onsemi BC547A

Overview

BC547A from ON Semiconductor is a general-purpose NPN epitaxial silicon transistor used for low-power switching and linear amplification in discrete analog circuits. It features V_CEO = 45 V, I_C = 100 mA, h_FE = 110–220 (Class A), f_T = 300 MHz, and TO-92 package - commonly deployed in signal conditioning stages of sensor interfaces and low-voltage logic-level translators.

For engineers reviewing the BC547A datasheet, pinout, applications, or equivalent options, key selection criteria include DC current gain tolerance, saturation voltage at defined drive conditions, noise figure in audio preamp use, and compatibility with legacy through-hole PCB layouts requiring TO-92 footprint and lead spacing.

Technical Context

The BC547A operates as a bipolar junction transistor with epitaxial base construction, enabling stable h_FE across temperature and improved high-frequency response versus diffused-base variants. Its V_CEO rating of 45 V and V_CBO of 50 V define safe operating limits for collector-to-emitter and collector-to-base reverse bias in common-emitter configurations.

Designed for Class A/B linear amplification and saturated-switching operation, it supports I_C up to 100 mA with P_C = 500 mW at T_A = 25°C, and exhibits V_CE(sat) ≤ 250 mV at I_C = 10 mA / I_B = 0.5 mA - critical for minimizing conduction loss in relay drivers and LED switches.

Key Specifications

Pinout & Package

BC547A is housed in a JEDEC TO-92 3-lead molded plastic package with straight leads (bulk/ammo/tape-and-reel variants). Lead assignment follows standard configuration: Pin 1 = Collector, Pin 2 = Base, Pin 3 = Emitter - verified per Fairchild/ON Semiconductor mechanical drawings Rev. 1.1.1.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar NPN general-purpose transistor applications.

Compared with BC547B and 2N3904, BC547A offers the narrowest h_FE range (110–220), simplifying base bias design for predictable saturation in switching circuits while maintaining full compatibility with legacy TO-92 footprints and thermal derating curves.

Availability

BC547A is available at Aetrix Electronics and suitable for audio preamplifiers, microcontroller interface circuits, discrete oscillator modules, and linear regulator designs requiring stable component supply across prototyping, pilot production, and long-lifecycle industrial deployments.

Supply support for BC547A 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

ON Semiconductor is a global semiconductor manufacturer specializing in energy-efficient power management, analog, and discrete components for automotive, industrial, and consumer applications.

BC547A belongs to ON Semiconductor's legacy general-purpose transistor product line - originally developed by Fairchild - designed for cost-sensitive, high-reliability discrete signal conditioning and switching in through-hole assembled systems.

FAQ

What is the maximum collector-emitter voltage rating for BC547A?

The BC547A has a V_CEO rating of 45 V, meaning it can safely sustain up to 45 volts between collector and emitter terminals under open-base conditions. This value is confirmed in the Absolute Maximum Ratings table of the official ON Semiconductor datasheet Rev. 1.1.1. Exceeding this voltage risks avalanche breakdown and permanent device failure. Always apply derating for temperature and reliability in BC547A designs.

Does BC547A have a specified noise figure, and what is its typical value?

Yes, BC547A has a documented noise figure (NF) of 2.0–10.0 dB at 1 kHz, measured under V_CE = 5 V, I_C = 200 μA, and R_G = 2 kΩ. This range reflects unit-to-unit variation within the Class A h_FE bin and makes BC547A suitable for low-noise preamplifier applications where SNR preservation is critical. The BC547A datasheet specifies this parameter explicitly in the Electrical Characteristics section.

What is the pin configuration of BC547A in the TO-92 package?

The BC547A uses the standard TO-92 pinout: Pin 1 = Collector, Pin 2 = Base, Pin 3 = Emitter - with leads viewed from the flat side of the package, left-to-right. This configuration is confirmed in the Physical Dimensions section (Figure 7) of the BC547A datasheet Rev. 1.1.1 and matches industry-standard orientation for NPN transistors in this family. No alternate pinouts are specified for BC547A.

How does BC547A differ from BC547B in terms of DC current gain?

The BC547A has an h_FE range of 110–220 at V_CE = 5 V and I_C = 2 mA, whereas BC547B is binned to 200–450 under identical test conditions. This difference affects base bias design: BC547A requires less conservative base drive margin but offers tighter gain predictability, while BC547B delivers higher average gain at the cost of wider statistical spread. Both share identical packaging, voltage ratings, and thermal limits.

Is BC547A suitable for use as a saturated switch in microcontroller-driven circuits?

Yes, BC547A is widely used as a saturated switch with microcontrollers. At I_C = 10 mA and I_B = 0.5 mA, its V_CE(sat) is guaranteed ≤250 mV, ensuring low conduction loss and minimal self-heating. Its h_FE ≥110 guarantees reliable saturation even with modest GPIO drive strength (e.g., 3.3 V MCU outputs driving through 10 kΩ base resistors). This behavior is validated in the BC547A datasheet's Electrical Characteristics table.