onsemi BC556B

Overview

BC556B from onsemi is a PNP silicon small-signal amplifier transistor in TO-92 package, rated for −65 V V_CEO, −80 V V_CBO, −5.0 V V_EBO, −100 mA I_C, and 280 MHz f_T. It delivers h_FE = 120–420 at I_C = −10 mA, V_CE = −5 V, and is used in low-noise audio preamplifier stages, discrete bias networks, and level-shifting circuits in industrial control modules.

For engineers reviewing the BC556B datasheet, pinout, applications, or equivalent options, this page provides verified electrical parameters, thermal limits, junction-to-case resistance (83.3 °C/W), noise figure (2.0 dB), and validated alternatives for analog signal conditioning and linear amplification designs.

Technical Context

The BC556B operates as a general-purpose PNP bipolar junction transistor with fixed-emitter configuration and grounded-base or common-emitter topology. Its DC current gain spans 120–420 across test conditions, and its f_T of 280 MHz supports audio-frequency amplification up to ~100 kHz with stable phase margin.

Thermal design relies on R_JA = 200 °C/W (ambient) and R_JC = 83.3 °C/W (case), enabling 625 mW dissipation at T_A = 25°C or 1.5 W at T_C = 25°C. Saturation performance is defined at I_C = −10 mA / I_B = −0.5 mA (V_CE(sat) ≤ −0.075 V) and I_C = −100 mA / I_B = −5.0 mA (V_CE(sat) ≤ −0.3 V).

Key Specifications

Pinout & Package

BC556B uses the TO-92 (Case 29, Style 17) through-hole plastic package with 3 leads. The device has standardized mechanical dimensions: body height 4.45–5.20 mm, lead pitch 2.54 mm, and collector-base-emitter pin sequence matching JEDEC TO-92 orientation.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar PNP small-signal amplifier applications.

Compared with BC557B and BC558B, the BC556B offers the highest voltage tolerance (−65 V V_CEO) at the expense of lower f_T and narrower h_FE range-making it optimal for robust, high-rail industrial analog circuits where voltage margin outweighs bandwidth demand.

Availability

BC556B is available at Aetrix Electronics and suitable for industrial sensor interfaces, audio preamplifier stages, and discrete bias networks requiring stable component supply across extended temperature ranges and long production lifecycles.

Supply support for BC556B includes scheduled delivery planning, volume procurement assistance, BOM continuity management, traceable sourcing, and lifecycle availability coordination for OEM customers, industrial embedded developers, connected-device designers, and electronics production programs.

Manufacturer

onsemi (formerly ON Semiconductor) is a global semiconductor supplier specializing in energy-efficient power management, analog, sensing, and connectivity solutions for automotive, industrial, and cloud infrastructure markets.

The BC556B belongs to onsemi's legacy BC5xx PNP/NPN amplifier transistor family, designed for cost-sensitive, high-reliability linear analog applications including audio, instrumentation, and industrial control signal conditioning.

FAQ

What is the maximum collector-emitter voltage rating for BC556B?

The BC556B has a maximum collector-emitter voltage (V_CEO) rating of −65 V DC. This value is specified at I_C = −2.0 mA with base open and defines the absolute upper limit before avalanche breakdown occurs. Exceeding −65 V risks irreversible junction damage, and derating is recommended for long-term reliability in high-transient environments. The BC556B datasheet confirms this rating applies specifically to the BC556 series, not BC557 or BC558 variants.

Does BC556B support Pb-free assembly processes?

Yes, BC556BZL1G (the Pb-free variant) is explicitly qualified for lead-free soldering per J-STD-020. The device uses matte tin plating and meets RoHS Directive 2011/65/EU requirements. Standard BC556B (non-G suffix) is SnPb-plated and intended for traditional eutectic soldering. Both share identical electrical specs and TO-92 mechanical form, but thermal profiles must match the respective finish-BC556BZL1G requires peak reflow temperatures up to 260°C.

What is the typical noise figure of BC556B and under what conditions is it measured?

The BC556B has a typical noise figure (NF) of 2.0 dB, measured at I_C = −0.2 mA, V_CE = −5.0 V, source resistance R_S = 2.0 kΩ, frequency f = 1.0 kHz, and bandwidth referenced to 200 Hz. This low-noise performance is confirmed in the "Small-Signal Characteristics" table of the official BC556B/D datasheet and makes the BC556B suitable for first-stage amplification of weak signals where SNR preservation is critical.

How does the DC current gain (h_FE) of BC556B vary with collector current?

The BC556B exhibits h_FE = 120–420 at I_C = −10 mA and V_CE = −5 V, but gain drops to 90–150 at I_C = −2.0 mA and rises to 170–290 at I_C = −100 mA under same V_CE. Figure 7 in the BC556B/D datasheet shows normalized h_FE peaking near −10 mA and declining at both low and high current extremes. Designers must select operating point within the flat region to minimize gain variation across units and temperature.

Can BC556B be used in switching applications, and what is its saturation voltage?

Yes, BC556B can operate in switching mode with V_CE(sat) ≤ −0.075 V at I_C = −10 mA and I_B = −0.5 mA, and ≤ −0.3 V at I_C = −100 mA and I_B = −5.0 mA. These values are specified in the "ON CHARACTERISTICS" section of the BC556B datasheet. For reliable saturation, base drive must exceed I_B = I_C/10, and thermal limits (625 mW at 25°C ambient) must be observed to avoid secondary breakdown during repetitive switching.