MSD42WT1 Equivalent & Substitute Parts

Part Overview

The MSD42WT1 is an NPN bipolar junction transistor (BJT) manufactured by onsemi, rated for 300 V collector-emitter breakdown voltage and 150 mA maximum collector current in a surface mount SC-70 (SOT-323) package. This component is classified as obsolete product status. Equivalent and substitute parts are necessary to maintain design continuity and ensure component availability for new production builds and field replacements where the original part is no longer readily available through standard distribution channels.

Key Parameters

Parameter	Value	Unit
Transistor Type	NPN	—
Voltage - Collector Emitter Breakdown (Max)	300	V
Current - Collector (Ic) (Max)	150	mA
Power - Max	150	mW
Vce Saturation (Max) @ Ib, Ic	500mV @ 2mA, 20mA	—
DC Current Gain (hFE) (Min) @ Ic, Vce	40 @ 30mA, 10V	—
Current - Collector Cutoff (Max)	100	nA
Operating Temperature Range	-55 to 150	°C
Package / Case	SC-70, SOT-323	—
Mounting Type	Surface Mount	—
RoHS Status	RoHS non-compliant	—

Substitute Part Grouping Explanation

Substitution of the MSD42WT1 is determined by strict equivalence across the following critical electrical and mechanical parameters:

Primary Substitution Criteria:

Transistor type: NPN
Voltage - Collector Emitter Breakdown (Max): 300 V minimum
Package / Case: SC-70 or SOT-323 compatible
Mounting Type: Surface Mount
Current - Collector (Ic) (Max): Equal to or greater than 150 mA
Vce Saturation (Max) @ Ib, Ic: 500mV @ 2mA, 20mA
DC Current Gain (hFE) (Min) @ Ic, Vce: 40 @ 30mA, 10V
Current - Collector Cutoff (Max): 100nA or lower

Substitute parts are classified into two categories:

Direct Equivalent: Parts with identical electrical specifications and packaging, differing only in product status or packaging format (tape & reel versus bulk).

Functional Equivalent: Parts meeting or exceeding all critical electrical parameters within the same package family, with allowable variations in secondary characteristics such as maximum power dissipation, transition frequency, or collector current rating, provided the part can safely operate within the original design constraints.

Parameter Comparison

Parameter	MSD42WT1	MSD42WT1G	BF820W,115	BF820W,135	FMMTA42TA	MMSTA42-7-F	MMSTA42-TP	PMSTA42,115
Manufacturer	onsemi	onsemi	Nexperia USA Inc.	NXP USA Inc.	Diodes Incorporated	Diodes Incorporated	Micro Commercial Co	Nexperia USA Inc.
Transistor Type	NPN	NPN	NPN	NPN	NPN	NPN	NPN	NPN
Voltage - Collector Emitter Breakdown (Max)	300 V	300 V	300 V	300 V	300 V	300 V	300 V	300 V
Current - Collector (Ic) (Max)	150 mA	150 mA	50 mA	50 mA	200 mA	200 mA	200 mA	100 mA
Power - Max	150 mW	150 mW	200 mW	200 mW	330 mW	200 mW	200 mW	200 mW
Vce Saturation (Max) @ Ib, Ic	500mV @ 2mA, 20mA	500mV @ 2mA, 20mA	600mV @ 5mA, 30mA	600mV @ 5mA, 30mA	500mV @ 2mA, 20mA	500mV @ 2mA, 20mA	500mV @ 2mA, 20mA	500mV @ 2mA, 20mA
DC Current Gain (hFE) (Min) @ Ic, Vce	40 @ 30mA, 10V	40 @ 30mA, 10V	50 @ 25mA, 20V	50 @ 25mA, 20V	40 @ 30mA, 10V	40 @ 30mA, 10V	40 @ 30mA, 10V	40 @ 30mA, 10V
Current - Collector Cutoff (Max)	100 nA	100 nA	10 nA	10 nA	100 nA	100 nA	100 nA	100 nA
Operating Temperature Range	-55 to 150°C	-55 to 150°C	150°C (Max)	150°C (Max)	-55 to 150°C	-55 to 150°C	-55 to 150°C	150°C (Max)
Package / Case	SC-70, SOT-323	SC-70, SOT-323	SC-70, SOT-323	SC-70, SOT-323	TO-236-3, SC-59, SOT-23-3	SC-70, SOT-323	SC-70, SOT-323	SC-70, SOT-323
Mounting Type	Surface Mount	Surface Mount	Surface Mount	Surface Mount	Surface Mount	Surface Mount	Surface Mount	Surface Mount
Product Status	Obsolete	Active	Active	Active	Active	Active	Active	Active
RoHS Status	RoHS non-compliant	ROHS3 Compliant	ROHS3 Compliant	Not specified	ROHS3 Compliant	ROHS3 Compliant	ROHS3 Compliant	ROHS3 Compliant
Frequency - Transition	Not specified	Not specified	60 MHz	60 MHz	50 MHz	50 MHz	50 MHz	50 MHz
Qualification	Not specified	Not specified	AEC-Q101	AEC-Q101	Not specified	Not specified	Not specified	AEC-Q101

Engineering Selection Recommendations

Direct Equivalent (Recommended Primary Substitute):

MSD42WT1G is the direct equivalent of MSD42WT1, manufactured by onsemi with identical electrical specifications and SC-70 (SOT-323) packaging. The primary distinction is product status: MSD42WT1G is active and widely available, whereas MSD42WT1 is obsolete. MSD42WT1G is ROHS3 compliant, addressing regulatory requirements for new designs. This part is suitable for direct replacement in all applications where the original MSD42WT1 was specified.

Functional Equivalents (Secondary Substitutes):

MMSTA42-7-F and MMSTA42-TP are functionally equivalent parts manufactured by Diodes Incorporated and Micro Commercial Co respectively. Both parts feature 200 mA maximum collector current (exceeding the 150 mA requirement), identical saturation voltage and DC current gain specifications, and SC-70 (SOT-323) packaging. Both are ROHS3 compliant and active products. These parts are suitable for applications where the design can accommodate the higher current rating.

FMMTA42TA, manufactured by Diodes Incorporated, provides 200 mA collector current and 330 mW power dissipation in a SOT-23-3 package. This part meets all electrical specifications but uses a different package footprint (SOT-23-3 versus SOT-323). FMMTA42TA is ROHS3 compliant and active. This part is suitable only if the PCB layout can accommodate SOT-23-3 package dimensions.

PMSTA42,115, manufactured by Nexperia USA Inc., provides 100 mA maximum collector current with identical saturation voltage and DC current gain specifications in SC-70 (SOT-323) packaging. This part is ROHS3 compliant, active, and AEC-Q101 qualified for automotive applications. PMSTA42,115 is suitable for applications where collector current requirements do not exceed 100 mA.

BF820W,115 and BF820W,135, manufactured by Nexperia USA Inc. and NXP USA Inc. respectively, are rated for 50 mA maximum collector current. These parts exceed the 300 V voltage requirement and feature 60 MHz transition frequency and AEC-Q101 automotive qualification. These parts are suitable only for applications where collector current does not exceed 50 mA.

Compliance Considerations:

The original MSD42WT1 is RoHS non-compliant. All recommended substitute parts (MSD42WT1G, MMSTA42-7-F, MMSTA42-TP, FMMTA42TA, PMSTA42,115) are ROHS3 compliant, meeting current regulatory requirements for new product designs and manufacturing.

Frequently Asked Questions (FAQ)

Q: Can MSD42WT1G be used as a direct replacement for MSD42WT1?

A: Yes. MSD42WT1G is manufactured by onsemi with identical electrical specifications, package type (SC-70/SOT-323), and performance characteristics. The primary difference is product status: MSD42WT1G is active and ROHS3 compliant, whereas MSD42WT1 is obsolete and RoHS non-compliant. MSD42WT1G is suitable for direct replacement in all applications.

Q: What is the difference between SC-70 and SOT-323 packaging?

A: SC-70 and SOT-323 refer to the same package standard. These designations are equivalent and interchangeable. Both describe a three-lead surface mount package with identical pin configuration and footprint.

Q: Can MMSTA42-7-F replace MSD42WT1 in a design rated for 150 mA collector current?

A: Yes. MMSTA42-7-F is rated for 200 mA maximum collector current, which exceeds the 150 mA requirement. The part meets all other electrical specifications including saturation voltage, DC current gain, and voltage rating. MMSTA42-7-F is ROHS3 compliant and active.

Q: Why do BF820W,115 and BF820W,135 have lower collector current ratings?

A: BF820W,115 and BF820W,135 are rated for 50 mA maximum collector current, which is lower than the MSD42WT1 specification of 150 mA. These parts are suitable only for applications where the design current requirement does not exceed 50 mA. These parts feature higher transition frequency (60 MHz) and AEC-Q101 automotive qualification.

Q: Is FMMTA42TA compatible with existing PCB layouts designed for MSD42WT1?

A: FMMTA42TA uses SOT-23-3 packaging, whereas MSD42WT1 uses SC-70 (SOT-323) packaging. These packages have different footprints and pin spacing. FMMTA42TA is not compatible with existing PCB layouts without redesign. However, FMMTA42TA meets all electrical specifications and is ROHS3 compliant.

Q: What does ROHS3 compliance mean?

A: ROHS3 compliance indicates the part meets the Restriction of Hazardous Substances Directive (RoHS 3), which restricts the use of specific hazardous materials in electrical and electronic equipment. All recommended substitute parts except the original MSD42WT1 are ROHS3 compliant, meeting current regulatory requirements for new designs and manufacturing.

Q: Can PMSTA42,115 be used in applications requiring 150 mA collector current?

A: No. PMSTA42,115 is rated for 100 mA maximum collector current, which is below the 150 mA requirement. This part is suitable only for applications where the design current does not exceed 100 mA. PMSTA42,115 is ROHS3 compliant, active, and AEC-Q101 qualified.

Q: What is AEC-Q101 qualification?

A: AEC-Q101 is an automotive qualification standard that certifies components for use in automotive applications. Parts with AEC-Q101 qualification (BF820W,115, BF820W,135, and PMSTA42,115) meet stringent reliability and performance requirements for automotive environments.

Q: Are all substitute parts available in the same packaging formats as MSD42WT1?

A: No. MSD42WT1 is available in standard packaging. Substitute parts are available in different packaging formats: MSD42WT1G is available in Tape & Reel (TR); MMSTA42-7-F and MMSTA42-TP are available in Tape & Reel (TR); FMMTA42TA is available in Cut Tape (CT) & Digi-Reel; PMSTA42,115 is available in Tape & Reel (TR); BF820W,115 is available in Tape & Reel (TR); BF820W,135 is available in Bulk. Packaging format selection depends on production volume and supply chain requirements.

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