Transistors - Bipolar (BJT)

Transistors - Bipolar (BJT) - Single

Part Number	Description / PDF	Quantity
BC549BBK Diotec Semiconductor	BJT TO-92BK 30V 100MA	0
BC556BBK Diotec Semiconductor	BJT TO-92BK 65V 100MA	245000
BC857A Diotec Semiconductor	BJT SOT-23 45V 100MA	51000
BC847B-AQ Diotec Semiconductor	BJT SOT-23 45V 100MA	0
BCX56-16 Diotec Semiconductor	BJT SOT-89 80V 1000MA	0
BC847CW-AQ Diotec Semiconductor	BJT SOT-323 45V 100MA	0
BC846AW Diotec Semiconductor	BJT SOT-323 65V 100MA	0
BC328-25 Diotec Semiconductor	BJT TO-92 25V 800MA	12000
BC847BR13 Diotec Semiconductor	BJT SOT-23 45V 100MA	0
BCP55-10 Diotec Semiconductor	BJT SOT-223 60V 1000MA	0
BCP53-10 Diotec Semiconductor	BJT SOT-223 80V 1000MA	0
BC857AW Diotec Semiconductor	BJT SOT-323 45V 100MA	0
BC847BW Diotec Semiconductor	BJT SOT-323 45V 100MA	0
BCP56-6 Diotec Semiconductor	BJT SOT-223 80V 1000MA	0
BC337-25 Diotec Semiconductor	SMALL SIGNAL BIPOLAR TRANSISTOR	0
BC857BR13 Diotec Semiconductor	BJT SOT-23 45V 100MA	0
MMBTA42-AQ Diotec Semiconductor	BJT SOT-23 300V 500MA	0
MMBTA94 Diotec Semiconductor	BJT SOT-23 400V 300MA	0
BC850A Diotec Semiconductor	BJT SOT-23 45V 100MA	0
BC327-25BK Diotec Semiconductor	BJT TO-92BK 45V 800MA	30000

Transistors - Bipolar (BJT) - Single

1. Overview

Bipolar Junction Transistors (BJTs) are three-terminal semiconductor devices that use both electron and hole charge carriers. They form the foundation of analog electronics through their ability to amplify signals and control current flow. BJTs remain critical in modern electronics for applications ranging from audio amplifiers to power management circuits, offering superior linearity and robustness in switching operations.

2. Main Types & Functional Classification

Type	Functional Characteristics	Application Examples
NPN Transistor	Majority carriers: electrons. Requires positive base current for conduction.	Low-noise amplifiers, digital logic circuits
PNP Transistor	Majority carriers: holes. Conducts with negative base current.	Power supply circuits, motor controllers
High-Frequency BJT	Optimized for RF/microwave signal amplification (f_T > 100 MHz)	Wireless communication systems, radar
Power BJT	High current/voltage ratings (I_C > 1A, V_CE > 50V)	Switch-mode power supplies, motor drives

3. Structure & Composition

BJTs consist of three doped semiconductor regions forming two p-n junctions:

Emitter: Heavily doped region emitting charge carriers
Base: Thin, lightly doped middle region controlling carrier flow
Collector: Moderately doped region collecting carriers

Manufactured using silicon (common) or germanium (historic) with planar processing technology. The structure forms either NPN (n-type emitter/base/collector) or PNP configuration, with metal contacts for external connections.

4. Key Technical Specifications

Parameter	Description	Importance
Current Gain (h_FE)	Ratio of collector to base current (10-1000)	Determines amplification capability
Transition Frequency (f_T)	Frequency at which current gain drops to 1	Limits high-frequency performance
Max Collector Current (I_Cmax)	Maximum allowable continuous collector current	Defines power handling capability
Breakdown Voltage (V_CEO)	Max voltage between collector and emitter	Prevents device failure under stress
Saturation Voltage (V_CEsat)	Voltage drop in fully conducting state	Affects power efficiency in switching

5. Application Areas

Consumer Electronics: Audio amplifiers, LED drivers
Automotive: Engine control units, electric vehicle inverters
Industrial: PLCs, motor controllers
Telecommunications: RF power amplifiers, fiber optic transceivers
Aerospace: Avionics systems, satellite transponders

6. Leading Manufacturers & Products

Manufacturer	Product Series	Key Specifications	Typical Use
ON Semiconductor	2N3904	hFE: 100-300, fT: 300 MHz	General-purpose switching
Infineon	BC547	VCEO: 50V, ICmax: 100mA	Analog signal amplification
STMicroelectronics	2SD2656	ICmax: 15A, VCEO: 80V	Power inverter applications
Diodes Inc.	BFR93A	fT: 10 GHz, Noise Figure: 2dB	High-frequency front-end amplifiers

7. Selection Guidelines

Determine operating frequency: Select fT > 3 target frequency
Power requirements: Ensure Icmax and VCEO exceed circuit requirements by 20%
Thermal considerations: Calculate power dissipation (P=V_CE I_C)
Package type: TO-92 for low power, TO-220 for high-power applications
Environmental factors: Consider temperature ratings for industrial/military use

8. Industry Trends

Future developments include:

High-frequency BJTs operating beyond 100 GHz for 6G communication
Integrated BJT-MOSFET hybrid devices (BiCMOS) for mixed-signal applications
Wide-bandgap materials (SiC/GaN) for higher power density
Miniaturization through chip-scale packaging
Improved thermal management solutions for automotive applications