The factor of this change is called beta(). BJTs transistor are known as current controlledġ0 TRANSISTOR CHARACTERISTICS AND PARAMETERSĪs previously discussed, base-emitter current changes yields large changes in collector-emitter current. Small changes in base-emitter current yields a large change in collector-current. Note that the emitter leg serves as a conductor for both circuits.The amount of current flow in the base-emitter circuit controls the amount of current that flows in the collector circuit. Look at this one circuit as two separate circuits, the base-emitter(left side) circuit and the collector-emitter(right side) circuit. ![]() The operation of pnp transistor is the same as for the npn except that the roles of electrons and holes, the bias voltage polarities and the current directions are all reversed. The electron now move through the collector region out through the collector lead into the positive terminal of the collector voltage source. Once in this region they are pulled through the reverse-biased BC junction by the electric field set up by the force of attraction between the positive and negative ions. ![]() Most of electrons from the emitter diffuse into the BC depletion region. A few recombined electrons flow out of the base lead as valence electrons, forming the small base electron current. Thus only a small percentage of all the electrons flowing through the BE junction can combine with the available holes in the base. The base region is lightly doped and very thin so that it has a very limited number of holes. The heavily doped n-type emitter region is teeming with conduction-band (free ) electrons that easily diffuse through BE junction into the p-type base region where they become minority carriers. Npn transistor operation: The forward bias from base to emitter narrow the BE depletion region, and the reverse bias from base to collector widens the BC depletion region. IE = IC + IB IC = IC majority + ICO (minority) ICO (minority) is called leakage current Fig Forward-biased junction of a pnp transistor.įig Majority and minority carrier flow of a pnp transistor. Collector –largest and moderately doped region.ģ Symbol pnp transistor npn transistor Pointing in Not pointing inįig Reverse-biased junction of a pnp transistor. 3 regions are called emitter, base and collector. 1 Chapter 3 Bipolar Junction Transistor (BJT)ĭMT 121 Electronic I Chapter 3 Bipolar Junction Transistor (BJT)Ģ Transistor Structure BJT (bipolar junction transistor) constructed with three layer semiconductor device consisting either TWO n- and ONE p-type layer (npn transistor) OR TWO-p and ONE n-type layer of material (pnp transistor) BJT is constructed with 3 doped semiconductor regions separated by 2 p-njunctions.
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