Chapter 3 (Boylestad) - Bipolar Junction Transistors

Bipolar Junction Transistor (BJT)

A three-terminal semiconductor device consisting of two p-n junctions, used for amplification and switching.

Emitter (E)

The terminal of a BJT that injects charge carriers into the base.

Base (B)

The thin middle region of a BJT that controls the flow of charge carriers.

Collector (C)

The terminal of a BJT that collects the charge carriers from the emitter.

Common-Base Configuration

A BJT configuration where the base is the common terminal between the input and output.

Common-Emitter Configuration

A BJT configuration where the emitter is the common terminal between the input and output, often used for amplification.

Common-Collector Configuration

A BJT configuration where the collector is the common terminal between the input and output, primarily used for impedance matching.

Alpha (α)

The current gain of a common-base BJT, defined as the ratio of collector current to emitter current (α = I_C / I_E).

Beta (β)

The current gain of a common-emitter BJT, defined as the ratio of collector current to base current (β = I_C / I_B).

Cutoff Region

The state of a transistor where both the base-emitter and collector-base junctions are reverse biased, resulting in no significant current flow.

Saturation Region

The state of a transistor where both the base-emitter and collector-base junctions are forward biased, allowing maximum current flow.

Active Region

The operational state of a transistor where the base-emitter junction is forward biased and the collector-base junction is reverse biased, allowing controlled amplification.

DC Beta (β_dc or h_fe)

The ratio of DC collector current to DC base current at a specific operating point.

AC Beta (β_ac or h_fe)

The small-signal current gain of a transistor, representing the change in collector current relative to the change in base current.

Leakage Current (I_CO)

The small reverse-bias current present in a transistor even when the base current is zero.

Collector Cutoff Current (I_CBO)

The leakage current flowing from collector to base with the emitter open.

Base-Emitter Voltage (V_BE)

The voltage required between the base and emitter to turn the transistor on, typically around 0.7V for silicon BJTs.

Collector-Emitter Voltage (V_CE)

The voltage between the collector and emitter terminals, affecting the transistor's mode of operation.

Power Dissipation (Pc)

The product of the collector-emitter voltage and collector current, determining the heat generated by the transistor.

Current Gain-Bandwidth Product (f_T)

The frequency at which the current gain of a transistor falls to unity, indicating the transistor's speed capability.

Transistor Specification Sheet

A datasheet providing the maximum ratings, thermal characteristics, and electrical characteristics of a transistor.

Avalanche Effect

A phenomenon where excessive reverse voltage causes rapid increase in current due to carrier multiplication, potentially damaging the transistor.

Impedance Matching

A technique in circuit design where impedances are adjusted to maximize power transfer or minimize signal reflection, often achieved using a common-collector configuration.

Early Effect

A phenomenon where an increase in collector-emitter voltage reduces the effective base width, increasing collector current.

Thermal Runaway

A self-reinforcing increase in temperature leading to excessive current and potential destruction of the transistor.

Transistor Casing and Terminal Identification

The physical packaging of a transistor, with markings to indicate the emitter, base, and collector terminals.