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I'm not quite sure whether or not my LEDs will draw too much current. I can't put the schematic right now, but basically I'm using just using the power line from the USB 2.0 port on my board, and it has to power:

x12 WS2812B SMD RGB LEDS

x1 ATMega32u4

also, if you could tell what kind of resistor I should put on the power line, if I need one at all, that would be super helpful.

sorry for not knowing anything

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  • \$\begingroup\$ Why do you think it needs a resistor to begin with? \$\endgroup\$
    – Justme
    Apr 21, 2021 at 15:54
  • \$\begingroup\$ because I know nothing about circuits :/ \$\endgroup\$ Apr 21, 2021 at 16:04

3 Answers 3

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The current draw of one WS1812B is approximately 50 mA each (source). Twelve of them will draw as much as 50 mA * 12 = 600 mA in the worst case, which exceeds the limit (500 mA) that can be drawn from a normal USB port.

It may be possible to use a USB power supply, but you will need to communicate with it to request a higher current limit, which leads to extra complexity.

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  • \$\begingroup\$ I was never planning on running them at full power, that would be far to bright for the application im using them in, so would it work then? Also would I just set that in the controller, or would I want to put a resistor in to accomplish that? \$\endgroup\$ Apr 21, 2021 at 15:49
  • \$\begingroup\$ use two USB ports ... put six LEDs on each one \$\endgroup\$
    – jsotola
    Apr 21, 2021 at 16:34
  • \$\begingroup\$ @BradyDavis You would need to set it in the controller. The WS2812B LEDs include active control circuitry and expect 5 V; you should not insert a resistor in the supply path. \$\endgroup\$
    – nanofarad
    Apr 21, 2021 at 17:03
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Based only on the information given, I don't think this will work. Fully illuminated, the LEDs will require more current than the default provided by a standard USB port.

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I'm pretty sure most 'cheap' power banks that have USB ports up to 2A with just the data pins bridged are quite happy to give up to 10W no questions asked. You probably wouldn't get the performance off a laptop USB port, but in your application I think a cheap/normal power bank would be just the device to use. Even 'smarter' power banks only negotiate more power as in QC3 or PD by changing voltage, a 'dumb' load should be able to get 1-2+A out of most power banks on the market today! (just putting a low value resistor between + and - on the USB port of a power bank will deliver current until tripped by over current sensing (2+ A load), the power bank has no way to detect/enforce a 500mA limit on 'dumb' USB clients)

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