How much resistor do i need

First name. Last name. Your cart is empty. We can therefore write this as: The resistance can be calculated using Ohms Law: LEDs typically require 10 to 20mA, the datasheet for the LED will detail this along with the forward voltage drop.

So the resistor needs to be ohms or as close as is available. Let your computer do the work We have added a great tool to the Kitronik website that takes the strain out of calculating the current limit resistor.

Kitronik's suggested additional learning. Tags: Electronic principles , News. Rob Haywood 30 April at am The formula in this case does give you 0 Ohms.

Mikael 28 April at pm Heey, thanks for a great tutorial. Kitronik Newsletter Sign up now to be the first to know about the latest products and resources! Your email. Follow us. Latest Resources. No Quibble Refunds If you don't like the product for whatever reason, send it back packaged and unused for a full refund. Product Support Free Email and telephone support on all our products. The important feature to note here is that the voltage value used in the calculation.

Since this is not a standard value I would use an ohm resistor. We also need to determine the power rating watts of the required resistor.

This is calculated by multiplying the voltage value dropped across the resistor by the current value flowing in it. For our example above, This will maintain the same voltage requirement but the current value will increase in direct proportion to the number of LEDs.

The wattage rating of the resistor may also increase. 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: This is the voltage required to turn on your LED. This is the current required by your LED for operation. This LED has a forward voltage of 3. I will be powering my circuit with a 9V battery.

Next you will want to make sure you calculate the wattage required for your resistor to ensure that your resistor can handle the load. In our example this would be 5. Yes these Digikey calculators are very useful.