10.37V : R1 = 390Ω, R2 = 2.7K

10.63V : R1 = 240Ω, R2 = 1.8K

11.25V : R1 = 150Ω, R2 = 1.2K

11.44V : R1 = 270Ω, R2 = 2.2K

11.48V : R1 = 330Ω, R2 = 2.7K

11.67V : R1 = 180Ω, R2 = 1.5K

11.83V : R1 = 390Ω, R2 = 3.3K

12.40V : R1 = 390Ω, R2 = 3.3K

12.71V : R1 = 240Ω, R2 = 2.2K

13.75V : R1 = 330Ω, R2 = 3.3K

15.31V : R1 = 240Ω, R2 = 2.7K

16.25V : R1 = 150Ω, R2 = 1.8K

16.53V : R1 = 270Ω, R2 = 3.3K

16.59V : R1 = 220Ω, R2 = 2.7K

18.44V : R1 = 240Ω, R2 = 3.3K

19.58V : R1 = 150Ω, R2 = 2.2K

20.00V : R1 = 220Ω, R2 = 3.3K

23.75V : R1 = 150Ω, R2 = 2.7K

24.17V : R1 = 180Ω, R2 = 3.3K

28.75V : R1 = 150Ω, R2 = 3.3K

For example, you need 4.5V from AA 1.5Vx3 in a series. But you do not have them. How to do? You have only LM317 and a lot of resistors. Yes, It can use it instead.

Look at the list above in 4.5V voltage we can use R1 = 150Ω, R2 = 390Ω.

It is easy, right?

### LM317 heat sink calculator

What is the size of the heat sink enough?

While The LM317 is running. It is so hot. Though it has an over-temperature cut-out. But we do not need it hot. We always install the heat sink.

Someone ask me. How much should you use the smallest heat sink? LM317 has a maximum temperature of 50 °C/W without a heat sink.

I found this site good with the LM317 heat sink calculator.

*You can find the LM317 on Amazon here if you’re interested.*

## For example LM317 circuit

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It can charge any size of the Gel cell batteries and extend the life of the Gel Cell battery. While the circuit is running, the LED indicates charging.**Nicad Battery Charger using LM317T**

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