I have to analyze a BIFET amplifier for a prelab. I have a pretty solid grasp of how to do it (with a help of some notes) however... all questions that I have done up to now provide Idss and Vp (Vgs off) values for you. Now I have to use the spec sheet to figure out what they are. Right now I am stuck on getting through the JFET...
In the specs for BF245 B, the range for Vp is -0.5V to -8V and the range for Idss is 6mA to 15mA. I know (or I think that I do) that these would represent the corresponding transfer functions and there are many more that fall in between (that could be generated using Shockley's eq'n). I still do not know how to pick a value to use in the calculations to find my q-point. It would seem that there are at least two correct answers... Using -8V and 15mA, I got Idq of 3.91 mA and Vgsq of -3.91V. Running this through multisim, the answer is quite a bit off as there Idq is 1.286 mA. My calculated values also give me a negative Vds ??
So, if someone could give a hint on how to pick those pesky values off of a spec sheet, thank you...
In the specs for BF245 B, the range for Vp is -0.5V to -8V and the range for Idss is 6mA to 15mA. I know (or I think that I do) that these would represent the corresponding transfer functions and there are many more that fall in between (that could be generated using Shockley's eq'n). I still do not know how to pick a value to use in the calculations to find my q-point. It would seem that there are at least two correct answers... Using -8V and 15mA, I got Idq of 3.91 mA and Vgsq of -3.91V. Running this through multisim, the answer is quite a bit off as there Idq is 1.286 mA. My calculated values also give me a negative Vds ??
So, if someone could give a hint on how to pick those pesky values off of a spec sheet, thank you...
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