@Micrified And how can you get away with using a small, high frequency transformer? Because there's a switching circuit on the high voltage side that chops the high voltage DC into pulses. It then regulates the output by varying the pulse width and/or frequency.

@Micrified The main check (for me) if a voltage/current source is linear, is how the device responsible for the output voltage is being controlled. If it's being switched between on and off, it's a switching stage. If it's normally operating in saturation(FET)/active(BJT) region, then linear.

good morning!

I'm not sure if this is relevant for a question. The datasheet for Silabs' EFM8BB2 series states "All pins 5 V tolerant under bias". What does "under bias" mean in that context?

Absolute maximum ratings table on page 28: V_in,max = 5.8 V if Vdd > 3V3, else V_in.max = Vdd+2.5 V. I guess this is relevant when the chip is not powered, but an I/O pin is pulled to 5V

@Christoph Yes, they mean 5V-tolerant with the processor powered up. The other interesting edge case is that it's not 5V tolerant at its minimum supply voltage of 2.2V

so to be sure that everything is ok, I'd have to switch pull-ups to 5 V on only when 3V3 is available

Yeah, a 5V pull-up where the processor could be powered-down would violate the absolute maximums