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Powering an Arduino: USB, VIN and the regulator

Embedded (Arduino) · Intermediate · about 15 minutes · part of Zen’s Electronics Design Mastery

On USB the board runs from the computer’s 5 V (through a 500 mA fuse on the Uno). On VIN or the barrel jack, the onboard regulator drops 7–12 V to 5 V and turns the difference into heat: P = (VIN − 5 V) × I. At 12 V it can only feed a couple of hundred milliamps before it overheats and shuts down, and the board resets. Never feed the 5V pin from more than 5 V.

Powering an Arduino: USB, VIN and the regulator: the circuit on the simulator's bench

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Try it on the bench

  1. With 12 V and a 47 Ω load (about 100 mA) the regulator gets hot but holds. Change the load to 22 Ω: it overheats, shuts down, and the board keeps resetting.
  2. Turn the supply down to 7 V: the same load runs cool. Below about 6.2 V the 5 V rail starts to sag (the regulator needs about 1 V of headroom).
  3. Move the red wire from VIN to the 5V pin with 12 V: that is how boards get destroyed.

Parts on the bench

In the course

Zen’s Electronics Design Mastery, module “Microcontrollers & Embedded”.

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