Thanks once again saand.
Now I understand what you mean by doing calculations.
As for doing actual work, the project is on hold for one month while I sort out my personal life (i.e. further education) and spend more time with my family - sailing Georgian Bay to Lake Huron for a week.
I'm still thinking about it, and reading online when I can.
I was reading this appnote:
http://www.national.com/an/AN/AN-558.pdf
At the bottom of Page 12 it reads:
Quote:
There
is also the possibility that the drain-source voltage will exceed
its maximum rated voltage due to ringing in the drain
circuit. A protective RC snubber circuit or zener diode may
be added to limit drain voltage to a safe level.
|
So here's the question - do I actually *have* to add capacitance to hold up my power rails, or can I just protect the mosfet by putting a 90V zener across Drain-Source?
I know what the correct solution is, but I specced out capacitors based on my values and the calculations you showed, and we're talking $100 of capacitors; there are already $50 on the board. I'm starting to feel silly here... There must be a compromise!
My last option is to start from scratch on the capacitor board. Clearly the one I have is too inductive, even with its hugely wide traces; they are just too long - and too far away from the mosfets!
I think that is why P+S's controller has the capacitors along the length of the controller. I thought with a short controller (come on its only four inches of HUGE buss bar) that I could get away without doing that.
Thoughts/opinions?