Quick Q&A
Question: Why are NPNs referred to as "Normally Off" Devices?





Answer:


NPN transistors are referred to as "Normally Off" devices because when you connect a NPN transistor to a circuit, it does not conduct across the emitter to collector, unless a sufficiently large enough current is applied to the base.

In other words, the NPN transistor does not conduct current without a current applied to the base. It is normally off, in the absence of any base current.


NPN transistors normally off devices

This is in contrast to PNP transistors (JFETs), which are referred to as "normally on" devices. PNP transistors conduct current across the emitter to collector without any current applied to the base of the transistor. When sufficient voltage is emitter terminal, current flows in the absence of any applied base current.

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