BU508AFI Equivalent & Substitute Parts

Part Overview

The BU508AFI is an NPN bipolar junction transistor manufactured by STMicroelectronics, rated for 700 V collector-emitter breakdown voltage and 8 A maximum collector current. This device is packaged in the ISOWATT-218FX configuration and is designed for through-hole mounting applications requiring high-voltage switching capability with 50 W maximum power dissipation.

The BU508AFI is classified as obsolete. Equivalent and substitute parts are necessary to maintain design continuity and ensure component availability for production, repair, and field replacement applications. Substitute devices within the BU508 series maintain electrical compatibility while offering alternative packaging options and enhanced specifications.

Substiute Parts

BU508AFI

STMicroelectronicsIn Stock: 1994BU508AFI Datasheet

Current PartRFQ

BU508AF

STMicroelectronicsIn Stock: 19872BU508AF Datasheet

SimilarRFQ

BU508AW

STMicroelectronicsIn Stock: 15866BU508AW Datasheet

SimilarRFQ

Key Parameters

Substitute Part Grouping Explanation

Substitution within the BU508 series is determined by electrical parameter compatibility and mechanical interface requirements. All substitute parts maintain the following core electrical specifications:

• Transistor Type: NPN
• Voltage - Collector Emitter Breakdown (Max): 700 V
• Current - Collector (Ic) (Max): 8 A
• Operating Temperature (TJ): 150°C
• Mounting Type: Through Hole
• RoHS Status: ROHS3 Compliant
• Base Product Number: BU508

Substitute parts differ in packaging configuration and maximum power dissipation rating. The BU508AF provides equivalent electrical performance in TO-3PF package, while the BU508AW offers enhanced thermal performance in TO-247-3 package with increased power rating. All substitutes are manufactured by STMicroelectronics and maintain active product status.

Parameter Comparison

Engineering Selection Recommendations

BU508AF (TO-3PF Package)

The BU508AF is an active substitute maintaining identical electrical ratings to the BU508AFI with equivalent 50 W power dissipation. This part is suitable for direct electrical replacement in applications where the TO-3PF package footprint is compatible with existing PCB layouts or mechanical assemblies. The BU508AF exhibits lower collector cutoff current (200µA versus 1mA), which may provide improved leakage characteristics in certain circuit topologies.

BU508AW (TO-247-3 Package)

The BU508AW is an active substitute with enhanced thermal performance, rated for 125 W maximum power dissipation compared to the 50 W rating of the BU508AFI. This part is suitable for applications requiring increased power handling capability or improved thermal management. The TO-247-3 package provides superior heat dissipation characteristics through enhanced lead geometry and mounting surface area. The BU508AW maintains identical voltage and current ratings while offering extended thermal headroom for high-power switching applications.

All substitute parts maintain ROHS3 compliance and active product status, ensuring long-term availability and supply chain continuity.

Frequently Asked Questions (FAQ)

Q: Can the BU508AF directly replace the BU508AFI in all applications?

A: The BU508AF maintains identical electrical specifications (700 V, 8 A, 50 W) and is electrically compatible. However, the package differs (TO-3PF versus ISOWATT-218FX). Physical compatibility depends on PCB layout, mechanical mounting provisions, and thermal management design. Verify package footprint compatibility with your specific application before implementation.

Q: What is the primary advantage of the BU508AW over the BU508AFI?

A: The BU508AW provides 125 W maximum power dissipation compared to the 50 W rating of the BU508AFI. This increased power rating enables operation at higher current levels or improved thermal margin in power-switching applications. The TO-247-3 package offers superior thermal characteristics through enhanced heat dissipation pathways.

Q: Are all three parts (BU508AFI, BU508AF, BU508AW) electrically interchangeable?

A: All three parts share identical voltage (700 V) and current (8 A) ratings and are electrically compatible in terms of switching characteristics. However, they differ in packaging, power rating, and product status. The BU508AFI is obsolete, while BU508AF and BU508AW are active products. Package differences require mechanical and thermal design verification.

Q: What does the difference in collector cutoff current (1mA versus 200µA) mean for circuit design?

A: The collector cutoff current represents leakage current in the off-state. The BU508AF and BU508AW exhibit lower leakage (200µA) compared to the BU508AFI (1mA). Lower leakage current reduces standby power consumption and improves circuit efficiency in applications with extended off-time periods.

Q: Which substitute part should be selected for new designs?

A: For new designs, select based on thermal requirements. The BU508AF is suitable for standard 50 W applications. The BU508AW is recommended for applications requiring higher power dissipation or enhanced thermal performance. Both parts are active products with established supply chains and long-term availability.

Q: Are there any compliance or certification differences between the three parts?

A: All three parts maintain ROHS3 compliance, REACH Unaffected status, and identical ECCN and HTSUS classifications. No compliance or certification differences exist between the BU508AFI, BU508AF, and BU508AW.