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• sztanozs veterán

  #45958

  #45957 Aryes

  2023-03-09 17:16:08

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  sztanozs

  veterán

  #45957 Aryes

  Az eredeti linken:
  The microUSB input port also has a 1.1 A polyfuse (700 mA "hold current") which may also have enough resistance (although much smaller than the 140 mA fuses) to cause a significant voltage drop on the board, even below its 1.1 A total current.

  Plusz a bejegyzesben hivatkozott polyfuses explained linken:
  100 mW polyfuse vs 100 mW load:
  If a regular current of something like 100mA runs through it the voltage across the fuse can be something like half a volt. This means that the USB device gets half a volt less, so if the board gets 5.0 Volt, the USB device (when it uses 100mA) gets just 4.5 Volt. Normal 5V logic will not work reliably, as it can tolerate no more than 5% undervoltage (0.25V), so at less than 4.75 Volts the device is being operated below design. Luckily the USB specification orders the manufactures of simple USB devices, such as keyboards and mice, devices that typically work behind a passive HUB (that gets its power from the computer, not from a separate PSU) that they should design their device so that it can work with the voltage behind a hub.
  ...
  The main power input fuse is much less problematic, but it too can misbehave in similar way.

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