Chapter 4: Difference between revisions

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*'''Active''': The normal mode of operation. This mode has the largest common-emitter current gain.
*'''Active''': The normal mode of operation. This mode has the largest common-emitter current gain.
*'''Reverse Active''': The collector and emitter roles are reversed. Most BJTs are not symmetrical, thus <math>\alpha</math> and <math>\beta</math> take on different values.
*'''Reverse Active''': The collector and emitter roles are reversed. Most BJTs are not symmetrical, thus <math>\alpha</math> and <math>\beta</math> take on different values.
*'''Saturation''':
*'''Saturation''': High current from the emitter to collector. Logical "on".
*'''Cutoff''':
*'''Cutoff''': Very little current flow. Logical "off".


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Revision as of 12:01, 3 March 2010

Bipolar Junction Transistor

Base, Emitter, Collector
  • NPN: Not Pointing iN
  • PNP: Pointing iN Please
  • The arrow is for the emitter current. For an NPN the current flows into the collector. For a PNP the current flows out of the collector.

How a BJT works

Large-Signal DC models

Base-Emitter Collector-Base Region
FB FB Saturation
FB RB Active
RB FB Reverse Active
RB RB Cutoff
Region NPN PNP
Saturation and and
Active and and
Cutoff and and
  • Active: The normal mode of operation. This mode has the largest common-emitter current gain.
  • Reverse Active: The collector and emitter roles are reversed. Most BJTs are not symmetrical, thus and take on different values.
  • Saturation: High current from the emitter to collector. Logical "on".
  • Cutoff: Very little current flow. Logical "off".
IMG 0288.jpg
IMG 0287.jpg
  • What are the Saturation, Reverse Active and Cutoff regions used for?
  • Why do we always seem to use a common emitter configuration?
  • What does the Reverse Active large-signal model look like? How about graphically?
  • What is the Triode region?
  • For the Saturation region, why is 0.2V the magic number for V_CE?