MPSA18G Equivalent & Substitute Parts

Part Overview

The MPSA18G is an NPN bipolar junction transistor manufactured by onsemi, designed for general-purpose switching and amplification applications. This device features a maximum collector current of 200 mA, collector-emitter breakdown voltage of 45 V, and a power dissipation rating of 625 mW in a through-hole TO-92 package. The MPSA18G is classified as obsolete, necessitating identification of equivalent and substitute components for new designs and ongoing production requirements. Active alternatives with comparable or enhanced electrical characteristics are available to ensure design continuity and supply chain reliability.

Key Parameters

Parameter	Value	Unit
Transistor Type	NPN	—
Current - Collector (Ic) Max	200	mA
Voltage - Collector Emitter Breakdown (Max)	45	V
Power - Max	625	mW
Frequency - Transition	160	MHz
Operating Temperature Range	-55 to 150	°C
Mounting Type	Through Hole	—
Package / Case	TO-92-3	—

Substitute Part Grouping Explanation

Substitution of the MPSA18G is determined by electrical and mechanical compatibility across the following critical parameters:

Electrical Compatibility Criteria:

Transistor type must be NPN
Collector-emitter breakdown voltage must equal or exceed 45 V
Maximum collector current must equal or exceed 200 mA
Power dissipation rating must support the application requirements
DC current gain (hFE) characteristics must be compatible with circuit design
Operating temperature range must encompass -55°C to 150°C

Mechanical Compatibility Criteria:

Package type determines physical fit and PCB layout compatibility
Through-hole packages (TO-92) are directly interchangeable in existing designs
Surface-mount packages (SOT-23) require PCB redesign but offer electrical equivalence

Two substitute categories are identified:

Direct Substitute (2N4401BU): Active product with identical through-hole TO-92 packaging, enhanced current capability (600 mA), and maintained voltage rating (40 V minimum). Suitable for direct replacement in existing through-hole designs.
Functional Equivalent (MMBT6429LT1G): Active product with identical electrical ratings (45 V, 200 mA) and enhanced frequency performance (700 MHz). Surface-mount SOT-23 package requires PCB redesign but provides superior performance characteristics and higher inventory availability.

Parameter Comparison

Parameter	MPSA18G (Main)	2N4401BU (Direct)	MMBT6429LT1G (Equivalent)
Manufacturer	onsemi	onsemi	onsemi
Product Status	Obsolete	Active	Active
Transistor Type	NPN	NPN	NPN
Current - Collector (Ic) Max	200 mA	600 mA	200 mA
Voltage - Collector Emitter Breakdown (Max)	45 V	40 V	45 V
Vce Saturation (Max)	300 mV @ 5 mA, 50 mA	750 mV @ 50 mA, 500 mA	600 mV @ 5 mA, 100 mA
DC Current Gain (hFE) Min	500 @ 10 mA, 5 V	100 @ 150 mA, 1 V	500 @ 100 µA, 5 V
Power - Max	625 mW	625 mW	225 mW
Frequency - Transition	160 MHz	250 MHz	700 MHz
Operating Temperature	-55 to 150 °C	-55 to 150 °C	-55 to 150 °C
Mounting Type	Through Hole	Through Hole	Surface Mount
Package / Case	TO-92-3	TO-92-3	SOT-23-3
RoHS Status	Not specified	ROHS3 Compliant	ROHS3 Compliant
REACH Status	REACH Unaffected	REACH Unaffected	REACH Unaffected

Engineering Selection Recommendations

For Through-Hole PCB Designs:

The 2N4401BU is the appropriate selection for direct replacement of the obsolete MPSA18G in existing through-hole applications. Both devices share identical TO-92-3 packaging, enabling pin-for-pin substitution without PCB modification. The 2N4401BU is an active product with ROHS3 compliance and REACH unaffected status, ensuring regulatory compliance and long-term supply availability. The enhanced collector current rating (600 mA versus 200 mA) provides design margin for applications operating near the original specification limits. The reduced collector-emitter breakdown voltage (40 V versus 45 V) is acceptable for circuits designed to operate below 40 V. The lower DC current gain (100 versus 500) requires circuit verification for applications dependent on high gain characteristics.

For New Designs or Surface-Mount Implementations:

The MMBT6429LT1G provides functional equivalence with superior performance characteristics. This device maintains the original 45 V breakdown voltage and 200 mA collector current ratings while offering significantly enhanced transition frequency (700 MHz versus 160 MHz). The SOT-23-3 surface-mount package requires PCB redesign but enables higher circuit density and improved thermal performance. The MMBT6429LT1G is an active product with ROHS3 compliance, REACH unaffected status, and substantially higher inventory availability (155,200 pieces in stock). The reduced power dissipation rating (225 mW versus 625 mW) is acceptable for low-power switching applications but requires thermal analysis for high-power designs.

Frequently Asked Questions (FAQ)

Q: Can the 2N4401BU directly replace the MPSA18G without circuit modification?

A: The 2N4401BU is pin-compatible with the MPSA18G in TO-92-3 through-hole applications. However, circuit verification is required for applications dependent on the original DC current gain specification (500 minimum). The 2N4401BU specifies a minimum gain of 100 at 150 mA and 1 V, which differs significantly from the MPSA18G specification of 500 at 10 mA and 5 V. Applications operating at the original bias conditions require gain analysis to confirm acceptable performance.

Q: What is the primary difference between the 2N4401BU and MMBT6429LT1G substitutes?

A: The 2N4401BU maintains through-hole TO-92-3 packaging for direct PCB substitution, while the MMBT6429LT1G uses surface-mount SOT-23-3 packaging requiring PCB redesign. The MMBT6429LT1G offers superior frequency performance (700 MHz versus 250 MHz) and higher inventory availability. The 2N4401BU provides enhanced collector current capability (600 mA versus 200 mA).

Q: Is the 2N4401BU suitable for applications requiring 45 V collector-emitter breakdown voltage?

A: The 2N4401BU specifies a maximum collector-emitter breakdown voltage of 40 V, which is 5 V lower than the MPSA18G specification of 45 V. This device is suitable for applications designed to operate at or below 40 V. Applications requiring operation above 40 V must use the MMBT6429LT1G, which maintains the 45 V breakdown voltage specification.

Q: Can the MMBT6429LT1G be used in existing through-hole PCB designs?

A: The MMBT6429LT1G uses SOT-23-3 surface-mount packaging and cannot be directly installed in through-hole PCB designs without adapter components or PCB redesign. This device is suitable only for new designs or PCB revisions incorporating surface-mount technology.

Q: What are the compliance and supply considerations for these substitutes?

A: Both the 2N4401BU and MMBT6429LT1G are active products manufactured by onsemi with ROHS3 compliance and REACH unaffected status. The MMBT6429LT1G offers significantly higher inventory availability (155,200 pieces) compared to the 2N4401BU (9,900 pieces), providing superior long-term supply security for high-volume production requirements.

Q: Are there power dissipation differences that affect circuit design?

A: The MPSA18G and 2N4401BU both specify 625 mW maximum power dissipation. The MMBT6429LT1G specifies 225 mW maximum power dissipation, which is 400 mW lower. Applications requiring sustained power dissipation above 225 mW must use the 2N4401BU or verify thermal performance through detailed analysis.

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