Lecture22-Understanding BJT Circuits

Lecture22-Understanding BJT Circuits - Lecture 22 Bipolar...

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ECE 3040 - Dr. Alan Doolittle Georgia Tech Lecture 22 Bipolar Junction Transistors (BJT): Part 6 Understanding BJT Circuits - Clearing up some Confusion Reading: Notes
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ECE 3040 - Dr. Alan Doolittle Georgia Tech Understanding a BJT Circuit Why is the base current so much smaller than the emitter and collector currents in forward active mode? If the collector of an npn transistor was open circuited, it would look like a diode. When forward biased, the current in the base-emitter junction would consist of holes injected into the emitter from the base and electrons injected into the base from the emitter. But since there are MANY more electrons in the emitter than holes in the base, the vast majority of the current will be due to electrons. p n+ Hole Current Electron Current p n+ n Voltage Current
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ECE 3040 - Dr. Alan Doolittle Georgia Tech p n+ n When the reverse biased collector is added, it “sucks” the electrons out of the base. Thus, the base-emitter current is due predominantly to hole current (the smaller current component) while the collector-emitter current is due to electrons (larger current component due to more electrons from the n+ emitter doping). p
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Lecture22-Understanding BJT Circuits - Lecture 22 Bipolar...

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