To calculate the resistance when powering a LED use this:
- R: is the needed resistance
- Vpow: is the voltage of our source or power supply (e.g. battery)
- Vled: voltage of the LED
- I: the maximum of current that goes through our LED.
for a 2V (diode forward voltage) LED we need 20mA =0.02A (diode forward current)
So, for instance, if we have a 12V battery then: R=(12-2)/0,02= 10/0.02=500 Ohm
Another example is the use of multiple LEDs in an array. So, for an array of 4 LEDs with diode forward voltage 2V, diode forward current (0.02mA) and a Vpow of 12V we need:
4 x 1 array uses 4 LEDs exactly
- each 220000 ohm resistor dissipates 0.088 mW
- the wizard says the color code for 220000 is red red yellow
- the wizard thinks 1/4W resistors are fine for your application
- together, all resistors dissipate 0.088 mW
- together, the diodes dissipate 0.16 mW
- total power dissipated by the array is 0.248 mW
- the array draws current of 0.02 mA from the source.
Here is a calculator to automatically find your needed resistance [>>].