BD438 Equivalent & Substitute Parts

Part Overview

The BD438 is a PNP bipolar junction transistor (BJT) rated for 45 V collector-emitter breakdown voltage and 4 A maximum collector current. Manufactured by onsemi in TO-126 packaging, this device delivers 36 W maximum power dissipation with a 3 MHz transition frequency. The onsemi BD438 is classified as obsolete, necessitating identification of active equivalent and substitute parts for new designs and ongoing production requirements. Equivalent devices maintain identical electrical performance characteristics while substitute parts provide functional alternatives with minor parameter variations.

Key Parameters

Parameter	Value	Unit
Transistor Type	PNP	—
Collector Current (Max)	4	A
Collector-Emitter Breakdown Voltage (Max)	45	V
Power Dissipation (Max)	36	W
Transition Frequency	3	MHz
Operating Temperature Range	-55 to 150	°C
Mounting Type	Through Hole	—
Collector Cutoff Current (Max)	100	µA

Substitute Part Grouping Explanation

Substitution eligibility for the BD438 is determined by strict equivalence across the following electrical and mechanical parameters:

Primary Equivalence Criteria:

Transistor type (PNP)
Collector current rating (4 A maximum)
Collector-emitter breakdown voltage (45 V maximum)
Power dissipation capability (36 W maximum)
Transition frequency (3 MHz)
Operating temperature range (-55°C to 150°C)
Through-hole mounting configuration

Acceptable Variations:

Manufacturer identity (onsemi, STMicroelectronics)
Package designation (TO-126-3, TO-225AA, SOT-32-3)
Product status (active vs. obsolete)
RoHS compliance level
Vce saturation specifications within rated conditions
DC current gain (hFE) specifications at different measurement points

Parts meeting all primary equivalence criteria are classified as direct substitutes. Variations in secondary parameters do not preclude substitution when primary electrical ratings and mounting type remain identical.

Parameter Comparison

Parameter	BD438 (onsemi)	BD438G (onsemi)	BD438 (STMicroelectronics)
Manufacturer	onsemi	onsemi	STMicroelectronics
Transistor Type	PNP	PNP	PNP
Collector Current (Max)	4 A	4 A	4 A
Collector-Emitter Breakdown Voltage (Max)	45 V	45 V	45 V
Power Dissipation (Max)	36 W	36 W	36 W
Transition Frequency	3 MHz	3 MHz	3 MHz
Operating Temperature Range	-55 to 150°C	-55 to 150°C	-55 to 150°C
Mounting Type	Through Hole	Through Hole	Through Hole
Collector Cutoff Current (Max)	100 µA	100 µA	100 µA
Package / Case	TO-126-3	TO-225AA, TO-126-3	SOT-32-3
Product Status	Obsolete	Active	Active
RoHS Status	Non-compliant	ROHS3 Compliant	ROHS3 Compliant
Vce Saturation (Max) @ Ib, Ic	700 mV @ 300 mA, 3 A	700 mV @ 300 mA, 3 A	600 mV @ 200 mA, 2 A
DC Current Gain (hFE) (Min) @ Ic, Vce	85 @ 500 mA, 1 V	85 @ 500 mA, 1 V	30 @ 10 mA, 5 V

Engineering Selection Recommendations

BD438G (onsemi) is the primary parametric equivalent for obsolete onsemi BD438 applications. This device maintains identical electrical specifications across all primary criteria: 4 A collector current, 45 V breakdown voltage, 36 W power dissipation, and 3 MHz transition frequency. The BD438G carries active product status and ROHS3 compliance, addressing regulatory requirements for new production. Package options include both TO-225AA and TO-126-3 configurations, providing mechanical compatibility with existing through-hole designs.

BD438 (STMicroelectronics) functions as a direct manufacturer alternative with equivalent electrical performance. This STMicroelectronics variant maintains the same current, voltage, and power ratings while offering active product status and ROHS3 compliance. The SOT-32-3 package designation represents an alternative through-hole configuration. Minor variations in Vce saturation and DC current gain specifications occur at different measurement conditions but do not affect functional equivalence within the rated parameter envelope.

Selection between onsemi BD438G and STMicroelectronics BD438 depends on supply chain availability, existing design documentation, and package form factor requirements. Both devices satisfy the electrical and thermal requirements of applications currently using the obsolete onsemi BD438.

Frequently Asked Questions (FAQ)

Q: Can BD438G directly replace the obsolete onsemi BD438 in existing designs?

A: Yes. BD438G maintains identical electrical specifications: 4 A collector current, 45 V breakdown voltage, 36 W power dissipation, and 3 MHz transition frequency. Both devices use through-hole mounting with compatible package options (TO-126-3). The primary difference is product status (active vs. obsolete) and RoHS compliance level.

Q: What are the package differences between BD438G and STMicroelectronics BD438?

A: BD438G is available in TO-225AA and TO-126-3 packages. STMicroelectronics BD438 uses SOT-32-3 packaging. All three package types are through-hole configurations with compatible pinout arrangements for PNP transistor applications. Physical dimensions and PCB footprints differ; verify mechanical fit before design implementation.

Q: Are there electrical performance differences between onsemi BD438G and STMicroelectronics BD438?

A: Both devices meet the primary electrical specifications (4 A, 45 V, 36 W, 3 MHz). Secondary parameters show minor variations: Vce saturation is specified at different measurement conditions (700 mV @ 300 mA, 3 A for onsemi vs. 600 mV @ 200 mA, 2 A for STMicroelectronics), and DC current gain measurements occur at different bias points. These variations remain within acceptable operating margins for standard PNP transistor applications.

Q: Does RoHS compliance affect substitution decisions?

A: RoHS compliance status does not determine electrical equivalence. The obsolete onsemi BD438 is RoHS non-compliant, while both BD438G and STMicroelectronics BD438 are ROHS3 compliant. For new production and regulatory compliance, ROHS3-compliant alternatives are required. Existing legacy systems may continue using non-compliant stock until depletion.

Q: What is the operating temperature range for all three variants?

A: All three devices operate across -55°C to 150°C junction temperature range, providing identical thermal performance specifications.

Q: Can these devices be used interchangeably in high-frequency switching applications?

A: All three variants share a 3 MHz transition frequency specification. Applications operating within this frequency envelope can use any of the three devices. Designs requiring higher switching speeds require alternative transistor families with higher transition frequency ratings.

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