onsemi BC640BU

Overview

BC640BU from Fairchild Semiconductor is a PNP epitaxial silicon transistor designed for linear amplification and switching in low-voltage, medium-current circuits. It delivers V_CEO = −80 V, I_C = −1 A, h_FE = 25–160 (at I_C = −5 mA to −500 mA), and V_CE(sat) = −0.5 V at I_C = −500 mA / I_B = −50 mA - used in relay drivers, LED dimmers, and audio preamplifier stages.

For engineers reviewing the BC640BU datasheet, pinout, applications, or equivalent options, key selection criteria include guaranteed h_FE range across operating current, TO-92 thermal derating behavior, V_ER rating with base-emitter resistor biasing, and complementary pairing with BC639 in push-pull amplifier designs.

Technical Context

This discrete PNP bipolar junction transistor operates in active, saturation, and cutoff regions with defined DC gain linearity across three collector current tiers (−5 mA, −150 mA, −500 mA). Its f_T = 100 MHz enables stable operation up to mid-VHF frequencies in small-signal amplifiers.

The device features V_ER = −100 V (R_BE = 1 kΩ) for enhanced switching robustness under inductive load conditions, and exhibits low leakage: I_CBO ≤ −0.1 μA at V_CB = −30 V, supporting high-impedance bias networks in battery-powered sensor interfaces.

Key Specifications

Pinout & Package

BC640BU is housed in a standard TO-92 plastic package (3-lead, through-hole), with lead-to-lead spacing of 1.27 mm and overall height ≤ 4.58 mm. Pin identification follows JEDEC TO-92 orientation: flat side facing viewer, leads down, left-to-right = Emitter (1), Collector (2), Base (3).

Key Features

Applications

Equivalent & Alternatives

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

Compared with MPSA92 and BC636, BC640BU offers balanced V_CEO/h_FE/I_C trade-offs for 24–48 V industrial control - delivering verified gain linearity across its rated current range while maintaining sufficient breakdown margin for relay and motor drive use cases.

Availability

BC640BU is available at Aetrix Electronics and suitable for relay driver circuits, DC motor speed controllers, audio pre-amplifier stages, and LED constant-current dimmers requiring stable component supply and long-term industrial availability.

Supply support for BC640BU 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 BC640BU belongs to Fairchild's legacy general-purpose bipolar transistor family, engineered for cost-sensitive industrial and consumer applications demanding reliability, standardized TO-92 fit, and validated DC performance across temperature and current ranges.

FAQ

What is the maximum continuous collector current rating for BC640BU?

The BC640BU has an absolute maximum continuous collector current (I_C) rating of −1 A at T_A = 25°C. Derating is required above 25°C ambient: approximately −8.3 mA/°C beyond 25°C, based on its 1 W total package power dissipation limit and thermal resistance. This rating applies only when the device is mounted on a standard FR-4 PCB with minimal copper; actual usable current depends on heatsinking and airflow.

Does BC640BU have a specified V_ER rating, and how is it used in circuit design?

Yes, BC640BU specifies V_ER = −100 V with R_BE = 1 kΩ - a key parameter for inductive switching applications. This rating reflects improved breakdown robustness when a base-emitter resistor is present, allowing safer commutation of relay coils or solenoids without external clamping diodes. Designers use this value to size the base resistor and confirm safe operation under transient voltage spikes.

How does the h_FE of BC640BU vary with collector current, and why is this important?

The BC640BU specifies three h_FE values: min 25 at I_C = −5 mA, min 40 at I_C = −150 mA, and min 25 at I_C = −500 mA. This non-monotonic behavior confirms gain optimization for both small-signal amplification and medium-current switching. It matters because base drive must be sized for worst-case h_FE at the target operating point - e.g., using h_FE = 25 at −500 mA ensures saturation even under low-gain conditions.

Is BC640BU pin-compatible with BC639, and what is their relationship?

No, BC640BU is not pin-compatible with BC639 - they are complementary devices (PNP vs NPN), not drop-in replacements. BC640BU (PNP) and BC639 (NPN) share identical TO-92 packaging and mirrored electrical ratings (e.g., V_CEO = −80 V / +80 V, I_C = −1 A / +1 A), enabling matched push-pull or complementary symmetry amplifier designs when used together with correct pin orientation.

What is the typical base-emitter on voltage (V_BE(on)) for BC640BU under rated conditions?

The BC640BU has a typical V_BE(on) of −1.0 V at V_CE = −2 V and I_C = −500 mA. This value is critical for calculating base resistor values in saturated switch configurations. At lower currents (e.g., −5 mA), V_BE drops to approximately −0.75 V; designers should reference the datasheet's Figure 4 for precise V_BE vs I_C curves across temperature.