Electrical Circuits and Electronics课件（华南理工）Lecture 28.pptVIP

Chapter 11 Bipolar Junction Transistors (BJT) Aim Understand bipolar junction transistor operation in amplifier circuits; Analysis bias circuits; Use small-signal equivalent circuits to analysis BJT amplifiers; Compute performance of several important amplifier configuration; Select an amplifier configuration appropriate for a given application. Lecture 28 Bipolar Junction Transistors Bipolar Junction Transistors Structure of BJTs BJTs are constructed as layers of semiconductor materials doped with suitable impurities; In n-type material, conduction is due mainly to negatively charged electrons; In p-type material, conduction is due mainly to positively charged holes. npn Transistor An npn transistor consists of a layer of p-type material between two layers of n-type material; Each pn junction forms a diode; The junctions are made very close together in a single crystal of the semiconductor, the current of on junction affects the current in another junction. Fluid-Flow Analogy npn Transistors Equations of Operation The base-collector junction is reverse biased and the base-emitter junction is forward biased; We defined the parameter as the ratio of the collector current to the emitter current: Equations of Operation Values for rangers from 0.9 to 0.999, with 0.99 being very typical; We define the parameter as the ratio of the collector current to the base current: Values for range from about 10 to 1000, and a very common value is 100. pnp Transistors The base is a layer of n-type material between p-type emitter and collector region; Aside from the differences in voltage polarity and current directions, the two types of devices are nearly identical. pnp Transistors Equations of Operation For pnp transistors, we can write the following equations: Common-Emitter Characteristics Summary Electrical Circuits and Electronics School of Electric Power Electrical Circuits and Electronics School of Electric Power Electrical Circuits and Electronics School of El