onsemi BD138

Overview

BD138 from onsemi is a PNP epitaxial silicon transistor in the BD136 series, rated for −60 V V_CEO, −1.5 A continuous collector current, and 12.5 W case power dissipation at T_C = 25°C; used as a medium-power amplifier or switch in complementary audio output stages with BD137.

For engineers reviewing the BD138 datasheet, pinout, applications, or equivalent options, key selection criteria include its TO-126 package, guaranteed h_FE ≥ 63 at I_C = −150 mA, V_CE(sat) ≤ −0.5 V at I_C = −500 mA/I_B = −50 mA, and Pb-free compliance per JESD97.

Technical Context

The BD138 operates as a general-purpose PNP bipolar junction transistor with fixed emitter-base and collector-base junction structures optimized for linear amplification and switching in DC-coupled circuits. Its safe operating area (SOA) is defined up to 10 s pulse width at T_C = 25°C, with derating to zero power at 150°C case temperature.

It features a single-crystal epitaxial base region enabling stable h_FE across I_C = −5 mA to −500 mA, with V_BE(on) = −1.0 V typical at I_C = −0.5 A and V_CE = −2 V - supporting predictable biasing in Class AB push-pull stages.

Key Specifications

Pinout & Package

BD138 is housed in a TO-126 (Case 340AS) plastic package with three leads: Emitter (Lead 1), Collector (Lead 2), Base (Lead 3), mounted with collector tab electrically connected to lead 2 and thermally coupled to heatsink.

Key Features

Applications

Equivalent & Alternatives

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

Compared with MJD13005G and BC557B, BD138 uniquely balances −60 V rating, −1.5 A current, TO-126 thermal performance, and h_FE binning - making it optimal for cost-sensitive, medium-power linear and switching applications where footprint and thermal coupling matter.

Availability

BD138 is available at Aetrix Electronics and suitable for audio amplifier output stages, relay drivers, and negative-rail regulator pass elements requiring stable component supply and Pb-free compliance.

Supply support for BD138 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

onsemi (formerly ON Semiconductor) is a global semiconductor supplier specializing in energy-efficient power, analog, sensor, and connectivity solutions for automotive, industrial, cloud, and IoT markets.

The BD136 series - including BD138 - was designed specifically for complementary medium-power linear amplification and switching in cost-sensitive consumer and industrial equipment.

FAQ

What is the maximum continuous collector current rating for BD138?

The BD138 has a maximum continuous collector current (I_C) rating of −1.5 A at T_C = 25°C. This value assumes proper heatsinking; derating applies above 25°C case temperature per the 12.5 W power dissipation limit and Figure 5 thermal curve. The BD138 must not exceed this current in DC operation without thermal risk.

Is BD138 pin-compatible with BD137?

No - BD138 is a PNP transistor while BD137 is its NPN complement; they share identical TO-126 pinout (Emitter-Collector-Base), but polarity reversal means direct substitution would invert circuit function. BD138 and BD137 are intended for complementary use in push-pull pairs, not pin-for-pin replacement.

What does the "16" suffix in BD13816STU indicate?

The "16" in BD13816STU denotes the h_FE gain bin: devices marked BD13816 guarantee h_FE between 100 and 160 at V_CE = −2 V and I_C = −150 mA. This binning enables tighter matching in differential or feedback-critical circuits compared to the BD13810 variant (h_FE = 63–100).

Can BD138 be used in switching power supplies?

Yes - BD138 is suitable for low-frequency switching applications such as relay drivers or linear regulator pass elements, but not for high-frequency SMPS due to limited f_T (not specified in datasheet) and relatively slow storage time. For > 20 kHz operation, dedicated fast-switching transistors like MJD122 are preferred over BD138.

Does BD138 require a heatsink in all applications?

BD138 requires a heatsink when dissipating more than ~1.25 W continuously (its P_C = 1.25 W at T_A = 25°C). At full 12.5 W rating, a substantial heatsink is mandatory. For < 500 mA loads with low V_CE, board copper may suffice; always verify junction temperature using θ_JC = 2.5°C/W and θ_CA estimates per application conditions.