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

onsemi 2N4124TA

Name: 2N4124TA
Brand: onsemi
SKU: 2N4124TA
Price: 2.40 USD
Availability: InStock
Rating: 5 (2 reviews)

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Part No.:: 2N4124TA

Manufacturer:: onsemi

Category:: Single Bipolar Transistors

Package:: TO-226-3, TO-92-3 (TO-226AA) Formed Leads

Datasheet:: 2N4124TA.pdf

Description:: TRANS NPN 25V 0.2A TO-92-3

Quantity:: RFQ Add To RFQ list

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Product details

Overview

2N4124TA from Fairchild Semiconductor is an NPN general-purpose bipolar junction transistor (BJT) designed for amplification and switching in low-to-medium power circuits. It delivers DC current gain (h_FE) of 120–360 at 2 mA, supports 200 mA continuous collector current, withstands 25 V C-E breakdown voltage, and operates up to 100 MHz bandwidth - deployed in signal conditioning stages of industrial sensor interfaces and discrete logic-level translators.

For engineers reviewing the 2N4124TA datasheet, pinout, applications, or equivalent options, key selection criteria include its TO-92 package thermal resistance (R_θJA = 200 °C/W), saturation voltage (V_CE(sat) = 0.3 V @ 50 mA), noise figure (5.0 dB @ 100 µA), f_T = 300 MHz, and guaranteed operation across –55°C to +150°C junction temperature range.

Technical Context

The 2N4124TA functions as a silicon NPN BJT with epitaxial base construction optimized for linearity in small-signal amplification and sharp turn-on/turn-off behavior in digital switching. Its h_FE variation (120–360) reflects process-controlled beta spread, and f_T = 300 MHz confirms suitability for RF front-end pre-amplifiers up to VHF band.

Thermal design relies on FR-4 PCB mounting (1.6" × 1.6" × 0.06") per datasheet test condition, where R_θJA = 200 °C/W enables 625 mW dissipation at 25°C ambient, derating linearly by 5.0 mW/°C above that point - critical for sustained 100 mA switching duty cycles.

Key Specifications

Parameter	Value and Actual Design Meaning
V_CEO	25 V - Maximum safe collector-emitter voltage before breakdown; sets upper rail limit in common-emitter amplifier stages.
I_C (continuous)	200 mA - Continuous collector current rating; defines max load drive capability in relay drivers or LED switches.
h_FE	120–360 @ 2 mA - DC current gain range; determines base drive resistor sizing for predictable saturation in switching designs.
f_T	300 MHz - Unity-gain frequency; validates use in 10–50 MHz oscillator or RF amplifier stages without external compensation.
V_CE(sat)	0.3 V @ 50 mA - Low saturation voltage reduces conduction loss and self-heating in high-duty-cycle switch applications.
NF	5.0 dB @ 100 µA - Noise figure measured at audio/low-RF frequencies; supports low-noise preamp use in microphone or sensor signal chains.
R_θJA	200 °C/W - Junction-to-ambient thermal resistance on standard FR-4 board; informs heatsinking requirements for >150 mW average power.

Pinout & Package

2N4124TA is supplied in TO-92 plastic package (3-lead, through-hole), with standardized lead orientation: flat side facing viewer, leads down, left-to-right pin order = Emitter (E), Base (B), Collector (C).

Pin/Terminal	Circuit Role	Design Meaning
E (Emitter)	Current exit path for majority carriers	Connected to ground or low-impedance return; sets reference for V_BE biasing and emitter degeneration networks.
B (Base)	Control terminal for minority carrier injection	Receives current-limited drive (e.g., via 10 kΩ resistor); small-signal input impedance ~1–10 kΩ at 2 mA I_C.
C (Collector)	Current entry path and output node	Drives load to positive supply; requires pull-up or active load; voltage swing limited by V_CEO = 25 V rating.

Key Features

Feature	Design Value
High f_T bandwidth	300 MHz - Enables stable amplification up to VHF without neutralization or external compensation.
Low V_CE(sat)	0.3 V @ 50 mA - Minimizes power loss and thermal rise in saturated-switch configurations.
Wide operating temperature	–55°C to +150°C - Supports deployment in automotive under-hood, industrial PLC, and outdoor sensor enclosures.
Low noise performance	5.0 dB NF @ 100 µA - Suitable for analog front-ends where signal integrity dominates over power efficiency.
Controlled h_FE spread	120–360 - Allows predictable gain staging in multi-transistor amplifiers without individual binning.

Applications

Audio Pre-amplifier Stage	Industrial Sensor Signal Conditioning
Use Scenario: Amplifying low-level microphone or piezoelectric sensor outputs prior to ADC sampling in battery-powered data loggers. IC Role / Device Role / Timing Role: Small-signal NPN amplifier configured in common-emitter topology with emitter degeneration for linearity and stability. Use Value: 5.0 dB noise figure and 300 MHz f_T preserve SNR across 20 Hz–20 kHz while supporting anti-alias filtering up to 100 kHz.	Use Scenario: Converting 4–20 mA current-loop sensor outputs to 0–3.3 V logic-compatible voltage levels in factory-floor transmitters. IC Role / Device Role / Timing Role: Linear current-to-voltage converter using fixed emitter resistor and buffered output stage. Use Value: Tight h_FE spread (120–360) ensures consistent gain calibration across production batches without per-unit trimming.
Discrete Logic-Level Translator	Relay Driver Interface
Use Scenario: Shifting 5 V TTL signals to 12 V control rails for legacy industrial controllers interfacing with modern microcontrollers. IC Role / Device Role / Timing Role: Saturated switch in common-emitter configuration with base current limiting and collector pull-up. Use Value: V_CE(sat) ≤ 0.3 V ensures <100 mW dissipation at 50 mA, enabling direct drive without heatsink in space-constrained panels.	Use Scenario: Driving 12 V/400 mW electromagnetic relays from 3.3 V GPIO pins in HVAC control modules. IC Role / Device Role / Timing Role: High-gain (h_FE ≥ 120) saturated switch with flyback diode protection and fast turn-off (t_f < 500 ns). Use Value: 200 mA I_C rating and 100 MHz useful switching bandwidth support reliable relay actuation with <1 µs delay jitter.

Audio Pre-amplifier Stage

Industrial Sensor Signal Conditioning

Use Scenario: Amplifying low-level microphone or piezoelectric sensor outputs prior to ADC sampling in battery-powered data loggers.

IC Role / Device Role / Timing Role: Small-signal NPN amplifier configured in common-emitter topology with emitter degeneration for linearity and stability.

Use Value: 5.0 dB noise figure and 300 MHz f_T preserve SNR across 20 Hz–20 kHz while supporting anti-alias filtering up to 100 kHz.

Use Scenario: Converting 4–20 mA current-loop sensor outputs to 0–3.3 V logic-compatible voltage levels in factory-floor transmitters.

IC Role / Device Role / Timing Role: Linear current-to-voltage converter using fixed emitter resistor and buffered output stage.

Use Value: Tight h_FE spread (120–360) ensures consistent gain calibration across production batches without per-unit trimming.

Discrete Logic-Level Translator

Relay Driver Interface

Use Scenario: Shifting 5 V TTL signals to 12 V control rails for legacy industrial controllers interfacing with modern microcontrollers.

IC Role / Device Role / Timing Role: Saturated switch in common-emitter configuration with base current limiting and collector pull-up.

Use Value: V_CE(sat) ≤ 0.3 V ensures <100 mW dissipation at 50 mA, enabling direct drive without heatsink in space-constrained panels.

Use Scenario: Driving 12 V/400 mW electromagnetic relays from 3.3 V GPIO pins in HVAC control modules.

IC Role / Device Role / Timing Role: High-gain (h_FE ≥ 120) saturated switch with flyback diode protection and fast turn-off (t_f < 500 ns).

Use Value: 200 mA I_C rating and 100 MHz useful switching bandwidth support reliable relay actuation with <1 µs delay jitter.

Equivalent & Alternatives

The following parts are listed as comparable options for similar NPN general-purpose amplifier applications.

Alternative Part	Technical Difference	Application Difference	Selection Advice
MMBT4124	SOT-23 surface-mount package; identical electrical specs (V_CEO, h_FE, f_T, V_CE(sat)); R_θJA = 357 °C/W.	Requires rework for PCB layout; better suited for automated assembly and space-constrained designs.	Select MMBT4124 when footprint miniaturization and pick-and-place compatibility outweigh thermal derating penalties.
2N2222A	Higher V_CEO (40 V), lower f_T (250 MHz), wider h_FE spread (100–300); same TO-92 package.	Preferred in higher-voltage switching (e.g., 24 V solenoids); less optimal for >50 MHz amplification.	Choose 2N2222A only when V_CEO > 25 V is mandatory and RF bandwidth is secondary.

Compared with MMBT4124 and 2N2222A, the 2N4124TA offers the best balance of RF bandwidth (300 MHz), low-noise operation (5.0 dB), and through-hole manufacturability - making it ideal for prototyping, repair, and medium-volume industrial control boards where thermal margin and ease of hand-soldering are prioritized.

Availability

2N4124TA is available at Aetrix Electronics and suitable for industrial sensor interfaces, audio pre-amplifier stages, and relay driver circuits requiring stable component supply and long-term obsolescence management.

Supply support for 2N4124TA 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

Fairchild Semiconductor was a U.S.-based semiconductor company specializing in power management, analog, and discrete components before its acquisition by ON Semiconductor in 2016; its legacy BJT portfolio remains widely deployed in industrial and automotive systems.

The 2N4124TA belongs to Fairchild's general-purpose NPN transistor product line, engineered for robustness in mixed-signal interface and analog signal chain applications where reliability, temperature resilience, and predictable gain behavior are essential.

FAQ

What is the maximum continuous collector current rating for the 2N4124TA?

The 2N4124TA has a maximum continuous collector current (I_C) rating of 200 mA at T_A = 25°C. This rating assumes proper PCB thermal relief (1.6" × 1.6" FR-4) and derates linearly by 5.0 mW/°C above 25°C ambient. Exceeding this current without adequate heat sinking risks junction overheating beyond the 150°C limit.

Does the 2N4124TA support RF amplification up to 100 MHz?

Yes - the 2N4124TA is characterized for useful dynamic range up to 100 MHz as an amplifier, and its f_T is specified at 300 MHz (IC = 10 mA, V_CE = 20 V). This confirms stable small-signal gain well into the VHF band, making it suitable for tuned RF pre-amplifiers and local oscillator buffers below 150 MHz.

What is the typical noise figure of the 2N4124TA and under what conditions is it measured?

The 2N4124TA has a typical noise figure (NF) of 5.0 dB, measured at I_C = 100 µA, V_CE = 5.0 V, R_S = 1.0 kΩ, and frequency range 10 Hz to 15.7 kHz. This low-noise performance makes it appropriate for microphone pre-amplifiers and precision sensor signal conditioning where signal integrity is critical.

Can the 2N4124TA be used as a saturated switch in digital logic circuits?

Yes - the 2N4124TA is explicitly designed for switching applications, with V_CE(sat) = 0.3 V at I_C = 50 mA and I_B = 5.0 mA. Its fast turn-on (<100 ns), rise (<500 ns), and fall times (<500 ns) support reliable operation in 100 kHz–1 MHz digital interface circuits, including level translation and relay driving.

What is the operating junction temperature range for the 2N4124TA?

The 2N4124TA is rated for a junction temperature range of –55°C to +150°C. This wide range enables use in harsh environments such as automotive engine compartments, industrial motor controls, and outdoor instrumentation - provided PCB layout and power dissipation remain within thermal limits defined by R_θJA = 200 °C/W.

2N4124TA Specifications

Product attributes: Attribute value

Manufacturer:: onsemi

Series:: -

Package/Case:: TO-226-3, TO-92-3 (TO-226AA) Formed Leads

Packaging:: Tape & Box (TB)

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:: 625 mW

Frequency - Transition:: 300MHz

Operating Temperature:: -55°C ~ 150°C (TJ)

Grade:: -

Qualification:: -

Mounting Type:: Through Hole

Supplier Device Package:: TO-92-3

2N4124TA FAQ

1.How can I place an order for 2N4124TA through Aetrix?

Please submit a Request for Quotation (RFQ) for 2N4124TA 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 2N4124TA reliable?

The price and inventory of 2N4124TA are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for 2N4124TA is usually 5 days.

3.What payment methods are accepted for 2N4124TA?

We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for 2N4124TA transactions.

Note: Certain payment methods may incur a processing fee.

4.How is shipping managed for 2N4124TA?

2N4124TA orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.

Once your 2N4124TA 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 2N4124TA?

For technical support, including 2N4124TA datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your 2N4124TA requirements.

6.How does Aetrix verify that 2N4124TA is sourced from the original manufacturer or authorized distributors?

All 2N4124TA 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 2N4124TA meets industry standards.

7.What is the process for return or replacement of 2N4124TA?

All 2N4124TA units undergo pre-shipment inspection (PSI). If there is an issue with 2N4124TA, 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 2N4124TA part is unused and in its original packaging.

Return procedure for 2N4124TA:

1.Submit a request within 90 days.

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

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