STMicroelectronics 2STF1550 NPN Bipolar Transistor Equivalent & Substitute Parts

Part Overview

The STMicroelectronics 2STF1550 is an NPN bipolar junction transistor (BJT) rated for 50 V collector-emitter breakdown voltage and 5 A maximum collector current in a surface mount SOT-89-3 package. This device is classified as obsolete, necessitating identification of functionally equivalent active alternatives for new designs and production continuity. The 2STF1550 delivers 1.4 W maximum power dissipation with a minimum DC current gain of 135 at 2 A collector current and 2 V collector-emitter voltage.

Key Parameters

Parameter	Value	Unit
Transistor Type	NPN	—
Voltage - Collector Emitter Breakdown (Max)	50	V
Current - Collector (Ic) (Max)	5	A
Power - Max	1.4	W
Vce Saturation (Max) @ Ib, Ic	450mV @ 300mA, 3A	—
DC Current Gain (hFE) (Min) @ Ic, Vce	135 @ 2A, 2V	—
Operating Temperature (TJ)	150	°C
Package / Case	TO-243AA (SOT-89-3)	—
Mounting Type	Surface Mount	—
RoHS Status	ROHS3 Compliant	—
Product Status	Obsolete	—

Substitute Part Grouping Explanation

Substitution of the 2STF1550 is determined by the following critical electrical and mechanical parameters:

Primary Substitution Criteria:

Transistor type must be NPN
Collector-emitter breakdown voltage must be greater than or equal to 50 V
Maximum collector current must be greater than or equal to 5 A
Package must be TO-243AA (SOT-89-3) for mechanical compatibility
Surface mount configuration required
Operating temperature range must support 150°C junction temperature

Secondary Compatibility Factors:

Power dissipation capability
Saturation voltage characteristics
DC current gain specifications
RoHS3 compliance and MSL rating

Substitute parts are grouped into two categories based on electrical performance:

Category A: Full Current Rating Equivalents (5 A) The ZXTN25060BZTA from Diodes Incorporated maintains the 5 A collector current specification of the original 2STF1550, with enhanced voltage rating (60 V) and higher power dissipation (2.4 W). This part provides direct functional replacement with improved performance margins.

Category B: Reduced Current Rating Alternatives (2 A to 3 A) The Nexperia PBSS4250X and PBSS4350X series provide reduced collector current ratings (2 A and 3 A respectively) but maintain the 50 V voltage specification. These parts are suitable for applications where the full 5 A capability is not required. The PBSS4330X series offers 30 V voltage rating with 3 A current capability, appropriate for lower voltage applications.

All substitute parts are active products with AEC-Q100 automotive qualification and ROHS3 compliance, ensuring long-term availability and regulatory conformance.

Parameter Comparison

Parameter	2STF1550 (Main)	PBSS4250X,115	PBSS4250X,135	PBSS4330X,115	PBSS4330X,135	PBSS4350X,115	PBSS4350X,135	PBSS4350X,146	PBSS4350X,147	ZXTN25060BZTA
Transistor Type	NPN	NPN	NPN	NPN	NPN	NPN	NPN	NPN	NPN	NPN
Voltage - Collector Emitter Breakdown (Max)	50 V	50 V	50 V	30 V	30 V	50 V	50 V	50 V	50 V	60 V
Current - Collector (Ic) (Max)	5 A	2 A	2 A	3 A	3 A	3 A	3 A	3 A	3 A	5 A
Power - Max	1.4 W	1 W	1 W	1.6 W	1.6 W	1.6 W	1.6 W	1.6 W	1.6 W	2.4 W
Vce Saturation (Max) @ Ib, Ic	450mV @ 300mA, 3A	320mV @ 200mA, 2A	320mV @ 200mA, 2A	300mV @ 300mA, 3A	300mV @ 300mA, 3A	370mV @ 300mA, 3A	370mV @ 300mA, 3A	370mV @ 300mA, 3A	370mV @ 300mA, 3A	305mV @ 500mA, 5A
DC Current Gain (hFE) (Min) @ Ic, Vce	135 @ 2A, 2V	300 @ 1A, 2V	300 @ 1A, 2V	270 @ 1A, 2V	270 @ 1A, 2V	300 @ 1A, 2V	300 @ 1A, 2V	300 @ 1A, 2V	300 @ 1A, 2V	100 @ 10mA, 2V
Frequency - Transition	—	100 MHz	100 MHz	100 MHz	100 MHz	100 MHz	100 MHz	100 MHz	100 MHz	185 MHz
Operating Temperature (TJ)	150°C	150°C	150°C	150°C	150°C	150°C	150°C	150°C	150°C	-55°C ~ 150°C
Package / Case	TO-243AA	TO-243AA	TO-243AA	TO-243AA	TO-243AA	TO-243AA	TO-243AA	TO-243AA	TO-243AA	TO-243AA
Mounting Type	Surface Mount	Surface Mount	Surface Mount	Surface Mount	Surface Mount	Surface Mount	Surface Mount	Surface Mount	Surface Mount	Surface Mount
RoHS Status	ROHS3 Compliant	ROHS3 Compliant	ROHS3 Compliant	ROHS3 Compliant	ROHS3 Compliant	ROHS3 Compliant	ROHS3 Compliant	ROHS3 Compliant	ROHS3 Compliant	ROHS3 Compliant
Product Status	Obsolete	Active	Active	Active	Active	Active	Active	Active	Active	Active

Engineering Selection Recommendations

For Direct Replacement with Full Performance Retention:

The ZXTN25060BZTA from Diodes Incorporated is the primary substitute for applications requiring the full 5 A collector current specification. This part maintains electrical compatibility with the 2STF1550 while offering superior performance characteristics: 60 V breakdown voltage (versus 50 V), 2.4 W power dissipation (versus 1.4 W), and 185 MHz transition frequency. The ZXTN25060BZTA is an active product with AEC-Q100 automotive qualification and ROHS3 compliance, ensuring long-term supply availability and regulatory conformance.

For Current-Limited Applications:

The Nexperia PBSS4350X series (available in variants 115, 135, 146, and 147) provides a suitable alternative for applications where collector current does not exceed 3 A. These parts maintain the 50 V voltage specification and offer improved saturation voltage characteristics (370 mV at 3 A versus 450 mV at 3 A for the 2STF1550). All PBSS4350X variants are active products with AEC-Q100 qualification and automotive-grade reliability.

For Lower Voltage Applications:

The PBSS4330X series (variants 115 and 135) is appropriate for circuits operating at 30 V or below. These parts deliver 3 A maximum collector current with 1.6 W power dissipation and improved saturation voltage (300 mV at 3 A). Both variants maintain active product status and AEC-Q100 qualification.

For Reduced Current Applications:

The PBSS4250X series (variants 115 and 135) accommodates applications limited to 2 A collector current at 50 V breakdown voltage. These parts feature 1 W power dissipation and 100 MHz transition frequency, with active product status and AEC-Q100 automotive qualification.

All substitute parts are ROHS3 compliant with MSL 1 (unlimited moisture sensitivity level) and REACH unaffected status, matching the regulatory profile of the original 2STF1550.

Frequently Asked Questions (FAQ)

Q: Can the ZXTN25060BZTA directly replace the 2STF1550 in all applications?

A: The ZXTN25060BZTA is mechanically and electrically compatible with the 2STF1550 in the TO-243AA (SOT-89-3) package. Both devices are NPN transistors with surface mount configuration. The ZXTN25060BZTA provides enhanced specifications: 60 V breakdown voltage (5 V higher), 2.4 W power dissipation (1 W higher), and 185 MHz transition frequency. Applications designed for the 2STF1550 specifications will operate within the ZXTN25060BZTA performance envelope. Circuit board layout and thermal management remain unchanged due to identical package geometry.

Q: What is the difference between the PBSS4350X variants (115, 135, 146, 147)?

A: The PBSS4350X variants differ in DC current gain (hFE) binning. Variant 115 specifies hFE minimum of 115, variant 135 specifies 135, variant 146 specifies 146, and variant 147 specifies 147. All variants share identical electrical specifications for voltage (50 V), current (3 A), power (1.6 W), and saturation voltage (370 mV at 3 A). Selection between variants depends on circuit requirements for base drive current and switching speed. Higher hFE values require lower base current for equivalent collector current.

Q: Why is the PBSS4250X rated for only 2 A when the 2STF1550 is rated for 5 A?

A: The PBSS4250X is a distinct device optimized for lower current applications. Maximum collector current is a fundamental design parameter determined during device development. The PBSS4250X delivers 1 W power dissipation at 2 A, while the 2STF1550 delivers 1.4 W at 5 A. Applications requiring sustained collector currents above 2 A must use the PBSS4350X (3 A) or ZXTN25060BZTA (5 A) alternatives.

Q: Are all substitute parts automotive qualified?

A: All Nexperia PBSS4250X, PBSS4330X, and PBSS4350X variants carry AEC-Q100 automotive qualification. The Diodes Incorporated ZXTN25060BZTA does not list AEC-Q100 qualification in the provided specifications. For automotive applications requiring AEC-Q100 certification, the Nexperia PBSS series is the appropriate selection.

Q: What is the significance of the TO-243AA package designation?

A: The TO-243AA package is the standardized designation for the SOT-89-3 surface mount package. All listed substitute parts use identical package geometry and pin configuration, ensuring direct mechanical compatibility on printed circuit boards. No layout modifications or rework are required when substituting between parts with TO-243AA packaging.

Q: Can the PBSS4330X be used in place of the 2STF1550 in a 50 V circuit?

A: The PBSS4330X is rated for 30 V maximum collector-emitter breakdown voltage. Using this device in a 50 V circuit exceeds the absolute maximum rating and creates risk of device failure. The PBSS4330X is suitable only for applications where the operating voltage does not exceed 30 V. For 50 V circuits, use the PBSS4350X or ZXTN25060BZTA alternatives.

Q: What is the difference between the 2STF1550 and ZXTN25060BZTA saturation voltage specifications?

A: The 2STF1550 specifies 450 mV saturation voltage at 300 mA base current and 3 A collector current. The ZXTN25060BZTA specifies 305 mV saturation voltage at 500 mA base current and 5 A collector current. The ZXTN25060BZTA exhibits lower saturation voltage across its operating range, resulting in reduced power dissipation in saturated switching applications. This characteristic improves efficiency in high-current switching circuits.

Q: Are moisture sensitivity levels identical across all substitute parts?

A: All listed parts, including the 2STF1550 and all substitutes, carry MSL 1 (unlimited) moisture sensitivity level rating. This classification indicates no moisture-related storage or handling restrictions. Parts may be stored and handled under standard industrial conditions without desiccant packaging or time-limited shelf life constraints.

Q: What is the operating temperature range for the ZXTN25060BZTA?

A: The ZXTN25060BZTA specifies an operating junction temperature range of -55°C to 150°C. The 2STF1550 and all Nexperia PBSS variants specify a maximum junction temperature of 150°C without a stated minimum. The ZXTN25060BZTA provides extended low-temperature operation capability, suitable for applications requiring cold-start performance or cryogenic environments.

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