BUL128FP Equivalent & Substitute Parts

Part Overview

The BUL128FP is an NPN bipolar junction transistor manufactured by STMicroelectronics, rated for 400 V collector-emitter breakdown voltage and 4 A maximum collector current in a TO-220FP through-hole package. This component is classified as obsolete, making identification of equivalent and substitute parts essential for ongoing design support and production continuity. Substitute parts must maintain electrical compatibility across voltage, current, and power dissipation parameters while accommodating available packaging options.

Substiute Parts

BUL128FP

STMicroelectronicsIn Stock: 1368BUL128FP Datasheet

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BUJ103AX,127

WeEn SemiconductorsIn Stock: 1166BUJ103AX,127 Datasheet

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MJF18004G

onsemiIn Stock: 2190MJF18004G Datasheet

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Key Parameters

Substitute Part Grouping Explanation

Substitute parts for the BUL128FP are selected based on the following electrical and mechanical compatibility criteria:

Primary Substitution Parameters:

• Transistor Type: NPN configuration required
• Voltage Rating: Minimum 400 V collector-emitter breakdown voltage
• Current Rating: Minimum 4 A maximum collector current
• Power Dissipation: Minimum 26 W maximum power rating
• Mounting: Through-hole configuration
• Package: TO-220 family variants (TO-220F, TO-220FP)

Substitution Logic: Parts meeting or exceeding the BUL128FP electrical specifications are classified as functional equivalents. The BUJ103AX,127 maintains identical voltage and current ratings with reduced power dissipation (26 W versus 31 W), suitable for applications within the original design envelope. The MJF18004G exceeds all primary electrical parameters (450 V, 5 A, 35 W) and includes transition frequency specification (13 MHz), providing enhanced performance margin for high-frequency switching applications.

Parameter Comparison

Engineering Selection Recommendations

BUJ103AX,127 (WeEn Semiconductors): This part provides direct electrical equivalence to the BUL128FP with identical voltage and current ratings. The BUJ103AX,127 is classified as active product status, ensuring long-term availability and supply chain continuity. RoHS compliance is confirmed. The reduced power rating (26 W versus 31 W) requires thermal design verification for applications operating at maximum current and voltage simultaneously. The isolated tab variant of the TO-220 package may require mechanical redesign of heatsink mounting interfaces.

MJF18004G (onsemi): This part exceeds the BUL128FP specifications across all primary electrical parameters: 450 V breakdown voltage, 5 A collector current, and 35 W power dissipation. The MJF18004G includes transition frequency specification (13 MHz) and extended operating temperature range (−65°C to 150°C), providing performance margin for demanding applications. Active product status and ROHS3 compliance confirm regulatory alignment. The enhanced electrical ratings support direct substitution in applications requiring improved performance headroom or extended temperature operation.

Frequently Asked Questions (FAQ)

Q: Can the BUJ103AX,127 be used as a direct replacement for the BUL128FP?

A: The BUJ103AX,127 maintains identical voltage (400 V) and current (4 A) ratings, enabling functional substitution in circuits designed for the BUL128FP. The reduced power dissipation rating (26 W versus 31 W) requires thermal analysis to confirm adequate heat dissipation in the target application. The isolated tab variant of the TO-220 package may require mechanical modification of heatsink mounting.

Q: What are the advantages of using the MJF18004G over the BUL128FP?

A: The MJF18004G provides higher voltage (450 V), current (5 A), and power (35 W) ratings, offering performance margin for applications approaching the BUL128FP limits. The specified transition frequency (13 MHz) supports high-frequency switching applications. Extended operating temperature range (−65°C to 150°C) accommodates wider environmental conditions. Active product status ensures long-term availability.

Q: Are there package compatibility considerations between these parts?

A: All three parts use TO-220 through-hole packages suitable for standard PCB mounting and heatsink attachment. The BUJ103AX,127 features an isolated tab variant, which may differ mechanically from standard TO-220FP packages. Heatsink mounting interfaces and thermal interface materials should be verified for compatibility with the specific package variant selected.

Q: How do saturation voltage differences affect circuit performance?

A: Saturation voltage (Vce) varies across the three parts: BUL128FP (500 mV @ 1A, 4A), BUJ103AX,127 (1 V @ 600mA, 3A), and MJF18004G (750 mV @ 500mA, 2.5A). These differences affect power dissipation and switching characteristics. Applications with tight voltage margin requirements or high-frequency switching should evaluate saturation voltage specifications at the intended operating point.

Q: What is the significance of the DC current gain (hFE) differences?

A: DC current gain specifications are provided at different operating points across the three parts. The BUL128FP and MJF18004G specify hFE at 14 (minimum), while the BUJ103AX,127 specifies 12 (minimum). These variations reflect different measurement conditions and do not preclude substitution. Base drive circuit design should accommodate the minimum hFE value of the selected part.

Q: Are all three parts RoHS compliant?

A: The BUL128FP and MJF18004G are ROHS3 compliant. The BUJ103AX,127 is RoHS compliant. Both compliance levels satisfy current regulatory requirements for electronic component manufacturing and distribution.