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Home > Products > Discrete Semiconductor Products > Transistors > Bipolar (BJT) > Single Bipolar Transistors

onsemi KST4124MTF

Name: KST4124MTF
Brand: onsemi
SKU: KST4124MTF
Price: 2.40 USD
Availability: InStock
Rating: 5 (2 reviews)

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Part No.:: KST4124MTF

Manufacturer:: onsemi

Category:: Single Bipolar Transistors

Package:: TO-236-3, SC-59, SOT-23-3

Datasheet:: KST4124MTF.pdf

Description:: TRANS NPN 25V 0.2A SOT-23-3

Quantity:: RFQ Add To RFQ list

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Product details

Overview

KST4124MTF from ON Semiconductor (formerly Fairchild) is an NPN epitaxial silicon general-purpose transistor in SOT-23 package, rated for 25 V V_CEO, 200 mA I_C, and 350 mW P_C, commonly used in low-power switching and amplification stages of consumer and industrial signal conditioning circuits.

For engineers reviewing the KST4124MTF datasheet, pinout, applications, or equivalent options, key selection considerations include DC current gain (h_FE = 120–360 at I_C = 2–50 mA), saturation voltages (V_CE(sat) = 0.3 V, V_BE(sat) = 0.95 V), f_T = 300 MHz, noise figure = 5 dB, and SOT-23 thermal and layout constraints.

Technical Context

The KST4124MTF operates as a discrete bipolar junction transistor with fixed NPN polarity, optimized for linear amplification and digital switching in low-voltage, low-current signal paths. Its h_FE variation across I_C (120 min at 2 mA, 60 min at 50 mA) supports both small-signal gain stability and robust saturation drive capability.

Designed for surface-mount implementation, it features a 3-pin SOT-23 footprint with emitter-grounded configuration in typical common-emitter layouts. The device meets standard JEDEC SOT-23 mechanical dimensions and exhibits Cob = 4 pF at V_CB = 5 V, supporting RF-coupled applications up to ~100 MHz.

Key Specifications

Parameter	Value and Actual Design Meaning
V_CEO	25 V - Maximum collector-emitter voltage before breakdown under open-base condition; defines safe operating range in switching applications.
I_C	200 mA - Continuous collector current limit; sets upper bound for load-driving capability in driver or buffer stages.
P_C	350 mW - Total power dissipation at T_A = 25°C; determines thermal derating requirements on PCBs without heatsinking.
h_FE	120–360 - DC current gain range at V_CE = 1 V; enables predictable base drive sizing for saturation or linear operation.
f_T	300 MHz - Current gain bandwidth product; confirms suitability for audio and low-MHz RF amplification tasks.
V_CE(sat)	0.3 V @ I_C = 50 mA, I_B = 5 mA - Low saturation voltage ensures minimal conduction loss in digital switch mode.

Pinout & Package

SOT-23 plastic surface-mount package with gull-wing leads; standardized 3-pin configuration (1 = Emitter, 2 = Base, 3 = Collector), 1.30 mm pitch, 2.90 mm × 1.30 mm body size, and 0.95 mm height.

Pin/Terminal	Circuit Role	Design Meaning
1	Emitter	Current sink terminal; typically connected to ground or low-impedance return path in common-emitter configurations.
2	Base	Control input; requires current-limited drive (e.g., via series resistor) to bias transistor into active or saturated region.
3	Collector	Current source terminal; connects to load or pull-up network; voltage swing limited by V_CEO = 25 V rating.

Key Features

Feature	Design Value
Low V_CE(sat)	0.3 V enables efficient switching in battery-powered logic interfaces and LED drivers with minimal voltage drop.
High f_T	300 MHz supports stable small-signal amplification in audio preamps and IF stages without external compensation.
Low noise figure	5 dB at 100 µA/5 V makes KST4124MTF suitable for low-level analog front-end amplification where SNR matters.
Standard SOT-23 footprint	Enables drop-in replacement with industry-common NPN transistors (e.g., MMBT3904, PN2222A variants) on automated assembly lines.

Applications

Audio Signal Amplification	Microcontroller GPIO Interface
Use Scenario: Amplifying line-level audio signals in portable media players and headset amplifiers. IC Role / Device Role / Timing Role: Small-signal NPN amplifier in common-emitter configuration with emitter degeneration for gain stability. Use Value: 300 MHz f_T and 5 dB noise figure preserve fidelity across 20 Hz–20 kHz band without added distortion.	Use Scenario: Level-shifting and current boosting between 3.3 V microcontroller outputs and 5 V peripheral inputs. IC Role / Device Role / Timing Role: Digital switch translating logic-high states to higher-voltage rails using saturated NPN operation. Use Value: 0.3 V V_CE(sat) minimizes power loss and heat generation during sustained ON-state operation.
LED Driver Circuit	Signal Conditioning Front-End
Use Scenario: Driving indicator LEDs or low-current status lamps in industrial HMI panels and sensor nodes. IC Role / Device Role / Timing Role: Constant-current switch controlling LED anode connection to supply rail via collector load. Use Value: 200 mA I_C rating supports multiple parallel LEDs while maintaining reliable saturation at 5 mA base drive.	Use Scenario: Buffering weak sensor outputs (e.g., thermistor dividers, photodiode amps) before ADC sampling. IC Role / Device Role / Timing Role: Unity-gain emitter-follower providing high-input impedance and low-output impedance isolation. Use Value: h_FE ≥ 120 ensures sufficient current drive into 10 kΩ ADC input loads without signal attenuation.

Audio Signal Amplification

Microcontroller GPIO Interface

Use Scenario: Amplifying line-level audio signals in portable media players and headset amplifiers.

IC Role / Device Role / Timing Role: Small-signal NPN amplifier in common-emitter configuration with emitter degeneration for gain stability.

Use Value: 300 MHz f_T and 5 dB noise figure preserve fidelity across 20 Hz–20 kHz band without added distortion.

Use Scenario: Level-shifting and current boosting between 3.3 V microcontroller outputs and 5 V peripheral inputs.

IC Role / Device Role / Timing Role: Digital switch translating logic-high states to higher-voltage rails using saturated NPN operation.

Use Value: 0.3 V V_CE(sat) minimizes power loss and heat generation during sustained ON-state operation.

LED Driver Circuit

Signal Conditioning Front-End

Use Scenario: Driving indicator LEDs or low-current status lamps in industrial HMI panels and sensor nodes.

IC Role / Device Role / Timing Role: Constant-current switch controlling LED anode connection to supply rail via collector load.

Use Value: 200 mA I_C rating supports multiple parallel LEDs while maintaining reliable saturation at 5 mA base drive.

Use Scenario: Buffering weak sensor outputs (e.g., thermistor dividers, photodiode amps) before ADC sampling.

IC Role / Device Role / Timing Role: Unity-gain emitter-follower providing high-input impedance and low-output impedance isolation.

Use Value: h_FE ≥ 120 ensures sufficient current drive into 10 kΩ ADC input loads without signal attenuation.

Equivalent & Alternatives

The following parts are listed as comparable options for similar NPN transistor applications.

Alternative Part	Technical Difference	Application Difference	Selection Advice
MMBT3904LT1G	V_CEO = 40 V, h_FE = 100–300, P_C = 310 mW, same SOT-23 package	Higher voltage margin but lower power dissipation; less suitable for sustained 200 mA loads	Preferred when system supply exceeds 25 V or when tighter h_FE binning is required
PN2222A	TO-92 package, V_CEO = 40 V, I_C = 600 mA, P_C = 1 W, not SMT-compatible	Higher power handling but incompatible with automated SMT assembly; requires through-hole layout	Select only for prototyping or legacy through-hole designs where board space and assembly method permit

Compared with MMBT3904LT1G and PN2222A, the KST4124MTF offers optimal balance of SMT compatibility, 25 V/200 mA rating, and 350 mW dissipation-making it ideal for compact, medium-current switching where thermal headroom and footprint efficiency are prioritized over maximum voltage or current headroom.

Availability

KST4124MTF is available at Aetrix Electronics and suitable for audio amplification, microcontroller interface, LED driving, and signal conditioning applications requiring stable component supply and consistent parametric performance across production batches.

Supply support for KST4124MTF includes scheduled delivery planning, volume procurement assistance, BOM continuity management, traceable sourcing, and lifecycle availability coordination for OEM customers, industrial embedded developers, connected-device designers, and electronics production programs.

Manufacturer

ON Semiconductor is a global semiconductor supplier delivering energy-efficient, intelligent power and sensing solutions for automotive, industrial, cloud, medical, and IoT applications.

The KST4124MTF belongs to ON Semiconductor's general-purpose bipolar transistor product line, engineered for cost-sensitive, high-volume signal switching and amplification in consumer and industrial electronics.

FAQ

What is the maximum collector-emitter voltage rating for KST4124MTF?

The KST4124MTF has a maximum collector-emitter voltage (V_CEO) rating of 25 V at T_A = 25°C. This value represents the highest voltage that can be applied between collector and emitter with the base open before breakdown occurs. Exceeding this rating risks permanent device failure. Designers must ensure operating conditions-including transients and ripple-remain within this limit across the full temperature range.

Does KST4124MTF support linear amplification applications?

Yes, the KST4124MTF supports linear amplification due to its specified f_T = 300 MHz, h_FE = 120–360, and low noise figure of 5 dB at 100 µA. These parameters enable stable small-signal gain in common-emitter or emitter-follower configurations. The KST4124MTF is routinely used in audio preamplifier stages and sensor signal buffering where bandwidth and SNR are critical.

What is the pin configuration of KST4124MTF in the SOT-23 package?

The KST4124MTF uses a standard SOT-23 pinout: Pin 1 is Emitter, Pin 2 is Base, and Pin 3 is Collector. This matches JEDEC MO-215 and is consistent across ON Semiconductor's KST-series transistors. The marking "ZC" on the top surface aligns with this orientation. Always verify physical orientation using the datasheet diagram before PCB layout or rework.

Can KST4124MTF replace MMBT3904 in existing designs?

KST4124MTF can serve as a functional alternative to MMBT3904 in many low-voltage, medium-current applications, but differences exist: KST4124MTF has lower V_CEO (25 V vs. 40 V) and higher P_C (350 mW vs. 310 mW). If the original design operates below 25 V and draws ≤200 mA, the KST4124MTF is viable; otherwise, voltage margin or thermal validation is required.

What is the typical noise figure of KST4124MTF and under what conditions is it measured?

The typical noise figure of KST4124MTF is 5 dB, measured at I_C = 100 µA, V_CE = 5 V, R_S = 1 kΩ, and frequency range 10 Hz to 15.7 kHz. This specification reflects its suitability for low-noise preamplification of weak analog signals. The KST4124MTF maintains this performance across its qualified operating temperature range, making it appropriate for precision sensor interfaces where signal integrity is essential.

KST4124MTF Specifications

Product attributes: Attribute value

Manufacturer:: onsemi

Series:: -

Package/Case:: TO-236-3, SC-59, SOT-23-3

Packaging:: Tape & Reel (TR)

Product Status:: Obsolete

Transistor Type:: NPN

Current - Collector (Ic) (Max):: 200 mA

Voltage - Collector Emitter Breakdown (Max):: 25 V

Vce Saturation (Max) @ Ib, Ic:: 300mV @ 5mA, 50mA

Current - Collector Cutoff (Max):: 50nA (ICBO)

DC Current Gain (hFE) (Min) @ Ic, Vce:: 120 @ 2mA, 1V

Power - Max:: 350 mW

Frequency - Transition:: 300MHz

Operating Temperature:: -

Grade:: -

Qualification:: -

Mounting Type:: Surface Mount

Supplier Device Package:: SOT-23-3

KST4124MTF FAQ

1.How can I place an order for KST4124MTF through Aetrix?

Please submit a Request for Quotation (RFQ) for KST4124MTF on Aetrix. Our sales agent will provide a competitive quotation and guide you through the order confirmation once you accept the terms.

2.Are the price and stock information for KST4124MTF reliable?

The price and inventory of KST4124MTF are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for KST4124MTF is usually 5 days.

3.What payment methods are accepted for KST4124MTF?

We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for KST4124MTF transactions.

Note: Certain payment methods may incur a processing fee.

4.How is shipping managed for KST4124MTF?

KST4124MTF orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.

Once your KST4124MTF order is processed, you will receive an email with the shipment details and tracking number.

Note: Tracking information may take up to 24 hours to appear. Express delivery typically takes 3–5 business days.

5.How can I obtain technical support or documentation for KST4124MTF?

For technical support, including KST4124MTF datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your KST4124MTF requirements.

6.How does Aetrix verify that KST4124MTF is sourced from the original manufacturer or authorized distributors?

All KST4124MTF products on Aetrix are procured from qualified distributors and authorized channels. Our dedicated quality assurance team conducts strict verification, including traceability checks and, if necessary, third-party testing. This ensures that KST4124MTF meets industry standards.

7.What is the process for return or replacement of KST4124MTF?

All KST4124MTF units undergo pre-shipment inspection (PSI). If there is an issue with KST4124MTF, returns or replacements are accepted under the following conditions:

1.Quantity discrepancies, incorrect items, or visible external defects (such as breakage or corrosion), acknowledged by Aetrix.

2.The issue is reported within 90 days of delivery.

3.The KST4124MTF part is unused and in its original packaging.

Return procedure for KST4124MTF:

1.Submit a request within 90 days.

2.Obtain a Return Material Authorization (RMA) from Aetrix.

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