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

STMicroelectronics BD135

Name: BD135
Brand: STMicroelectronics
SKU: BD135
Price: 2.40 USD
Availability: InStock
Rating: 5 (2 reviews)

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Part No.:: BD135

Manufacturer:: STMicroelectronics

Category:: Single Bipolar Transistors

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

Datasheet:: BD135.pdf

Description:: TRANS NPN 45V 1.5A SOT-32-3

Quantity:: RFQ Add To RFQ list

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Inventory:6,717

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Product details

Overview

BD135 from STMicroelectronics is an NPN epitaxial planar bipolar junction transistor in SOT-32 package, rated for 45 V V_CBO, 1.5 A I_C, and 12.5 W P_TOT at T_C ≤ 25 °C. It delivers h_FE = 25–250 (IC = 5–500 mA, V_CE = 2 V) and is pre-selected for DC current gain consistency. It serves as a medium-power audio driver in complementary quasi-complementary amplifier stages.

For engineers reviewing the BD135 datasheet, BD135 pinout, BD135 application, or BD135 equivalent, key selection criteria include its 45 V collector-base rating, 1.5 A continuous collector current capability, thermal resistance of 10 °C/W junction-to-case, safe operating area under pulsed conditions, and compatibility with SOT-32 PCB footprint and thermal management constraints.

Technical Context

The BD135 operates as a linear amplifying device with fixed-polarity NPN structure and epitaxial base design optimized for audio-frequency signal gain and low-distortion current sourcing. Its h_FE grouping (e.g., BD135-16) enables matched pair use with BD136 in Class-B or AB output stages.

It exhibits V_CE(sat) = 0.5 V at I_C = 0.5 A / I_B = 0.05 A and V_BE ≈ 1 V under same conditions-enabling predictable base drive requirements in discrete power amplifier designs. Thermal derating follows R_thj-amb = 100 °C/W for ambient-limited operation.

Key Specifications

Parameter	Value and Actual Design Meaning
V_CBO	45 V - maximum reverse bias before collector-base junction breakdown; sets upper limit for supply rail headroom in common-emitter amplifiers
I_C	1.5 A - continuous collector current rating; defines usable output stage current capacity without forced cooling
P_TOT (T_C ≤ 25 °C)	12.5 W - total dissipation at case temperature ≤25 °C; requires heatsink for sustained >1 W operation
h_FE	25–250 - DC current gain range across operating points; supports stable biasing from small-signal to medium-power drive
R_thj-case	10 °C/W - junction-to-case thermal resistance; determines minimum heatsink requirement when mounted on metal tab
V_CE(sat)	0.5 V @ I_C=0.5 A, I_B=0.05 A - low saturation voltage reduces conduction loss in switching or Class-AB output stages

Pinout & Package

SOT-32 (TO-126 compatible) plastic package with insulated collector tab for direct heatsink mounting; standardized 3-pin through-hole outline with emitter (pin 1), base (pin 2), collector (pin 3) terminal assignment.

Pin/Terminal	Circuit Role	Design Meaning
Pin 1 (E)	Emitter	Reference node for bias network; connected to ground or negative rail in common-emitter configuration
Pin 2 (B)	Base	Current-controlled input; requires ~0.05 A drive for full 0.5 A collector conduction
Pin 3 (C)	Collector	Main power output node; electrically isolated metal tab enables direct thermal coupling to heatsink

Key Features

Feature	Design Value
Pre-selected h_FE groups	BD135-16 offers h_FE = 100–160 at I_C = 150 mA, enabling matched push-pull pairing with BD136-16
Epitaxial planar structure	Improved frequency response and reduced leakage vs. alloy-junction transistors; supports audio bandwidth up to ~100 kHz
ECOPACK® lead-free packaging	Complies with JEDEC JESD97; second-level interconnect free of lead, suitable for RoHS-constrained industrial assembly
High safe operating area (SOA)	Rated for 3 A peak collector current with 300 µs pulse width and 1.5% duty cycle-supports transient overload handling

Applications

Audio Power Amplifier Output Stage

DC Motor Driver (Low-Voltage)

Use Scenario: Medium-power stereo amplifier output stage delivering up to 10 W into 8 Ω load using quasi-complementary topology.

IC Role / Device Role / Timing Role: NPN current source in push-pull pair; handles positive half-cycle conduction while BD136 handles negative half-cycle.

Use Value: Low V_CE(sat) minimizes heat generation during high-current peaks; h_FE consistency ensures symmetrical gain and reduced crossover distortion.

Use Scenario: H-bridge motor control for 12 V brushed DC motors in industrial actuators or lab equipment.

IC Role / Device Role / Timing Role: High-side NPN switch in discrete half-bridge; driven by TTL-compatible base resistor network.

Use Value: 45 V V_CBO provides margin against inductive kickback; 1.5 A I_C supports motors drawing ≤1 A continuous current.

Linear Voltage Regulator Pass Element

Discrete Class-A Preamp Driver

Use Scenario: Series pass transistor in adjustable 0–30 V, 1 A bench power supply with foldback current limiting.

IC Role / Device Role / Timing Role: Continuously biased NPN transistor regulating output voltage via emitter-follower configuration.

Use Value: 12.5 W P_TOT at T_C ≤ 25 °C allows regulated operation up to ~10 W dissipation with modest heatsinking.

Use Scenario: First-stage voltage amplifier in tube-hybrid guitar preamp, driving tone stack and phase inverter.

IC Role / Device Role / Timing Role: Common-emitter small-signal amplifier with emitter degeneration resistor for linearity.

Use Value: h_FE ≥ 40 at I_C = 5 mA ensures stable 20–30 dB midband gain; low ICBO (<0.1 µA) preserves DC bias stability over temperature.

Equivalent & Alternatives

The following parts are listed as comparable options for similar NPN medium-power audio amplifier applications.

Alternative Part	Technical Difference	Application Difference	Selection Advice
BD235	Higher V_CBO = 60 V, higher h_FE min = 40, same SOT-32 package	Supports higher supply rails (±24 V systems); better suited for 20 W+ amplifiers	Select BD235 when designing for >45 V rail voltage or requiring tighter h_FE lower bound
TIP31A	Same V_CBO = 45 V but higher I_C = 3 A, TO-220 package, R_thj-amb = 40 °C/W	Requires different footprint and heatsink interface; better for higher continuous power	Choose TIP31A only if board layout accommodates TO-220 and thermal budget exceeds SOT-32 limits

Compared with BD235 and TIP31A, the BD135 offers optimal balance of gain consistency, thermal interface simplicity (SOT-32 tab mount), and proven reliability in legacy audio designs-making it preferred where footprint, cost, and established performance outweigh raw power scaling.

Availability

BD135 is available at Aetrix Electronics and suitable for audio power amplifiers, DC motor drivers, linear voltage regulators, and discrete preamplifier stages requiring stable component supply and long-term obsolescence resilience.

Supply support for BD135 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, Switzerland, designing and manufacturing analog, digital, and mixed-signal ICs and discrete devices for industrial, automotive, and consumer markets.

The BD135 belongs to ST's legacy bipolar power transistor family, engineered specifically for cost-sensitive, medium-power linear and switching applications in audio, power supply, and motion control systems.

FAQ

Is BD135 RoHS-compliant?

Yes, BD135 is manufactured in ECOPACK® packaging with lead-free second-level interconnect, compliant with JEDEC Standard JESD97 and EU RoHS Directive 2011/65/EU. The inner box label indicates lead-free status per ST's environmental marking convention.

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

At T_C = 70 °C, BD135's power dissipation must be derated linearly from 12.5 W at 25 °C using R_thj-case = 10 °C/W. Maximum allowable P_TOT = 12.5 W × (1 − (70−25)/125) = 8.0 W. With V_CE(sat) ≈ 0.5 V, max continuous I_C ≈ √(8.0 W / 0.5 V) ≈ 4 A-but limited by absolute max I_C = 1.5 A. So 1.5 A remains the hard limit regardless of temperature.

Can BD135 be used in parallel with another BD135 for higher current?

No-BD135 lacks built-in emitter ballasting resistors and exhibits positive thermal runaway risk when paralleled. Its h_FE increases with junction temperature, causing current hogging. For higher current, use a single higher-rated device like TIP31A or implement external emitter resistors (≥0.1 Ω) with matched h_FE units and shared heatsink.

Does BD135 require a heatsink in typical audio amplifier use?

Yes-when dissipating >1 W continuously (e.g., 0.5 A × 2 V V_CE), junction temperature rise exceeds safe limits without heatsinking. With R_thj-amb = 100 °C/W, even 1 W raises T_j by 100 °C above ambient. A minimum 20 cm² aluminum heatsink (R_th ≈ 30 °C/W) is recommended for sustained operation above 500 mW.

BD135 Specifications

Product attributes: Attribute value

Manufacturer:: STMicroelectronics

Series:: -

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

Packaging:: Tube

Product Status:: Active

Transistor Type:: NPN

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

Voltage - Collector Emitter Breakdown (Max):: 45 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

BD135 FAQ

1.How can I place an order for BD135 through Aetrix?

Please submit a Request for Quotation (RFQ) for BD135 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 BD135 reliable?

The price and inventory of BD135 are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for BD135 is usually 5 days.

3.What payment methods are accepted for BD135?

We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for BD135 transactions.

Note: Certain payment methods may incur a processing fee.

4.How is shipping managed for BD135?

BD135 orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.

Once your BD135 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 BD135?

For technical support, including BD135 datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your BD135 requirements.

6.How does Aetrix verify that BD135 is sourced from the original manufacturer or authorized distributors?

All BD135 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 BD135 meets industry standards.

7.What is the process for return or replacement of BD135?

All BD135 units undergo pre-shipment inspection (PSI). If there is an issue with BD135, 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 BD135 part is unused and in its original packaging.

Return procedure for BD135:

1.Submit a request within 90 days.

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

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