onsemi 2N3859A

Overview

2N3859A from Fairchild Semiconductor is an NPN epitaxial silicon transistor designed for general-purpose amplification and switching in low-to-medium power circuits, with V_CEO = 60 V, I_C = 500 mA continuous, h_FE = 75–200 at 1 mA/1 V, f_T = 90–250 MHz, and TO-92 package. It serves as a discrete gain stage or saturated switch in audio preamps, signal routing, and relay drivers.

For engineers reviewing the 2N3859A datasheet, pinout, applications, or equivalent options, key selection considerations include its DC current gain range, 60 V breakdown rating, thermal resistance (R_θJA = 200 °C/W), and suitability for linear amplification versus hard-switching duty cycles.

Technical Context

The 2N3859A operates as a single NPN bipolar junction transistor with epitaxial base construction, optimized for stable DC gain and moderate RF performance. Its h_FE is specified across three test points (1 mA, 10 mA, 150 mA), supporting both small-signal amplification and switching up to 300 mA collector current.

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. Junction temperature must remain ≤150°C; storage range extends from –55°C to +150°C.

Key Specifications

Pinout & Package

2N3859A is housed in a standard TO-92 plastic package with 3 leads. Lead identification (flat side facing viewer, leads down): Pin 1 = Emitter, Pin 2 = Collector, Pin 3 = Base.

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 2N3859A offers superior voltage headroom (60 V) and higher continuous current capability (500 mA), making it preferable in industrial relay drivers and 24–48 V amplifier stages where margin against transients and load surges is critical.

Availability

2N3859A is available at Aetrix Electronics and suitable for audio preamplifiers, relay drivers, DC motor controls, and signal routing switches requiring stable component supply and long-term industrial availability.

Supply support for 2N3859A 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 designer and manufacturer of analog and discrete semiconductors, acquired by ON Semiconductor in 2016. Known for reliability and broad legacy product coverage.

The 2N3859A belongs to Fairchild's general-purpose NPN transistor family, engineered for cost-effective, thermally robust amplification and switching in industrial and consumer equipment where moderate speed and high voltage tolerance are required.

FAQ

What is the maximum collector-emitter voltage rating for the 2N3859A?

The 2N3859A has a maximum collector-emitter voltage (V_CEO) rating of 60 V at T_A = 25°C. This rating assumes an open-base condition and is based on a maximum junction temperature of 150°C. Exceeding this voltage risks irreversible breakdown. The 2N3859A maintains this rating across its full operating temperature range, making it suitable for 24 V and 48 V system interfaces where transient suppression is managed externally.

Does the 2N3859A support switching applications, and what is its safe current limit?

Yes, the 2N3859A is explicitly designed for switching applications up to 300 mA collector current, as stated in its functional description. Its absolute maximum continuous collector current is 500 mA, but sustained operation above 300 mA requires careful thermal management due to P_D = 625 mW and R_θJA = 200 °C/W. The 2N3859A achieves reliable saturation with appropriate base drive and is commonly used in relay and LED driver circuits.

What is the DC current gain (h_FE) range of the 2N3859A, and at what conditions is it specified?

The 2N3859A exhibits a DC current gain (h_FE) range of 75 to 200, measured at V_CE = 1.0 V and I_C = 1.0 mA. Gain varies with operating point: typical values drop at higher currents (e.g., ~50–120 at I_C = 150 mA). This h_FE spread must be accounted for in bias network design. The 2N3859A's gain consistency supports repeatable performance in production-grade amplifier and switch circuits.

Is the 2N3859A packaged in TO-92, and how are its pins arranged?

Yes, the 2N3859A uses the industry-standard TO-92 plastic package. With the flat side facing the viewer and leads pointing downward, the pinout is: Pin 1 = Emitter, Pin 2 = Collector, Pin 3 = Base. This configuration matches JEDEC TO-92 outline drawings and is compatible with automated assembly and manual prototyping. The 2N3859A's mechanical dimensions align with Fairchild's Rev. B package drawing dated July 2002.

How does the 2N3859A's transition frequency (f_T) affect its use in amplifier designs?

With f_T ranging from 90 MHz to 250 MHz at I_C = 2.0 mA and V_CE = 10 V, the 2N3859A supports small-signal amplification up to approximately 30 MHz while maintaining acceptable gain and phase margin. Its f_T enables use in IF amplifiers, oscillator buffers, and wideband sensor signal conditioning. The 2N3859A's usable bandwidth is limited not by f_T alone but also by external parasitics and bias-dependent h_FE, requiring proper layout and decoupling.