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Questions relating to designing PCBs
By denki
#49776
hi,

newbie's first post here. i'm planning to use a luxeon 3W led as a beacon pulsed intermittently. since i wont be using it continuously do i need to worry about heat dissipation? or can i just solder direct to the pcb using the sfe provided footprint.

as far as using the aluminum breakout board, i figure i could fasten it to the pcb with some spacers so that the aluminum backing is exposed to air, but then how to get the power and ground connections to it?

thanks,
denki
By winston
#49900
I use 6 x 1 watt Luxeons for an intermittent flash, and it doesn't detectably warm up and there's no heat sink. It all depends on the length of your duty cycle and flash frequency.

It's possibly worth getting a 3W Luxeon and making a simple prototype circuit with a 555 timer on breadboard to see if it works for you (use the control pin, pin 5, on the 555 to control the duty cycle and adjust it with a potentiometer, that way you can get instant results).
User avatar
By phalanx
#49976
With power LEDs you should always have to take thermal management into account. Depending on your duty cycle, it is still possible to generate large amounts of heat. You should have a look at the Lumileds application brief that covers thermal management and apply it to your intended application to see where you stand:

http://www.lumileds.com/pdfs/AB05.pdf

-Bill
User avatar
By ohararp
#50083
denki,

I made a strobe that flashes on for 50 milliseconds and then off for 950 milliseconds. Heat is not an issue with this pcb in a single sided configuration and not thermal pads.

I would consider not using heatsinks if you have a similar duty cycle. One word of caution is to make sure you drive the control pin to the driver low in a "control failutre" situation. Because if your strobe got stuck on you would be screwed and your leds would burn out.
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