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Chapter 3: Bipolar Junction Transistors

By Steven T. Karris
From Electronic Devices and Amplifier Circuits

This is a long chapter devoted to bipolar junction transistors. The NPN and PNP transistors are defined and their application as amplifiers is well illustrated with numerous examples. The small and large signal equivalent circuits along with the h-parameter and T-equivalent circuits are presented, and the Ebers-Moll model is discussed in detail.

3.1 Introduction

Transistors are three terminal devices that can be formed with the combination of two separate PN junction materials into one block as shown in Figure 3.1.


Figure 3.1: NPN and PNP transistor construction and symbols

As shown in Figure 3.1, an NPN transistor is formed with two PN junctions with the P-type material at the center, whereas a PNP transistor is formed with two PN junctions with the N-type material at the center. The three terminals of a transistor, whether it is an NPN or PNP transistor, are identified as the emitter, the base, and the collector. Can a transistor be used just as a diode? The answer is yes, and Figure 3.2 shows several possible configurations and most integrated circuits employ transistors to operate as diodes.


Figure 3.2: Transistors configured as diodes

Transistors are used either as amplifiers or more commonly as electronic switches. We will discuss these topics on the next section. Briefly, a typical NPN transistor will act as a closed switch when the voltage V BE between its base and emitter terminals is greater than 0.7 V but no greater than 5 V to avoid possible damage. The...

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Bipolar RF Transistors
Bipolar RF transistors consist of an N-type or P-type layer sandwiched between two layers of the opposite type. They are designed to handle high-power radio frequency (RF) signals in devices such as stereo amplifiers, radio transmitters, and television monitors.
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Transistors are electronic devices made of semiconductor material that amplify a signal or open or close a circuit.
Darlington Transistors
Darlington transistors (Darlington pairs) are semiconductor devices that combine two bipolar transistors in a single device. They provide high current gain (commonly written ß) and require less space than configurations that use two discrete transistors.
Small-Signal Bipolar Transistors (BJT)
Small-signal bipolar transistors (BJT) are semiconductors that amplify small AC or DC signals. They consist of a base n-type or p-type layer sandwiched between emitter and collector layers of the opposite type.
Power Bipolar Transistors
Power bipolar transistors are semiconductors in which a base n-type or p-type layer is sandwiched between emitter and collector layers of the opposite type. The junctions between the semiconductor sections amplify weak incoming electrical signals.
Topics of Interest

3.2 NPN Transistor Operation For proper operation, the NPN and PNP transistors must be biased as shown in Figure 3.5. Figure 3.5: Biased NPN and PNP Transistors for proper operation The...

This is a long chapter devoted to bipolar junction transistors. The NPN and PNP transistors are defined and their application as amplifiers is well illustrated with numerous examples. The small and...

3.10 Piecewise-Linear Analysis of the Transistor Amplifier The circuit shown in Figure 3.50 is a model to represent the transistor where the two ideal diodes are included to remind us of the two PN...

Bipolar transistors, having 2 junctions, are 3 terminal semiconductor devices. The three terminals are emitter, collector, and base. A transistor can be either NPN or PNP. See the schematic...

3.3 The Bipolar Junction Transistor as an Amplifier When a transistor is used as an amplifier, it is said to be operating in the active mode. Since a transistor is a 3-terminal device, there are...