On Thu, 24 Jan 2019 at 04:31, David Van Horn <
david.vanhorn@backcountryaccess.com> wrote:

> Here's an odd question:   Take a common P Fet, in this case an AO3435 fro=
m
> Alpha and Omega.
> Ground the drain. (Actually connected to a small winding on a transformer=
,
> but <<1 ohm DC path to ground)
> Connect the source to ground through 47k
> Connect the gate to the source through 100k.
> Connect a 100uF capacitor to the source and ground.
>
> Is the FET on, or off in this condition?
>
> If the transformer has AC on it:

On Vtransformer =3D Vt =3D Vdrain positive excursion > 1 diode drop, Csg wi=
ll
charge positive via FET body diode.

On Vt < gnd excursions, Millar capacitance Cdg may drive gate negative
relative to source depending on gate voltage slew rate compared to gate
time constant (Cgs.Rgs + C...)

So FET may turn on part way into negative cycles and discharge C100uF until
source tends to assymptote towards drain by Vgsth, but period is also
dependant on gate time constant.

it turn on blips or maybe long on's part way through negative drain
transitions.

Needed: Waveform on drain - frequency , voltage , shape.

         Russell
--=20
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