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

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) 6 years ago
I am pretty sure my ipod takes something more than 100mA !
lemonie6 years ago

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
Re-design6 years ago
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.
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.
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.
You're right. ANY fully compliant port is supposed to allocate 100mA, until negotiation.
I thought that's what I learned form You.