Well of course if the gate voltage is 5V, then the high side of the MOSFET
will actually be Rds x Id, which will typically be <<1V. When the high side
voltage is 5V (or 12V) the gate voltage will be 0V. As far as I'm aware
there's actually no requirement that the high side voltage (when switched
off) is even higher than the (on) gate voltage - the two aren't really that
closely related.

Chris


On Mon, Jan 6, 2014 at 8:59 PM, Josh Koffman <joshybear@gmail.com> wrote:

> Hi all,
>
> I'm adding something on to a project I designed awhile ago, and I just
> want to double check something.
>
> I am adding an N-Channel MOSFET to an existing project of mine to
> allow for a greater load capacity. It will be on/off, but might
> involve PWM. At the moment I'm looking at the STP36NF06L, mainly
> because I've seen it used in a few examples and I can get it easily,
> but I am open to other easy to drive parts.
>
> The question is, if I'm adding this on the low side, as long as the
> high side is greater or equal to the gate voltage, am I ok? For now
> the MOSFET high side will be at 5V, same as Vdd, but in the future I
> might want it a bit higher to switch something else (say 12V). I
> believe I'm fine at 12V, but I want to make sure that having the high
> side at 5V and the gate voltage (coming from the PIC) at 5V won't
> cause something I haven't thought of.
>
> Thanks!
>
> Josh
> --
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> completely foolproof is to underestimate the ingenuity of complete
> fools.
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