Lecture20a - Lecture 20. VOLTAGE FOLLOWERS Topics: BJT...

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Lecture 20. VOLTAGE FOLLOWERS Objectives: Topics: Describe operation of voltage followers Perform analysis of voltage followers Obtain the transfer characteristics BJT Voltage Follower MOSFET Voltage Follower
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Voltage Follower - buffer (reproduces input voltage and drives load while drawing minimum current from the input circuit) Load is shared by both input and output loops Device input voltage:
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BJT Voltage Follower - also known as common-collector amplifier B f X B R V v i = v X =v IN -v OUT Middle term – feedback (i B depends on itself) Assume C.C.R.: B F C i i β =
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BJT Voltage Follower (Cont’d) ) ( C B E OUT i i R v + = (*) is good only for C.C.R. In most cases (*) could be simplified If β F is large or R B is small, - equivalent to ignoring R B i B compared to v OUT v OUT replicates v IN except for V f
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EXAMPLE V CC =12V, R B =10k , R C =10k , V sat =0.3V .v OUT (v IN ) - ? a) Cutoff region (v IN < V f ) b) C.C.R. (v IN > V f and v CE > V sat ) ) 1 ( ) 1 ( ) ( + + + = F E B F E f IN OUT R R R V v v β use previously derived:
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This note was uploaded on 06/30/2010 for the course EECE 315 taught by Professor Nikulin during the Fall '08 term at Binghamton University.

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Lecture20a - Lecture 20. VOLTAGE FOLLOWERS Topics: BJT...

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