onsemi BD238S

Overview

BD238S from Fairchild Semiconductor is a PNP epitaxial silicon transistor in TO-126 package, rated for -100 V collector-base voltage, -80 V collector-emitter voltage, -2 A DC collector current, 25 W collector dissipation at TC=25°C, and 3 MHz current gain bandwidth product - used in medium-power linear amplification and switching circuits such as power supply regulators and motor drivers.

For engineers reviewing the BD238S datasheet, pinout, applications, or equivalent options, key selection criteria include VCEO(sus) = -80 V at IC = -100 mA, hFE ≥ 25 at IC = -1 A, VCE(sat) = -0.6 V at IC = -1 A/IB = -0.1 A, and safe operating area compliance up to 100 µs pulse width under specified thermal conditions.

Technical Context

The BD238S operates as a medium-power PNP bipolar junction transistor with fixed emitter-base and collector-base junction structures optimized for linear gain stability and switching robustness. Its VCEO(sus) rating of -80 V ensures reliable operation under inductive load turn-off transients, while fT = 3 MHz supports audio-frequency amplification and low-speed switching.

Thermal design is constrained by TJ(max) = 150°C and PC = 25 W at TC = 25°C, requiring heatsinking for continuous >1 A operation. The device exhibits ICBO ≤ -100 µA at VCB = -100 V and IEBO = -1 mA at VEB = -5 V, confirming low leakage performance suitable for stable bias networks.

Key Specifications

Pinout & Package

BD238S uses the TO-126 package: molded plastic case with metal tab for heatsinking, standardized pin layout, and 16.10 mm × 13.06 mm footprint. Pin 1 is Emitter, Pin 2 is Collector (connected to tab), Pin 3 is Base.

Key Features

Applications

Equivalent & Alternatives

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

Compared with MJD2955 and BD240C, the BD238S offers superior pulse current capability (-6 A), tighter hFE binning at high current, and proven thermal performance in TO-126 through-hole systems - making it optimal for legacy industrial controls and repair replacements requiring mechanical robustness and serviceability.

Availability

BD238S is available at Aetrix Electronics and suitable for industrial motor drives, analog power supplies, and relay interface circuits requiring stable component supply across long-life production cycles.

Supply support for BD238S 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

Fairchild Semiconductor was a U.S.-based semiconductor company specializing in power management, analog, and discrete devices before its acquisition by ON Semiconductor in 2016.

The BD238S belongs to Fairchild's legacy medium-power PNP transistor family, engineered for reliability in industrial linear and switching applications where thermal stability and voltage margin are critical.

FAQ

What is the maximum collector-emitter voltage rating for BD238S?

The BD238S has a maximum collector-emitter voltage (VCEO) rating of -80 V at TC = 25°C. This value is confirmed in the Absolute Maximum Ratings table and further validated by the VCEO(sus) parameter of -80 V measured at IC = -100 mA with IB = 0. Exceeding this voltage risks avalanche breakdown and permanent device failure. Derating is required above 25°C case temperature per the power derating curve in the BD238S datasheet.

Does BD238S have a complementary NPN transistor in the same family?

Yes, the BD238S is explicitly designated as the PNP complement to the BD237 NPN transistor. Both share identical TO-126 packaging, matching voltage ratings (BD237: VCEO = +80 V), and comparable current handling (BD237: IC = +2 A), enabling balanced push-pull amplifier and H-bridge driver designs. This pairing is documented in the "Complement to BD 233/235/237 respectively" note on the BD234/236/238 datasheet cover page.

What is the safe operating area (SOA) limitation for BD238S at 100 µs pulse width?

At 100 µs pulse width, the BD238S SOA chart shows a maximum collector current of approximately -4.5 A at VCE = -20 V, decreasing to -2.5 A at VCE = -60 V. These boundaries assume TC = 25°C and single-pulse conditions. Operation beyond these points risks second breakdown. The BD238S SOA curve is provided in Figure 3 of the original Fairchild datasheet Rev. A, February 2000.

Can BD238S be used in surface-mount designs?

No, BD238S is exclusively offered in the through-hole TO-126 package with leads designed for axial insertion and wave soldering. It has no official surface-mount variant. For SMT alternatives, consider the MJD2955 (TO-252) or FZT790A (SOT-223), though neither matches the BD238S's exact voltage/current profile or thermal interface. Board redesign is required to substitute BD238S with any SMT part.

What is the base-emitter on voltage for BD238S under typical operating conditions?

The BD238S exhibits a base-emitter on voltage (VBE(on)) of -1.3 V at VCE = -2 V and IC = -1 A, as specified in the Electrical Characteristics table. This value reflects forward-biased PNP junction behavior and must be accounted for when calculating base resistor values in switching applications. At lower currents (e.g., IC = -150 mA), VBE(on) drops to approximately -1.1 V, per typical characteristic curves in the datasheet.