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howtocalc forw. current vs pulse period for infrared led?

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dpechman

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hello,
i need a help to understand how to calculate the forward current of an infrared led...(the limits)
ex.
LED55C
continuous forward current = 100mA
forward current @ 1uS / 200Hz = 10A

but, what duty cycle shoud i use if i want less than 10A?
ex.
if i want 200mA @ 200Hz
how many uS turned on shoud be the LED limit ????
im totally lost!!! can some one help me???? :(
 

flatulent

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data sheet

From the data sheet it looks like 50% at 200 mA. http://www.fairchildsemi.com/ds/LE/LED55C.pdf Note the graph for continuous current goes up to 500 mA. I suspect that the 100 mA max is due to life limits and not catastrophic damage. The limits for short pulses is the local heating. Note that the graph for 80 us pulses goes up to 2 A.
 

dpechman

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so, i can safely work with 500uS turn on and 4500uS turn off with 200mA ???
 

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yes

Yes that looks proper.

One further design thing you can do is put two diodes in series if you are going to drive them from 5 V. This will double your output so that you can draw less current. This is a big help in battery operated systems.
 

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