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

onsemi BD438

Name: BD438
Brand: onsemi
SKU: BD438
Price: 2.40 USD
Availability: InStock
Rating: 5 (2 reviews)

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Part No.:: BD438

Manufacturer:: onsemi

Category:: Single Bipolar Transistors

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

Datasheet:: BD438.pdf

Description:: TRANS PNP 45V 4A TO-126

Quantity:: RFQ Add To RFQ list

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Product details

Overview

BD438 from onsemi is a plastic medium-power silicon PNP bipolar junction transistor rated for 45 V V_CEO, 4.0 A I_C, and 36 W power dissipation at T_C = 25°C, with h_FE ≥ 30 at I_C = 10 mA and ≥ 40 at I_C = 2.0 A, used in linear amplifiers and high-current switching circuits such as relay drivers and power supply control stages.

For engineers reviewing the BD438 datasheet, pinout, applications, or equivalent options, key selection considerations include its TO-225 package thermal resistance (R_θJC = 3.5°C/W), V_CE(sat) ≤ 0.7 V at I_C = 3.0 A/I_B = 0.3 A, complementary pairing with BD437, and discontinuation status requiring legacy design support planning.

Technical Context

The BD438 operates as a medium-power PNP BJT optimized for linear amplification and saturated switching, with guaranteed h_FE performance across three collector current ranges (10 mA, 500 mA, and 2.0 A) and specified V_BE(ON) = 1.1 V at I_C = 2.0 A. Its safe operating area includes secondary breakdown limits up to 150°C junction temperature.

Designed for discrete power stage implementation, it features low saturation voltage, robust thermal performance via TO-225 case mounting, and Pb-free RoHS-compliant packaging. It is not recommended for new designs per onsemi's discontinuation notice but remains supported for legacy industrial and automotive subsystems.

Key Specifications

Parameter	Value and Actual Design Meaning
V_CEO	45 V - Maximum collector-emitter voltage before breakdown under open-base conditions; defines maximum supply rail compatibility in PNP switch configurations.
I_C	4.0 A - Continuous DC collector current rating; supports load switching up to ~3.5 A with derating above 25°C case temperature.
P_D @ T_C = 25°C	36 W - Total device power dissipation limit at 25°C case temperature; requires heatsinking for sustained operation near rated current.
h_FE (I_C = 2.0 A)	≥ 40 - Minimum DC current gain at high current; ensures reliable base drive sizing for switching applications with 10:1 I_C/I_B ratio.
V_CE(sat)	≤ 0.7 V @ I_C = 3.0 A, I_B = 0.3 A - Low saturation voltage reduces conduction loss and heat generation in power switching duty cycles.
R_θJC	3.5 °C/W - Junction-to-case thermal resistance; enables thermal modeling for heatsink selection when mounted to metal chassis or PCB copper planes.
f_T	3.0 MHz - Current-gain bandwidth product; suitable for audio-frequency amplification and PWM switching below ~100 kHz without significant gain roll-off.

Pinout & Package

BD438 is housed in a TO-225 package (Case 77-09, Style 1), featuring a metal tab connected to the collector (pins 2 and 4), emitter at pin 1, and base at pin 3. The package supports mechanical mounting via the collector tab for thermal conduction and electrical grounding.

Pin/Terminal	Circuit Role	Design Meaning
Pin 1	Emitter	Primary current exit path for PNP operation; connects to system ground or low-side reference in common-emitter configurations.
Pins 2 & 4	Collector	Shared collector terminals tied to internal die; electrically and thermally connected to metal tab for heatsinking and high-current return path.
Pin 3	Base	Control input for biasing; requires current-limited drive (max I_B = 1.0 A) to ensure safe saturation and avoid second breakdown.

Key Features

Feature	Design Value
Pb-free / RoHS compliant	Meets EU Directive 2011/65/EU; eliminates lead in solderability and environmental handling without compromising thermal or electrical performance.
Discrete PNP switching capability	Supports high-current (up to 3.0 A) saturated switching with V_CE(sat) ≤ 0.7 V, reducing power loss in relay, solenoid, and motor-control driver stages.
Multi-range h_FE specification	Guaranteed minimum gain at 10 mA (≥30), 500 mA (≥85), and 2.0 A (≥40), enabling predictable base drive design across linear and switching operating points.
TO-225 thermal interface	Low R_θJC of 3.5°C/W allows direct mounting to heatsinks or chassis, supporting stable operation up to 150°C junction temperature in industrial environments.

Applications

DC Power Supply Regulation	Industrial Relay Driver
Use Scenario: Used as pass transistor in linear voltage regulators delivering up to 3 A output current with adjustable output voltage. IC Role / Device Role / Timing Role: PNP series pass element controlling output voltage by modulating base current in response to error amplifier feedback. Use Value: Low V_CE(sat) minimizes dropout voltage and improves efficiency; high h_FE reduces base drive burden on control circuitry.	Use Scenario: Drives 24 VDC industrial relays with coil currents up to 2.5 A in PLC output modules and machine control panels. IC Role / Device Role / Timing Role: High-current saturated switch turning relay coil on/off under microcontroller GPIO control through base resistor network. Use Value: Guaranteed h_FE ≥ 40 at 2.0 A ensures full saturation with ≤ 0.3 A base current, eliminating need for Darlington staging.
Audio Amplifier Output Stage	Automotive Lamp Control
Use Scenario: Serves as emitter-follower output device in Class-A/B audio amplifiers delivering 1–2 W into 4–8 Ω loads. IC Role / Device Role / Timing Role: Linear PNP output transistor providing low-output-impedance current sourcing with minimal crossover distortion. Use Value: f_T = 3.0 MHz supports flat frequency response up to 20 kHz; wide SOA prevents thermal runaway during dynamic signal peaks.	Use Scenario: Controls headlamp, fog lamp, or auxiliary lighting circuits in 12 V automotive systems with PWM dimming capability. IC Role / Device Role / Timing Role: High-side PNP switch regulating lamp current via base-pulse-width modulation synchronized to vehicle CAN bus commands. Use Value: V_CEO = 45 V exceeds automotive load-dump transients (ISO 7637-2 Pulse 5a); TO-225 package withstands under-hood thermal cycling.

DC Power Supply Regulation

Industrial Relay Driver

Use Scenario: Used as pass transistor in linear voltage regulators delivering up to 3 A output current with adjustable output voltage.

IC Role / Device Role / Timing Role: PNP series pass element controlling output voltage by modulating base current in response to error amplifier feedback.

Use Value: Low V_CE(sat) minimizes dropout voltage and improves efficiency; high h_FE reduces base drive burden on control circuitry.

Use Scenario: Drives 24 VDC industrial relays with coil currents up to 2.5 A in PLC output modules and machine control panels.

IC Role / Device Role / Timing Role: High-current saturated switch turning relay coil on/off under microcontroller GPIO control through base resistor network.

Use Value: Guaranteed h_FE ≥ 40 at 2.0 A ensures full saturation with ≤ 0.3 A base current, eliminating need for Darlington staging.

Audio Amplifier Output Stage

Automotive Lamp Control

Use Scenario: Serves as emitter-follower output device in Class-A/B audio amplifiers delivering 1–2 W into 4–8 Ω loads.

IC Role / Device Role / Timing Role: Linear PNP output transistor providing low-output-impedance current sourcing with minimal crossover distortion.

Use Value: f_T = 3.0 MHz supports flat frequency response up to 20 kHz; wide SOA prevents thermal runaway during dynamic signal peaks.

Use Scenario: Controls headlamp, fog lamp, or auxiliary lighting circuits in 12 V automotive systems with PWM dimming capability.

IC Role / Device Role / Timing Role: High-side PNP switch regulating lamp current via base-pulse-width modulation synchronized to vehicle CAN bus commands.

Use Value: V_CEO = 45 V exceeds automotive load-dump transients (ISO 7637-2 Pulse 5a); TO-225 package withstands under-hood thermal cycling.

Equivalent & Alternatives

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

Alternative Part	Technical Difference	Application Difference	Selection Advice
MJD44H11G	Higher V_CEO (100 V), lower h_FE (min 20 @ 2 A), same TO-225 package and pinout.	Better suited for higher-voltage industrial motor controls where BD438's 45 V rating is marginal.	Select MJD44H11G when operating above 40 V supply rails or requiring extended SOA at elevated voltages.
BD437	Complementary NPN type (not PNP), identical V_CEO/I_C/package; h_FE min 40 @ 10 mA, 85 @ 500 mA.	Used in push-pull amplifier stages or H-bridge half-bridges where matched NPN/PNP pairs are required.	Choose BD437 only when building complementary output stages; not a functional replacement for BD438 in single-PNP roles.

Compared with BD438, MJD44H11G offers higher voltage margin but reduced gain consistency at high current, while BD437 serves as its complementary NPN partner-not a drop-in substitute-making BD438 irreplaceable in standalone high-current PNP switching where polarity and gain profile are critical.

Availability

BD438 is available at Aetrix Electronics and suitable for industrial relay drivers, linear power supply regulation, audio amplifier output stages, and automotive lamp control circuits requiring stable component supply despite its discontinued status.

Supply support for BD438 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 consumer markets.

The BD438 belongs to onsemi's legacy medium-power discrete transistor family designed for cost-sensitive, high-reliability linear and switching applications in industrial automation and automotive subsystems.

FAQ

Is BD438 still in active production?

No, BD438 is officially discontinued per onsemi documentation (Note 1, datasheet Rev. 17). It is not recommended for new designs. However, Aetrix Electronics maintains inventory and supports legacy production runs with traceable, date-code-controlled stock and lifecycle coordination for ongoing manufacturing needs.

What is the correct pinout configuration for BD438 in TO-225 package?

The BD438 uses TO-225 Style 1 pinout: Pin 1 = Emitter, Pins 2 & 4 = Collector (internally connected to metal tab), Pin 3 = Base. This configuration is confirmed in the mechanical outline diagram (Case 77-09) and applies exclusively to BD438G and BD438TG variants.

Can BD438 be used as a direct replacement for BD436G?

No - BD438 is not a direct replacement for BD436G. While both share the same package and pinout, BD438 has higher voltage ratings (V_CEO = 45 V vs. 32 V) and different h_FE characteristics (min 30 vs. 40 at 10 mA). Substitution requires verification of voltage margin, gain stability, and SOA in the target circuit.

What is the maximum safe continuous collector current for BD438 at 70°C case temperature?

At T_C = 70°C, BD438's power dissipation must be derated from 36 W at 25°C using the 288 mW/°C derating factor. This yields P_D = 36 W − (45°C × 0.288 W/°C) = 23.04 W. With V_CE(sat) ≈ 0.7 V, max continuous I_C ≈ √(P_D/R_CE(sat)) ≈ 3.2 A assuming resistive load - but actual limit depends on thermal design and ambient conditions.

Does BD438 support pulse operation beyond its DC current rating?

Yes - BD438's Safe Operating Area (SOA) curve (Figure 4) permits short-duration pulses up to 10 A at V_CE < 10 V for ≤ 5 ms, provided peak junction temperature remains below 150°C. Pulse operation requires careful thermal transient analysis and adherence to secondary breakdown limits shown in the datasheet.

BD438 Specifications

Product attributes: Attribute value

Manufacturer:: onsemi

Series:: -

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

Packaging:: Bulk

Product Status:: Obsolete

Transistor Type:: PNP

Current - Collector (Ic) (Max):: 4 A

Voltage - Collector Emitter Breakdown (Max):: 45 V

Vce Saturation (Max) @ Ib, Ic:: 700mV @ 300mA, 3A

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

DC Current Gain (hFE) (Min) @ Ic, Vce:: 85 @ 500mA, 1V

Power - Max:: 36 W

Frequency - Transition:: 3MHz

Operating Temperature:: -55°C ~ 150°C (TJ)

Grade:: -

Qualification:: -

Mounting Type:: Through Hole

Supplier Device Package:: TO-126

BD438 FAQ

1.How can I place an order for BD438 through Aetrix?

Please submit a Request for Quotation (RFQ) for BD438 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 BD438 reliable?

The price and inventory of BD438 are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for BD438 is usually 5 days.

3.What payment methods are accepted for BD438?

We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for BD438 transactions.

Note: Certain payment methods may incur a processing fee.

4.How is shipping managed for BD438?

BD438 orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.

Once your BD438 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 BD438?

For technical support, including BD438 datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your BD438 requirements.

6.How does Aetrix verify that BD438 is sourced from the original manufacturer or authorized distributors?

All BD438 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 BD438 meets industry standards.

7.What is the process for return or replacement of BD438?

All BD438 units undergo pre-shipment inspection (PSI). If there is an issue with BD438, 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 BD438 part is unused and in its original packaging.

Return procedure for BD438:

1.Submit a request within 90 days.

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

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