From: Sean Breheny <shb7@cornell.edu>
To: Microcontroller discussion list - Public. <piclist@mit.edu>
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Date: Wed, 8 Jan 2020 00:19:03 -0800
Subject: Re: [EE]: LTSpice Question
Thread-Topic: [EE]: LTSpice Question
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I think that you would need to either manually enter parameters for a
depletion mode MOSFET into an instance of one of the MOSFET simulation
models or (as Bob suggested) get a model for a depletion mode MOSFET online=
..

As Bob also pointed out, JFETs are inherently depletion-mode devices.

I once had a reason to use a depletion-mode device in a commercial design.
To ensure a clean reset behavior, we wanted to make sure that the
capacitance on an internal bus of the device would be fully discharged
quickly in the event of power loss, but without adding any additional
current drain under normal circumstances. Using a JFET was a nice solution
to this because we could just bias the gate into pinchoff (the OFF state)
during normal operation but on loss of power, the gate would float and the
drain-source connection would look like a fairly low (about 1k ohm)
resistor.

On Tue, Jan 7, 2020 at 6:30 PM Ryan O'Connor <rocifier@gmail.com> wrote:

> Looking forward to later hearing about a practical reason to use depletio=
n
> mode mosfets!
>
> Ryan
>
> On Wed, 8 Jan 2020 at 09:00, Jim <jim@jpes.com> wrote:
>
> >
> >  All,
> >
> >  I have a need to simulate a circuit using a Depletion Mode MOSFET usin=
g
> > LTSpice.
> >  I have looked at the list of MOSFETs included in the application, but =
I
> > don't see any Depletion Mode FETs.
> >  Does anyone have any idea what part number in LTSpice could be a
> > Depletion Mode MOSFET?  Or does anyone have a model of
> >  an N Channel Depletion Mode MOSFET that will run under LTSpice?
> >  The parameters of the particular part number aren't an important issue
> > at this time.  I just need a functional model
> >  for a quick proof of concept for a new circuit for a new product at
> > work.   I can't elaborate on this further at the
> >  moment, but later, if all works out, I'll let everyone know that is
> > interested what the circuit is intended to do, and
> >  if it does what it's supposed to.
> >
> >  Anyway, if anyone knows if any of the MOSFET part numbers listed in
> > LTSpice are Depletion Mode FET's, please let me
> >  know.
> >
> >
> >  Thanks and Regards,
> >
> >  Jim
> >
> >
> > --
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