BC557 PNP p-type, General Purpose Transistors (max. 100mA) - TO-92

  • RM0.30

  • Product Code: BC557
  • Availability: In Stock


BC557 is a widely used PNP bipolar junction transistor manufactured in small TO-92 package. It is a general purpose PNP transistor that can be used as a switch or amplifier in electronic circuits. Its HFE ratings are 125 to 800 which makes it an ideal transistor to use as a small signal amplifier in electronic circuits for example for audio signal amplification or other, the HFE ratings of BC557 can be determined by the last letter after its number for example BC557A HFE ratings are 110-220, BC557B HFE ratings are 200-450 and BC557C HFE ratings are 420-800. The max collector dissipation is 500 milliwatt which is also an another good point to use it in amplification stages. Moreover it will also perform well when used it as a switch for load under 100mA. The transistor has also good collector to emitter (VCE) value that is -45V, therefore you can easily use it in circuits using 40 to 45 volts DC.

Beside these uses BC557 is also a good general purpose PNP transistor to use in your hobby electronics projects therefore it is a must to have transistor in your electronics LAB.



  • Bi-Polar PNP Transistor
  • DC Current Gain (hFE) is 300 maximum
  • Continuous Collector current (IC) is under 0.1mA or 100mA
  • Emitter Base Voltage (VBE) is 6V
  • Base Current(IB) is 5mA maximum
  • Preamplifier
  • Small signal audio amplifier
  • Any general purpose application that comes under its ratings.



  • Package Type: TO-92
  • Transistor Type: PNP
  • Max Collector Current(IC): -100mA
  • Max Collector-Emitter Voltage (VCE): -45V
  • Max Collector-Base Voltage (VCB): -50V
  • Max Emitter-Base Voltage (VBE): -5V
  • Max Collector Dissipation (Pc): 500 Milliwatt
  • Max Transition Frequency (fT): 100 MHz
  • Minimum & Maximum DC Current Gain (hFE): 125 to 800


Package Content

  • 1 x BC557 TO-92


BC557 Transistor as switch

When a transistor is used as a switch it is operated in the Saturation and Cut-Off Region as explained above. As discussed a transistor will act as an Open switch during Forward Bias and as a Closed switch during Reverse Bias, this biasing can be achieved by supplying the required amount of current to the base pin. As mentioned the biasing current should maximum of 5mA. Anything more than 5mA will kill the Transistor; hence a resistor is always added in series with base pin. The value of this resistor (RB) can be calculated using below formulae.

RB  = VBE / IB

Where, the value of VBE should be 5V for BC557 and the Base current (IB depends on the Collector current (IC). The value of Ishould not exceed mA.


BC557 Transistor as Amplifier

A Transistors 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 are

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

Of the above types common emitter type is the popular and mostly used configuration. When uses as an Amplifier the DC current gain of the Transistor can be calculated by using the below formulae

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


BC557 Complementary NPN Transistors


Replacement and Equivalent PNP

  • 2N3906, 2N4403, BC556, BC558, BC327, BC157, 2SA1943, BD140, S8550, TIP127, TIP42
    output pins of some equivalents are different please see pinout details of the equivalent transistor before replacing in the circuit.


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Tags: PNP, Amplifier Transistor