19 - Talking Electronics

506 Principles of ElectronicsIn the previous chapters, we have discussed the cir-cuit applications of an ordinary transistor . In thistype of transistor , both holes and electrons play partin the conduction process. For this reason, it is some-times called a bipolar transistor . The ordinary or bipo-lar transistor has two principal disadvantages. First, ithas a low input impedance because of forward biasedemitter junction. Secondly, it has considerable noiselevel. Although low input impedance problem may beimproved by careful design and use of more than onetransistor, yet it is difficult to achieve input impedancemore than a few megaohms.

Field Effect Transistors 511 (iv) A bipolar transistor uses a current into its base to control a large current between collectorand emitter whereas a JFET uses voltage on the ‘gate’ ( = base) terminal to control the current be- tween drain (= collector) and source ( = emitter). Thus a bipolar transistor gain is characterised by current gain

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  Transistor, Bipolar, Bipolar transistor

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