[quote author=Nick Gammon link=topic=150619.msg1131096#msg1131096 date=1361737286]
Watch this, all is revealed:
[/quote]That's clever. I'll have to check which of my p-channel MOSFETs suit because anything I have made where the source closely matched the voltage required has been unprotected against reversing the polarity up to now. Thanks for pointing that out Nick.
Geoff