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BC557 Transistor Datasheet, Pinout, Equivalent and Uses

Update Time: Aug 02, 2023      Readership: 3946

BC557 Transistor

The BC557 transistor is a fundamental component in the realm of electronics, widely utilized for its versatile applications in amplification and switching circuits. This article serves as a comprehensive guide, providing essential details about the BC557 transistor, including its datasheet, pinout configuration, and equivalent variants. Additionally, it delves into the various practical uses of the BC557 transistor in diverse electronic circuits, shedding light on its significance in modern-day electronics. This article aims to offer valuable insights into harnessing the capabilities of the BC557 transistor effectively.

What is The BC557 Transistor?

The BC557 transistor is a type of PNP (Positive-Negative-Positive) bipolar junction transistor (BJT). It is made of semiconductor material, typically silicon, and is used in electronic circuits for amplification and switching purposes. The BC557 is commonly used in low-power applications due to its low current and voltage requirements.

As a PNP transistor, it operates by allowing current to flow from the emitter to the collector when a small current is applied to the base. This characteristic enables it to function as a current-controlled switch or as an amplifier.

BC557 Transistor

The BC557 is available in a variety of packages, including TO-92, SOT-23, and other surface-mount packages, making it easily adaptable to various circuit designs. It finds use in audio amplifiers, signal processing circuits, voltage regulators, and other low-power electronic devices.

To use the BC557 effectively in a circuit, it is crucial to refer to its datasheet, which contains essential information about its electrical characteristics, pinout configuration, and maximum ratings. Understanding these specifications ensures safe and optimized operation within the intended circuitry.

BC557 Transistor Specs

1. Transistor Type: PNP Bipolar Junction Transistor (BJT)
2. Package Type: Available in TO-92, SOT-23, and other surface-mount packages.
3. Maximum Collector-Base Voltage (Vcbo): Typically around 50V.
4. Maximum Collector-Emitter Voltage (Vceo): Typically around 45V.
5. Maximum Emitter-Base Voltage (Vebo): Typically around 5V.
6. Continuous Collector Current (Ic): Typically around 100mA to 200mA.
7. Power Dissipation (Pd): Typically around 625mW.
8. DC Current Gain (hfe): Typically ranges from 110 to 800.
9. Operating Frequency: Suitable for low to moderate frequency applications.
10. Operating Temperature: Typically rated for a range between -55°C to 150°C.

BC557 Transistor

BC557 Transistor Features

Below is a table summarizing the features and common uses of the BC557 transistor:


Feature Description
Transistor Type
PNP Bipolar Junction Transistor (BJT)
Package Type
TO-92, SOT-23, and other surface-mount packages
Maximum Vcbo
Typically around 50V
Maximum Vceo
Typically around 45V
Maximum Vebo
Typically around 5V
Continuous Ic
Typically around 100mA to 200mA
Power Dissipation (Pd)
Typically around 625mW
DC Current Gain (hfe)
Typically ranges from 110 to 800
Operating Frequency
Suitable for low to moderate frequency applications
Operating Temperature
Typically rated between -55°C to 150°C
Used for small-signal amplification
Switching Applications
Suitable for electronic switching circuits
Various Packages
Available in different package types
Low Noise
Generally exhibits low noise characteristics
Commonly Available
Widely accessible for electronic hobbyists and engineers

BC557 Transistor Pinout

The BC557 transistor has three pins that are crucial for its proper functioning. The pinout configuration of the BC557 transistor in TO-92 package is as follows:

BC557 Transistor Pinout

Pinout Description:

Collector (C): This is the pin where the current flows out of the transistor. In an NPN transistor, current flows into the collector, but in a PNP transistor like BC557, current flows out of the collector.

Base (B): The base pin is the control pin of the transistor. A small current flowing into the base can control a larger current flow between the emitter and collector, making it operate as an amplifier or a switch.

Emitter (E): This is the pin from where the current flows into the transistor. In a PNP transistor, current flows into the emitter.

BC557 Transistor Equivalent Parts

Here are a few transistors that are often considered equivalent or substitutes for the BC557:

  • 2N3906: This is a PNP transistor commonly used in low-power applications, similar to the BC557. It has similar electrical characteristics and can be a suitable replacement in many circuits.
  • BC327: The BC327 is another PNP transistor with comparable specifications to the BC557. It is often used as a substitute in various electronic circuits.
  • BC558: While the BC558 is a PNP transistor, it is complementary to the BC557 (NPN). If you need a complementary pair for a specific circuit configuration, you can consider using the BC558.
  • 2SA1015: This is a general-purpose PNP transistor that can be used as an alternative to the BC557 in some applications.
  • PN2222A: Although this is an NPN transistor, it can be used as a substitute in circuits designed for the BC557 with some modifications.

BC557 Transistor

BC557 Transistor Uses

The BC557 transistor, being a versatile component, is commonly employed in a variety of electronic circuits for amplification and switching purposes. One of its primary uses lies in small-signal amplification, where it can amplify weak signals without requiring significant power input. This makes it suitable for applications in audio circuits, RF circuits, and other systems that deal with low-power signals. In audio amplifiers, the BC557 aids in boosting audio signals for headphones, small speakers, and portable audio devices, contributing to better sound quality.

Another important application of the BC557 transistor is in switching circuits. Its ability to function as a current-controlled switch allows it to regulate the flow of current in various digital applications. For instance, it is commonly used in logic gates, timers, and LED drivers, where it facilitates precise control over switching events. Its low-power capabilities make it suitable for use in battery-operated devices, ensuring efficient power management and longer battery life.

BC557 Transistor

The BC557 also finds utility in voltage regulation circuits, where it helps maintain a stable output voltage despite fluctuations in input voltage. By acting as a voltage regulator, it contributes to the reliability and performance of low-power electronic devices. Additionally, the transistor plays a role in signal processing circuits, such as filters, oscillators, and modulators, ensuring proper signal manipulation for communication and signal conditioning applications.

Furthermore, the BC557 can be integrated into various sensing circuits. For instance, it is used in temperature and light sensor circuits, enabling accurate temperature and light measurements. Infrared proximity detectors and obstacle detection circuits also leverage the transistor's capabilities for proximity sensing, enhancing electronic security systems and automation applications.

Overall, the BC557 transistor's versatility and low-power characteristics make it a popular choice in a wide range of electronic applications. Its extensive use in amplification, switching, voltage regulation, signal processing, and sensor circuits highlights its importance as a fundamental building block in modern electronics. Engineers and hobbyists alike rely on the BC557 transistor to optimize performance and enhance functionality in their electronic designs.

BC557 Transistor

BC557 Transistor Datasheet

The BC557 transistor datasheet provides essential technical information about this versatile PNP bipolar junction transistor. Covering specifications such as maximum voltage ratings, continuous current capacity, and DC gain, this datasheet aids engineers and hobbyists in understanding the transistor's characteristics and optimal usage in various electronic circuits.

Click and view:

BC557 Transistor Datasheet


In conclusion, the BC557 transistor stands as a crucial and versatile component in the world of electronics. Its PNP bipolar junction configuration, coupled with low-power capabilities, makes it an ideal choice for amplification and switching applications. From small-signal amplification in audio and RF circuits to precise current control in switching circuits, the BC557 proves its worth across a diverse array of functions.

Its applications extend beyond mere amplification and switching; the BC557 plays an essential role in voltage regulation, signal processing, and sensor circuits, providing stability, precision, and reliability. Moreover, its use in proximity detectors and electronic security systems showcases its role in enhancing safety and automation.

BC557 Transistor

In essence, the BC557 transistor remains an indispensable part of the electronics landscape, continuing to shape and empower technological advancements across industries. Its adaptability, efficiency, and reliability make it an enduring favorite, serving as a fundamental building block in countless electronic devices and systems worldwide.



  • Can the BC557 be used as a replacement for a BC547 transistor in a circuit?

    Yes, in certain cases, the BC557 can be used as a replacement for a BC547 transistor. However, as the BC557 is a PNP transistor, and the BC547 is an NPN transistor, the circuit may require some modifications to ensure proper operation. Always refer to the datasheets and consider the circuit requirements before using it as a substitute.

  • What is the typical cutoff frequency of the BC557 transistor?

    The cutoff frequency (fT) of the BC557 transistor is typically in the range of a few tens of megahertz (MHz), making it suitable for low to moderate frequency applications.

  • Can the BC557 transistor handle high-power applications?

    No, the BC557 is designed for low-power applications with a maximum power dissipation (Pd) of around 625mW. It is not suitable for high-power applications due to its limited power handling capability.

Stella Brinkley

Stella Brinkley is a senior electronics engineer with 6 years of experience, specializing in the detailed study of resistor, transistor and package design. Her comprehensive knowledge allows her to drive innovation and excellence in the electronics industry.

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