LectureNotes_5 - Bipolar Junction Transistor(BJT The(npn...

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Bipolar Junction Transistor (BJT) The (npn) BJT consists of three semiconductor regions: the emitter region (n-type), the base (p-type), and the collector region (n-type). n-type Emitter region n-type Collector region p-type Base region Emitter-Base Junction (EBJ) Collector-Base Junction (CBJ) Metal contact Metal contact Emitter (E) Collector (C) Base (B) The transistor consists of two pn junctions, the emitter-base junction (EBJ) and the collector-base junction (CBJ). Depending on the bias conditions (forward or reverse) of each of these junctions, different modes of operation of the BJT are obtained. MODE EBJ CBJ Cutoff Reverse Reverse Active Forward Reverse Saturation Forward Forward The active mode is the one used if the transistor is to operate as an amplifier. Switching applications (for example: logic circuits) utilize both the saturation and cutoff modes.
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Operation of the npn Transistor in the Active Mode n n p Recombined electrons I B2 Metal contact Metal contact Emitter (E) Collector (C) Base (B) Injected electrons Diffusing electrons Collected electrons Injected holes I E Forward-biased Reverse-biased I c I B1 I B I B - V BE + - V BE + - V CB + - V CB + I c I E Only diffusion-current components are considered. Drift currents due to thermally generated minority carriers are usually very small and can be neglected. The forward-bias on the EBJ will cause current to flow across the junction.
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LectureNotes_5 - Bipolar Junction Transistor(BJT The(npn...

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