onsemi 2N4124

Overview

2N4124 from Motorola is an NPN silicon small-signal transistor optimized for general-purpose amplification and switching in low-power analog and digital circuits. It features V_CEO = 25 V, I_C = 200 mA, h_FE = 25–360 (at I_C = 2–50 mA), f_T = 300 MHz, and V_CE(sat) ≤ 0.3 V - enabling reliable operation in audio preamps, pulse generators, and logic interface stages.

For engineers reviewing the 2N4124 datasheet, pinout, applications, or equivalent options, key selection criteria include its TO-92 package compatibility, DC current gain range across operating currents, saturation voltage at I_C/I_B = 10, thermal resistance (R_JA = 200 °C/W), and noise figure of 5.0 dB at 1 kHz with 100 µA I_C.

Technical Context

The 2N4124 operates as a discrete bipolar junction transistor with fixed-emitter configuration and base-controlled conduction. Its h_FE varies from 25 (min at I_C = 50 mA) to 360 (max at I_C = 2 mA), supporting both linear amplification and saturated switching modes. The device exhibits f_T = 300 MHz and C_ibo = 8.0 pF, indicating suitability for RF-coupled signal paths up to VHF.

Thermal design relies on R_JC = 83.3 °C/W and R_JA = 200 °C/W, with maximum junction temperature rated at +150°C. Electrical safety margins include V_(BR)CBO = 30 V and V_(BR)EBO = 5.0 V, limiting reverse-bias stress in common-emitter and common-base configurations.

Key Specifications

Pinout & Package

2N4124 is housed in a TO-92 (CASE 29–04, STYLE 1) plastic package with 3 leads. Pin 1 is Emitter, Pin 2 is Base, Pin 3 is Collector - verified per Motorola's official device data sheet and mechanical drawing.

Key Features

Applications

Equivalent & Alternatives

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

Compared with BC547B and PN2222A, the 2N4124 offers the lowest V_CEO but best noise figure (5.0 dB) and widest h_FE range - making it optimal for low-noise, low-voltage analog gain stages where precision biasing is less critical than signal integrity.

Availability

2N4124 is available at Aetrix Electronics and suitable for audio pre-amplifiers, pulse generators, logic level translators, and DC power switches requiring stable component supply across industrial, instrumentation, and legacy design refresh programs.

Supply support for 2N4124 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

Motorola Semiconductor (now part of ON Semiconductor) was a pioneering U.S. semiconductor manufacturer known for high-reliability discrete devices and early integrated circuits.

The 2N4124 belongs to Motorola's legacy 2N-series small-signal transistor family, designed specifically for cost-sensitive, high-volume analog and digital interface applications in consumer, industrial, and communications equipment.

FAQ

What is the maximum collector-emitter voltage rating for the 2N4124?

The 2N4124 has a maximum collector-emitter voltage rating (V_CEO) of 25 Vdc under open-base conditions. This value is confirmed in Motorola's official device data sheet and defines the absolute maximum voltage that can be applied between collector and emitter before breakdown occurs. Exceeding this rating risks permanent device failure. Designers should maintain at least 20% derating margin in production circuits to ensure long-term reliability.

Does the 2N4124 have a specified noise figure, and under what conditions?

Yes, the 2N4124 has a specified noise figure of 5.0 dB, measured at I_C = 100 µAdc, V_CE = 5.0 Vdc, f = 1.0 kHz, and bandwidth = 1.0 Hz. This parameter is documented in Motorola's "AUDIO SMALL–SIGNAL CHARACTERISTICS" section and confirms the device's suitability for low-noise pre-amplification tasks. The 2N4124's noise performance is superior to many general-purpose transistors in its class, making it appropriate for microphone and sensor signal conditioning where SNR preservation is critical.

What is the DC current gain (h_FE) range for the 2N4124, and how does it vary with operating conditions?

The 2N4124 exhibits a DC current gain (h_FE) range of 25 to 360, depending on collector current and test conditions. At I_C = 50 mAdc and V_CE = 1.0 Vdc, h_FE is specified as 25 (min) to 60 (max); at I_C = 2.0 mAdc and same V_CE, it rises to 120 (min) to 360 (max). This wide variation is inherent to bipolar transistor physics and must be accounted for in bias network design. The 2N4124's h_FE curve is validated across –55°C to +150°C in Motorola's Figure 9.

What package type and pin configuration does the 2N4124 use?

The 2N4124 uses a TO-92 plastic package (CASE 29–04, STYLE 1) with three leads arranged in a straight-line configuration. Pin 1 is Emitter, Pin 2 is Base, and Pin 3 is Collector - as explicitly defined in Motorola's mechanical drawing and device data sheet. This pinout is consistent across all 2N412x series transistors and is compatible with standard TO-92 sockets and PCB footprints used in legacy and modern through-hole assemblies.

Can the 2N4124 be used in RF amplifier applications, and what is its transition frequency?

Yes, the 2N4124 is qualified for RF amplifier use with a transition frequency (f_T) of 300 MHz, measured at I_C = 10 mAdc, V_CE = 20 Vdc, and f = 100 MHz. This specification confirms usable small-signal gain up to approximately 100 MHz in properly matched common-emitter configurations. While not optimized for microwave frequencies, the 2N4124's f_T and low C_ibo (8.0 pF) support stable VHF oscillator and broadband amplifier designs found in amateur radio, test equipment, and wireless sensor transmitters.