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The LM317 Adjustable Voltage Regulator

In my previous article about Power Supply for Breadboards, I decided to make a custom power supply for my bigger breadboards using the LM317. I chose an adjustable voltage linear regulator like the LM317 because of the simplicity of being able to toggle between a 3.3v and 5.5v supply depending on the requirements of the project.

The LM317 chip is an adjustable voltage linear regulator that you can use to provide power to electronics projects. It has an output voltage range of 1.25 to 37 depending on the values of resistors you use on the basic circuit. It offers a decent maximum current output of 1.5 amperes which is enough for most “Internet of Things (IoT)” projects. The TO220 packaging allows you to buy and use readily available TO220 heat sinks for the LM317 in case you plan to use it at its maximum current rating.

The LM317 only has three pins — the voltage adjustment pin, the voltage output pin and the voltage input pin. Checkout the pinout for the LM317 below:

The LM317 has a basic circuit shown below. When using the circuit, you have to compute for the output voltage that you need. The output voltage depends on the value of the resistors R1 and R2 on the image below.

For example, let’s assume that the value of R1 is 240 ohms and we require an output of voltage of 5 volts. Computing for the value of R2 using the formula should be equal to 720 ohms. It’s that easy. With the basic knowledge of the LM317 and the formula, I can now make the circuit design for a flexible power supply for breadboards. I’ll write about my circuit design on a future article.

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Gerry Ilagan

Gerry Ilagan is into mobile apps and WordPress development at @speeqs. He loves to write about electronics, the Internet of Things, mobile phones, and #crazyideas.

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