MPSA42G Equivalent & Substitute Parts

Part Overview

The MPSA42G is an NPN bipolar junction transistor manufactured by onsemi, rated for 300 V collector-emitter breakdown voltage and 500 mA maximum collector current in a Through Hole TO-92 package. This device is classified as obsolete, necessitating identification of equivalent and substitute components for ongoing design requirements and production continuity. Substitute parts maintain electrical and mechanical compatibility while offering active product status and improved availability.

Key Parameters

Parameter	Value	Unit
Transistor Type	NPN	—
Voltage - Collector Emitter Breakdown (Max)	300	V
Current - Collector (Ic) (Max)	500	mA
Vce Saturation (Max) @ Ib, Ic	500 mV @ 2 mA, 20 mA	—
Current - Collector Cutoff (Max)	100	nA
Power - Max	625	mW
Frequency - Transition	50	MHz
Operating Temperature Range	-55 to 150	°C
Mounting Type	Through Hole	—
Package / Case	TO-92-3 (TO-226)	—

Substitute Part Grouping Explanation

Substitution of the MPSA42G is determined by equivalence across the following critical parameters: NPN transistor type, 300 V collector-emitter breakdown voltage, 500 mA maximum collector current, 625 mW power dissipation, 50 MHz transition frequency, and Through Hole mounting configuration. Substitute parts are grouped into two categories based on package type:

Category 1: Through Hole TO-92 Package Substitutes — Direct mechanical and electrical equivalents maintaining the original TO-92-3 form factor. These parts preserve pin compatibility and board layout requirements.

Category 2: Surface Mount SOT-23 Package Substitute — Electrical equivalent with modified mounting technology. This category applies to designs undergoing package migration or modernization while maintaining electrical performance specifications.

All substitute parts maintain the specified voltage, current, and frequency ratings. Variations in DC current gain (hFE) specifications and power dissipation do not preclude substitution when the substitute part meets or exceeds the minimum required performance in the application circuit.

Parameter Comparison

Parameter	MPSA42G (onsemi)	KSP42BU (onsemi)	MMBTA42LT1G (onsemi)	MPSA42 (Diotec)
Product Status	Obsolete	Active	Active	Active
Transistor Type	NPN	NPN	NPN	NPN
Voltage - Collector Emitter Breakdown (Max)	300 V	300 V	300 V	300 V
Current - Collector (Ic) (Max)	500 mA	500 mA	500 mA	500 mA
Vce Saturation (Max) @ Ib, Ic	500 mV @ 2 mA, 20 mA	500 mV @ 2 mA, 20 mA	500 mV @ 2 mA, 20 mA	500 mV @ 2 mA, 20 mA
Current - Collector Cutoff (Max)	100 nA	100 nA	100 nA	100 nA
Power - Max	625 mW	625 mW	225 mW	625 mW
Frequency - Transition	50 MHz	50 MHz	50 MHz	50 MHz
Operating Temperature Range	-55 to 150 °C	Up to 150 °C	-55 to 150 °C	-55 to 150 °C
Mounting Type	Through Hole	Through Hole	Surface Mount	Through Hole
Package / Case	TO-92-3 (TO-226)	TO-92-3 (TO-226AA)	SOT-23-3 (TO-236)	TO-92-3 (TO-226AA)
RoHS Status	REACH Unaffected	ROHS3 Compliant	ROHS3 Compliant	REACH Vendor Undefined

Engineering Selection Recommendations

For Through Hole TO-92 Applications:

KSP42BU (onsemi) and MPSA42 (Diotec) are direct substitutes for MPSA42G in Through Hole TO-92 configurations. Both parts maintain identical electrical specifications and package form factor. KSP42BU carries active product status and ROHS3 compliance, providing long-term supply assurance. MPSA42 from Diotec offers equivalent electrical performance with active status. Selection between these options depends on supply chain requirements and compliance certifications applicable to the end application.

For Surface Mount Migration:

MMBTA42LT1G (onsemi) provides electrical equivalence in a Surface Mount SOT-23-3 package. This part is suitable for designs transitioning from Through Hole to surface mount technology. The reduced power dissipation rating (225 mW versus 625 mW) requires verification that application circuit current and voltage conditions remain within this lower envelope. MMBTA42LT1G carries ROHS3 compliance and active product status.

Compliance Considerations:

KSP42BU and MMBTA42LT1G both carry ROHS3 compliance certification. MPSA42 from Diotec does not specify RoHS status. All three substitute parts maintain REACH Unaffected or equivalent regulatory standing. Selection should align with end-product regulatory requirements and supply chain compliance mandates.

Frequently Asked Questions (FAQ)

Q: Can KSP42BU directly replace MPSA42G in existing PCB designs?

A: Yes. KSP42BU maintains identical TO-92-3 package pinout, electrical ratings (300 V, 500 mA, 50 MHz), and saturation characteristics. No circuit modifications are required for direct substitution in Through Hole applications.

Q: What is the primary difference between KSP42BU and MPSA42 (Diotec)?

A: Both parts are electrically equivalent with identical voltage, current, and frequency specifications. The primary difference is manufacturer source. KSP42BU is manufactured by onsemi with ROHS3 compliance. MPSA42 from Diotec offers equivalent performance with different supply chain and compliance documentation.

Q: Is MMBTA42LT1G suitable as a substitute in all MPSA42G applications?

A: MMBTA42LT1G is electrically equivalent but differs in two aspects: (1) Surface Mount SOT-23-3 package requires PCB redesign and different assembly processes, and (2) maximum power dissipation is 225 mW versus 625 mW. Substitution is valid only when application circuit power dissipation remains below 225 mW and surface mount technology is acceptable.

Q: What does "obsolete" product status mean for MPSA42G?

A: Obsolete status indicates the part is no longer manufactured or supported by the original supplier. Existing inventory may be available from distributors, but long-term supply cannot be assured. Substitution to active-status parts (KSP42BU, MMBTA42LT1G, or MPSA42 from Diotec) is recommended for new designs and production continuity.

Q: Are there temperature range differences between substitute parts?

A: MPSA42G and MMBTA42LT1G specify -55 to 150 °C operating range. KSP42BU specifies operation up to 150 °C without explicit lower temperature limit. MPSA42 from Diotec specifies -55 to 150 °C. For applications requiring full -55 to 150 °C range, MMBTA42LT1G or MPSA42 (Diotec) are preferred.

Q: What is the significance of DC Current Gain (hFE) differences listed in the parameter table?

A: MPSA42G specifies hFE minimum of 25 @ 1 mA, 10 V. Substitute parts specify hFE minimum of 40 @ 30 mA, 10 V. These are measured at different bias points and do not indicate incompatibility. Both specifications ensure adequate gain for typical switching and amplification applications. Circuit design should not depend on specific hFE values below the stated minimums.

Q: Can MPSA42G be used interchangeably with KSP42BU in high-reliability applications?

A: KSP42BU is preferred for new high-reliability designs due to active product status, ROHS3 compliance, and ongoing manufacturer support. MPSA42G, being obsolete, lacks these assurances. Existing designs using MPSA42G may continue operation, but new production should transition to KSP42BU or equivalent active-status parts.

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