Bipolar Junction Transistors

Heat sink

A mounting surface for semiconductor devices that is intended to carry away excessive heat from the semiconductor by dissipating it into the surrounding air.

P-type material

A semiconductor material that has an excess number of holes compared to electrons pulsating DC: a varying voltage that is one polarity, as opposed to reverse polarity as AC does.

N-type material

A semiconductor material that has an excess of electrons as compared to holes.

Bipolar junction transistor (BJT)

A three terminal, bipolar semiconductor containing both majority and minority current carriers. The device has alternate layers of P and N-type semiconductor materials (which form two PN junction diodes). This transistor requires the flow of both types of charge carriers (electrons and holes) to complete the path for current flow through it. Examples are the NPN and the PNP transistor.

NPN transistor

A transistor made of P material sandwiched between two outside N material areas. Then, going from end-to-end, the transistor is an NPN type. The symbol for the NPN transistor shows the emitter arrow going away from the base.

Emitter current (I /E)

The amount of current found at the emitter terminal of a BJT.

Collector emitter voltage (V /CE)

The amount of voltage present between the emitter and collector terminals of a BJT. For proper operation of the BJT, this voltage must have a polarity such that the flow of majority charge carriers is from emitter to collector.

Base

The center of the NPN or PNP sandwich in a BJT that separates the emitter and the collector transistor regions.

Forward bias

The external voltage applied to a semiconductor junction that causes forward conduction, for example, positive to P-type material and negative to N-type material.

Reverse bias

The external voltage applied to a semiconductor junction that causes the semiconductor not to conduct; for example, negative to P-type material and positive to N-type material.

Base current (I /B)

The level of current that flows into or out of the base terminal on a BJT. This current is normally due to the forward biasing of the emitter-base P-N junction.

Emitter

The portion of a BJT that emits charge carriers into a device.

Colector

The transistor electrode that receives current carriers that have transversed from the emitter through the base region; the electrode that removes carriers from the base-collector junction.

Collector current (I /C)

The value of the current measured at the collector terminal of a BJT.