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Subject: Re: Designing current source?
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Date: 10/25/03 at 6:54 PM
Posted by: Russ Kincaid
E-mail: russlk-nospam[AT55]yahoo.com (replace [AT55] with @ to reply)
In Reply to: Designing current source? posted by Ben Blonder on 10/25/03 at 1:32 PM:
How is the LED array connected? Each LED has a slightly different voltage drop, so you can't connect them in parallel. In order to have the array operate at 9 volts, there must be 4 LEDs in series, or else there is a resistor in series, or both. The power wasted is: (14.4-9)*2.8 = 15.12 watts. I makes no difference whether you dissapate the power in a constant current source or in a resistor. The resistor value is 1.9 ohms (2 ohms is probably close enough. A 2 ohm, 25 watt resistor from Mouser (www.mouser.com) costs $1.09, part number280-CR25-2.0.
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