How much current can an LED receive?

Question

For a Project im doing i need to knoe what resistor would be good for a simple LED

Answer 1

Depends on the LED and how meny,

this might help you

http://ourworld.compuserve.com/homepages...

Answer 2

Depends on the LED your using standard leds are about 20mA MAX you then move into the high brighness area, which will take you up to a few amps and the top end of the technology.

Standard design rules for a 5 volt supply with a standard 5mm led will tell us to use a 330 ohm resistor, which gives 15mA which is a little below there ratings.

but when using leds it's best not to drive them to their max, as their efficiancy drops at the top end, and their life is not that good.

But it depends what you want, if you just want to see the led turn on then you don't need it to be too bright, so you may as well use a larger resistor and save energy (yes i know it's not a lot).

When designing for an led we use the voltage drop across the led to calculate, a standard Red LED is about 1.7V it differs depending on colour. high brightness leds are around 3.3V

Use ohms law V=IR to calculate you needed value

eg 12V supply with a 1.7V 20mA LED (we will drive at 15mA)

so we want 1.7 volts across the led but have a 12V supply, therfore we need to drop  10.3V accross a resistor, since the resitor is in series with the led we know that it will have the same current flowing through it 15mA

using ohm law R= V/I

R = 10.7/0.015  (15mA) =713 ohms

Obviously you cant get a 713 ohm resistor so choose the nearest value you have either a 680 ohm or an 750 ohm.

Answer 3

5 volts, 220 ohms (brown, brown, black),  23 ma.  

about 20 is a good estimate.

Answer 4

the resistor value depends on what current you want to send through the LED (call it I), the voltage drop of the LED (Vf) and the battery voltage (E).

R = (E-Vf) / I

Answer 5

Surly you would use the resistor to limit the voltage not current?

usually around 2 volts?

Answer 6

You can try any value between about 200 ohms to about 4.7K.  all should allow most LED's to work when using 5Volts as a source.  Brightness will vary with teh value selected.  Led's generally draw from 2 to 20 mA current at about 2volts acress the LED.

A higher voltage source will require a proportionaly higher resistor value.