onsemi BSR18A

Overview

BSR18A from ON Semiconductor is a PNP general-purpose bipolar junction transistor (BJT) designed for low-to-medium current switching and amplification in discrete analog and digital circuits, with V_CEO = −40 V, I_C = −200 mA continuous, h_FE = 60–300 (depending on I_C), and f_T = 250 MHz - used in signal conditioning stages of industrial sensor interfaces and power management enable/disable logic.

For engineers reviewing the BSR18A datasheet, pinout, applications, or equivalent options, this page delivers verified package mapping (SOT-23), validated terminal roles (C/B/E), confirmed thermal limits (T_J = −55 to +150°C), and real-world switching performance (t_s = 275 ns, t_f = 75 ns) - all directly extracted from Fairchild/ON Semiconductor Rev. 1.1.0 documentation.

Technical Context

The BSR18A operates as a silicon PNP BJT fabricated in Fairchild's Process 66, optimized for general-purpose linear amplification and saturated switching at collector currents from 10 μA to 100 mA. Its DC current gain (h_FE) varies from 60 at I_C = −100 mA to 300 at I_C = −1.0 mA, and its transition frequency (f_T) remains stable at 250 MHz under V_CE = −20 V, enabling RF-capable small-signal use up to ~100 MHz.

Thermal design is constrained by R_θJA = 357°C/W on FR-4 PCB (40 mm × 40 mm × 1.5 mm), limiting usable power dissipation to 350 mW at T_A = 25°C with 2.8 mW/°C derating. Breakdown ratings (V_CEO, V_CBO, V_EBO) are symmetrically rated at −40 V, −40 V, and −5 V respectively - confirming robust reverse-bias tolerance for rail-to-rail switching in negative-supply domains.

Key Specifications

Pinout & Package

SOT-23 (JEDEC TO-236AB) 3-lead surface-mount package with standard lead frame geometry: 2.92 mm × 1.30 mm footprint, 1.20 mm max height, gull-wing leads. Marking "T92" identifies BSR18A on top surface.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar PNP general-purpose amplifier applications.

Compared with BC807-40 and MMBT4403, the BSR18A offers superior f_T/R_θJA balance for medium-speed, thermally constrained PNP switching - making it optimal for space-limited industrial control boards where 250 MHz bandwidth and 357°C/W thermal resistance jointly reduce component count and layout complexity.

Availability

BSR18A is available at Aetrix Electronics and suitable for industrial sensor interfaces, microcontroller GPIO load switching, DC-DC enable logic, and negative-rail power sequencing requiring stable component supply across extended temperature ranges and long production lifecycles.

Supply support for BSR18A 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 (formerly Fairchild Semiconductor) is a global semiconductor manufacturer specializing in power management, analog, sensor, and discrete solutions for automotive, industrial, and cloud infrastructure markets.

The BSR18A belongs to ON Semiconductor's legacy general-purpose bipolar transistor product line, originally developed by Fairchild for cost-sensitive, high-reliability discrete signal switching and amplification in industrial and consumer electronics.

FAQ

What is the maximum operating temperature for the BSR18A?

The BSR18A has a specified junction and storage temperature range of −55°C to +150°C. Its absolute maximum junction temperature is 150°C, and sustained operation above this threshold risks permanent degradation. Derating begins at T_A = 25°C, with thermal resistance R_θJA = 357°C/W on standard FR-4 PCB - meaning ambient temperature must be limited to ≤85°C to keep T_J ≤ 125°C at full 200 mA load. The BSR18A is qualified for industrial-grade thermal environments.

Does the BSR18A support high-frequency amplification applications?

Yes, the BSR18A supports high-frequency amplification with a transition frequency (f_T) of 250 MHz at I_C = −10 mA and V_CE = −20 V. Its low collector-base capacitance (C_cb = 4.5 pF) and consistent h_fe response up to 100 MHz make it suitable for VHF preamplifier stages, RF detector buffers, and wideband signal conditioning - provided proper biasing and impedance matching are implemented per the BSR18A datasheet curves.

What is the pin configuration of the BSR18A in SOT-23 package?

The BSR18A uses standard SOT-23 pinout: Pin 1 = Emitter, Pin 2 = Base, Pin 3 = Collector - viewed from top with marking "T92" oriented left-to-right. This matches JEDEC TO-236AB mechanical specification and is identical to BC807, MMBT4403, and other PNP SOT-23 transistors. No alternate pinouts or variants exist for the BSR18A; all official documentation confirms this terminal assignment.

How does the BSR18A compare to NPN alternatives like the BSR16A?

The BSR18A is a PNP device, while the BSR16A is its complementary NPN counterpart - sharing identical SOT-23 packaging, voltage ratings (V_CEO = −40 V / +40 V), and thermal specs, but opposite polarity and current flow direction. They are designed for matched pair use in push-pull amplifiers or level-shifting circuits. Unlike the BSR16A, the BSR18A sinks current from its collector and sources from its emitter - making it ideal for high-side switching in negative-rail systems where NPN devices cannot be directly substituted.

Is the BSR18A suitable for automotive applications?

The BSR18A is not AEC-Q101 qualified and lacks formal automotive qualification documentation. However, its −55°C to +150°C operating range, robust breakdown ratings (V_CEO = −40 V), and proven reliability in industrial motor controls and power supplies mean it may be deployed in under-hood non-safety-critical subsystems - such as cabin HVAC fan control or lighting drivers - subject to customer-specific validation. For ASIL-B/C systems, ON Semiconductor's AEC-Q101-certified PNP transistors (e.g., NSS40301MR6T1G) are recommended instead of the BSR18A.