> The patent number should be 6,043,695, issued March 2000, filed in 1998.
If
> I recall correctly, it was the reverse insertion of an N-channel Mosfet in
> the low side of the load.  I found this patent interesting about a year
ago
> or so and we examined it thoroughly.  I also discovered 2 issuances of
prior
> art, much greater than the one year prior to filing.

Yes - there is any amount of prior art re the use of a "reverse" MOSFET for
battery protection. A recent Siliconix tech note cites a much prior version,
very possibly in order to expressly counter this unmeritorious patent. I
haven't seen the diagrams for their other variants with 2 transistors but
they apparently build on this basic "concept". The basic claim is clearly
(IMHO) without any merit whatsoever. The original idea was clever enough but
it was not THEIR original idea. This is either a blatant attempt at theft of
public domain intellectual property or an atrociously researched application
by inadequately informed developers. Either way the basic claim in the
patent is worthless.

The addition of a zener to protect a FET gate against excessive drive
voltage and the resistor to provide said gate drive is utterly standard
practice for driving FETs (and I use circuits that do just that). Pray tell,
how else are you going to do it in a minimal configuration? Using prior art
in conjunction with other prior art can sometimes create innovation
(especially in the eyes of a Patent Attorney) but I wot that in this
instance it just creates bunkum. GM and their no doubt well paid patent
attorneys may opine otherwise.



            Russell McMahon

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