> Sure thing!
>
> I saved the lab to a word doc and put it on my Google Drive.
> drive.google.com/file/d/0Bw1n2tiO8ikQVzlaekYyblVYaXM/
> view?usp=sharing
>
> --
> Sincerely,
>
> James Burkart
> *Filmmaker & Documentarian*
>
> *Burkart Studios*
> 925.667.7175 <(925)%20667-7175> | Personal
> 415.738.2071 <(415)%20738-2071> | Office
>
> *Web:* burkartstudios.com
> *Facebook:* facebook.com/burkartstudios
>
> On Mon, Sep 11, 2017 at 8:31 PM, Sean Breheny <
shb7EraseME
cornell.edu> wrote:
>
>> Could you post a photo of the original problem so we could see if somehow
>> you are interpreting it differently than we would?
>>
>> I just tried the physical circuit (I used a J310 because I don't have a
>> 2N4860 and J310 seems very similar) and I can't get anything like the
>> voltages they describe by making any one resistor open or shorted,
>> regardless of whether I use a 10Mohm input impedance voltmeter or a 10G
>> ohm
>> impedance voltmeter. If I open the source resistor and measure Vs, I get
>> about 3V with either the Rin=10Mohm meter or the Rin=10Gohm meter.
>>
>>
>> On Mon, Sep 11, 2017 at 9:04 PM, James Burkart <
RemoveMEjamesEraseME
spam_OUTburkartstudios.com>
>> wrote:
>>
>> > Actually I meant Vgs closer to 0V, not Vg.
>> >
>> > --
>> > Sincerely,
>> >
>> > James Burkart
>> > *Filmmaker & Documentarian*
>> >
>> > *Burkart Studios*
>> > 925.667.7175 | Personal
>> > 415.738.2071 | Office
>> >
>> > *Web:* burkartstudios.com
>> > *Facebook:* facebook.com/burkartstudios
>> >
>> > On Mon, Sep 11, 2017 at 7:02 PM, James Burkart <
>>
@spam@jamesRemoveME
EraseMEburkartstudios.com>
>> > wrote:
>> >
>> > > Raising the value of Rs serves to increase negative biasing the gate,
>> > > which raises the value of Vds. Lowering it brings Vg closer to 0V, but
>> > > increases Id, and increases the voltage drop across Rd.
>> > >
>> > > Opening Rs pulls Vg to ~-5V, and the transistor is in cutoff. In this
>> > case
>> > > I do get 15V at Vd since there is virtually no current through the
>> > > transistor (spice simulation shows 177pA) but then Vds becomes ~10V.
>> > >
>> > > --
>> > > Sincerely,
>> > >
>> > > James Burkart
>> > > *Filmmaker & Documentarian*
>> > >
>> > > *Burkart Studios*
>> > > 925.667.7175 <(925)%20667-7175> | Personal
>> > > 415.738.2071 <(415)%20738-2071> | Office
>> > >
>> > > *Web:* burkartstudios.com
>> > > *Facebook:* facebook.com/burkartstudios
>> > >
>> > > On Mon, Sep 11, 2017 at 1:10 PM, Dwayne Reid <
EraseMEdwayner
@spam@planet.eon.net>
>> > > wrote:
>> > >
>> > >> Hi there, Sean.
>> > >>
>> > >> You are forgetting about current that flows through the gate resistor
>> > >> to Ground. This is a J-FET, so the gate diode junction is forward
>> > >> biased if Rs is open.
>> > >>
>> > >> Another possibility that Rs is very high value. I haven't bothered
>> > >> to work out the math for the possible high value.
>> > >>
>> > >> dwayne
>> > >>
>> > >>
>> > >> At 11:58 AM 9/11/2017, Sean Breheny wrote:
>> > >> >I might be missing something but I don't think this problem is well
>> > >> >designed. I think we can narrow it down to Rs being open but
>> > technically
>> > >> it
>> > >> >isn't possible, as far as I can see, to get exactly the voltages
>> > >> mentioned.
>> > >> >Vd=15V implies that absolutely no current is flowing from the
>> supply,
>> > so
>> > >> >there shouldn't be ANY voltage drop across the drain-source
>> connection.
>> > >> >
>> > >> >Here's my train of thought:
>> > >> >
>> > >> >If Rd were open, Vd would be zero.
>> > >> >If Rd were shorted, the current would be limited by the negative Vgs
>> > >> which
>> > >> >would develop (I am defining negative Vgs as Vs>Vg, which reverse
>> > biases
>> > >> >the gate junction for an N JFET), so there would be some Vds drop of
>> > >> >several volts.
>> > >> >
>> > >> >If Rg were open, I think the FET behavior would tend toward the
>> Vgs=0
>> > >> >behavior where almost the maximum current flows, but then Vd would
>> be
>> > >> less
>> > >> >than 15V.
>> > >> >
>> > >> >If Rg were shorted, the circuit would behave almost as if nothing
>> were
>> > >> >wrong, unless 15V was enough to cause reverse breakdown of the gate
>> > >> >junction, but in that case Vd would be less than 15V since an
>> excessive
>> > >> >leakage current would flow.
>> > >> >
>> > >> >If Rs were shorted, Vs would be zero.
>> > >> >If Rs is open, then we would expect Vds=0 (Vd=Vs=15). This is the
>> > closest
>> > >> >to what we observe. In the real world, the 10Meg input impedance of
>> a
>> > >> >typical multimeter would probably produce something similar to what
>> is
>> > >> >claimed here (it would act as a very high value of Vs) but Vd would
>> not
>> > >> be
>> > >> >identically 15V.
>> > >> >
>> > >> >
>> > >> >On Mon, Sep 11, 2017 at 12:57 PM, Dwayne Reid <
>>
@spam@dwaynerspam_OUT
.....planet.eon.net>
>> > >> >wrote:
>> > >> >
>> > >> > > Hi there.
>> > >> > >
>> > >> > > Consider what happens if Rs goes open. Also consider that the
>> gate
>> > >> > > junction becomes forward-biased when Vgs goes negative.
>> > >> > >
>> > >> > > dwayne
>> > >> > >
>> > >> > >
>> > >> > > At 06:40 AM 9/11/2017, James Burkart wrote:
>> > >> > > >Hello all!
>> > >> > > >
>> > >> > > >I am working on a lab for a class and we are given a simple
>> > >> self-biased
>> > >> > > >N-channel JFET circuit: Rd = 4.7k, Rs = 1k, Rg = 2M, Q1 =
>> 2N4860,
>> > >> Vdd =
>> > >> > > >+15V.
>> > >> > > >
>> > >> > > >Then we are given the scenario: Vds = 66.5mV, Vd = 15V, Vs =
>> 14.9V.
>> > >> > > >
>> > >> > > >Assuming only one component can be bad, what is the likely
>> problem?
>> > >> > > >
>> > >> > > >I built the circuit in MPLab and tried everything I could think
>> of
>> > to
>> > >> > > >recreate the voltages, but everything I tried does not work.
>> > >> Shorting Rd
>> > >> > > >was my first thought, but that also results in Vds being 12.6V..
>> > What
>> > >> am I
>> > >> > > >missing? Can anyone get me on the right track? I have shorted
>> and
>> > >> opened
>> > >> > > >all resistors, the only thing I can't do (or don't know how to
>> do)
>> > is
>> > >> > > >recreate a faulty FET.
>> > >> > > >
>> > >> > > >--
>> > >> > > >Sincerely,
>> > >> > > >
>> > >> > > >James Burkart
>> > >> > > >*Filmmaker & Documentarian*
>> > >> > > >
>> > >> > > >*Burkart Studios*
>> > >> > > >925.667.7175 <(925)%20667-7175> | Personal
>> > >> > > >415.738.2071 <(415)%20738-2071> | Office
>> > >> > > >
>> > >> > > >*Web:* burkartstudios.com
>> > >> > > >*Facebook:* facebook.com/burkartstudios
>> > >>
>> > >>
>> > >> --
>> > >> Dwayne Reid <
spamBeGonedwaynerEraseME
planet.eon.net>
>> > >> Trinity Electronics Systems Ltd Edmonton, AB, CANADA
>> > >> 780-489-3199 voice 780-487-6397 fax 888-489-3199 Toll Free
>> > >>
http://www.trinity-electronics.com
>> > >> Custom Electronics Design and Manufacturing
>> > >>
>> > >> --
>> > >>
http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive
>> > >> View/change your membership options at
>> > >> mailman.mit.edu/mailman/listinfo/piclist
>> > >>
>> > >
>> > >
>> > --
>> >
http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive
>> > View/change your membership options at
>> > mailman.mit.edu/mailman/listinfo/piclist
>> >
>> --
>>
http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive
>> View/change your membership options at
>> mailman.mit.edu/mailman/listinfo/piclist
>>
>
>