gnupic: Re: [gnupic] sanity check, pic12f675 first project
Subject:
Re: [gnupic] sanity check, pic12f675 first project
From:
Peter Stuge ####@####.####
Date:
22 Jul 2009 17:59:17 -0000
Message-Id: <20090722175904.3316.qmail@stuge.se>
Mark Rages wrote:
> I don't think you'll find a significant brightness increase with
> modern LEDs:
>
> http://members.misty.com/don/ledp.html
This page says "UPDATED .. 2001" and there has certainly been a lot
of development in LED products over the last decade.
I think it is safe to say that high current PWM is the easiest way
to get the most performance out of any LED.
The improved efficiency (as mentioned back in 01) can of course also
be a deciding factor, not only brightness.
But in particular the high-power white LEDs really must be driven
with PWM.
> > Better match the supply voltage to the forward voltage of your LEDs,
> > then there's no extra voltage that needs to be dropped by other
> > components.
>
> The resistor is doing more than dropping voltage. It is acting as a
> crude current source, to maintain the LED current as the forward
> voltage shifts over temperature, age, manufacturing tolerances etc.
> So no matter how carefully you select the supply voltage, you can't
> remove the resistor without some other means of regulating current.
Yes, sure, a resistor should still be there to limit current. I find
dropping some 10V over it to be excessive, however.
//Peter
