onsemi 2N3904_D81Z

Overview

2N3904_D81Z from ON Semiconductor is a silicon NPN general-purpose bipolar junction transistor used for low-power amplification and switching in discrete analog and digital circuits. It delivers DC current gain (h_FE) of 70–300 at I_C = 1.0 mA, V_CE = 1.0 V; supports 100 MHz current-gain bandwidth (f_T); and operates with V_CEO = 40 V, I_C = 200 mA continuous, in TO-92 package - widely deployed in signal conditioning stages of sensor interfaces and microcontroller GPIO drivers.

For engineers reviewing the 2N3904_D81Z datasheet, pinout, applications, or equivalent options, this page provides verified electrical specifications, thermal derating data, switching timing parameters (t_d, t_r, t_s, t_f), noise figure (5.0 dB @ 10 Hz–15.7 kHz), and real-world application context for discrete BJT selection in cost-sensitive, low-voltage embedded systems.

Technical Context

The 2N3904_D81Z implements a planar epitaxial NPN structure optimized for high-speed switching and linear amplification up to 100 MHz. Its base-emitter junction exhibits V_BE(sat) = 0.65–0.85 V at I_C = 10 mA/I_B = 1.0 mA, while collector-emitter saturation voltage remains ≤0.2 V under same conditions - enabling efficient low-side switch operation with minimal conduction loss.

Thermal design relies on R_θJA = 200°C/W (TO-92, FR-4 PCB), with total power dissipation rated at 625 mW at 25°C ambient and derated by 5.0 mW/°C above that temperature. The device supports pulsed operation per Fairchild's test conditions (pulse width ≤300 μs, duty cycle ≤2.0%), and its C_obo = 4.0 pF and C_ibo = 8.0 pF support stable high-frequency biasing in RF preamp stages.

Key Specifications

Pinout & Package

2N3904_D81Z is packaged in TO-92 (3-lead plastic case), with standardized E-B-C (Emitter-Base-Collector) terminal arrangement viewed from flat side with leads downward. Pin assignment follows JEDEC TO-92 outline: lead 1 = Emitter, lead 2 = Base, lead 3 = Collector.

Key Features

Applications

Equivalent & Alternatives

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

Compared with MMBT3904 and PZT3904, the 2N3904_D81Z offers optimal balance of manufacturability, thermal margin, and legacy design compatibility - delivering full-spec performance in the industry-standard TO-92 form factor without SMT rework or thermal derating compromises.

Availability

2N3904_D81Z is available at Aetrix Electronics and suitable for audio signal conditioning, microcontroller peripheral interfacing, discrete oscillator circuits, and low-power linear regulation requiring stable component supply across prototyping, pilot production, and long-life industrial programs.

Supply support for 2N3904_D81Z 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

ON Semiconductor is a global semiconductor manufacturer specializing in energy-efficient power management, analog, sensing, and connectivity solutions for automotive, industrial, cloud, and consumer markets.

The 2N3904_D81Z belongs to ON Semiconductor's legacy general-purpose bipolar transistor product line - designed for broad applicability in discrete analog signal chains, cost-sensitive switching, and educational/prototyping platforms where reliability and second-source availability are essential.

FAQ

What is the maximum collector-emitter voltage rating for the 2N3904_D81Z?

The 2N3904_D81Z has a V_CEO rating of 40 V, meaning it can safely withstand up to 40 volts between collector and emitter with base open. This rating applies under DC or pulsed conditions per datasheet test conditions (pulse width ≤300 μs, duty cycle ≤2.0%). Exceeding this voltage risks avalanche breakdown and permanent damage to the 2N3904_D81Z.

Does the 2N3904_D81Z support high-frequency amplification?

Yes, the 2N3904_D81Z delivers a current-gain bandwidth product (f_T) of 300 MHz at I_C = 10 mA and V_CE = 20 V, confirming usable small-signal gain up to approximately 100 MHz. Its C_obo = 4.0 pF and C_ibo = 8.0 pF further support stable high-frequency biasing - making the 2N3904_D81Z suitable for RF preamplifiers, oscillator cores, and wideband audio stages.

What is the typical DC current gain (h_FE) of the 2N3904_D81Z at 10 mA collector current?

At I_C = 10 mA and V_CE = 1.0 V, the 2N3904_D81Z exhibits h_FE = 100–300 per datasheet specifications. This range reflects process variation across units and ensures sufficient gain margin for reliable biasing in both switching and linear modes - a key design parameter when calculating base resistor values for the 2N3904_D81Z in any application.

Can the 2N3904_D81Z be used as a saturated switch in digital logic circuits?

Yes, the 2N3904_D81Z is routinely used as a saturated NPN switch in TTL/CMOS interface circuits. With I_B ≥ I_C/10 (e.g., 1 mA base drive for 10 mA collector load), it achieves V_CE(sat) ≤ 0.2 V and t_s = 200 ns - enabling fast, low-loss switching in LED drivers, relay controls, and level-shifting applications. Its robust SOA ensures reliability in repetitive digital switching when operated within I_C ≤ 200 mA limits.

What is the thermal resistance (R_θJA) of the 2N3904_D81Z in its TO-92 package?

The 2N3904_D81Z has a junction-to-ambient thermal resistance (R_θJA) of 200°C/W when mounted on a standard 1.6″ × 1.6″ FR-4 PCB per JEDEC JESD51-2. This value assumes no added heatsinking and defines the temperature rise above ambient per watt dissipated - critical for validating safe operating area in linear regulator or high-duty-cycle switching applications using the 2N3904_D81Z.