KST43MTF Equivalent & Substitute Parts

Part Overview

The KST43MTF is an NPN bipolar junction transistor manufactured by onsemi, designed for general-purpose switching and amplification applications. This device features a 200 V collector-emitter breakdown voltage rating, 500 mA maximum collector current, and 50 MHz transition frequency in a surface mount SOT-23-3 package. The KST43MTF is classified as obsolete, making identification of equivalent and substitute parts essential for ongoing design support and production continuity. Substitute parts must maintain electrical compatibility within the specified parameter ranges while meeting current availability and compliance requirements.

Key Parameters

Parameter	KST43MTF Value	Unit
Transistor Type	NPN	—
Voltage - Collector Emitter Breakdown (Max)	200	V
Current - Collector (Ic) (Max)	500	mA
Vce Saturation (Max) @ Ib, Ic	500mV @ 2mA, 20mA	V
Current - Collector Cutoff (Max)	100	nA
DC Current Gain (hFE) (Min) @ Ic, Vce	40 @ 30mA, 10V	—
Power - Max	350	mW
Frequency - Transition	50	MHz
Operating Temperature	-55 to 150	°C
Mounting Type	Surface Mount	—
Package / Case	SOT-23-3	—
Product Status	Obsolete	—

Substitute Part Grouping Explanation

Substitute parts for the KST43MTF are classified into two categories based on electrical parameter compatibility:

Direct Substitutes maintain all critical electrical parameters within acceptable ranges for drop-in replacement:

Voltage - Collector Emitter Breakdown rating equal to or greater than 200 V
Current - Collector (Ic) rating equal to or greater than 500 mA
DC Current Gain (hFE) minimum of 40 @ 30mA, 10V or equivalent
Vce Saturation characteristics compatible with 500mV @ 2mA, 20mA
Transition frequency of 50 MHz or greater
SOT-23-3 package compatibility
Operating temperature range of -55°C to 150°C or greater

Similar Substitutes share the same package and basic NPN transistor topology but differ in one or more critical electrical parameters, requiring application-level verification:

Reduced voltage or current ratings
Different transition frequency characteristics
Modified gain or saturation parameters

Parameter Comparison

Parameter	KST43MTF	MMBTA42LT1G	MMBT6429LT1G	MMBTA43-TP	PBHV8118T,215
Manufacturer	onsemi	onsemi	onsemi	Micro Commercial Co	Nexperia USA Inc.
Transistor Type	NPN	NPN	NPN	NPN	NPN
Voltage - Collector Emitter Breakdown (Max)	200 V	300 V	45 V	200 V	180 V
Current - Collector (Ic) (Max)	500 mA	500 mA	200 mA	500 mA	1 A
Vce Saturation (Max) @ Ib, Ic	500mV @ 2mA, 20mA	500mV @ 2mA, 20mA	600mV @ 5mA, 100mA	500mV @ 2mA, 20mA	50mV @ 20mA, 100mA
Current - Collector Cutoff (Max)	100 nA	100 nA	100 nA	100 nA	100 nA
DC Current Gain (hFE) (Min) @ Ic, Vce	40 @ 30mA, 10V	40 @ 30mA, 10V	500 @ 100µA, 5V	40 @ 30mA, 10V	50 @ 500mA, 10V
Power - Max	350 mW	225 mW	225 mW	225 mW	300 mW
Frequency - Transition	50 MHz	50 MHz	700 MHz	50 MHz	30 MHz
Operating Temperature	-55 to 150°C	-55 to 150°C	-55 to 150°C	-55 to 150°C	to 150°C
Package / Case	SOT-23-3	SOT-23-3	SOT-23-3	SOT-23-3	SOT-23-3
Product Status	Obsolete	Active	Active	Active	Active
RoHS Status	ROHS3 Compliant	ROHS3 Compliant	ROHS3 Compliant	Not specified	ROHS3 Compliant

Engineering Selection Recommendations

MMBTA42LT1G (onsemi) is the primary direct substitute for KST43MTF applications. This part maintains identical DC current gain, saturation voltage, and transition frequency specifications while providing enhanced voltage rating (300 V vs. 200 V). The MMBTA42LT1G is active in production with full RoHS3 compliance and unlimited moisture sensitivity level. The reduced maximum power rating (225 mW vs. 350 mW) requires verification that thermal dissipation remains within acceptable limits for the target application.

MMBTA43-TP (Micro Commercial Co) provides electrical parameter equivalence to KST43MTF with identical voltage, current, gain, and saturation characteristics. This part is active in production and housed in SOT-23-3 packaging. Compliance certifications are not specified in available documentation. Lower inventory availability (1,085 units) compared to MMBTA42LT1G may impact procurement timelines.

PBHV8118T,215 (Nexperia USA Inc.) is suitable for applications requiring higher collector current capability (1 A vs. 500 mA) within a similar voltage envelope (180 V vs. 200 V). This part carries AEC-Q100 automotive qualification and is active in production. The reduced transition frequency (30 MHz vs. 50 MHz) and significantly lower saturation voltage (50 mV vs. 500 mV) indicate different switching characteristics that require application-level assessment.

MMBT6429LT1G (onsemi) is classified as a similar substitute only. The 45 V maximum voltage rating and 200 mA maximum collector current are substantially reduced from KST43MTF specifications. This part is suitable only for low-voltage, low-current applications and is not recommended for direct replacement in circuits designed for 200 V operation.

Frequently Asked Questions (FAQ)

Q: Can MMBTA42LT1G be used as a direct replacement for KST43MTF?

A: Yes. MMBTA42LT1G maintains all critical electrical parameters including DC current gain (40 @ 30mA, 10V), saturation voltage (500mV @ 2mA, 20mA), transition frequency (50 MHz), and collector current rating (500 mA). The higher voltage rating (300 V) provides additional design margin. Maximum power dissipation is reduced to 225 mW; verify thermal requirements for your application.

Q: What is the key difference between MMBTA42LT1G and MMBTA43-TP?

A: Both parts provide equivalent electrical performance to KST43MTF. MMBTA42LT1G is manufactured by onsemi with confirmed RoHS3 compliance and higher inventory availability. MMBTA43-TP is manufactured by Micro Commercial Co with lower documented inventory. Selection should be based on supplier availability and procurement requirements.

Q: Why is MMBT6429LT1G listed as a substitute if it has lower ratings?

A: MMBT6429LT1G is classified as a similar substitute for applications where voltage and current requirements are significantly lower than the original KST43MTF design. This part shares the same package and NPN topology but operates in a different electrical regime (45 V, 200 mA). It is not suitable for circuits requiring 200 V operation or 500 mA collector current.

Q: Is PBHV8118T,215 compatible with KST43MTF circuits?

A: PBHV8118T,215 is compatible for applications where higher collector current capability (1 A) is beneficial. However, the reduced transition frequency (30 MHz vs. 50 MHz) and significantly lower saturation voltage (50 mV vs. 500 mV) indicate different switching performance. Applications operating at 50 MHz or higher frequencies require verification that the reduced transition frequency does not degrade circuit performance.

Q: Are all substitute parts available in the same SOT-23-3 package?

A: All substitute parts are housed in SOT-23-3 or equivalent surface mount packages (TO-236-3, SC-59). Pinout compatibility is maintained across all listed substitutes, enabling direct PCB footprint compatibility.

Q: What compliance certifications should I verify for substitute selection?

A: MMBTA42LT1G, MMBTA43-TP, and PBHV8118T,215 are all RoHS3 compliant or unaffected by REACH regulations. PBHV8118T,215 carries AEC-Q100 automotive qualification. Verify that selected substitute meets your application's specific compliance requirements before implementation.

Q: How does the reduced power rating of MMBTA42LT1G (225 mW vs. 350 mW) affect circuit design?

A: The reduced power rating indicates lower thermal dissipation capability. Calculate maximum power dissipation in your application using P = Vce × Ic. If calculated dissipation exceeds 225 mW, thermal management modifications or alternative parts may be required. PBHV8118T,215 offers 300 mW rating as an intermediate option.

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