onsemi 2N3905TFR

Overview

2N3905TFR from Fairchild Semiconductor is a PNP general-purpose bipolar junction transistor used for low-power amplification and switching in discrete analog and digital circuits, with V_CEO = 40 V, I_C = 200 mA continuous, h_FE ≥ 30 at I_C = 0.1 mA, and TO-92 package. It operates across –55°C to +150°C and supports applications such as signal inversion, level shifting, and load switching in consumer and industrial control boards.

For engineers reviewing the 2N3905TFR datasheet, pinout, applications, or equivalent options, key selection criteria include its PNP polarity, DC current gain range (30–150), saturation voltage (V_CE(sat) ≤ 0.40 V at I_C = 50 mA), thermal resistance (R_θJA = 200 °C/W), and compatibility with through-hole prototyping and legacy PCB layouts.

Technical Context

The 2N3905TFR functions as a silicon PNP BJT with fixed-emitter biasing capability and operates in active, saturation, and cutoff regions depending on base drive. Its small-signal h_fe reaches 200 at I_C = 1.0 mA and f = 100 MHz, while noise figure is 5.0 dB at 100 µA and 1 kHz bandwidth - confirming suitability for low-noise preamplifier stages.

Switching performance is characterized by t_d = 35 ns, t_r = 35 ns, t_s = 200 ns, and t_f = 60 ns under pulsed conditions (≤300 µs, ≤2% duty cycle), enabling use in moderate-speed logic interface and relay driver circuits where propagation delay and storage time are design-critical.

Key Specifications

Pinout & Package

2N3905TFR is housed in a TO-92 plastic package with standard three-terminal configuration: emitter, base, and collector arranged in linear pin order (E-B-C when viewed with flat side facing outward and leads downward). The package supports manual soldering, wave soldering, and socket-based prototyping.

Key Features

Applications

Equivalent & Alternatives

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

Compared with MPSA56 and BC557, the 2N3905TFR offers tighter h_FE consistency at low currents, lower noise, and superior thermal stability - making it preferred for precision bias networks and low-level analog signal paths where repeatability matters.

Availability

2N3905TFR is available at Aetrix Electronics and suitable for audio signal inversion, discrete logic level shifting, and relay driver interface applications requiring stable component supply, long-term obsolescence management, and consistent parametric performance across manufacturing lots.

Supply support for 2N3905TFR 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.

The 2N3905TFR belongs to Fairchild's legacy general-purpose transistor family, designed specifically for cost-effective, reliable amplification and switching in non-critical analog and digital subsystems.

FAQ

What is the maximum collector-emitter voltage rating for the 2N3905TFR?

The 2N3905TFR has a maximum collector-emitter voltage (V_CEO) rating of 40 V at T_A = 25°C. This value remains valid up to +125°C ambient, but designers must verify derated voltage limits per application-specific thermal conditions. Exceeding 40 V risks irreversible avalanche breakdown and permanent device failure. The 2N3905TFR datasheet specifies this as an absolute maximum rating, not a recommended operating condition.

Does the 2N3905TFR support surface-mount assembly?

No, the 2N3905TFR uses a through-hole TO-92 package and is not compatible with standard SMT reflow or pick-and-place processes. It requires axial or radial lead insertion and wave or hand soldering. For surface-mount equivalents, consider SOT-23-packaged PNP transistors like the MMBT3906, but note that those differ in pinout, thermal performance, and gain characteristics versus the 2N3905TFR.

What is the typical noise figure of the 2N3905TFR and under what conditions is it measured?

The 2N3905TFR exhibits a typical noise figure (NF) of 5.0 dB when 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 is confirmed in Fairchild's official datasheet Rev A and reflects performance in low-current, low-frequency small-signal amplification - making the 2N3905TFR suitable for microphone preamplifiers and sensor front-ends where noise minimization is critical.

Can the 2N3905TFR be used in switching applications above 100 kHz?

The 2N3905TFR achieves usable switching performance up to approximately 100 kHz in resistive-load applications, based on its specified t_d = 35 ns, t_r = 35 ns, t_s = 200 ns, and t_f = 60 ns under pulsed test conditions. However, storage time (t_s) dominates at higher frequencies, limiting efficiency in PWM-driven inductive loads. For >200 kHz switching, the 2N3905TFR is not recommended; instead, consider RF-optimized or Schottky-clamped PNP devices.

How does the DC current gain (h_FE) of the 2N3905TFR vary with collector current?

The 2N3905TFR's h_FE peaks near 10–20 mA (typically 100–150), decreases to ~50 at I_C = 100 mA, and drops to ≥30 at I_C = 0.1 mA - as verified in the "Typical Pulsed Current Gain vs Collector Current" graph in the Fairchild datasheet. This non-linear behavior must be accounted for in bias design; the 2N3905TFR performs best in mid-range I_C (1–50 mA) for stable amplification and switching.