onsemi BD440S

Overview

BD440S from ON Semiconductor is a PNP epitaxial silicon power transistor in TO-126 package, rated for −60 V V_CEO, −4 A continuous collector current, 36 W power dissipation at T_C = 25°C, DC current gain (h_FE) of 20–140 at I_C = −10 mA to −2 A, and f_T = 3 MHz - used in medium-power linear regulation and switching circuits such as relay drivers and power supply pass elements.

For engineers reviewing the BD440S datasheet, pinout, applications, or equivalent options, key selection considerations include its PNP polarity, −60 V/−4 A rating, TO-126 thermal performance, V_CE(sat) ≤ −0.8 V at I_C = −2 A/I_B = −0.2 A, and complementary pairing with BD439 in push-pull output stages.

Technical Context

The BD440S operates as a medium-power PNP bipolar junction transistor optimized for linear and switching applications where robust safe operating area (SOA), stable DC gain across collector current range, and low saturation voltage are required. Its design supports base-driven operation with V_EB(on) = −0.58 V at I_C = −10 mA and −1.5 V at I_C = −2 A.

Thermal management is enabled by its TO-126 package with case temperature derating from 36 W at 25°C to zero at 175°C, and maximum junction temperature of 150°C. It exhibits ICBO ≤ −100 µA at V_CB = −60 V and V_CEO(sus) = −60 V under open-base conditions.

Key Specifications

Pinout & Package

BD440S is housed in a TO-126 plastic package with integral metal tab for heatsink mounting. The case is electrically connected to the collector terminal.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar PNP power transistor applications.

Compared with MJD44H11T4G and BD440, the BD440S offers identical legacy performance in through-hole form with updated nomenclature, while MJD44H11T4G provides SMT compatibility at higher voltage rating - choice depends on assembly method and voltage margin requirements.

Availability

BD440S is available at Aetrix Electronics and suitable for relay drivers, linear regulator pass elements, half-bridge motor controls, and overcurrent protection circuits requiring stable component supply and proven thermal reliability in TO-126 format.

Supply support for BD440S 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 supplier specializing in power management, analog, sensor, and logic devices for automotive, industrial, and consumer markets.

The BD440S belongs to ON Semiconductor's legacy bipolar power transistor family, designed specifically for cost-sensitive, medium-power linear and switching applications where ruggedness, SOA integrity, and complementary pairing are essential.

FAQ

What is the pin configuration of the BD440S?

The BD440S uses a TO-126 package with three terminals: Pin 1 is Emitter, Pin 2 is Collector (connected to the metal tab), and Pin 3 is Base. This configuration is standardized across Fairchild/ON Semiconductor's BD4xx series and verified in the official datasheet Rev. A1. Correct orientation is critical-reversing emitter and collector will cause immediate failure. Always confirm pinout using the physical tab alignment and silkscreen markings on the PCB footprint before soldering BD440S.

Is BD440S electrically identical to BD440?

Yes, BD440S is functionally and electrically identical to BD440. Per ON Semiconductor's Fairchild integration notice, the "S" suffix replaces the underscore in legacy Fairchild part numbers (e.g., BD440 became BD440S) to comply with ON Semi's ordering system requirements. All absolute maximum ratings, electrical characteristics, package dimensions, and thermal data remain unchanged in the BD440S datasheet. BD440S is the current orderable part number for the same silicon and construction as BD440.

What is the maximum safe continuous collector current for BD440S?

The BD440S is rated for −4 A continuous collector current (I_C) at case temperature T_C = 25°C. However, this value decreases linearly with rising case temperature - derating begins at 25°C, reaching zero at T_C = 175°C. For reliable operation at ambient temperatures above 50°C or without forced airflow, actual usable I_C must be reduced per the power derating curve in the BD440S datasheet Figure 6. Exceeding the derated limit risks thermal runaway and permanent failure of the BD440S.

Can BD440S be used as a direct replacement for BD442?

No, BD440S is not a direct replacement for BD442. While both are PNP TO-126 transistors, BD442 has higher voltage ratings: V_CEO = −80 V versus −60 V for BD440S. Substituting BD440S in a BD442-design circuit risks premature breakdown if the collector-emitter voltage exceeds −60 V. BD440S and BD442 share identical pinout and package, but their absolute maximum ratings differ - always verify voltage stress margins before interchanging BD440S and BD442 in any application.

What is the typical V_CE(sat) of BD440S under full load?

The BD440S specifies V_CE(sat) ≤ −0.8 V at I_C = −2 A and I_B = −0.2 A, corresponding to a forced beta (I_C/I_B) of 10. This value is confirmed in the "Electrical Characteristics" table of the BD440S datasheet. At lower currents (e.g., I_C = −1 A), V_CE(sat) drops further - typically −0.5 V - making BD440S efficient for medium-load switching. Always measure V_CE(sat) under actual operating conditions, as it varies with junction temperature and base drive consistency.