onsemi 2N3903

Overview

2N3903 from Fairchild Semiconductor is an NPN general-purpose bipolar junction transistor (BJT) designed for low-power amplification and switching applications up to 100 mA collector current. It features a V_CEO of 40 V, V_CBO of 60 V, and operates across –55°C to +150°C. Its h_FE ranges from 20 to 150 depending on bias conditions, and it is packaged in TO-92 for through-hole prototyping and industrial control circuits.

For engineers reviewing the 2N3903 datasheet, pinout, applications, or equivalent options, key selection criteria include DC current gain at multiple operating points, saturation voltage under defined I_C/I_B, thermal resistance (R_θJA = 200°C/W), noise figure (6.0 dB at 100 µA), and switching times (t_d = 35 ns, t_s = 175 ns).

Technical Context

The 2N3903 operates as a discrete NPN BJT with fixed-emitter configuration and base-controlled conduction. Its small-signal h_fe reaches 200 at 1 mA and 50 MHz, while its output admittance (h_oe) spans 1–40 µmhos and input impedance (h_ie) ranges from 1.0–8.0 kΩ at 1 kHz - enabling predictable linear amplification in audio preamp and signal conditioning stages.

Switching behavior is characterized by storage time (t_s = 175 ns) and fall time (t_f = 50 ns) under pulsed 3 V/10 mA test conditions. Thermal design requires attention to derating: 5.0 mW/°C above 25°C ambient, with R_θJC = 83.3°C/W and maximum P_D = 625 mW at T_A = 25°C.

Key Specifications

Pinout & Package

2N3903 is housed in a standard TO-92 plastic package with 3 leads. The package has a flat side facing the viewer, with leads arranged left-to-right as Emitter (E), Base (B), Collector (C) when viewed from the flat side with leads pointing downward.

Key Features

Applications

Equivalent & Alternatives

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

Compared with 2N2222A and BC547B, the 2N3903 offers the best balance of low noise (6.0 dB), moderate gain stability (50–150 h_FE over 0.1–100 mA), and tight V_CE(sat) spec - making it uniquely suitable for precision analog switching and low-level amplification where both linearity and thermal predictability matter.

Availability

2N3903 is available at Aetrix Electronics and suitable for audio pre-amplifiers, industrial control logic interfaces, linear regulator pass elements, and signal level-shifting circuits requiring stable component supply and long-term obsolescence management.

Supply support for 2N3903 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 2N3903 belongs to Fairchild's general-purpose NPN transistor family, engineered for reliability in amplification and switching roles across commercial and extended temperature environments - particularly where low noise, repeatable h_FE, and TO-92 mechanical compatibility are prioritized.

FAQ

What is the maximum continuous collector current rating for the 2N3903?

The 2N3903 has an absolute maximum continuous collector current (I_C) rating of 200 mA at T_A = 25°C. However, the device is functionally specified for general-purpose amplification and switching up to 100 mA, ensuring margin for thermal stability and long-term reliability. Derating applies above 25°C ambient per the 5.0 mW/°C thermal coefficient.

Does the 2N3903 have a documented noise figure, and under what conditions is it measured?

Yes, the 2N3903 has a specified noise figure of 6.0 dB, measured at V_CE = 5.0 V, I_C = 100 µA, R_S = 1.0 kΩ, and bandwidth from 10 Hz to 15.7 kHz. This value reflects its suitability for low-noise pre-amplifier applications, especially in sensor interface and audio front-end designs where signal integrity is critical.

What are the key differences between the 2N3903 and the 2N2222A in terms of DC current gain and switching performance?

The 2N3903 specifies h_FE ≥ 50 at I_C = 10 mA, whereas the 2N2222A guarantees only h_FE ≥ 35 under the same condition. In switching, the 2N3903 shows lower output capacitance (C_ob = 4.0 pF vs. 8.0 pF) and faster storage time (t_s = 175 ns vs. ~225 ns typical for 2N2222A), giving it an advantage in low-noise, medium-speed digital interfacing.

Is the 2N3903 available in surface-mount packages, or is it TO-92 only?

The 2N3903 is exclusively offered in the through-hole TO-92 package per Fairchild's original datasheet and packaging documentation. No official SMT variants (e.g., SOT-23 or SOT-223) were released for this specific part number. Designers requiring surface-mount compatibility must select alternatives like the MMBT3903 or PZT3903, which are not direct replacements but share similar electrical characteristics.

How does the thermal resistance of the 2N3903 affect its power dissipation capability in real-world PCB layouts?

The 2N3903 has R_θJA = 200°C/W in free-air, meaning a 625 mW dissipation raises junction temperature by 125°C above ambient. On a standard FR-4 PCB with minimal copper, actual R_θJA may improve to ~150°C/W - allowing ~830 mW before hitting 150°C T_J. For sustained operation >300 mW, thermal relief pads or local copper pours are recommended to avoid exceeding the 150°C maximum junction temperature.