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Comment by ComputerGuru | Hacker News Reader

If, as a result of the voltage and current regultors in the AVR, the AVR only sources X amount of current, adding load past that point will not magically introduce more current (and thus, heat) into the equation, though... Assuming the maximum supported load is also the maximum physically available, the maximum heat generated should be tolerated OK.

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Yes, that's true.

One has to wonder, though, that if the AVR had its own current-limiting circuitry, why would the author of this article add his own?

Furthermore, reducing the power unilaterally may protect the chip from thermal overload, but it will also probably cause the chip to reset, causing undefined behavior in the circuit it's controlling.

So I'm really not completely sure what's going on.

As jrockway mentions, the ATMega does not have a power regulator. That would be inefficient as regulators work by dissipating excess energy as heat. So, even if the chip had onboard regulators to limit the combined current draw of the output ports to 200mA the chip would still be susceptible to overheating.

That said, I'd guess the weak link that puts the 200mA limit in place is not actually in the I/O circuitry but is how much current can safely be drawn by the I/O pins when the chip is otherwise fully utilized - peripherals and CPU both consuming max power.

The atmega may not, but the Arduino itself does; the output of that regulator flows into the ATMega...

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