Overview

The BC557 (and its gain sub-variants BC557A, BC557B, and BC557C) is the standard European general-purpose PNP Bipolar Junction Transistor (BJT) manufactured by STMicroelectronics, ON Semiconductor, and Fairchild. It is the direct PNP complementary match to the BC547 NPN transistor.

Housed in a 3-pin TO-92 plastic package, the BC557 is rated for a collector-emitter breakdown voltage (VCEOV_{CEO}) of −45 Volts-45\text{ Volts} and continuous collector current (ICI_C) of −100 mA-100\text{ mA}.

Quick reference

Transistor TypeGeneral-Purpose PNP Bipolar Junction Transistor (BJT)
PackageTO-92 (Flat face front, leads pointing down) / SOT-23 (BC857)
Pinout (TO-92)Pin 1: Collector (C), Pin 2: Base (B), Pin 3: Emitter (E) — C-B-E
Collector-Emitter Voltage (VCEOV_{CEO})−45 V-45\text{ V} max
Collector-Base Voltage (VCBOV_{CBO})−50 V-50\text{ V} max
Continuous Collector Current (ICI_C)−100 mA-100\text{ mA} continuous
DC Current Gain (hFEh_{FE})110…220110\dots 220 (A) / 200…450200\dots 450 (B) / 420…800420\dots 800 (C)
Transition Frequency (fTf_T)300 MHz300\text{ MHz} typ
Power Dissipation (PDP_D)500 mW500\text{ mW} at TA=25∘CT_A = 25^\circ\text{C}

Pinout (TO-92 Package)

Looking at the flat face of the TO-92 package with leads pointing down:

text
        ┌─────────────┐
        │   BC557B    │  (Flat Package Face)
        └─┬───┬───┬───┘
          1   2   3
          C   B   E
PinNameDescription
1COLLECTOR (C)Collector terminal (High-side load output)
2BASE (B)Base input control terminal (Connect via resistor)
3EMITTER (E)Emitter terminal (Connect to +VCC+V_{CC} positive supply rail)
Important

Pinout Differences (BC557 vs 2N3906):

  • BC557 (European standard): Pin 1 = Collector, Pin 2 = Base, Pin 3 = Emitter (C-B-E).
  • 2N3906 (US standard): Pin 1 = Emitter, Pin 2 = Base, Pin 3 = Collector (E-B-C).

Gain Classification Suffixes

  • BC557A: Low DC Current Gain (hFE=110…220h_{FE} = 110 \dots 220).
  • BC557B: Medium DC Current Gain (hFE=200…450h_{FE} = 200 \dots 450) — Most common kit variant.
  • BC557C: High DC Current Gain (hFE=420…800h_{FE} = 420 \dots 800).

Specifications

ParameterSymbolMinTypMaxUnitConditions
Collector Breakdown VoltageV(BR)CEOV_{(BR)CEO}-45——VIC=−10mA,IB=0I_C = -10\text{mA}, I_B = 0
Emitter Breakdown VoltageV(BR)EBOV_{(BR)EBO}-5.0——VIE=−10 μA,IC=0I_E = -10\ \mu\text{A}, I_C = 0
Collector Saturation VoltsVCE(sat)V_{CE(sat)}—-90-250mVIC=−10mA,IB=−0.5mAI_C = -10\text{mA}, I_B = -0.5\text{mA}
Base Saturation VoltageVBE(sat)V_{BE(sat)}—-700-900mVIC=−10mA,IB=−0.5mAI_C = -10\text{mA}, I_B = -0.5\text{mA}

Common mistakes

  • Reversing Emitter and Collector pins: Inserting a BC557 with its flat face facing the wrong way connects Collector to VCCV_{CC} and Emitter to Load. The transistor will operate in reverse-active mode with extremely low current gain (hFE<5h_{FE} < 5).
  • Exceeding -100mA continuous collector current: The BC557 is limited to 100 mA100\text{ mA}. For high-current PNP power switching, use a power PNP transistor (like the TIP127 or BD140).

Notes

  • BC557 vs BC547: BC557 is PNP; BC547 is its complementary NPN transistor.

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