I have two questions regarding the PSM:
Does the PSM provide short circuit protection for the power bricks? I.e., is it a good idea to put a diode in line with the power bricks so that a short on one of them does not short both? Looking at the schematic, I guess it’s meant to act as an ideal diode, but I wanted to be sure.
When the PSM is selecting the power source with the highest voltage, is there some voltage or time hysteresis to prevent flip-flopping between inputs due to voltage sag?
It doesn’t look like there is any current limiting on the INPUT side of the PSM. Depending on where the short is it would not do anything to stop it from the input supplies point of view. Not that it should, normally the source of the power would handle that.
I probably wouldn’t put a diode in line, there really isn’t that many opportunities for a short between your power supply and the output protection of the PSM (as long as your wiring is robust).
Theoretically the diode would do that job but then your going to have a pretty significant voltage drop and it would probably put your power supply out of spec and that’s before considering thermal management of that diode.
The IC on the PSM looks to be a LT4417 if you want to read up on how it works. I think there is some hysteresis.
Aha, thanks for identifying the chip. Looks like they left it with the default hysteresis, which is 30mV.
I probably wouldn’t put a diode in line, there really isn’t that many opportunities for a short between your power supply and the output protection of the PSM (as long as your wiring is robust).
Agreed, except that in my setup (and many others, I suspect), the second power input is also powering the servo rail which can have any arbitrary device plugged into it, which introduces opportunities for overcurrent or shorts. I was thinking about protecting the FC from a stalled servo or something.
Theoretically the diode would do that job but then your going to have a pretty significant voltage drop and it would probably put your power supply out of spec and that’s before considering thermal management of that diode.
True, although in my case I have control of the input voltage, and many people use Mauch power boards which provide 5.3V, in which case the ~.35V drop from a Schottky diode would still provide an acceptable input.
Anyway, instead of staring at the schematic some more, I decided to test it. It appears that the PSM does indeed act like an ideal diode - a shorted input does not affect the other inputs.