Week #8: Transistor Biasing & CE Amplifiers

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rjagodowski: Posts: 2383; Joined: Fri Sep 04, 2015 6:59 pm

Week #8: Transistor Biasing & CE Amplifiers

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Post by rjagodowski » Tue Oct 22, 2019 7:29 am

This week we'll continue to discuss some of the circuits investigated in the Transistor Biasing Lab from Week #7.

A key point to keep in mind during this discussion: The current gain parameter, beta (also known as hFE), generally has a wide range of values within a specific part number. For example the 2N2222 transistor may have a beta range between 50 to 300. One goal of the various biasing circuits we are discussing is to stabilized the bias point, known as the Q-point, with respect to variations in beta.

We will begin analyzing a Common Emitter Voltage Divider Biased NPN transistor amplifier for A.C. operation. The example we will work through is the one presented in our Week #8 lab experiment.

Transistor Analysis and A.C. Modeling

Here's a pdf of a sample of a Transistor Text book. It has a lot more detail than we'll cover, but it also presents the majority of concepts we'll discuss, so you might find it helpful. Specifically, take a look at the "Simplified r-Parameter Model" it presents in Figures 6-5 & 6-6, and the associated reading.

TransistorAmplifierAnalysis_PearsonSampleText_0134420101.pdf: (3.86 MiB) Downloaded 47 times

Here's a discussion of transistor models from EEEGuide.com. This is far more detailed than we need to understand at this point in our studies, however, so just give it a quick look-over.

Here's one more transistor related document you might find useful:

TransistorAnalysis_College_ECE312_lec04.pdf: (2.39 MiB) Downloaded 42 times

This presentation was created and used for a college course taught in Egypt.

We will also discuss some of the parameters for the 2N2222A & 2N3904 transistor spec sheets, specifically those dealing with beta (hFE on the sheet). Here are the pdfs for these two transistors: