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Home > Products > Discrete Semiconductor Products > Transistors > Bipolar (BJT) > Single Bipolar Transistors

STMicroelectronics BD138

Name: BD138
Brand: STMicroelectronics
SKU: BD138
Price: 2.40 USD
Availability: InStock
Rating: 5 (2 reviews)

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Part No.:: BD138

Manufacturer:: STMicroelectronics

Category:: Single Bipolar Transistors

Package:: TO-225AA, TO-126-3

Datasheet:: BD138.pdf

Description:: TRANS PNP 60V 1.5A SOT-32-3

Quantity:: RFQ Add To RFQ list

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Inventory:11,988

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Product details

Overview

BD138 from STMicroelectronics is a silicon epitaxial planar PNP bipolar junction transistor in SOT-32 (TO-126) package, rated for V_CEO = −60 V, I_C = −1.5 A, P_tot = 12.5 W at T_c ≤ 25 °C, and designed for audio amplifier output stages and quasi-complementary driver circuits.

For engineers reviewing the BD138 datasheet, BD138 pinout, BD138 application, or BD138 equivalent, key selection criteria include safe operating area under pulsed conditions, h_FE grouping (BD138-10/BD138-16), V_CE(sat) at −0.5 A, thermal resistance (R_thj-case = 10 °C/W), and compatibility with complementary NPN BD137.

Technical Context

The BD138 operates as a medium-power PNP switching and linear amplifier transistor with fixed three-terminal configuration (Emitter, Base, Collector), supporting DC and low-frequency AC operation up to ~3 MHz (f_T not specified but consistent with audio-band use). Its design emphasizes ruggedness in quasi-complementary push-pull output stages.

It features guaranteed h_FE ranges (63–100 for group-10; 160–250 for group-16) at I_C = −150 mA, V_CE = −2 V, and maintains V_CEO(sus) = −60 V under pulsed conditions (300 µs, 1.5% duty cycle), enabling reliable operation in Class AB audio drivers.

Key Specifications

Parameter	Value and Actual Design Meaning
V_CEO	−60 V: Maximum collector-emitter voltage before breakdown under open-base condition; defines safe DC rail limit in amplifier output stage.
I_C	−1.5 A: Continuous DC collector current rating; sets maximum quiescent load capability in linear mode.
P_tot (T_c ≤ 25 °C)	12.5 W: Total power dissipation at case temperature ≤25 °C; requires heatsink for sustained operation above ~2 W.
R_thj-case	10 °C/W: Junction-to-case thermal resistance; determines temperature rise per watt dissipated when mounted on heatsink.
h_FE (I_C = −150 mA)	63–250: DC current gain range across two factory groups; impacts base drive requirements and bias stability.
V_CE(sat)	−0.5 V @ I_C = −0.5 A, I_B = −0.05 A: Saturation voltage defining conduction loss in switching applications.
V_EBO	−5 V: Maximum reverse emitter-base voltage; limits base bias network design margin.

Pinout & Package

SOT-32 (TO-126) plastic package with molded epoxy body, intended for through-hole mounting and heatsink attachment via collector tab. Pin 1 = Base, Pin 2 = Collector (electrically connected to tab), Pin 3 = Emitter.

Pin/Terminal	Circuit Role	Design Meaning
1 (Base)	Control input terminal	Receives base current to regulate collector-emitter conduction; requires current-limiting resistor in most driver circuits.
2 (Collector)	High-current output terminal	Electrically tied to metal tab; must be insulated from heatsink unless common-collector topology is used.
3 (Emitter)	Reference terminal for current flow	Typically connected to positive supply rail in PNP high-side switch or amplifier configurations.

Key Features

Feature	Design Value
Complementary pairing	Matched with NPN BD137 for quasi-complementary audio output stages, minimizing crossover distortion.
Factory h_FE grouping	Two gain bins (BD138-10 and BD138-16) enable precise matching in push-pull pairs without manual sorting.
Pulsed SOA compliance	Guaranteed V_CEO(sus) = −60 V at I_C = −30 mA pulse ensures reliability during transient overloads in amplifier protection schemes.
Thermal robustness	R_thj-case = 10 °C/W enables >10 W continuous dissipation with modest heatsinking, supporting compact audio module designs.

Applications

Audio Power Amplifier Output Stage

Quasi-Complementary Driver

Use Scenario: Final output stage in 10–20 W Class AB audio amplifiers driving 4–8 Ω speakers.

IC Role / Device Role / Timing Role: PNP output transistor delivering negative half-cycle current in push-pull configuration.

Use Value: Low V_CE(sat) reduces conduction loss and heat generation, while h_FE grouping ensures matched gain with BD137 for symmetric clipping behavior.

Use Scenario: Driver stage preceding power transistors in discrete audio amplifiers or motor control H-bridges.

IC Role / Device Role / Timing Role: Medium-power PNP buffer amplifying preamp signal to drive high-capacitance bases of output devices.

Use Value: 12.5 W dissipation headroom allows stable operation under reactive loads, and −60 V V_CEO supports ±30 V rails.

DC Motor Direction Control

Linear Voltage Regulator Pass Element

Use Scenario: High-side switch in bidirectional brushed DC motor control using dual H-bridge topology.

IC Role / Device Role / Timing Role: PNP switch controlling current flow from positive supply to motor winding.

Use Value: −1.5 A I_C rating handles stall currents up to 1.2 A continuously; SOT-32 tab enables direct heatsink mounting for thermal management.

Use Scenario: Series pass transistor in adjustable linear regulators delivering up to 1 A output current.

IC Role / Device Role / Timing Role: Current-controlled series element regulating output voltage by dissipating excess input-output differential.

Use Value: Guaranteed h_FE range simplifies base drive design; R_thj-case = 10 °C/W supports regulated operation at 5–8 W dissipation with standard heatsinks.

Equivalent & Alternatives

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

Alternative Part	Technical Difference	Application Difference	Selection Advice
BD140	V_CEO = −80 V, V_CBO = −80 V; otherwise identical pinout, package, and gain grouping.	Supports higher supply rails (±40 V) and improved surge tolerance in industrial motor drives.	Select BD140 when operating beyond ±30 V rails or requiring enhanced avalanche ruggedness.
MJD13005	TO-252 (DPAK) surface-mount package; V_CEO = −60 V, I_C = −1.5 A, but h_FE min = 20 (no factory grouping).	Enables automated PCB assembly but lacks gain binning for matched pair design.	Choose MJD13005 only for space-constrained SMT layouts where manual gain matching is acceptable.

Compared with BD140, the BD138 trades 20 V lower breakdown for tighter h_FE control and legacy through-hole compatibility; versus MJD13005, it offers factory gain bins and proven thermal performance in audio-grade heatsinked assemblies.

Availability

BD138 is available at Aetrix Electronics and suitable for audio amplifier production, industrial motor control systems, and linear regulator modules requiring stable component supply and long-term manufacturability.

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

STMicroelectronics is a global semiconductor leader headquartered in Geneva, designing and manufacturing analog, digital, and mixed-signal ICs and discrete components for automotive, industrial, and consumer markets.

The BD138 belongs to ST's legacy bipolar power transistor family, engineered specifically for cost-sensitive, high-reliability audio and power linear applications where thermal stability and gain consistency are critical.

FAQ

Is BD138 pin-compatible with BD136 or BD140?

Yes - all three share identical SOT-32 (TO-126) mechanical footprint and pinout (Base=1, Collector=2, Emitter=3). Electrical differences lie in voltage ratings: BD136 (−45 V), BD138 (−60 V), BD140 (−80 V), so substitution requires verification of circuit voltage margins.

What is the maximum continuous collector current at 70 °C case temperature?

Derating from 12.5 W at 25 °C case temperature at 0.1 W/°C yields ~8 W at 70 °C, supporting I_C ≈ −1.1 A continuously with adequate heatsinking. Full −1.5 A rating applies only when T_c ≤ 25 °C.

Does BD138 require a base resistor in switching applications?

Yes - base current must be limited to avoid exceeding I_B = −0.5 A absolute maximum. For I_C = −1 A and h_FE = 100, a 470 Ω resistor (with 5 V drive) delivers ~10 mA base current, ensuring saturation while staying within safe operating limits.

Can BD138 replace BD139 in a complementary pair?

No - BD139 is an NPN transistor; BD138 is PNP. The correct complementary NPN for BD138 is BD137. Using BD139 would invert polarity and prevent proper push-pull operation in amplifier or driver circuits.

BD138 Specifications

Product attributes: Attribute value

Manufacturer:: STMicroelectronics

Series:: -

Package/Case:: TO-225AA, TO-126-3

Packaging:: Tube

Product Status:: Active

Transistor Type:: PNP

Current - Collector (Ic) (Max):: 1.5 A

Voltage - Collector Emitter Breakdown (Max):: 60 V

Vce Saturation (Max) @ Ib, Ic:: 500mV @ 50mA, 500mA

Current - Collector Cutoff (Max):: 100nA (ICBO)

DC Current Gain (hFE) (Min) @ Ic, Vce:: 40 @ 150mA, 2V

Power - Max:: 1.25 W

Frequency - Transition:: -

Operating Temperature:: 150°C (TJ)

Grade:: -

Qualification:: -

Mounting Type:: Through Hole

Supplier Device Package:: SOT-32-3

BD138 FAQ

1.How can I place an order for BD138 through Aetrix?

Please submit a Request for Quotation (RFQ) for BD138 on Aetrix. Our sales agent will provide a competitive quotation and guide you through the order confirmation once you accept the terms.

2.Are the price and stock information for BD138 reliable?

The price and inventory of BD138 are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for BD138 is usually 5 days.

3.What payment methods are accepted for BD138?

We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for BD138 transactions.

Note: Certain payment methods may incur a processing fee.

4.How is shipping managed for BD138?

BD138 orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.

Once your BD138 order is processed, you will receive an email with the shipment details and tracking number.

Note: Tracking information may take up to 24 hours to appear. Express delivery typically takes 3–5 business days.

5.How can I obtain technical support or documentation for BD138?

For technical support, including BD138 datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your BD138 requirements.

6.How does Aetrix verify that BD138 is sourced from the original manufacturer or authorized distributors?

All BD138 products on Aetrix are procured from qualified distributors and authorized channels. Our dedicated quality assurance team conducts strict verification, including traceability checks and, if necessary, third-party testing. This ensures that BD138 meets industry standards.

7.What is the process for return or replacement of BD138?

All BD138 units undergo pre-shipment inspection (PSI). If there is an issue with BD138, returns or replacements are accepted under the following conditions:

1.Quantity discrepancies, incorrect items, or visible external defects (such as breakage or corrosion), acknowledged by Aetrix.

2.The issue is reported within 90 days of delivery.

3.The BD138 part is unused and in its original packaging.

Return procedure for BD138:

1.Submit a request within 90 days.

2.Obtain a Return Material Authorization (RMA) from Aetrix.

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