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JFET Current at Drain Question

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GlennF

New Member
H i,

I am currently working way through a book (Complete Electronics Self Teaching Guide) learning about electronics circuits and I'm stuck:)

I have linked the image of the question, I understand the example(maybe I don't) I need to know how the answer for Question A is calculated. B also but hopefully your answer will enlighten me, Your assistance is greatly appreciated.jfet question.png
 

audioguru

Well-Known Member
Most Helpful Member
It is a silly question with obvious answers. But the answers shown are completely wrong.
"A" and "B" do not show a negative Vgs so maybe the Jfet has its gate-source diode blown up with the very positive high voltage?
If "A" and "B" Vgs voltages are negative then since the drain current is zero when the voltage is -4V then it is still zero with the negative Vgs voltages shown.

I show the correct Vgs question for the A current answer on the graph:
 

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GlennF

New Member
Awsome, thank you, -1.5v does match to 4.7mA. After checking the 2nd answer at 9.2mA that works out for .5v As you say at 21.5v the Transistor would have been destroyed and at -21.5 volts the (correct me please if I'm wrong) the transistor would be off so 0 current. It is a problem with the book or Kindle, I have seen equations not displaying correctly with brackets or symbols missing. If the question was -1.5 and -0.5, then no problem, replacing the 2 in 20.5 or 21.5 with a negative symbol makes everything make sense. Thank again for your help.
 
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