LED Flashlight - Electronic Circuits Projects Diagrams Free

Dave the Embalmer · 7th March 2003, 08:07 PM

Ok, I'm building an LED flashlight. It uses 12 high power LEDs, and what it all comes down to is that at 4.5V (3 "D" cells), I only need 5 Ohms of resistance. Now, a whole lot of energy goes into heating up that 5 Ohm resistor a whole lot. Is there a more effecient way? What I'd like is to be able to perhaps use PWM to short the battery out through the leds in quick bursts or something to that effect. I can use discreet components, but preferably stuff I could control from a uC. (Transistor, ADC for voltage/current sense built-in with the uC I'm using, a PIC16F876).

Thanks!

Sebi · 7th March 2003, 09:50 PM

Need more data abot LED: max current? forward voltage? for considerations.

Dave the Embalmer · 7th March 2003, 10:39 PM

http://www.allelectronics.com/spec/LED-94.pdf

They want 30mA, but I'm considering either 25 or 20mA for better efficiency. (It doesn't look that much dimmer). The forward voltage is around 2V. I'm thinking of using a step-down regulator (97% efficiency, from National Semi) to give a PIC a constant 2.xV, and then drive the LEDs directly from the PIC by shorting the outputs to ground through the LED. The outputs on PICs can sink/source 25mA, so...

Is that idea any good?

Pilot · 8th March 2003, 12:41 AM

Hi Dave,

There is quite a lot of info & circuits on the web of people experimenting with led torches.

Just as an example - if you have not seen it...

http://www.pacificsites.com/~brooke/LED.shtml

and

http://www.sentman.com/led/

Have fun and experiment.

:lol: :lol:

Dave the Embalmer · 8th March 2003, 02:24 AM

Hey, thanks for the links, Pilot.

The PIC thing is intersting, I'll need to look into that, considering I have several 12F675s on hand.

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7th March 2003, 08:07 PM	(permalink (permalink))
Dave the Embalmer	LED Flashlight Ok, I'm building an LED flashlight. It uses 12 high power LEDs, and what it all comes down to is that at 4.5V (3 "D" cells), I only need 5 Ohms of resistance. Now, a whole lot of energy goes into heating up that 5 Ohm resistor a whole lot. Is there a more effecient way? What I'd like is to be able to perhaps use PWM to short the battery out through the leds in quick bursts or something to that effect. I can use discreet components, but preferably stuff I could control from a uC. (Transistor, ADC for voltage/current sense built-in with the uC I'm using, a PIC16F876). Thanks!

7th March 2003, 09:50 PM	(permalink (permalink))
Sebi	Need more data abot LED: max current? forward voltage? for considerations.

7th March 2003, 10:39 PM	(permalink (permalink))
Dave the Embalmer	http://www.allelectronics.com/spec/LED-94.pdf They want 30mA, but I'm considering either 25 or 20mA for better efficiency. (It doesn't look that much dimmer). The forward voltage is around 2V. I'm thinking of using a step-down regulator (97% efficiency, from National Semi) to give a PIC a constant 2.xV, and then drive the LEDs directly from the PIC by shorting the outputs to ground through the LED. The outputs on PICs can sink/source 25mA, so... Is that idea any good?

8th March 2003, 12:41 AM	(permalink (permalink))
Pilot	Hi Dave, There is quite a lot of info & circuits on the web of people experimenting with led torches. Just as an example - if you have not seen it... http://www.pacificsites.com/~brooke/LED.shtml and http://www.sentman.com/led/ Have fun and experiment. :lol: :lol:

8th March 2003, 02:24 AM	(permalink (permalink))
Dave the Embalmer	Hey, thanks for the links, Pilot. The PIC thing is intersting, I'll need to look into that, considering I have several 12F675s on hand.