normalize LED...

I used 100 ohm and a 4118 diodes. they are connect to 5 +ve and gnd from a PC. I found the strong yellow LED. I do not think it is normal.

Should I change 100 ohm to ? ohm.

please suggest.

Reply to
mark
Loading thread data ...

To compute the resistor value, you need to know the forward voltage drop across the led (Vf) and the forward current which makes the led as bright as you would like it (If).

I dont have access to the specs for your specific led, but lets say that it has a Vf = 2.2V at a current of If = 10mA.

Since you are powering it from 5V, the required series resistor (Rs) is

Rs = (5-Vf)/If = (5-2.2)/0.010 = 280 Ohms

You need to look up the specs for your led and rework the problem.

100 Ohms does sound too low, though.

MikeM

Reply to
mikem

Depends on your led. I guess that it should be somewhere between 250 and 1K. If it is too bright, then double the resistor...

Reply to
mikem

should I try 1 K ohm?

Reply to
mark

thanks I will try.

Reply to
mark

For something like this its more useful to build an LED Vf tester consisting of a pair of sockets for meter probes and a 30mA constant current source. Measure the Vf of the LED at 30mA and then calculate the resistor acordingly- saves a lot of time and takes a few minutes to build.

You can use the closest value you have (e.g. if it specifies 365 ohms then 360 ohms will work) - parallel and series resistors to get the exact value where needed.

*Note* If you are using the newer LEDs then those don't like static or reverse voltage so double check the polarity before powering, resistor or no resistor.

-A

Reply to
Andre

ElectronDepot website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.