Model Making Materials

+44 (0)20 7264 1288

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)

EU10053

LED 3mm white

-

47 Ohms

150 Ohms

270 Ohms

430 Ohms

20

3.6

2500

EU10055

LED 5mm super green

39 Ohms

150 Ohms

220 Ohms

330 Ohms

470 Ohms

20

2.2

200

EU10057

LED 5mm white

-

47 Ohms

150 Ohms

270 Ohms

430 Ohms

20

3.6

8000

EU11009

LED 3mm red

47 Ohms

150 Ohms

220 Ohms

330 Ohms

470 Ohms

20

2

160

EU11011

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

Guide to LED's and resistors

As an example in the circuit below the resistor needed is worked out as below:

Guide to LED's and resistors

This resistor will then work for a number of LED’s wired in a parallel circuit using one resistor for each LED.

Guide to LED's and resistors

For series circuits the resistor for the circuit below is calculated in the following way.

Guide to LED's and resistors

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.