Author Topic: JFET approximations (gate-Voltage)  (Read 767 times)

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Offline sspj9

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JFET approximations (gate-Voltage)
« on: February 04, 2016, 05:17:51 am »
I designed a JFET to output a constant current of 10mA for an assignment. Using 2N3819 with Vdd 20 V, we assumed that Vg is 4V, however we need to explain to why we set it to 4V. I mean we could set it to any value right and just change the resistors. Can anyone help?
« Last Edit: February 04, 2016, 05:29:50 am by sspj9 »

Offline Simon

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Re: JFET approximations (gate-Voltage)
« Reply #1 on: February 04, 2016, 05:52:42 am »
Not sure, the other way of asking the question is explain why you chose the resistors, presumably you have cme up with a suitable compromise of resistors and Vgs New stock now in of EEVblog 121GW and Brymen 235 Now selling a selection of Probe Master probes.

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Offline Gyro

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Re: JFET approximations (gate-Voltage)
« Reply #2 on: February 04, 2016, 06:21:20 am »
This Vishay App note might be of some help to you:

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Offline T3sl4co1l

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Re: JFET approximations (gate-Voltage)
« Reply #3 on: February 04, 2016, 09:42:40 am »
2N3819 isn't a very good choice for this... in most cases, Vg would need to be forward biased.

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Offline alsetalokin4017

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Re: JFET approximations (gate-Voltage)
« Reply #4 on: February 04, 2016, 09:52:28 am »
"...because it works...."    ?


No, I guess that answer might be ok in a physics class, but probably not in an engineering class.

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