BUL45G Equivalent & Substitute Parts

Part Overview

The BUL45G is an NPN bipolar junction transistor manufactured by onsemi, rated for 400 V collector-emitter breakdown voltage and 5 A maximum collector current in a TO-220 through-hole package. This device is part of the SWITCHMODE™ series and is classified as obsolete. Due to its obsolete status, equivalent and substitute parts are necessary for ongoing design support, production continuity, and system maintenance. Substitute devices must maintain electrical compatibility within the specified parameter ranges while meeting current manufacturing and compliance standards.

Key Parameters

Parameter	BUL45G Value	Unit
Transistor Type	NPN	—
Voltage - Collector Emitter Breakdown (Max)	400	V
Current - Collector (Ic) (Max)	5	A
Power - Max	75	W
Frequency - Transition	12	MHz
Operating Temperature	-65 to 150	°C (TJ)
Mounting Type	Through Hole	—
Package / Case	TO-220-3	—

Substitute Part Grouping Explanation

Substitution of the BUL45G is determined by the following critical electrical and mechanical parameters:

Primary Substitution Criteria:

Transistor Type: NPN (required match)
Voltage - Collector Emitter Breakdown: minimum 400 V (equal or higher acceptable)
Current - Collector (Ic) (Max): minimum 5 A (equal or higher acceptable)
Mounting Type: Through Hole (required match)
Package / Case: TO-220-3 or compatible TO-220 variant (required match)

Secondary Compatibility Factors:

Power dissipation rating: 75 W or higher
Operating temperature range: must encompass -65°C to 150°C or be compatible with application requirements
Frequency - Transition: 12 MHz or higher preferred for switching applications

Substitute parts are grouped into two categories: Direct Equivalents (matching all primary criteria with active product status) and Compatible Alternatives (meeting electrical requirements with minor parameter variations).

Parameter Comparison

Part Number	Manufacturer	Vce Breakdown (V)	Ic Max (A)	Power Max (W)	Frequency (MHz)	Product Status	Package
BUL45G	onsemi	400	5	75	12	Obsolete	TO-220-3
MJE18004G	onsemi	450	5	75	13	Active	TO-220-3
BUL138	STMicroelectronics	400	5	80	—	Active	TO-220-3
BUL38D	STMicroelectronics	450	5	80	—	Active	TO-220-3
BUL49D	STMicroelectronics	450	5	80	—	Active	TO-220-3
BUJ303B,127	WeEn Semiconductors	400	5	100	—	Active	TO-220-3
TSC742CZ C0G	Taiwan Semiconductor Corporation	420	5	70	—	Active	TO-220-3
BUJ103A,127	WeEn Semiconductors	400	4	80	—	Active	TO-220-3
BUL742C	STMicroelectronics	400	4	70	—	Active	TO-220-3
ST13005	STMicroelectronics	400	4	75	—	Active	TO-220-3
STL128D	STMicroelectronics	400	4	65	—	Active	TO-220-3

Engineering Selection Recommendations

Tier 1 - Direct Equivalents (Recommended Primary Substitutes):

MJE18004G (onsemi): Maintains 5 A collector current and 75 W power rating with active product status. Voltage rating increased to 450 V provides enhanced margin. ROHS3 compliant. Transition frequency of 13 MHz exceeds original specification.
BUL138 (STMicroelectronics): Matches 400 V voltage and 5 A current specifications exactly. Active product status with ROHS3 compliance. Power rating increased to 80 W. Unlimited moisture sensitivity level (MSL 1).
BUL38D (STMicroelectronics): Provides 5 A current capability with 450 V voltage rating. Active status with ROHS3 compliance. 80 W power rating. Unlimited MSL rating.
BUL49D (STMicroelectronics): Supports 5 A collector current and 450 V breakdown voltage. Active product with ROHS3 compliance. 80 W power dissipation capability.

Tier 2 - Compatible Alternatives (For Current-Limited Applications):

BUJ303B,127 (WeEn Semiconductors): Matches 400 V and 5 A specifications with 100 W power rating. Active product with RoHS compliance. Suitable for applications where higher power dissipation margin is beneficial.
TSC742CZ C0G (Taiwan Semiconductor Corporation): Provides 420 V breakdown voltage and 5 A current. Active product with ROHS3 compliance. 70 W power rating. MSL 3 rating requires moisture control during storage and handling.

Tier 3 - Reduced Current Alternatives (For 4 A Applications):

BUJ103A,127 (WeEn Semiconductors): Rated for 4 A maximum collector current with 400 V breakdown voltage. Active product with RoHS compliance. 80 W power rating. Suitable only for applications where 4 A current is acceptable.
BUL742C (STMicroelectronics): 4 A collector current, 400 V voltage, 70 W power. Active product with ROHS3 compliance. Unlimited MSL rating.
ST13005 (STMicroelectronics): 4 A collector current, 400 V voltage, 75 W power. Active product with ROHS3 compliance. Unlimited MSL rating.
STL128D (STMicroelectronics): 4 A collector current, 400 V voltage, 65 W power. Active product with ROHS3 compliance. Unlimited MSL rating.

All substitute parts are manufactured in TO-220-3 through-hole packages compatible with BUL45G footprints. Selection should prioritize Tier 1 equivalents for direct replacement in existing designs. Tier 2 and Tier 3 alternatives require circuit evaluation to confirm current and power requirements.

Frequently Asked Questions (FAQ)

Q: Can MJE18004G directly replace BUL45G in all applications?

A: MJE18004G meets or exceeds all critical electrical parameters of BUL45G: 450 V breakdown voltage (versus 400 V), 5 A collector current (matching), 75 W power rating (matching), and 13 MHz transition frequency (exceeding 12 MHz). The TO-220-3 package is identical. Direct substitution is supported for applications operating within BUL45G specifications.

Q: What is the difference between BUL138 and BUL38D?

A: Both are STMicroelectronics NPN transistors in TO-220-3 packages with 5 A collector current and 80 W power rating. BUL138 is rated for 400 V breakdown voltage, while BUL38D is rated for 450 V. BUL38D provides higher voltage margin and is suitable for applications with voltage transients or higher supply voltages.

Q: Why are some substitute parts rated for only 4 A instead of 5 A?

A: Parts such as BUL742C, ST13005, BUJ103A,127, and STL128D are designed for lower collector current applications. These devices are listed as compatible alternatives only for circuits where maximum collector current does not exceed 4 A. For applications requiring the full 5 A capability of BUL45G, Tier 1 equivalents must be selected.

Q: Are all substitute parts RoHS compliant?

A: All listed substitute parts carry either RoHS or ROHS3 compliance certification. BUL45G is classified as REACH Unaffected. All substitute parts maintain REACH Unaffected status. Compliance documentation should be verified with the specific manufacturer for the production lot being procured.

Q: What does MSL (Moisture Sensitivity Level) mean for component selection?

A: Moisture Sensitivity Level indicates the component's sensitivity to moisture absorption during storage and handling. BUL45G and most substitutes carry MSL 1 (Unlimited), meaning no moisture control is required. TSC742CZ C0G carries MSL 3 (168 Hours), requiring storage in dry conditions and limiting the time the component can be exposed to ambient humidity before soldering. MSL 1 components are preferred for standard manufacturing environments.

Q: Can BUJ303B,127 be used in place of BUL45G despite higher power rating?

A: Yes. BUJ303B,127 matches the 400 V breakdown voltage and 5 A collector current of BUL45G. The 100 W power rating (versus 75 W) provides additional thermal margin and does not create compatibility issues. The TO-220-3 package is identical. This substitution is valid for all applications within BUL45G specifications.

Q: What is the significance of the SWITCHMODE™ series designation on BUL45G?

A: SWITCHMODE™ is an onsemi product series designation indicating the transistor is optimized for switching applications. MJE18004G also carries the SWITCHMODE™ designation, confirming its suitability as a direct equivalent. Other substitute parts do not carry this designation but are electrically compatible for switching applications based on their electrical parameters.

Q: Are there package variations among the substitute parts?

A: All substitute parts are manufactured in TO-220-3 or compatible TO-220 through-hole packages. BUJ103A,127 and BUJ303B,127 specify TO-220AB variant, which is mechanically and electrically compatible with standard TO-220-3. No package adapter or modification is required for substitution.

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