Comment by nomel
5 years ago
If your system is pulling 500 watts at 120V, that's around 4A of line voltage. If you drop down 20% to 100V, the output will happily still pull its regulated voltage, but now the line components are seeing ~20% more, at 5A. For brown out, you need to overrate your components, and/or shut everything off if the line voltage goes too low.
I used to do electrical compliance testing in a previous life, with brown out testing being one of our safety tests. You would drape a piece of cheese cloth over the power supply and slowly ramp the line voltage down. At the time, the power supplies didn't have good line side voltage monitoring. There was almost always smoke, and sometimes cheese cloth fires. Since this was safety testing, pass/fail was mostly based on if the cheese cloth caught fire, not if the power supply was damaged.
Why wouldn't the power supply shut down due to overcurrent protection?
That's likely on the output side, which doesn't see overcurrent.
"output will happily still pull its regulated voltage" you mean power, right?
All standard computer components require a regulated voltage, then they consume power as a consequence of their operation. The steady voltage is required because the transistors in ICs will break down if voltages go too high, or stop operating if they go too low. Forcing something like an IC to always use the same amount of power, even if it were idle, isn't really possible, because nobody would build it that way.