Transistors - Bipolar (BJT)

Transistors - Bipolar (BJT) - Single

Part Number	Description / PDF	Quantity
2N3905 PBFREE Central Semiconductor	TRANS PNP 40V TO-92	6256
BU406 PBFREE Central Semiconductor	THROUGH-HOLE TRANSISTOR BIPOLAR	0
2N3708 PBFREE Central Semiconductor	TRANS NPN 30V TO-92	2312
CXT3904 TR PBFREE Central Semiconductor	TRANS NPN 40V 0.2A SOT89	7745
CZTA27 TR PBFREE Central Semiconductor	TRANS NPN DARL 60V 0.5A SOT223	183664000
CMUT3904 BK PBFREE Central Semiconductor	TRANS NPN 40V 0.2A SOT523	0
BC847BT TR PBFREE Central Semiconductor	TRANS NPN 45V 0.1A SOT523	333878000
CJD127 TR13 Central Semiconductor	TRANS PNP 100V 8A DPAK	2147
TIP32 PBFREE Central Semiconductor	THROUGH-HOLE TRANSISTOR-BIPOLAR	0
2N2270 PBFREE Central Semiconductor	TRANS NPN 45V 1A TO-39	69
TIP32B PBFREE Central Semiconductor	THROUGH-HOLE TRANSISTOR-BIPOLAR	0
2N3711 PBFREE Central Semiconductor	TRANS NPN 30V TO-92	15
BU806 PBFREE Central Semiconductor	THROUGH-HOLE TRANSISTOR BIPOLAR	0
CMST2907A BK PBFREE Central Semiconductor	TRANS PNP 60V 0.6A SOT323	0
2N6432 PBFREE Central Semiconductor	THROUGH-HOLE TRANSISTOR-SMALL SI	0
CZT4033 TR PBFREE Central Semiconductor	TRANS PNP 80V 1A SOT223	871
2N6428 PBFREE Central Semiconductor	THROUGH-HOLE TRANSISTOR-SMALL SI	0
TIP32A PBFREE Central Semiconductor	THROUGH-HOLE TRANSISTOR-BIPOLAR	0
2N5884 PBFREE Central Semiconductor	TRANS PNP 80V 25A TO-3	281120
BC857C TR PBFREE Central Semiconductor	TRANS PNP 80V SOT23	0

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