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

onsemi 2N4123TAR

Name: 2N4123TAR
Brand: onsemi
SKU: 2N4123TAR
Price: 2.40 USD
Availability: InStock
Rating: 5 (2 reviews)

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Part No.:: 2N4123TAR

Manufacturer:: onsemi

Category:: Single Bipolar Transistors

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

Datasheet:: 2N4123TAR.pdf

Description:: TRANS NPN 30V 0.2A TO-92-3

Quantity:: RFQ Add To RFQ list

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Product details

Overview

2N4123TAR from Fairchild Semiconductor is an NPN general-purpose bipolar junction transistor (BJT) designed for low-to-medium current amplification and switching applications up to 100 mA collector current. It features a V_CEO of 30 V, V_CBO of 40 V, and h_FE ranging from 50 to 150 at I_C = 2.0 mA, with f_T = 250 MHz - suitable for audio preamplifiers, signal buffering, and digital logic interface circuits.

For engineers reviewing the 2N4123TAR datasheet, pinout, applications, or equivalent options, key selection considerations include its TO-92 package thermal resistance (R_θJA = 200 °C/W), saturation voltage (V_CE(sat) = 0.3 V @ I_C = 50 mA), noise figure (6.0 dB @ 100 µA), and guaranteed h_FE minimum across operating temperature range.

Technical Context

The 2N4123TAR operates as a standard NPN BJT with fixed-emitter biasing capability and exhibits predictable DC current gain (h_FE) over I_C = 0.1–100 mA and T_A = –55°C to +150°C. Its small-signal parameters - including h_fe = 50–200, C_ob = 4.0 pF, and f_T = 250 MHz - support mid-frequency analog amplification and fast-switching behavior in linear and saturated modes.

Thermal design is constrained by R_θJA = 200 °C/W and P_D = 625 mW at 25°C, derating linearly at 5.0 mW/°C above ambient. The device's low V_BE(sat) = 0.95 V and tight V_(BR)CEO distribution (min 30 V) enable reliable operation in battery-powered and rail-limited circuits without external compensation.

Key Specifications

Parameter	Value and Actual Design Meaning
V_CEO	30 V - Maximum safe collector-emitter voltage before breakdown; defines upper rail limit in common-emitter amplifier stages.
I_C (max)	200 mA - Continuous collector current rating; supports switching loads up to ~100 mA with margin under typical PCB layout conditions.
h_FE	50–150 - DC current gain at V_CE = 1.0 V; enables stable biasing in Class-A amplifiers and emitter-follower buffers.
f_T	250 MHz - Unity-gain bandwidth; permits use in RF front-end stages up to ~50 MHz with adequate gain margin.
NF	6.0 dB - Noise figure at 100 µA, 1 kHz–15.7 kHz BW; suitable for low-noise preamplification in sensor interfaces and audio inputs.
R_θJA	200 °C/W - Junction-to-ambient thermal resistance in TO-92; requires minimal copper area for thermal management in non-high-power applications.
V_CE(sat)	0.3 V @ I_C/I_B = 50 mA/5 mA - Low saturation voltage reduces conduction loss in digital switching and relay driver circuits.

Pinout & Package

2N4123TAR is housed in a through-hole TO-92 package with standard three-terminal configuration. Lead spacing and body dimensions comply with JEDEC TO-92 outline (4.57 mm × 3.05 mm × 4.06 mm), enabling compatibility with legacy through-hole assembly processes and manual prototyping.

Pin/Terminal	Circuit Role	Design Meaning
E (Emitter)	Current sink terminal	Reference node for bias network; connects to ground or low-impedance return path in common-emitter configurations.
B (Base)	Control input terminal	Receives forward-biased current to modulate collector current; requires series resistor for current limiting in digital drive applications.
C (Collector)	Current source terminal	Delivers amplified output current; connects to load or next-stage input; must remain within V_CEO and power dissipation limits.

Key Features

Feature	Design Value
Guaranteed h_FE range	50–150 at I_C = 2.0 mA ensures consistent bias point stability across production lots in amplifier designs.
Low V_CE(sat)	0.3 V enables efficient switching in 5 V logic-controlled loads with <150 mW conduction loss at 50 mA.
High f_T	250 MHz supports broadband analog gain stages and pulse amplification up to 50 MHz without external compensation.
Wide T_J range	–55°C to +150°C junction operation allows deployment in automotive under-hood and industrial control environments.
Low noise figure	6.0 dB at 100 µA makes it viable for microphone preamps and precision sensor signal conditioning where SNR > 60 dB is required.

Applications

Audio Preamp Stage	Digital Logic Interface
Use Scenario: Amplifying weak signals from electret microphones or piezoelectric sensors in portable audio recorders. IC Role / Device Role / Timing Role: NPN BJT configured in common-emitter topology providing 20–40 dB voltage gain with minimal added noise. Use Value: Achieves 6.0 dB noise figure and h_FE-stabilized biasing to maintain SNR > 62 dB across temperature and supply variation.	Use Scenario: Level-shifting and current boosting between 3.3 V microcontroller GPIO and 5 V TTL-compatible peripherals. IC Role / Device Role / Timing Role: Switching transistor operating in saturation mode to drive LED indicators or optocoupler inputs. Use Value: Delivers reliable on/off control with V_CE(sat) ≤ 0.3 V and t_r/t_f < 50 ns, minimizing transition losses in 1–10 kHz digital signaling.
DC Motor Driver (Small)	Signal Buffering
Use Scenario: Driving miniature 3–6 V brushed DC motors in robotics or actuator modules using PWM from MCU outputs. IC Role / Device Role / Timing Role: Low-side switch controlling motor current path to ground with base-driven saturation. Use Value: Handles 100 mA continuous motor current with P_D margin and thermal stability up to 125°C ambient.	Use Scenario: Isolating and impedance-matching between high-output-impedance sensor nodes and ADC input stages. IC Role / Device Role / Timing Role: Emitter-follower configured for unity-gain voltage buffering with low output impedance. Use Value: Provides h_ie > 1 kΩ input impedance and <50 Ω output impedance, reducing loading effects on sensitive analog sources.

Audio Preamp Stage

Digital Logic Interface

Use Scenario: Amplifying weak signals from electret microphones or piezoelectric sensors in portable audio recorders.

IC Role / Device Role / Timing Role: NPN BJT configured in common-emitter topology providing 20–40 dB voltage gain with minimal added noise.

Use Value: Achieves 6.0 dB noise figure and h_FE-stabilized biasing to maintain SNR > 62 dB across temperature and supply variation.

Use Scenario: Level-shifting and current boosting between 3.3 V microcontroller GPIO and 5 V TTL-compatible peripherals.

IC Role / Device Role / Timing Role: Switching transistor operating in saturation mode to drive LED indicators or optocoupler inputs.

Use Value: Delivers reliable on/off control with V_CE(sat) ≤ 0.3 V and t_r/t_f < 50 ns, minimizing transition losses in 1–10 kHz digital signaling.

DC Motor Driver (Small)

Signal Buffering

Use Scenario: Driving miniature 3–6 V brushed DC motors in robotics or actuator modules using PWM from MCU outputs.

IC Role / Device Role / Timing Role: Low-side switch controlling motor current path to ground with base-driven saturation.

Use Value: Handles 100 mA continuous motor current with P_D margin and thermal stability up to 125°C ambient.

Use Scenario: Isolating and impedance-matching between high-output-impedance sensor nodes and ADC input stages.

IC Role / Device Role / Timing Role: Emitter-follower configured for unity-gain voltage buffering with low output impedance.

Use Value: Provides h_ie > 1 kΩ input impedance and <50 Ω output impedance, reducing loading effects on sensitive analog sources.

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
PN2222A	V_CEO = 40 V (higher), h_FE min = 100 @ I_C = 10 mA, R_θJA = 200 °C/W same	Better suited for higher-voltage switching; slightly higher gain uniformity at medium currents	Select when V_CC > 30 V or tighter h_FE spread is required; identical TO-92 footprint.
BC547B	V_CEO = 45 V, h_FE = 200–450, P_D = 500 mW (lower), f_T = 300 MHz	Higher gain and frequency response but lower power handling; optimized for low-current signal paths	Prefer for low-noise, high-gain preamp stages below 50 mA; verify thermal margin in sustained conduction.

Compared with PN2222A and BC547B, the 2N4123TAR offers balanced performance across voltage rating, gain linearity, and thermal robustness - making it ideal for cost-sensitive, moderate-speed general-purpose designs where 30 V operation and 200 mA peak current are sufficient.

Availability

2N4123TAR is available at Aetrix Electronics and suitable for audio preamplifiers, digital logic interface circuits, and small DC motor drivers requiring stable component supply and long-term obsolescence management.

Supply support for 2N4123TAR 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 consumer systems.

The 2N4123TAR belongs to Fairchild's general-purpose NPN transistor family, engineered for reliability and consistency in amplification and switching roles across commercial and industrial temperature ranges.

FAQ

What is the maximum collector current rating for the 2N4123TAR?

The 2N4123TAR has a maximum continuous collector current (I_C) rating of 200 mA at T_A = 25°C. Derating applies above this temperature per the specified 5.0 mW/°C thermal coefficient. For reliable switching operation, design practice limits sustained I_C to ≤100 mA to maintain margin against thermal runaway and ensure long-term reliability in TO-92 packaging.

Does the 2N4123TAR support audio-frequency amplification?

Yes, the 2N4123TAR supports audio-frequency amplification with verified performance up to 20 kHz. Its noise figure of 6.0 dB at 100 µA and h_fe ≥ 50 at 1 kHz make it suitable for microphone preamplifiers and line-level buffers. The device's f_T = 250 MHz provides ample gain-bandwidth headroom, and typical distortion remains below 0.5% THD at 1 kHz with proper biasing.

What is the pin configuration of the 2N4123TAR in TO-92 package?

The 2N4123TAR uses standard TO-92 pinout: viewed from the flat side with leads pointing downward, left-to-right is Emitter (E), Base (B), Collector (C). This matches JEDEC TO-92 outline and is compatible with PN2222A and other industry-standard NPN transistors. No alternate pinouts are documented for this part number.

Is the 2N4123TAR RoHS compliant?

Yes, the 2N4123TAR is RoHS compliant per EU Directive 2011/65/EU. Fairchild's original documentation confirms lead-free terminations and halogen-free molding compound. Aetrix Electronics supplies only RoHS-compliant batches with full material declarations available upon request for compliance validation in medical and industrial end equipment.

Can the 2N4123TAR replace the 2N2222 in existing designs?

The 2N4123TAR can serve as a functional alternative to the 2N2222 in many low-power amplifier and switching applications, but direct substitution requires verification. While both share TO-92 packaging and NPN topology, the 2N4123TAR has lower V_CEO (30 V vs. 40 V) and different h_FE distribution. Review circuit voltage margins and gain stability requirements before replacement.

2N4123TAR 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):: 30 V

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

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

DC Current Gain (hFE) (Min) @ Ic, Vce:: 50 @ 2mA, 1V

Power - Max:: 625 mW

Frequency - Transition:: 250MHz

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

Grade:: -

Qualification:: -

Mounting Type:: Through Hole

Supplier Device Package:: TO-92-3

2N4123TAR FAQ

1.How can I place an order for 2N4123TAR through Aetrix?

Please submit a Request for Quotation (RFQ) for 2N4123TAR 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 2N4123TAR reliable?

The price and inventory of 2N4123TAR are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for 2N4123TAR is usually 5 days.

3.What payment methods are accepted for 2N4123TAR?

We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for 2N4123TAR transactions.

Note: Certain payment methods may incur a processing fee.

4.How is shipping managed for 2N4123TAR?

2N4123TAR orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.

Once your 2N4123TAR 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 2N4123TAR?

For technical support, including 2N4123TAR datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your 2N4123TAR requirements.

6.How does Aetrix verify that 2N4123TAR is sourced from the original manufacturer or authorized distributors?

All 2N4123TAR 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 2N4123TAR meets industry standards.

7.What is the process for return or replacement of 2N4123TAR?

All 2N4123TAR units undergo pre-shipment inspection (PSI). If there is an issue with 2N4123TAR, 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 2N4123TAR part is unused and in its original packaging.

Return procedure for 2N4123TAR:

1.Submit a request within 90 days.

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

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