Re: [TenTec] LED Dropping resister

[Ken Brown <ken.d.brown@verizon.net>]

> R = (Vsupply - Vled) / Iled
>
> R       : resistor value
> Vsupply : power supply voltage, must be > Vled
> Vled    : voltage drop on LED, generally from 1.6 V to 2.7 V
> Iled    : current, try 5 mA = 0.005 A
>
> Example:
>  Vsupply = 12 V
>  Vled    =  2 V
>  Iled    =  5 mA = 0.005 A
>  R       = (12 - 2) / 0.005 = 2000 Ohms (use 1800 or 2200 Ohms)
>
>  
V led and I led are generally available from the manufacturer or vendor 
of the leds. The LED will not light at all untill the voltage gets up to 
around V led. When the voltage gets high enough it will start to draw 
some current, and from that point on as the current goes up so will the 
brightness. You will want to limit the current to a value no greater 
than what the manufacturer recommends, so that you don't blow it up. And 
you may want to limit it to some lower value to get less than maximum 
brightness.