onsemi BC557ATA

Overview

BC557ATA from onsemi is a PNP epitaxial silicon transistor designed for general-purpose switching and linear amplification in low-power analog and digital circuits. It features V_CEO = −45 V, I_C = −100 mA, h_FE = 110–800 (Class A/B/C), f_T = 150 MHz, and operates with V_BE(on) ≈ −660 mV at I_C = −2 mA - commonly deployed in discrete amplifier stages, level shifters, and load switches in industrial control and consumer audio.

For engineers reviewing the BC557ATA datasheet, pinout, applications, or equivalent options, key selection criteria include its TO-92-3 (case 135AR) package, complementary pairing with BC547/BC548 NPN devices, −45 V V_CEO rating, low-noise capability (NF = 2–10 dB), and Class A/B h_FE binning - all critical for bias-stable small-signal designs.

Technical Context

The BC557ATA is a discrete PNP bipolar junction transistor optimized for medium-speed switching and low-distortion amplification. Its h_FE classification (A or B per marking) defines DC current gain range, while V_CE(sat) ≤ −300 mV at I_C = −10 mA / I_B = −0.5 mA ensures efficient saturation in logic-level interface circuits.

Thermal performance is defined by R_JA = 250 °C/W (FR-4 PCB, 76 mm × 114 mm), PD = 500 mW at 25°C with 4.0 mW/°C derating - enabling reliable operation up to T_J = 150°C. Its Cob = 6 pF at V_CB = −10 V supports stable high-frequency gain without unintended resonance in RF-adjacent stages.

Key Specifications

Pinout & Package

BC557ATA is housed in a TO-92-3 plastic package (case 135AR), lead-formed for through-hole mounting. Dimensions: 4.83 mm × 4.76 mm × 3.6 mm. Pin 1 = Collector, Pin 2 = Base, Pin 3 = Emitter - verified per onsemi mechanical drawing 98AON13879G.

Key Features

Applications

Equivalent & Alternatives

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

Compared with BC557ATA, BC557BTA offers higher and narrower h_FE range for improved bias predictability, while MMBT557LT1G provides identical functionality in a surface-mount package - enabling miniaturization at the cost of manual assembly compatibility and thermal dissipation margin.

Availability

BC557ATA is available at Aetrix Electronics and suitable for industrial control, consumer audio, and embedded sensor interface applications requiring stable component supply and long-term manufacturability.

Supply support for BC557ATA 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 manufacturer specializing in energy-efficient power, analog, sensing, and connectivity solutions for automotive, industrial, cloud, and IoT markets.

The BC557ATA belongs to onsemi's legacy BC5xx family of general-purpose bipolar transistors, engineered for reliability, wide temperature operation, and seamless complementarity with NPN counterparts in discrete analog signal chains.

FAQ

What is the maximum collector-emitter voltage rating for BC557ATA?

The BC557ATA has a maximum collector-emitter voltage (V_CEO) rating of −45 V. This specifies the highest reverse voltage that can be safely applied between collector and emitter with the base open. Exceeding this value risks avalanche breakdown and permanent device damage. The rating is validated per onsemi's absolute maximum ratings table at T_A = 25°C and applies across the full operating temperature range of −65°C to +150°C.

Is BC557ATA pin-compatible with BC547 or other BC5xx series transistors?

BC557ATA is electrically complementary-not pin-compatible-with BC547 (NPN). Both use TO-92-3 packages with identical pinouts (E-B-C), but polarity reversal means direct substitution without circuit modification will cause functional failure. BC557ATA pin 1 is Collector, pin 2 is Base, pin 3 is Emitter - matching BC547's physical layout but requiring inverted biasing and load connections in design.

What h_FE classification does BC557ATA have, and how is it marked?

BC557ATA is classified as h_FE Class A, with a guaranteed DC current gain range of 110–220 at V_CE = −5 V and I_C = −2 mA. The "A" suffix in the part number corresponds to this bin; the device is laser-marked "BC557A" on the package body per onsemi's ordering information table and marking diagram.

Can BC557ATA be used in low-noise audio amplifier designs?

Yes, BC557ATA is specified for low-noise operation with a noise figure (NF) of 2–10 dB at 1 kHz, V_CE = −5 V, and I_C = −200 µA. This makes it suitable for first-stage preamplifiers in microphones, guitar effects, and sensor interfaces where signal integrity is critical. Its Cob = 6 pF also helps maintain bandwidth without introducing phase distortion in audio-band gain stages.

What is the thermal resistance and power dissipation limit of BC557ATA?

BC557ATA has a junction-to-ambient thermal resistance (R_JA) of 250 °C/W on a standard FR-4 PCB (76 mm × 114 mm), with a maximum power dissipation (P_D) of 500 mW at 25°C ambient. Power must be derated by 4.0 mW/°C above 25°C, limiting usable dissipation to ~300 mW at 75°C ambient - a key constraint for continuous conduction in amplifier or driver applications.