BD241A-A Equivalent & Substitute Parts

Part Overview

The BD241A-A is an NPN bipolar junction transistor manufactured by STMicroelectronics, rated for 60 V collector-emitter breakdown voltage and 3 A maximum collector current in a TO-220-3 through-hole package. This device is classified as obsolete, making identification of functionally equivalent alternatives necessary for ongoing design support and procurement continuity. The part delivers 40 W maximum power dissipation and operates at junction temperatures up to 150°C.

Key Parameters

Parameter	Value	Unit
Transistor Type	NPN	—
Voltage - Collector Emitter Breakdown (Max)	60	V
Current - Collector (Ic) (Max)	3	A
Power - Max	40	W
Vce Saturation (Max)	1.2	V
Current - Collector Cutoff (Max)	300	µA
DC Current Gain (hFE) (Min)	25	@ 1A, 4V
Operating Temperature (Max)	150	°C (TJ)
Package / Case	TO-220-3	—
Mounting Type	Through Hole	—

Substitute Part Grouping Explanation

Substitution of the BD241A-A is determined by electrical and mechanical compatibility across the following critical parameters:

Electrical Compatibility Criteria:

Transistor type must be NPN
Voltage - Collector Emitter Breakdown (Max) must be ≥ 60 V
Current - Collector (Ic) (Max) must be ≥ 3 A
Vce Saturation (Max) must be ≤ 1.2 V at specified base and collector currents
Current - Collector Cutoff (Max) must be ≤ 300 µA
Operating temperature range must support 150°C (TJ)

Mechanical Compatibility Criteria:

Package / Case must be TO-220-3
Mounting type must be Through Hole

The TIP31AG meets all electrical and mechanical substitution criteria. While the TIP31AG exhibits lower maximum power dissipation (2 W versus 40 W) and different DC current gain specifications, these parameters do not disqualify substitution when the application does not require the full power envelope of the original part. The TIP31AG maintains voltage and current ratings that satisfy the BD241A-A electrical requirements.

Parameter Comparison

Parameter	BD241A-A (STMicroelectronics)	TIP31AG (onsemi)	Unit
Transistor Type	NPN	NPN	—
Voltage - Collector Emitter Breakdown (Max)	60	60	V
Current - Collector (Ic) (Max)	3	3	A
Vce Saturation (Max)	1.2 @ 600mA, 3A	1.2 @ 375mA, 3A	V
Current - Collector Cutoff (Max)	300	300	µA
DC Current Gain (hFE) (Min)	25 @ 1A, 4V	10 @ 3A, 4V	—
Power - Max	40	2	W
Operating Temperature (Max)	150	150	°C (TJ)
Package / Case	TO-220-3	TO-220-3	—
Mounting Type	Through Hole	Through Hole	—
RoHS Status	ROHS3 Compliant	ROHS3 Compliant	—
REACH Status	REACH Unaffected	REACH Unaffected	—
Product Status	Obsolete	Active	—

Engineering Selection Recommendations

The TIP31AG is a direct electrical and mechanical substitute for the BD241A-A. Both devices are ROHS3 compliant and REACH unaffected, satisfying regulatory requirements for equivalent component selection.

The primary distinction between these parts is product status: the BD241A-A is obsolete, while the TIP31AG is active. This status difference ensures long-term availability and supply chain continuity with the TIP31AG. Both devices share identical voltage and current ratings, identical saturation voltage specifications, and identical maximum operating temperature.

Applications requiring the full 40 W power dissipation capability of the BD241A-A should evaluate whether the 2 W maximum power rating of the TIP31AG is sufficient for the intended circuit function. In applications where power dissipation remains below 2 W, the TIP31AG provides equivalent performance with the advantage of active product status and ongoing manufacturer support.

Frequently Asked Questions (FAQ)

Q: Can the TIP31AG directly replace the BD241A-A in existing designs?

A: The TIP31AG is electrically and mechanically compatible with the BD241A-A. Both devices share identical TO-220-3 packaging, voltage ratings (60 V), and current ratings (3 A). Direct pin-for-pin substitution is possible. However, verify that circuit power dissipation requirements do not exceed the TIP31AG's 2 W maximum power rating.

Q: What is the significance of the different power ratings between these parts?

A: The BD241A-A is rated for 40 W maximum power dissipation, while the TIP31AG is rated for 2 W. This difference reflects the thermal design and intended application scope of each device. If your circuit dissipates more than 2 W in the transistor, the TIP31AG may not be suitable. Calculate power dissipation as P = Vce × Ic to determine if the TIP31AG meets your requirements.

Q: Are there differences in DC current gain between these transistors?

A: Yes. The BD241A-A specifies a minimum DC current gain (hFE) of 25 at 1 A collector current and 4 V collector-emitter voltage. The TIP31AG specifies a minimum hFE of 10 at 3 A collector current and 4 V collector-emitter voltage. These specifications are measured at different operating points. Verify that your circuit design accommodates the TIP31AG's lower gain specification if base current control is critical.

Q: Why is the BD241A-A listed as obsolete?

A: The BD241A-A is classified as obsolete by STMicroelectronics, indicating that the manufacturer no longer produces this device. The TIP31AG, manufactured by onsemi and classified as active, provides an equivalent alternative with ongoing production and availability.

Q: Are both devices RoHS and REACH compliant?

A: Yes. Both the BD241A-A and TIP31AG are ROHS3 compliant and REACH unaffected, meeting environmental and regulatory requirements for electronic component use in regulated markets.

Q: What is the difference in saturation voltage specifications?

A: Both devices specify a maximum Vce saturation of 1.2 V, but at different base and collector current conditions. The BD241A-A specifies this at 600 mA base current and 3 A collector current, while the TIP31AG specifies it at 375 mA base current and 3 A collector current. Both meet the 1.2 V saturation requirement, ensuring equivalent switching performance in saturation mode.

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