onsemi BC639_D81Z

Overview

BC639_D81Z from Fairchild Semiconductor is an NPN epitaxial silicon transistor designed for switching and amplifier applications, with V_CEO = 80 V, I_C = 1 A, P_C = 1 W, h_FE ≥ 40 at I_C = 150 mA, and f_T = 100 MHz - used in relay drivers, power supplies, and audio preamplifiers.

For engineers reviewing the BC639_D81Z datasheet, pinout, applications, or equivalent options, key selection factors include collector-emitter breakdown voltage (80 V), DC current gain at high current (h_FE ≥ 40 @ 150 mA), saturation voltage (V_CE(sat) ≤ 0.5 V @ 500 mA), thermal rating (T_J = 150 °C), and TO-92 package compatibility.

Technical Context

This NPN bipolar junction transistor operates in linear amplification and saturated switching modes. Its V_CEO = 80 V and V_CER = 100 V (with R_BE = 1 kΩ) support robust overvoltage margin in inductive load switching. The h_FE range (40–160 at I_C = 150 mA) enables predictable base drive design across production lots.

With f_T = 100 MHz and C_ob < 10 pF at V_CB = 10 V, the BC639_D81Z supports medium-frequency amplification up to ~10–20 MHz in common-emitter configurations. Its V_BE(on) = 1 V at I_C = 500 mA ensures stable turn-on under moderate load conditions.

Key Specifications

Pinout & Package

BC639_D81Z is housed in a standard TO-92 plastic package with 3 leads: Emitter (pin 1), Collector (pin 2), Base (pin 3). Lead spacing and outline conform to JEDEC TO-92 outline variations for through-hole mounting and manual soldering.

Key Features

Applications

Equivalent & Alternatives

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

Compared with BC639_D81Z, BC639 offers identical performance and drop-in replacement capability, while PN2222A trades voltage headroom for higher gain and is restricted to lower-voltage applications where V_CEO < 40 V suffices.

Availability

BC639_D81Z is available at Aetrix Electronics and suitable for relay drivers, DC-DC converters, audio preamplifiers, and LED current regulators requiring stable component supply across industrial control, power management, and consumer electronics programs.

Supply support for BC639_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

Fairchild Semiconductor was a U.S.-based semiconductor company specializing in power management, analog, and discrete devices, acquired by ON Semiconductor in 2016.

The BC639_D81Z belongs to Fairchild's legacy BC63x NPN transistor family, engineered for cost-sensitive, medium-power linear and switching applications in industrial and consumer equipment.

FAQ

What is the maximum collector-emitter voltage rating for BC639_D81Z?

The BC639_D81Z has a V_CEO rating of 80 V - the maximum collector-emitter voltage with the base open. It also supports V_CER = 100 V when a 1 kΩ resistor is connected between base and emitter, providing enhanced surge tolerance in inductive switching. This value is confirmed in the December 2002 Fairchild datasheet Rev. B2.

Is BC639_D81Z pin-compatible with BC637 or BC635?

Yes, BC639_D81Z shares the same TO-92 package and pinout (Emitter–Collector–Base) as BC635 and BC637. However, it is not functionally interchangeable due to differing voltage ratings: BC639_D81Z has V_CEO = 80 V versus 60 V for BC637 and 45 V for BC635. Substitution requires verification of voltage stress margins in the target circuit.

What is the typical DC current gain (hFE) of BC639_D81Z at 150 mA collector current?

The BC639_D81Z exhibits h_FE ≥ 40 at V_CE = 2 V and I_C = 150 mA, with a typical value of 160 and maximum of 250 under those conditions. This gain range is specified in the Fairchild BC635/637/639 datasheet and enables predictable base drive design for saturation in switching applications.

Can BC639_D81Z be used in audio amplifier stages?

Yes, BC639_D81Z is suitable for low-to-medium frequency audio preamplifier stages due to its f_T = 100 MHz, low noise characteristics, and stable h_FE across I_C = 1–500 mA. Its V_BE(on) = 1 V at I_C = 500 mA simplifies biasing, and TO-92 thermal resistance allows modest dissipation in line-level gain blocks - as validated in Fairchild's typical characteristics curves.

What is the package type and lead configuration of BC639_D81Z?

BC639_D81Z uses the standard TO-92 plastic package with three leads arranged linearly: pin 1 = Emitter, pin 2 = Collector, pin 3 = Base. Dimensions and mechanical tolerances comply with JEDEC TO-92 outline specifications, enabling compatibility with automated through-hole insertion and wave soldering processes.