Once the electrons reach the base-collector depleted region, they are swept through the region by an electric field. When a positive voltage is applied to the base contact relative to the collector and emitter, the base-collector voltage as well as base-emitter voltage becomes positive.įor simplicity, V CE is assumed to be zero.ĭiffusion of electrons occur from the emitter to the base while diffusion of holes originates from the base to the emitter. In addition, the emitter current is positive when current leaves the emitter contact.
Therefore, the collector and base current are positive when a positive current meets the collector or base contact. The conventional signs of the currents for the emitter, base and collector are denoted by I E, I B and I C respectively.
The width of quasi-neutral of the emitter, base and collector are indicated above as W E’, W B’ and W C’. The BJT shown above consists of two diodes connected back to back, resulting in the depletion of the regions called quasi-neutral. The structure of a PNP bipolar transistor is shown below. This ensures contacts are made in all the regions that are base, collector and emitter. Symbols of a BJT Structure of a BJTĪ BJT has two P-N junctions connected back to back and sharing a common region B (base). Holes constitute the dominant charge carriers in P-type semiconductors while electrons are the main charge bearers in N-type semiconductors. It is known as a bipolar transistor since its operation requires two types of charge carriers (holes and electrons). It can act as a switch, amplifier or oscillator. A Bipolar Junction Transistor (BJT) is a transistor whose operation depends on the contact made by two semicondutors.
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