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What is the maximum number of LEDs I can fit on USB ? Answered

As Far as I know USB is 5V and wikipedia told me it supports 900mA Current Output.
What is the maximum number of LEDs I can hook upto to a USB port SAFELY ?
I have 3V LEDs (20mA I GUESS)and they come very cheap here around Rs.2 for 1 LED (25 for $1)
And how do I do that? Parallel would be the best I guess...,,I really don't know what current my PC can give safely...!
Thank You

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mayur.phadte (author)2010-10-16

I am pretty sure my ipod takes something more than 100mA !

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lemonie (author)2010-10-05


USB is only good for some things, don't use it as a power-supply. You've probably got a spare MOLEX inside the case. (unless it's a laptop)

L

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Re-design (author)2010-10-05

I don't think you can get more out of a usb than 100ma unless you have a circuit to tell the port to send more. In other words yoy must communicate to the port.

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frollard (author)Re-design2010-10-05

I thought they generally by spec put out 500mA but got really mad at you if you exceeded it, and shut it down out of spite. I know older 1.1 ports had the 100mA limit unless you communicated with the host.

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Re-design (author)frollard2010-10-05

You may be right, I'm going by memory and didn't check my facts before posting. SO, that means that it is just a fact to check up on before anyone constructs a circuit running off usb port.

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steveastrouk (author)Re-design2010-10-05

You're right. ANY fully compliant port is supposed to allocate 100mA, until negotiation.

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Re-design (author)steveastrouk2010-10-05

I thought that's what I learned form You.

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