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do i need resister if i am connecting 3 high brightness leds to be connected to usb??? Answered

i want to make a usb lamp....

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dalucero
dalucero

12 years ago

11010010110 is right. Use that link. You need to limit the current flowing through the LED. Figure out what your LED's safe operating points (forward voltage, current) are and go from there. 5 volts is probably not enough to power three LED's in series so you'll have to put them in parallel. Putting 5 volts across an LED will likely draw too much current for the LED to handle and it may burn out or worse. Putting a resistor in series with the LED will drop the voltage across the LED allowing a safe amount of current to flow while still lighting up the LED. Pick a resistor value that drops the LED's voltage down to what the LED's spec sheet says for a typical forward voltage.

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S1L3N7 SWAT
S1L3N7 SWAT

12 years ago

You might not even be able to power 3 high intensity LED's from a USB source because most USB ports have a 5v output. This would make your LED's quite dim (or not lit at all). Maybe I'm wrong, I think I've seen somewhere that said it gives out up to 7v, not sure.

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frollard
frollard

Answer 12 years ago

USB should put out (if spec) 5v regulated, and 500ma max.

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S1L3N7 SWAT
S1L3N7 SWAT

Answer 12 years ago

Crap! I just realized that a USB port can provide sufficient power to the LED's. Especially if they are ~3v. Even if they are 5v it should be fine. My bad.