What resistor should i use for an led

Remembered your password? Back to login. Already have an account? Login here. Choosing a resistor to work with an LED is fairly simple, but does require some knowledge of the LED and a small amount of maths. All other standard and bright LEDs will need a current limit resistor. When a diode is put in a circuit 0.

Similarly LEDs have a voltage dropped across them know as the forward voltage, though this is different for every LED. A proportion of the battery voltage is dropped across the LED the forward voltage and the rest of the voltage is dropped across the resistor. This is shown in the diagram top right. We can therefore write this as:. For example an ultra bright blue LED with a 9V battery has a forward voltage of 3.

However I have a 5th grader who designed a small artifact which has 4 LEDs in different colors. I just want to help her get it lit with a battery. Can anyone advise us? Reply 3 years ago. By Grathio Grathio Labs Follow.

More by the author:. About: Creative swashbuckler. Professional problem solver. Annoyingly curious. Hacker of all things from computers to clothe… More About Grathio ». So I've put together several different ways to figure it out. Lets get right to it: Each of the steps do the same thing. Step 1 is the simplest and we go downhill from there. No mater what way you choose you must first know these three things: Supply voltage This is how much power you're putting into the circuit.

Batteries and wall warts will have the output voltage printed on them somewhere. This is listed in milliamps or "mA". Both of these last two can be found on the packaging for your LEDs or on your supplier's web site. If they list a range "mA" pick a value in the middle 25 in this case. Here are some typical values, but use your own values to be sure you don't burn out your LEDs!

Introduction photo credits: LED photo by Luisanto. Resistor photo by oskay. Did you make this project? Therefore, the current value required will be 10 mA multiplied by 5. Using this in our formula ; Use the standard value of ohms. The wattage rating will now be higher The two examples will be repeated for Red LEDs. For a single Red LED: For 5 Red LEDs in parallel: As we can see, determining the resistor value for lighting LEDs is simple and straightforward, but we must take into consideration the color of the LED as well as the wattage rating of the required resistor and the number of LEDs in the circuit.

You can visit our store for a varied selection of LEDs and resistors. George Leger has a Masters in Electrical Engineering from Stanford University, worked in private industry pioneering surface-mount technology and in government research labs for twenty years, published several papers on surface-mount technology, co-authored papers published in national symposiums on accelerator technology, was past president of SMTA and an adjunct professor at the community college level, holds a patent, and is a certified microchip design partner, serving as a consultant to many companies developing electronic circuits.

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