BC557 Transistor Pin Configuration & Its Working

BC557 transistor pinout
Pinout BC557 fvml

The BC557 is a widely used PNP bipolar junction transistor general-purpose transistor. It is a well known BC series transistors. The BC557 transistor is a PNP transistor, It consists of three layers of semiconductor material, and the mostly charge carriers  are the ones responsible for current conduction. This article will explain transistor-BC557, Pin configuration, uses, alternate and other detail.

BC557 transistor pinout

BC557 pinout

Transistor BC557  Pin Configuration are:

  • Pin1 (Collector): The current supplies throughout the collector terminal
  • Pin2 (Base): The base terminal of this transistor controls the biasing
  • Pin3 (Emitter): Flow of current drains out through this terminal

BC557 transistor specification

The features and specifications of the BC 557 transistor include the following.

  • Type of package:  T0-92
  • Type: PNP
  • Voltage Ratings:
    • Collector-Emitter Voltage (VCEO): This typically ranges from 45V to 50V.
  • Current Ratings:
    • Collector Current (IC): 100mA to 800mA.
    • Base Current (IB): A few milliamperes.
  • Current Gain (hFE):
    • Commonly falls in the range of 200 to 800 hFE.
  • Power Dissipation (PD): Typically around 625mW.
  • Operating Temperature: Operating temperature range is from -55°C to 150°C.

BC557 transistor equivalent

As we look bc557 equivalent transistors then the following are the best alternate of 557 transistor.

  • 2N3906 is a widely used PNP transistor with voltage and current ratings similar to the BC557. It’s readily available and is often used as a substitute.
  • 2N2907 is another PNP transistor with similar ratings to the BC 557.
  • 2N4403 is a PNP transistor with a relatively high current rating and similar voltage ratings to the BC 557.

Complement of bc 557

BC547 is the best compliment of BC557 Transistor. It has similar rating like 557 but NPN.

smd equivalent

smd equivalent of this transistor are:

BC557 Transistor as a Switch

The BC557 is a PNP bipolar junction transistor widely used for low power switching and amplification. When using this transistor as a switch we use it for the flow of current through a load by toggling the transistor on and off. Here’s how you can use the BC557 transistor as a switch:

BC557 Transistor as a Switch

BC557 Transistor as Amplifier

Transistor acts as an Amplifier when operating in Active Region. It can amplify power, voltage and current at different configurations.

Some of the configurations used in amplifier circuits:

  1. Common base amplifier
  2. Common emitter amplifier
  3. Common collector amplifier

DC Current Gain = Collector Current (IC) / Base Current (IB)


The BC-557 is a three-layer semiconductor transistor with an emitter, base, and collector. It is used for current-controlled switch or amplifier. When a small current is applied to the base terminal biasing start from collector to emitter a big current pass through collector to emitter.

557 transistor uses

As we see the applications of this transistor. The BC557 is a versatile PNP bipolar junction transistor used in various electronic circuits. Some common uses of the transistor BC557 are given below:

  • Amplification
  • Switching
  • Voltage Regulation
  • Oscillator Circuits
  • Darlington Pair
  • Voltage-Level Shifting

BC557 transistor datasheet

bc557 transistor datasheet

Difference between transistor bc547 and bc557

The BC547 and BC557 transistors are complement of each other. BC547 is NPN (Negative-Positive-Negative) transistor, and the BC557 is PNP (Positive-Negative-Positive) transistor. the key differences between BC547 and BC557 are as follows:

  1. Type:
    • BC557: PNP transistor.
    • BC547: NPN transistor.
  2. Operation:
    • BC557 is used for sinking current from collector to emitter when it’s turned on (current flows from the emitter to the collector when the base is biased).
    • BC547 is used for sourcing current from collector to emitter when it’s turned on (current flows from the collector to the emitter when the base is biased).
  3. Voltage Polarity:
    • In the BC557, the emitter is more positive than the collector when it’s on.
    • In the BC547, the collector is more positive than the emitter when it’s on.
  4. Complementary Pair:
    • BC547 and BC557 are often used together in circuits where both NPN and PNP transistors are required. They work as complementary pairs for applications like signal amplification and switching.

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