This constitutes the emitter current I E.Īs these electrons flow through the p-type base, they tend to combine with holes. The forward bias cause the electrons in the n-type emitter to flow towards the base. Working of npn transistorįig.3 shows the npn transistor with forward bias to the emitter-base junction and reverse bias to the collector-base junction. Therefore, forward bias applied to the emitter diode is generally very small whereas reverse bias on the collector diode is much higher. (vii) The resistance of emitter diode is very small as compared to collector diode. (vi) The emitter diode is always forward biased and the collector diode is always reverse biased. The junction between emitter and base may be called emitter-base diode or simply the emitter diode.The junction between base and collector may be called collector-base diode or simply collector diode. (v) The transistor has two pn junctions that means it is like two diodes. And it can pass most of the emitter injected charge carriers to the collector. So that less than 5% of charge carriers coming from the emitter can recombine in the base. (iii) The base is lightly doped and very thin. (ii) The emitter is heavily doped so that it can inject a large number of charge carriers into the base. However for the sake of convenience the emitter and collector are usually shown to be of equal size. The base is much thinner than the emitter while the collector is wider than both. (i) The transistor has three regions, emitter,base and collector. Transistor Actionīefore discussing transistor action, it is important to keep in mind the following facts about the transistor: The base-collector junction is reverse biased and provides high resistance in the collector circuit. The base-emitter junction is forward biased and allows low resistance for the emitter circuit. (iii) Base: The middle section which forms two pn junctions between the emitter and collector is called the base. Similarly in fig.2(ii) ,the collector (n-type) of npn transistor has reverse bias and receives electrons. In fig.2(i), the collector (p-type) of pnp transistor has a reverse bias and receives hole charges that flow in the output circuit. Its function is to remove charges from its junction with the base. (ii) Collector: The section on the other side that collects the charges is called the collector. Similarly in fig.2(ii), the emitter (n-type) of npn transistor has a forward bias and supplies free electrons to its junction with the base. In fig.2(i), the emitter (p-type) of pnp transistor is forward biased and supplies holes to its junction with the base. base so that it can supply a large number of majority carriers. (i) Emitter: The section on one side that supplies charge carriers( electrons or holes) is called the emitter. The emitter is always forward biased w.r.t. The middle section is called the base and it forms two junctions between the emitter and collector. The section on one side is called emitter and the section on the opposite side is called collector. A transistor(npn or pnp) has three sections of doped semiconductors.
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