Thanks guys. I can still claim not to have lost my mind then :)

Yes, I think he was thinking bipolar initially and then was probably
too embarrassed to admit his mistake.

Cheers,
Zik

On 3/29/07, Herbert Graf <mailinglist3@farcite.net> wrote:
> On Thu, 2007-03-29 at 12:03 +1000, Zik Saleeba wrote:
> > I was having a conversation with the chief design engineer at my place
> > of work yesterday. He was saying he'd have to install an extra 3.3V
> > voltage regulator in our design because I'd just discovered that we
> > needed a second switched 3.3V supply. I suggested we used a high-side
> > FET switch instead  - a suggestion he dismissed by saying the voltage
> > drop across the FET was around 0.6V which would put the supply well
> > out of spec.
> >
> > This man is a chief hardware designer of 40 years experience. I'm just
> > a computer scientist who does electronics for a hobby. Am I crazy or
> > is he completely wrong on this one? I'd be expecting a voltage drop in
> > the millivolts at the low currents we're talking about - not 0.6V. Can
> > someone set me straight here?
>
> Assuming you are driving the gate high enough, the FET should appear as
> a low value resistor, so any voltage drop will be directly related to
> the current going through it. Assuming a very low current the voltage
> drop will be very small.
>
> The engineer was probably thinking BJTs. I wouldn't bother debating, get
> a spice program and show him what the situation would really be. TTYL
>
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