Oyvind's Circuit Tips: How to choose resistor for an LED

Did you know that an LED (Light-Emitting Diode) should always have a resistor in series to avoid it burning up? ​ ​ But to choose the resistor, you need to know the forward voltage of the LED and the current it needs. ​ ​How do you find these? The easiest way is to just look it up in the datasheet. But if you don't have the datasheet, here are two options: You could find the LED voltage by using a multimeter with diode function. The multimeter does the job for you and tells you the values. ​ You could connect the LED to a battery with a potentiometer. Start with high resistance on the potentiometer and gradually decrease it until you have a nice brightness. Then measure the voltage over the LED, and calculate the current going through the circuit. ​ ​ Let's say the LED needs 15 mA and has a voltage drop of 2 volts. If you have a 5V power source that you would like to power it with. What resistor value do you need? To find the resistor value, you start by finding the voltage drop over the resistor. Since there is a 2-volt drop over the LED, there will be a 3V drop over the resistor. So you have 3V across the resistor, and you want to have 15 mA going through it. To find the necessary resistor value, use Ohm's law: ​ So the necessary resistor value for the LED is 200 Ohms. ​ Keep On Soldering! Oyvind @ build-electronic-circuits.com PS! Whenever you're ready, here are two ways I can help you learn electronics: ​Getting Started With Electronics​ is a short and beginner-friendly eBook I wrote to help people get started. It contains clear and simple instructions to get started building electronics. Perfect for complete beginners. ​ ​​Join Ohmify​: Ohmify is for people interested in electronics who want to learn skills like PCB design, soldering, and project-building - while also getting a proper understanding of the basics.

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