Principle of the JFET

A JFET can have any of the various different forms. They all work in the same way: the current varies due to the effects of an electric field within device.

The workings inside JFET can be likened to control of water flow through the garden hose. Electrons or holes pass from source (S) electrode to drain (D). This results in the drain current, ID , which is generally the same as source current, IS. This is analogous to fact that water comes out of the garden hose at same rate it goes in (supposing that there are not any leaks in hose).

The rate of flow of charge carriers—which means, the current—depends on the voltage at the regulating electrode called as gate (G). Fluctuations in gate voltage, EG, create changes in current through the channel, ARE or ID. The small fluctuations occurring in the control voltage EG can cause large variations in flow of charge carriers through JFET. This translates into the voltage amplification in electronic circuits.