On 29 Jan 2017 at 21:40, IVP wrote:
> > It seems a bit strange to me to drive the gate of the mosfet from a sup=
ply
> > which is referenced to +16V and GND when the source of the fet is at
>=20
> Well, as it's a P FET I was thinking upside down, but evidently not think=
ing
> hard enough and it's come out as part N FET drive
>=20
> I've restored the circuit to how it originally was
>=20
> https://www.flickr.com/photos/97814409@N04/albums/72157675978832174
>=20
> Output is 2.2V into 6R8
>=20
> Gate voltage is from 1.3V to 8.8V. The test circuit in the ATP106 d/s
> shows gate drive from 0V to -10V, with source at 0V, which would be
> 0 to +10 for an N FET. As I figure it then, my gate is reaching only a
> relative -7.5V
>=20
> So I should be taking the emitter of the BC327 to at least a couple of
> volts below 0V if source is at +9V ? That would make the gate 11V
> below the source

Hi Joe,

ATP106 datasheet talks about gate drive as low as 4.5V gate drive, though 1=
0V=20
obviously gives better Rdson. Gate cutoff voltage is specified at 1.5V min =
to 2.6V=20
max (for 1mA drain current @ Vds =3D 10V), so your revised circuit & measur=
ed gate=20
voltages of 1.3V and 8.8V seem within workable range. Even if interpreted=20
differently and the 1.3 and 8.8V were measured wrt 0V, then translating tha=
t would=20
give Vgson =3D 9-1.3 =3D 7.7V, and Vgsoff =3D 9-8.8 =3D 0.2V, in other word=
s still fine.

Seems like drive circuit should be good enough. Sure some tweaking might he=
lp but=20
doesn't seem like it would make the difference between working and not-work=
ing.



--=20
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