Field-effect transistor: Difference between revisions

Revision as of 12:56, 9 October 2011

Revision as of 01:40, 10 October 2011

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Even though the conductive channel formed by gate-to-source voltage no longer connects source to drain during saturation mode, [[Charge carriers|carriers]] are not blocked from flowing. Considering again an n-channel device, a [[depletion region]] exists in the p-type body, surrounding the conductive channel and drain and source regions. The electrons which comprise the channel are free to move out of the channel through the depletion region if attracted to the drain by drain-to-source voltage. The depletion region is free of carriers and has a resistance similar to [[silicon]]. Any increase of the drain-to-source voltage will increase the distance from drain to the pinch-off point, increasing resistance due to the depletion region proportionally to the applied drain-to-source voltage. This proportional change causes the drain-to-source current to remain relatively fixed independent of changes to the drain-to-source voltage and quite unlike the linear mode operation. Thus in saturation mode, the FET behaves as a [[current source|constant-current source]] rather than as a resistor and can be used most effectively as a voltage amplifier. In this case, the gate-to-source voltage determines the level of constant current through the channel.

<math>I_({DSS)}</math> is the maximum drain current for JFET,defined by the condition <math>V_({GS)}</math>=0

== Composition ==