Re: LED rules of thumb

["Dave McLaughlin" <dave@xxxxxxx>]

Correct calcs are as follows:-

Vin - Vr
--------
    Ir

Vin = supply voltage
Vr = resistor forward voltage (nominally 2.4 but check the spec sheet)
Ir = required current through the LED (check specs for max allowed)

With the above, 12 with a RED LED with 2.4V and 20mA of current gives a
resistance value of 108 ohms. So choose a 120 ohm value and you will be
OK.

Dave...

----- Original Message -----
From: "Jon Payne" <jgpayne@xxxxxxx>
To: <ukha_d@xxxxxxx>
Sent: Tuesday, September 17, 2002 2:21 PM
Subject: Re: [ukha_d] LED rules of thumb


> Use Ohms law:
>
> V=IR, so R = V/I
>
> e.g. for 20mA at 12v
>
> R = 12v / 0.02A = 600 ohms
>
> However, the white/blue LEDs may have a large voltage drop
(haven't
checked)
> which I guess may effect things - anyone?
>
> jon

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