I want to make a controller for a golf cart motor and am considering using
paralleled MOSfets or HEXfets. I know that there can be problems with the
individual xsistors not sharing the load equally. Would it help if I had a
seperate line driving each one rather than hooking up to some common rail to
activate them? Any info would be much appreciated.
I'm sure you are already aware of "thermal runaway" in BJTs. But there have
been some comments about using paralleled hexfets on sci.electronics.design, a
few year ago, I believe. I gathered that safely paralleling power MOSFETs only
works well when switched completely on/off, where V(GS) is substantially above
the zero thermal coefficient point. Somewhere in the discussion about the
problems of the temperature coefficient for Id, given a fixed Vg, the Hitachi
2SJ160 and 2SK1056 family was mentioned as attractive because of their
zero/negative coefficient in this regard.
There may also be serious oscillations to worry about, particularly when
operated linearly, as well, if memory serves. I'm no expert in this, at all. I
haven't tried to analyze this problem; and never ever tried to do something like
you are going to try -- hopefully someone who has can comment. But controlling
large inductances at large currents with paralleled HEXFETs (or MOSFETs or BJTs)
and where the actual motor load/acceleration can vary in spurts and jerks, I'm
sure, will take some careful attention to get working well -- probably combining
mechanical and electrical means.
You might use google to look up some threads in sci.electronics.design and/or
otherwise post this question there.
Jon