Properties of a Bipolar Junction Transistor

This project is designed to be an instructional aid for teaching the fundamentals of bipolar junction transistors. Using many images and animations combined with an introductory level explanation, the student can learn about the different areas of interest such as semiconductor materials and applications of the BJT.

The student is first introduced to the basic semiconductor material concepts such as the crystal lattice structure and doping. Since silicon is the most commonly used semiconductor material, it is utilized throughout the presentation for explanation purposes.

For ease of understanding and computer simulations, it is convenient to represent a transistor with a combination of ideal, linear circuit elements called a device model. Several different models are discussed to represent the transistor in different operating modes and at different frequencies.

By applying different voltages across the terminals of the BJT, we can put the transistor into different operating regions. The different operating regions discussed are the forward active, saturation and cutoff modes.

Finally, applications such as switches, amplifiers and op-amps are explained.

This work was done by Jennifer Adams and Jason Zeakes in fulfillment of the class Scientific Visual Analysis and Multimedia (ESM 5984) at Virginia Tech. Questions or comments may be directed to or

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