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What's the current supply of a USB? Answered

I want put 3 LED's and a flashdrive into another container, and have the LED's turn on when plugged in, but I'm not sure how to go about wiring up the LED's. What's the supply current that I should use to find the right resistor?

If a poorly made diagram gives you a better idea of what I'm talking about you're in luck!

I know USB gives 5 volts, but I don't know about the current.

And would any problems arise from three LED's and the drive plugged into one USB?


No more than 100mA without smarts in the box you plug in, so three LEDs you should be fine.

You have all the information you need. Now just apply Ohms Law -- V=IR to calculate the resistance. If you want to make it even easier, use led.linear1.org/led.wiz . You have the diagram exactly right, 3 different leds with different resistors on each. Be sure to change the V(f) for each led because each colour will draw different voltage. Most leds are happy with 15-25mA each. Tip: underdrive them (less mA) so they are not obnoxiously bright and use less power.