onsemi BD442S

Overview

BD442S from ON Semiconductor is a PNP epitaxial silicon power transistor in TO-126 package, rated for -80 V V_CEO, -4 A continuous collector current, 36 W power dissipation at T_C = 25°C, and DC current gain (h_FE) of 15–140 at I_C = -500 mA to -2 A. It serves as a medium-power linear amplifier or switching device in industrial power supplies and motor control circuits.

For engineers reviewing the BD442S datasheet, pinout, applications, or equivalent options, key selection criteria include its -80 V V_CEO rating, -0.8 V V_CE(sat) at I_C = -2 A / I_B = -0.2 A, TO-126 thermal performance, and complementary pairing with BD441 in push-pull configurations.

Technical Context

The BD442S operates as a single PNP bipolar junction transistor with fixed emitter-base-collector terminal arrangement. Its safe operating area (SOA) supports pulsed currents up to -7 A (PW = 300 µs, duty cycle = 1.5%), and it exhibits f_T = 3 MHz at V_CE = -1 V, I_C = -250 mA - confirming suitability for audio-frequency switching and linear regulation.

Thermal design relies on case-to-ambient conduction via the TO-126 metal tab; derating begins at T_C > 25°C, reaching zero dissipation at 175°C. Junction temperature is limited to 150°C, and storage range spans -65°C to +150°C - aligning with industrial-grade reliability requirements.

Key Specifications

Pinout & Package

BD442S uses the TO-126 plastic package with integral metal tab for thermal and electrical connection to collector. The case is electrically connected to pin 2 (Collector), requiring isolation when mounting to heatsinks unless collector is at system ground potential.

Key Features

Applications

Equivalent & Alternatives

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

Compared with MJD44H11 and BD439, BD442S uniquely combines through-hole TO-126 mechanical robustness, -80 V blocking, and proven thermal interface for bolted heatsinks - making it preferred for repairable, serviceable, and high-reliability industrial power stages where leaded packages remain standard.

Availability

BD442S is available at Aetrix Electronics and suitable for industrial power supplies, DC motor controllers, and audio amplifier output stages requiring stable component supply and long-term manufacturability.

Supply support for BD442S 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 supplier delivering energy-efficient, intelligent power and sensing solutions for automotive, industrial, cloud, medical, and IoT applications.

The BD442S belongs to ON Semiconductor's legacy linear power transistor family, originally developed by Fairchild and optimized for medium-power analog and switching applications demanding ruggedness, thermal stability, and ease of heatsink integration.

FAQ

What is the maximum continuous collector current rating for BD442S?

The BD442S has a maximum continuous collector current (I_C) rating of -4 A at case temperature T_C = 25°C. This rating decreases with rising case temperature per the derating curve - at T_C = 100°C, the usable I_C drops to approximately -2.2 A. Adequate heatsinking is required to sustain rated current, and pulse operation up to -7 A is permitted under strict duty-cycle limits (PW = 300 µs, duty cycle = 1.5%).

Is BD442S pin-compatible with BD440?

Yes, BD442S is pin-compatible with BD440 - both use identical TO-126 package and pinout (Emitter-Collector-Base). However, BD442S offers higher voltage ratings (-80 V V_CEO vs. -60 V for BD440) and slightly different h_FE and V_CE(sat) characteristics. Substitution is possible in designs where the higher voltage margin is beneficial, but validation of SOA and thermal behavior under load is recommended.

Does BD442S require a heatsink in typical applications?

Yes, BD442S requires a heatsink in all applications operating above ~500 mA continuous current or dissipating more than ~2 W. With θ_JA ≈ 62.5°C/W (no heatsink), even 1 W dissipation raises junction temperature by 62.5°C above ambient - risking thermal runaway. The metal tab (pin 2) must be electrically isolated from chassis ground unless collector is referenced to system ground, and thermal interface material should be used between tab and heatsink.

What is the base-emitter forward voltage (V_BE(on)) of BD442S under typical operating conditions?

The BD442S exhibits V_BE(on) = -0.58 V at V_CE = -5 V and I_C = -10 mA, and -1.5 V at V_CE = -1 V and I_C = -2 A. This increase reflects higher base current demand at high collector current - consistent with its h_FE dropping from ~140 at low current to ~15 at I_C = -2 A. Drive circuitry must supply sufficient base current (≥ -0.2 A) to ensure saturation and avoid second breakdown.

Can BD442S be used as a direct replacement for BD442 without suffix?

Yes - BD442S is the updated ON Semiconductor designation for the legacy Fairchild BD442, following the post-acquisition nomenclature change where underscores were replaced with dashes. No electrical, mechanical, or parametric differences exist between BD442 and BD442S; they are identical devices. The "S" suffix reflects ON Semiconductor's standardized part numbering convention, not a revised version or enhanced variant.