Lecture 9_ Feb 7 2011

Lecture 9_ Feb 7 2011 - Chapter 5 Bipolar Junction...

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Unformatted text preview: Chapter 5 Bipolar Junction Transistors Lecture 9 Cover Sections: 5.11, 5.12 Biasing for BJT Goal of biasing is to establish known Q-point which in turn establishes initial operating region of the transistor. For a BJT, the Q-point is represented by ( I C , V CE ) for an npn transistor or ( I C , V EC ) for a pnp transistor. The Q-point controls values of diffusion capacitance, transconductance, input and output resistances. In general, during circuit analysis, we use simplified mathematical relationships derived for a specified operation region, and the Early voltage is assumed to be infinite. Two practical biasing circuits used for a BJT are: Four-Resistor Bias network Two-Resistor Bias network Chap 5.11 Four-Resistor Bias Network for BJT V E Q = V C C R 1 R 1 + R 2 R E Q = R 1 R 2 = R 1 R 2 R 1 + R 2 V E Q = R E Q I B + V B E + R E I E 4 = 12,000 I B + 0.7 + 16,000( F + 1) I B I B = V E Q- V B E R E Q + ( F + 1) R E = 4 V - 0.7 V 1.23 10 6 = 2.68 A I C = F I B = 201 A I E = ( F + 1) I B = 204 A V CE = V CC- R C I C- R E I E V CE = V CC- R C + R F F I C = 4.32 V F. A. region correct - Q-point is (201 F....
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Lecture 9_ Feb 7 2011 - Chapter 5 Bipolar Junction...

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