BC556 Transistor PNP 65V 100mA 625mW TO-92

BC556 PNP General Purpose Transistor (65V, 100mA) TO-92 is a versatile bi-polar junction transistor (BJT) that serves as a highly reliable workhorse for low-power switching and amplification tasks across diverse electronic circuits. As a PNP transistor, the BC556 requires a negative voltage or current at its base to activate, or turn ON, the current flow between the collector and emitter. Consequently, this characteristic makes it ideal for sinking current in interface applications, such as driving LED displays or relay coils. Operating with a maximum collector-emitter voltage (V_CE) of 65V and a continuous collector current (I_C) of 100mA, the BC556 offers sufficient power handling for most small-signal applications. Therefore, designers frequently choose this device for its low noise performance, high current gain (h_FE), and compact, industry-standard TO-92 package, guaranteeing easy integration into any PCB design.

Key Features:

• PNP Configuration: Functions as a current-sinking element, perfect for driving loads connected to the positive supply rail.
• High Voltage Rating: The transistor offers a Collector-Emitter breakdown voltage (V_CEO) of up to 65V, which accommodates higher supply voltage rails than typical 30V transistors.
• Low Noise Performance: Designers frequently specify the BC556 for use in pre-amplifiers and audio stages where signal integrity is paramount.
• High Current Gain (h_FE): Provides a minimum DC Current Gain of 110, allowing microcontrollers to control moderate loads with minimal base current.
• Standard TO-92 Package: The ubiquitous through-hole package simplifies mounting and manual assembly onto printed circuit boards.

Technical Specifications:

• Transistor Type: PNP Bi-polar Junction Transistor (BJT)
• Collector-Emitter Voltage (V_CEO): 65 V max
• Collector-Base Voltage (V_CB): 80 V max
• Continuous Collector Current (I_C): 100 mA max
• Collector Power Dissipation (P_D): 625 mW max
• DC Current Gain (h_FE): 110 to 800 (depending on suffix, e.g., BC556B ≈ 200 to 450)
• Transition Frequency (f_T): 150 MHz typical
• Operating Temperature Range: −55°C to +150°C

Mechanical Specifications:

• Package Style: TO-92 (Plastic, Through-Hole)
• Lead Count: 3
• Material: Silicon Planar Epitaxial
• Orientation: Emitter, Base, Collector (EBC) viewed from the flat side.

Dimensions:

• Body Height: ≈ 5.2 mm
• Body Diameter/Width: ≈ 4.0 mm
• Lead Pitch: 1.27 mm (0.05 inch) typical
• Overall Height (including leads): ≈ 15.5 mm

Pinout and Wiring:

• Pin 1 (E): Emitter. Connects to the ground or the most negative potential of the circuit.
• Pin 2 (B): Base. This is the control pin; pulling the base voltage below the emitter voltage turns the transistor ON.
• Pin 3 (C): Collector. Connects to the load (e.g., relay coil, LED resistor) and typically to the positive supply rail (V_CC).
• Wiring Note: Always place a current-limiting resistor in series with the base pin when connecting it to a digital control signal to prevent damaging the transistor junction.

Datasheet Reference:

• Download ON Semiconductor BC556 Datasheet

Commonly Used in:

• Audio Amplifiers: Used in pre-amplifier stages and driver stages where low noise is a requirement.
• Switching Circuits: Essential for current sinking, particularly in digital control of relays, solenoids, and small indicators.
• Voltage Regulation: Serves as a key component in low-power linear voltage regulators and current mirror circuits.

Applications:

• Signal Amplification: Provides efficient amplification of weak analog signals in sensors and measurement equipment.
• Logic Level Shifting: Creates interfaces between different voltage domains (e.g., 5V logic controlling 12V loads).
• LED and Display Drivers: Drives common-anode LEDs or seven-segment displays by sinking current to ground.

Equivalent Models:

• 2N3906: A common, similar PNP general-purpose transistor, often used interchangeably, although the pinout may differ (EBC vs. EBC/CBE).
• BC557: Electrically similar to the BC556 but with a lower V_CEO rating (45V), making it suitable for lower voltage applications.
• S8550: A functionally equivalent PNP transistor with a higher current capacity, providing a more robust option.

Package Includes:

• 1 x BC556 Transistor PNP 65V 100mA TO-92