BST40TA Equivalent & Substitute Parts

Part Overview

The BST40TA is an NPN bipolar junction transistor manufactured by Diodes Incorporated, designed for general-purpose switching and amplification applications. This device features a 250 V collector-emitter breakdown voltage rating and 500 mA maximum collector current in a surface mount SOT-89-3 package. The BST40TA is classified as obsolete, making identification of functionally equivalent alternatives necessary for ongoing design support and production continuity.

Key Parameters

Parameter	Value	Unit
Transistor Type	NPN	—
Voltage - Collector Emitter Breakdown (Max)	250	V
Current - Collector (Ic) (Max)	500	mA
Power - Max	1	W
Frequency - Transition	70	MHz
DC Current Gain (hFE) (Min)	40	@ 20mA, 10V
Vce Saturation (Max)	500	mV @ 4mA, 50mA
Operating Temperature Range	-65 to 150	°C
Package / Case	TO-243AA (SOT-89-3)	—
Mounting Type	Surface Mount	—

Substitute Part Grouping Explanation

Substitution of the obsolete BST40TA is based on electrical and mechanical parameter compatibility within the NPN bipolar transistor category. The primary substitution candidate, BF622,115 (Nexperia USA Inc.), shares the following critical parameters:

Matching Parameters:

Transistor Type: NPN
Voltage - Collector Emitter Breakdown (Max): 250 V
Package / Case: TO-243AA (SOT-89-3)
Mounting Type: Surface Mount
Operating Temperature Range: Supports -65 to 150°C operation

Substitution Basis: The BF622,115 maintains identical voltage rating and package configuration, enabling direct mechanical and electrical compatibility in existing PCB layouts. Both devices operate within the same thermal envelope and share the same surface mount footprint. The substitute part is classified as active product status with current manufacturing availability, addressing the obsolescence of the original BST40TA.

Parameter Comparison

Parameter	BST40TA (Diodes Inc.)	BF622,115 (Nexperia)	Unit
Transistor Type	NPN	NPN	—
Voltage - Collector Emitter Breakdown (Max)	250	250	V
Current - Collector (Ic) (Max)	500	50	mA
Power - Max	1.0	1.1	W
Frequency - Transition	70	60	MHz
DC Current Gain (hFE) (Min)	40	50	@ specified Ic, Vce
Vce Saturation (Max)	500	600	mV
Operating Temperature Range	-65 to 150	-65 to 150	°C
Package / Case	TO-243AA	TO-243AA	—
Mounting Type	Surface Mount	Surface Mount	—
RoHS Status	Non-compliant	ROHS3 Compliant	—
Product Status	Obsolete	Active	—

Engineering Selection Recommendations

Primary Substitute: BF622,115

The BF622,115 is the designated manufacturer-recommended substitute for the obsolete BST40TA. This selection is based on:

Electrical Compatibility: Identical 250 V collector-emitter breakdown voltage and matching surface mount package configuration (TO-243AA / SOT-89-3) ensure direct functional replacement in existing circuit designs.
Product Status: The BF622,115 maintains active product status with established manufacturing and supply chain support, eliminating obsolescence risk associated with the BST40TA.
Compliance Status: The BF622,115 is ROHS3 compliant and carries AEC-Q101 automotive qualification, providing enhanced regulatory alignment compared to the non-compliant BST40TA.
Current Rating Consideration: The BF622,115 specifies a maximum collector current of 50 mA, compared to the BST40TA's 500 mA rating. Circuit designs operating at collector currents exceeding 50 mA require evaluation to confirm the substitute part operates within its specified maximum ratings.
Thermal and Frequency Performance: The BF622,115 provides equivalent power dissipation capability (1.1 W) and maintains transition frequency performance (60 MHz) suitable for general-purpose switching applications.

Frequently Asked Questions (FAQ)

Q: Can the BF622,115 directly replace the BST40TA in all applications?

A: Direct replacement is possible for applications where collector current does not exceed 50 mA. The BST40TA supports up to 500 mA, while the BF622,115 is rated for 50 mA maximum. Circuit designs must be evaluated to confirm operation within the substitute part's current specifications.

Q: Are the package footprints identical between BST40TA and BF622,115?

A: Both devices use the TO-243AA package configuration (SOT-89-3 supplier designation), providing identical mechanical compatibility and PCB footprint requirements.

Q: What is the difference in saturation voltage between these parts?

A: The BST40TA specifies 500 mV maximum Vce saturation at 4 mA base current and 50 mA collector current. The BF622,115 specifies 600 mV maximum at 5 mA base current and 30 mA collector current. Circuit designs sensitive to saturation voltage performance require detailed evaluation of operating point conditions.

Q: Does the BF622,115 support the same operating temperature range?

A: Both devices support operation from -65°C to 150°C junction temperature, providing equivalent thermal performance envelope.

Q: What compliance advantages does the BF622,115 offer?

A: The BF622,115 is ROHS3 compliant and carries AEC-Q101 automotive qualification. The BST40TA is RoHS non-compliant. New designs and production requiring regulatory compliance should utilize the BF622,115.

Q: Are there inventory considerations for the BST40TA versus BF622,115?

A: The BST40TA is classified as obsolete with limited remaining inventory. The BF622,115 is an active product with established supply availability, supporting long-term production requirements.

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