CrazyEngineers Archive
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@pratap singh, upendra • 04 Jun, 2013 • 1 like
hello friends,

We all are aware that the gate current in the IGFET(insulated gate field effect transistor) is always zero owing to the oxide coating present between the gate and the substrate region.

Does the value of gate current remain zero even in a JFET(junction field effect transistor)? Is yes, why?
@Jeffrey Arulraj • 04 Jun, 2013 • 1 like The input resistance of the JFET is in the order of Giga ohms Check Data sheet for every FET you are using

So the current in the input is about a few nano amperes maximum

But due to some internal capacitor we give higher current to charge these up and so input current of power JFET is about .5 micro ampere
@Sindhu Chowdary • 14 Jun, 2013 • 2 likes In normal operation a gate voltage is applied to a JFET such that the p-n junction formed by the gate and the channel is never forward biased. For instance in a n-channel JFET the channel is n-type material and the gate is p-type, so the gate voltage must be zero or negative with respect to the source. A negative voltage causes the current through the channel to decrease.
If you applied a positive voltage to the gate of a N-channel JFET it would forward bias the junction and current would flow from gate to source and / or drain.
Because it acts like a reverse-biased diode, only leakage current flows which is usually down in the picoamps range.
@surya ramanathan • 22 Jul, 2018 • 1 like

its really nice link  to clear all doubts


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