Hi all, Over the last few days Oscar and myself have been pushing this investigation further. With a sprinkle of inspiration backed up by excellent experimentation we have come up with a very simple solution: one Schottky diode. http://www.milton.arachsys.com/nj71/index.php?menu=2&submenu=2&subsubmenu=3 Cheers, Neil -- http://www.njohnson.co.uk