[sdiy] driving blue LED

[John Luciani]

On 10/19/06, Bert Schiettecatte <bert at percussa.com> wrote:
> Hi All,
>
> I have been playing around with blue LEDs here and I have one that has a
> forward voltage of about 3.4V max. I'd like to drive it from a
> microcontroller, which is powered by three AAA batteries (1.2V nominal
> so varies between 3 and 3.6 V? ). Would it be possible to use one of the
> high current drive I/O pins (16mA) to add the necessary voltage/current
> on top of the battery voltage to create a higher voltage to drive the
> LED with?
>
> Thanks, and sorry if this is a silly question :-)

You can do this if you use the digital output in PWM mode and create a switching
power supply. You will need an inductor, diode and a cap. There should
be app-notes
on how to do this using your microcontroller.

For an LED you really want to regulate current not voltage. The better
way to do this
would be to use an LED driver. Check out LTC, Maxim and TI. The LT1932
should work
in your application but you may be able to find a device better suited
to drive a
single LED.

(* jcl *)

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