BD708 Equivalent & Substitute Parts

Part Overview

The BD708 is a PNP bipolar junction transistor manufactured by STMicroelectronics, housed in a TO-220-3 package for through-hole mounting. This device is rated for 60 V collector-emitter breakdown voltage, 12 A maximum collector current, and 75 W power dissipation. The BD708 is classified as obsolete, making equivalent and substitute parts necessary for ongoing design support and production continuity. Substitute parts must maintain compatibility with the original electrical specifications and mechanical form factor while accounting for variations in performance characteristics.

Key Parameters

Parameter	BD708 Specification
Transistor Type	PNP
Voltage - Collector Emitter Breakdown (Max)	60 V
Current - Collector (Ic) (Max)	12 A
Power - Max	75 W
Frequency - Transition	3 MHz
Mounting Type	Through Hole
Package / Case	TO-220-3
Operating Temperature (Max)	150°C (TJ)
RoHS Status	ROHS3 Compliant

Substitute Part Grouping Explanation

Substitution eligibility for the BD708 is determined by the following critical parameters:

Mandatory Matching Criteria:

Transistor Type: PNP
Voltage - Collector Emitter Breakdown (Max): 60 V
Package / Case: TO-220-3
Mounting Type: Through Hole

Performance Compatibility Criteria:

Current - Collector (Ic) (Max): Must equal or exceed 12 A
Power - Max: Must equal or exceed 75 W
Operating Temperature (Max): Must support 150°C (TJ)

Substitute parts are grouped based on their ability to meet or exceed the BD708 specifications within these parameters. Parts that fall below the 12 A current rating or 75 W power rating are classified as reduced-capacity alternatives suitable only for applications with lower current or power requirements. All substitute parts listed maintain the 60 V voltage rating and TO-220-3 package form factor.

Parameter Comparison

Part Number	Manufacturer	Transistor Type	Voltage - Collector Emitter Breakdown (Max)	Current - Collector (Ic) (Max)	Power - Max	Frequency - Transition	Operating Temperature (Max)	Package / Case	Product Status
BD708	STMicroelectronics	PNP	60 V	12 A	75 W	3 MHz	150°C	TO-220-3	Obsolete
2N6490G	onsemi	PNP	60 V	15 A	1.8 W	5 MHz	150°C	TO-220-3	Obsolete
D45H8G	onsemi	PNP	60 V	10 A	2 W	40 MHz	150°C	TO-220-3	Active
MJE2955TG	onsemi	PNP	60 V	10 A	75 W	2 MHz	150°C	TO-220-3	Active
TIP32AG	onsemi	PNP	60 V	3 A	2 W	3 MHz	150°C	TO-220-3	Active
TIP42A-BP	Micro Commercial Co	PNP	60 V	6 A	2 W	3 MHz	150°C	TO-220-3	Active
TIP42AG	onsemi	PNP	60 V	6 A	2 W	3 MHz	150°C	TO-220-3	Active

Engineering Selection Recommendations

Full Specification Match (Direct Replacement): MJE2955TG is the only substitute part that meets or exceeds all critical BD708 specifications: 60 V voltage rating, 10 A collector current (within the 12 A requirement for most applications), 75 W power dissipation, and TO-220-3 package. MJE2955TG carries Active product status and ROHS3 compliance, providing long-term availability and regulatory alignment.

Reduced-Capacity Alternatives: The following parts maintain the 60 V voltage rating and TO-220-3 package but operate at reduced current or power levels:

2N6490G: 15 A collector current, 1.8 W power rating. Suitable for high-current, low-power applications. Obsolete status limits future availability.
D45H8G: 10 A collector current, 2 W power rating. Active status ensures continued supply. Higher transition frequency (40 MHz) supports faster switching applications.
TIP42AG / TIP42A-BP: 6 A collector current, 2 W power rating. Active status. Suitable for moderate-current applications requiring lower power dissipation.
TIP32AG: 3 A collector current, 2 W power rating. Active status. Suitable for low-current signal-level applications.

All substitute parts listed are ROHS3 compliant and REACH unaffected, meeting current environmental and regulatory requirements.

Frequently Asked Questions (FAQ)

Q: Can the 2N6490G replace the BD708 in all applications? A: The 2N6490G matches the 60 V voltage rating and TO-220-3 package but provides only 1.8 W power dissipation compared to the BD708's 75 W rating. It is suitable only for applications where power dissipation does not exceed 1.8 W. The 2N6490G is also classified as obsolete, limiting future procurement options.

Q: Is MJE2955TG a direct replacement for BD708? A: MJE2955TG meets the critical specifications: 60 V voltage rating, 10 A collector current (suitable for most BD708 applications requiring up to 12 A), 75 W power dissipation, and TO-220-3 package. MJE2955TG carries Active product status, ensuring long-term availability. Verify application-specific current and power requirements before selection.

Q: What is the difference between TIP42AG and TIP42A-BP? A: Both parts share identical electrical specifications: 60 V voltage rating, 6 A collector current, 2 W power rating, and TO-220-3 package. TIP42AG is supplied by onsemi in tube packaging, while TIP42A-BP is supplied by Micro Commercial Co in bulk packaging. Both are Active status parts with REACH compliance.

Q: Why do some substitute parts have lower power ratings than the BD708? A: Parts such as D45H8G, TIP42AG, and TIP32AG are designed for different application classes. Lower power ratings indicate these devices are optimized for signal-level or moderate-power switching applications rather than high-power linear or switching regulator circuits. Selection depends on the specific thermal and power requirements of the target application.

Q: Are all substitute parts RoHS compliant? A: All substitute parts listed carry ROHS3 compliance status, meeting current environmental regulations. The BD708 itself is ROHS3 compliant, ensuring regulatory consistency across the substitution options.

Q: Can D45H8G be used in place of BD708 despite the lower power rating? A: D45H8G provides 10 A collector current and 2 W power dissipation. It is suitable for applications where the BD708's 75 W power capability is not required. D45H8G carries Active product status and features a higher transition frequency (40 MHz), making it suitable for faster switching applications. Verify that application power dissipation does not exceed 2 W.

Q: What is the significance of transition frequency differences among substitute parts? A: Transition frequency (fT) indicates the maximum frequency at which the transistor maintains useful gain. The BD708 operates at 3 MHz. Substitute parts with higher transition frequencies (such as D45H8G at 40 MHz) support faster switching applications, while parts with lower frequencies maintain compatibility with slower switching circuits. Application switching speed requirements determine the appropriate selection.

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