MMBT4124 Equivalent & Substitute Parts

Part Overview

The MMBT4124 is an NPN bipolar junction transistor (BJT) manufactured by onsemi, housed in a SOT-23-3 surface mount package. This component is rated for 25 V collector-emitter breakdown voltage, 200 mA maximum collector current, and 350 mW power dissipation. The MMBT4124 is classified as obsolete, necessitating identification of active equivalent and substitute parts for new designs and production continuity. Substitute parts must maintain electrical compatibility within the specified parameter ranges while meeting current manufacturing and compliance standards.

Key Parameters

Parameter	Value	Unit
Transistor Type	NPN	—
Voltage - Collector Emitter Breakdown (Max)	25	V
Current - Collector (Ic) (Max)	200	mA
Power - Max	350	mW
Frequency - Transition	300	MHz
DC Current Gain (hFE) (Min) @ Ic, Vce	120 @ 2mA, 1V	—
Vce Saturation (Max) @ Ib, Ic	300mV @ 5mA, 50mA	—
Operating Temperature Range	-55 to 150	°C
Package / Case	SOT-23-3	—
Mounting Type	Surface Mount	—

Substitute Part Grouping Explanation

Substitution of the MMBT4124 is determined by strict adherence to the following electrical and mechanical parameters:

Critical Parameters for Direct Substitution:

Transistor Type: NPN
Voltage - Collector Emitter Breakdown (Max): ≥ 25 V
Current - Collector (Ic) (Max): ≥ 200 mA
Package / Case: SOT-23-3 (TO-236-3, SC-59)
Mounting Type: Surface Mount

Secondary Parameters for Functional Compatibility:

DC Current Gain (hFE) (Min): ≥ 120 @ specified test conditions
Vce Saturation (Max): ≤ 300 mV @ specified test conditions
Operating Temperature Range: -55°C to 150°C minimum
Power - Max: ≥ 350 mW (preferred) or ≥ 225 mW (acceptable for reduced power applications)

Substitute parts are classified into two categories:

Direct Equivalents: Parts meeting all critical parameters with identical or superior electrical specifications and active product status.

Similar Substitutes: Parts meeting critical electrical parameters but with variations in secondary specifications (frequency, power rating, or current gain) that may require circuit evaluation for specific applications.

Parameter Comparison

Parameter	MMBT4124	MMBT4124LT1G	MMBT5089LT1G	MMBT6429LT1G	BC818-40-TP
Manufacturer	onsemi	onsemi	onsemi	onsemi	Micro Commercial Co
Product Status	Obsolete	Active	Active	Active	Active
Transistor Type	NPN	NPN	NPN	NPN	NPN
Voltage - Collector Emitter Breakdown (Max)	25 V	25 V	25 V	45 V	25 V
Current - Collector (Ic) (Max)	200 mA	200 mA	50 mA	200 mA	500 mA
Power - Max	350 mW	225 mW	300 mW	225 mW	300 mW
Frequency - Transition	300 MHz	300 MHz	50 MHz	700 MHz	170 MHz
DC Current Gain (hFE) (Min)	120 @ 2mA, 1V	120 @ 2mA, 1V	400 @ 100µA, 5V	500 @ 100µA, 5V	250 @ 100mA, 1V
Vce Saturation (Max)	300mV @ 5mA, 50mA	300mV @ 5mA, 50mA	500mV @ 1mA, 10mA	600mV @ 5mA, 100mA	700mV @ 50mA, 500mA
Operating Temperature Range	-55 to 150°C	-55 to 150°C	-55 to 150°C	-55 to 150°C	-55 to 150°C
Package / Case	SOT-23-3	SOT-23-3	SOT-23-3	SOT-23-3	SOT-23-3
Mounting Type	Surface Mount	Surface Mount	Surface Mount	Surface Mount	Surface Mount
RoHS Status	ROHS3 Compliant	ROHS3 Compliant	ROHS3 Compliant	ROHS3 Compliant	Not specified
Moisture Sensitivity Level (MSL)	1 (Unlimited)	1 (Unlimited)	1 (Unlimited)	1 (Unlimited)	Not specified

Engineering Selection Recommendations

MMBT4124LT1G (Direct Equivalent - Preferred)

The MMBT4124LT1G is the direct equivalent of the obsolete MMBT4124. This part is manufactured by onsemi with active product status and maintains identical electrical specifications including 25 V breakdown voltage, 200 mA collector current, 300 MHz transition frequency, and 120 minimum DC current gain. The primary difference is reduced power rating (225 mW versus 350 mW) and packaging format (Tape & Reel versus bulk). This part is ROHS3 compliant with MSL 1 rating. Selection of MMBT4124LT1G is appropriate for direct replacement in applications where the original MMBT4124 specifications are required.

MMBT6429LT1G (Higher Voltage Substitute)

The MMBT6429LT1G is suitable for applications requiring higher voltage tolerance. This onsemi part maintains 200 mA collector current and SOT-23-3 packaging but provides 45 V breakdown voltage (versus 25 V) and superior transition frequency (700 MHz versus 300 MHz). Power rating is 225 mW. This part is ROHS3 compliant with MSL 1 rating. Selection is appropriate when circuit voltage margins require higher breakdown voltage specification.

BC818-40-TP (Higher Current Substitute)

The BC818-40-TP manufactured by Micro Commercial Co provides higher collector current capability (500 mA versus 200 mA) while maintaining 25 V breakdown voltage and SOT-23-3 packaging. Transition frequency is 170 MHz. This part is suitable for applications requiring increased current handling capacity. Compliance certifications are not fully specified in available data.

MMBT5089LT1G (Lower Current Substitute)

The MMBT5089LT1G is an onsemi part with reduced collector current specification (50 mA versus 200 mA) and lower transition frequency (50 MHz versus 300 MHz). This part is not recommended as a direct substitute for the MMBT4124 due to insufficient current rating. Selection is appropriate only for applications with reduced current requirements where the MMBT4124 specifications exceed design needs.

Frequently Asked Questions (FAQ)

Q: Can MMBT4124LT1G directly replace MMBT4124 in existing designs?

A: Yes. MMBT4124LT1G is the direct equivalent with identical electrical specifications. The primary difference is packaging format (Tape & Reel versus bulk) and slightly reduced power rating (225 mW versus 350 mW). For applications operating below 225 mW, direct substitution is appropriate without circuit modification.

Q: What is the difference between MMBT4124 and MMBT4124LT1G?

A: Both parts are NPN transistors with identical electrical ratings: 25 V breakdown voltage, 200 mA collector current, 300 MHz transition frequency, and 120 minimum DC current gain. MMBT4124LT1G is the active production equivalent with Tape & Reel packaging and 225 mW power rating. MMBT4124 is obsolete with 350 mW power rating and bulk packaging.

Q: Can MMBT6429LT1G be used in place of MMBT4124?

A: MMBT6429LT1G is electrically compatible for applications where higher voltage tolerance is beneficial or required. This part provides 45 V breakdown voltage (versus 25 V) and 700 MHz transition frequency (versus 300 MHz). Substitution is appropriate when circuit design permits higher voltage rating. Power rating is 225 mW.

Q: Is BC818-40-TP a suitable substitute for MMBT4124?

A: BC818-40-TP is suitable for applications requiring higher collector current (500 mA versus 200 mA). Both parts maintain 25 V breakdown voltage and SOT-23-3 packaging. Transition frequency is lower (170 MHz versus 300 MHz). Substitution is appropriate when increased current capacity is required. Compliance certifications should be verified for specific applications.

Q: Why is MMBT5089LT1G not recommended as a substitute?

A: MMBT5089LT1G has insufficient collector current rating (50 mA versus 200 mA) and lower transition frequency (50 MHz versus 300 MHz). This part does not meet the critical parameter requirements for direct substitution. Selection is appropriate only for applications with reduced current requirements where MMBT4124 specifications exceed design needs.

Q: Are all substitute parts available in SOT-23-3 packaging?

A: Yes. All substitute parts listed are available in SOT-23-3 (TO-236-3, SC-59) surface mount packaging, maintaining mechanical compatibility with MMBT4124 PCB layouts.

Q: What compliance standards apply to these substitute parts?

A: MMBT4124LT1G, MMBT5089LT1G, and MMBT6429LT1G are ROHS3 compliant with MSL 1 (Unlimited) moisture sensitivity rating. All parts are REACH Unaffected and classified as EAR99 for export control purposes. BC818-40-TP compliance certifications are not fully specified in available data and should be verified for specific applications.

Q: Can these parts be used interchangeably in high-frequency applications?

A: Transition frequency varies among substitute parts. MMBT4124 and MMBT4124LT1G both operate at 300 MHz. MMBT6429LT1G provides superior frequency performance at 700 MHz. BC818-40-TP operates at 170 MHz. MMBT5089LT1G is limited to 50 MHz. Selection must match application frequency requirements.

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