I've come back to this hobby few weeks ago after a hiatus of maybe 20 years and I'm having a lot of fun.
This weekend I started investigating PWM, hardware side this means MOSFET. After a false start in which breadbord capacitance connection inductance and probably gremlins gave me a hell of ringings I switched to pre-drilled protoyping PCB (I don't know the english term, in italian they are called "thousand holes") and got consistent results. First I built a simple common source switch(very easy). Then and H-bridge to drive a DC motor (easy and fun).
Question 1) I grok all power MOS have body diodes. Are these enough to act as a freewheel (I think so) or am I supposed to add external part?
Easy successes and lots of fun led my hubris making me greedy: i decided to approach BLDC motors the hard way, i.e. from scratch. My thinking was "a 3 phase bridge is jus one leg more than an H-bridge". Then I realized that maybe I would have liked to look at currents in the windings and inserted small resistor. Then I realized that I had no idea of the magnitude of those currents so, maybe, I had better foresee some kind of variable gain in the sense. Then I realized that it would have been nice to have comparators to look for zero crossings... I mean I had no idea if any of those things would work as expected but that's the point of prototyping. It is not the more up-to date technology: most of the components were in my drawers for more than 20 years!
(decoupling capacitors 0.1uf and 1uf for TC4422 not shown)
It took me one day, with some undoing and redoing, I did a sketch of the placement of most components but then comparators were added at mid work and some noob mistake (after 20 years you get back to noob again) like not considering front-back view of pinout of one chip :-(.
Building it has been really instructive. As I was progressing I realized that there is an optimal order in connecting wires. After some hours I started to feel that something went wrong somewhere. Or I made a step too long or I'm not ready for this level of complexity with this prototyping technique) or whatever...
Point is that this object (It didn't work
) is not debuggable (not by me at least)
Question 2) How would you have realized such a prototype? with a different technique or just with a larger board?
It draws current at rest I even found a bug (a missing connection) but to no avail. It is nearly impossible to even see through the mess of cables. I'll keep it for onrment! :-D
Question 3) Is it worth some more time?
Even it was a failure I learned a lot by making it.
Now I know that for this level of complexity I will make a PCB probably most, if not all, in SMD so I have to buy new components. Now it's a good moment to amend errors, add new functions and so on. What I would like to do is a board that lets me to learn about BLDC control, sensored, sensorless, FOC, whatever... for fun. So definitely no fancy components "I do it all" that would fail the learning focus and bring out in hardware as much as possible (just the contrary of real world), as I want to see most signals on the scope. The idea is to stay within 15V limit (4 lipo cells) possibly even less. As for the current, the biggest motor I ordered is this one 4100KV
https://www.aliexpress.com/item/32833212767.html?spm=a2g0s.9042311.0.0.1ec64c4dPMJPJowhich I really don't understand
Question 4) what 80A means? (I hope peak) and
Question 5) what implication it has on dimensioning the MOSFETs
Most important:
Question 6) That's not a question, it is a suggestions session. Please criticize!