gnupic: Re: [gnupic] sanity check, pic12f675 first project
Subject:
Re: [gnupic] sanity check, pic12f675 first project
From:
Mark Rages ####@####.####
Date:
22 Jul 2009 04:57:09 -0000
Message-Id: <74ee72ca0907212156r535da49cr9e2da36512b6efee@mail.gmail.com>
On Tue, Jul 21, 2009 at 9:04 PM, Peter ####@####.#### wrote:
> Jason wrote:
>> Nice. I found a circuit a while back [1] for increasing the LED
>> brightness by pulsing it. I thought I'd replace the 555 timer with
>> a more flexible pic...
I don't think you'll find a significant brightness increase with modern LEDs:
http://members.misty.com/don/ledp.html
>
> Aha. Watch out with the voltage though - that circuit will make those
> R2-R3 resistors sweat a bit, and the Q1 transistor will also be a bit
> stressed.
R2 and R3 have the same low duty cycle as the LEDs.
If the LED current is really 500 mA each, that exceeds the design
rating of the BC547B by about 10X (Abs max Ic is 100 mA for that
part). Better to use a logic-level FET for this application I think.
>
> 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.
Regards,
Mark
markrages@gmail
--
Mark Rages, Engineer
Midwest Telecine LLC
####@####.####
