![]() ![]() 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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