onsemi BD538K

Overview

BD538K from Fairchild Semiconductor is a PNP epitaxial silicon power transistor in TO-220 package, rated for -80 V V_CEO, -8 A I_C, 50 W P_C, with h_FE = 15–25 at I_C = -2 A and V_CE = -2 V, used in medium-power linear regulation and switching applications such as DC motor control and relay drivers.

For engineers reviewing the BD538K datasheet, pinout, applications, or equivalent options, key selection factors include its -80 V collector-emitter breakdown rating, low -0.8 V V_CE(sat) at -2 A/-0.2 A drive, TO-220 thermal performance, complementary pairing with BD537, and h_FE group K classification for consistent gain binning.

Technical Context

The BD538K operates as a medium-power PNP bipolar junction transistor optimized for linear and switching duty in industrial power stages. Its design supports high-current DC operation up to -8 A with controlled saturation behavior, defined by V_CE(sat) ≤ -0.8 V at I_C = -2 A and I_B = -0.2 A, and maintains safe operation up to 150°C junction temperature.

It features a fixed three-terminal structure (Base, Collector, Emitter) in TO-220 package with metal tab connected to Collector, enabling direct heatsinking. The h_FE group K designation specifies DC current gain of 30–75 at V_CE = -2 V and I_C = -2 A, distinguishing it from J-group variants with lower gain range.

Key Specifications

Pinout & Package

BD538K is housed in a TO-220 package with insulated mounting tab (Collector-connected), standard 3-pin vertical lead configuration, and mechanical dimensions compliant with JEDEC TO-220AB outline (15.90 mm × 10.08 mm × 4.50 mm height).

Key Features

Applications

Equivalent & Alternatives

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

Compared with BD538K, MJD538G trades package form factor and thermal capacity for SMT compatibility, while BD538-16 offers higher and more consistent h_FE at same voltage/current ratings-enabling lower base drive power and improved gain stability in feedback-critical linear designs.

Availability

BD538K is available at Aetrix Electronics and suitable for DC motor control, relay driving, linear regulator pass elements, and switching power supply output stages requiring stable component supply and long-lifecycle support.

Supply support for BD538K 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 manufacturer specializing in power discrete devices, analog ICs, and interface solutions before its acquisition by ON Semiconductor in 2016.

The BD538K belongs to Fairchild's BD53x PNP transistor family, designed specifically for medium-power industrial switching and linear regulation where robust voltage rating, predictable gain binning, and TO-220 thermal reliability are essential.

FAQ

What is the maximum continuous collector current rating for BD538K?

The BD538K is rated for -8 A continuous collector current (I_C) under DC conditions at case temperature T_C = 25°C. Actual usable current depends on heatsinking: derating applies above 25°C per the power derating curve in the datasheet, reaching zero at 125°C case temperature. BD538K must be mounted on an appropriate heatsink to sustain full -8 A in real-world operation.

Is BD538K pin-compatible with BD537?

Yes, BD538K is the PNP complement to the NPN BD537, sharing identical TO-220 package outline and pin assignment (1=Base, 2=Collector, 3=Emitter). This allows direct use in push-pull, complementary symmetry, and H-bridge circuits without layout changes-provided polarity-aware biasing and drive circuitry are implemented.

What does the 'K' suffix indicate in BD538K?

'K' denotes the h_FE (DC current gain) group binning for BD538K: guaranteed 30–75 at V_CE = -2 V and I_C = -2 A. This distinguishes it from BD538J (15–40) and BD538-16 (100–150), enabling designers to select consistent gain characteristics for predictable base drive design and production yield control.

Can BD538K be used in switching power supplies?

Yes, BD538K is explicitly qualified for switching applications per its datasheet, with f_T up to 12 MHz and low -0.8 V V_CE(sat) supporting efficient operation in flyback, forward, and DC-DC converter output stages up to ~100 kHz. Its -80 V V_CEO rating provides margin for reflected voltages and ringing in transformer-coupled topologies.

What is the thermal resistance from junction to case (R_θJC) for BD538K?

The BD538K datasheet does not specify R_θJC numerically, but its 50 W power dissipation rating at T_C = 25°C implies an effective R_θJC ≈ 0.5°C/W when combined with the 150°C maximum junction temperature. Actual thermal performance depends on mounting pressure, thermal interface material, and heatsink design-Fairchild recommends using mica insulators and thermal paste for optimal R_θJA reduction.