GUIDE TO LED'S AND RESISTORS
RESISTOR NEEDED PER LED IN A PARALLEL CIRCUIT
|
stock code |
description |
supply voltage |
forward current |
forward voltage |
brightness |
||||
|
|
|
3V |
4.5V |
6V |
9V |
12V |
(mA) |
(V) |
(MCD) |
|
LED 3mm white |
- |
47 Ohms |
150 Ohms |
270 Ohms |
430 Ohms |
20 |
3.6 |
2500 |
|
|
LED 5mm super green |
39 Ohms |
150 Ohms |
220 Ohms |
330 Ohms |
470 Ohms |
20 |
2.2 |
200 |
|
|
LED 5mm white |
- |
47 Ohms |
150 Ohms |
270 Ohms |
430 Ohms |
20 |
3.6 |
8000 |
|
|
LED 3mm red |
47 Ohms |
150 Ohms |
220 Ohms |
330 Ohms |
470 Ohms |
20 |
2 |
160 |
|
|
LED 5mm blue |
- |
47 Ohms |
150 Ohms |
270 Ohms |
430 Ohms |
20 |
3.6 |
2500 |
When using LED’s you should always use at least one resistor to avoid the LED’s burning out. To work out what resistor is needed in your circuit use the following equation:
Resitance (Ohms) = (Supply voltage - LED voltage) / LED current mA) x1000
As an example in the circuit below the resistor needed is worked out as below:
This resistor will then work for a number of LED’s wired in a parallel circuit using one resistor for each LED.
For series circuits the resistor for the circuit below is calculated in the following way.
note: The sum of the LED’s forward voltage cannot exceed the voltage available so in the example above the maximum number of LEDs is 4.
FURTHER INFORMATION
Download our Guide to LED's and Resistors here (1.4Mb PDF)
Model Making Guides overview.