normalize LED...

[mark]

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.

 

[mikem]

On Mon, 20 Oct 2003 22:32:54 +0800, "mark" <biteme@spam.com> wrote:

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.

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

 

[mikem]

On Tue, 21 Oct 2003 07:29:41 +0800, "mark" <biteme@spam.com> wrote:

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.

should I try 1 K ohm?

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

 

[mark]

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.

should I try 1 K ohm?

 

[mark]

thanks I will try.



mikem <mladejov@CharleyEchoDelta.utah.edu> wrote in message
news:cor8pvsd7bdjaarst892opv9394ms0gdti@4ax.com...

On Tue, 21 Oct 2003 07:29:41 +0800, "mark" <biteme@spam.com> wrote:


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.

should I try 1 K ohm?



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

 

[Andre]

"mark" <biteme@spam.com> wrote in message news:<bn34d0$mj815@imsp212.netvigator.com>...

thanks I will try.

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

mikem <mladejov@CharleyEchoDelta.utah.edu> wrote in message
news:cor8pvsd7bdjaarst892opv9394ms0gdti@4ax.com...
On Tue, 21 Oct 2003 07:29:41 +0800, "mark" <biteme@spam.com> wrote:


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.

should I try 1 K ohm?



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