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Old 1st October 2005, 03:36 AM   #1
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Default 3 watt led driver

I am try to figure out how I can run my recently obtained 3 watt lumiled. I would like to run the led off of 4 AA NiMH batteries but depending on voltage/current limiting IC that might change. I was orginally just going to build a 555 timer PWM circuit to do my voltage reduction from around 5 voltage to the nessary 3.7 or so...but after doing some reading I found instead of regulation by voltage i should be looking at current regulation. I found some very easy strait forward pre built units but I can't pull my self to spend $20 Is there a cheap and efffecient way to do current regulation at 700 ma? Can i configure a 555 timer PWM circuit to use current as it's variable?

Unit thats 20 bucks but does exacly what i need
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Old 1st October 2005, 04:22 AM   #2
djQUAN is offline djQUAN  Philippines
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you could try this............


http://sound.westhost.com/appnotes/an003.htm


I have used it to drive an array of twelve 5mm LED's in parallel. works wonderfully.
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Old 1st October 2005, 11:22 PM   #3
Eva is offline Eva  Spain
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That circuit could be easily improved by employing a standard LM393 comparator with hysteresis to sense turn-on and turn-off current, thus allowing for a very low voltage drop in the sense resistor. The other comparator of the dual package may be used for under voltage lockout. Finally, I would connect a CD4049 buffer to the output of the current comparator and I would use it to drive a standard IRF540 switch in order to maximize efficiency (maybe a logic gated one for <6V operation).

Still three active devices, standard components and very low-cost
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