Quick Q&A
Question: Why are JFETs referred to as "Normally On" Devices?


JFETs are referred to as "Normally On" devices because when you connect a JFET to a circuit, the JFET conducts across the drain to source, regularly, even when there is no voltage applied to its gate terminal.

In other words, the JFET conducts with no voltage applied to its gate terminal. It is normally on, in the absence of any gate voltage.

JFET Normally On Device

This is in contrast to bipolar junction transistors, which are referred to as "normally off" devices. BJTs conduct current across the collector to emitter junction only when a base current is applied to the base of the transistor. In the absence of a base current, the BJT is off and does not conduct across the collector-emitter junction.

A JFET has the opposite configuration in which a gate voltage applied to its gate shuts it off. And the JFET conducts and is normally on without any applied voltage.

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