onsemi BC635

Overview

BC635 from Fairchild Semiconductor is an NPN epitaxial silicon transistor designed for switching and amplifier applications, with V_CEO = 45 V, I_C = 1 A, P_C = 1 W, and h_FE ≥ 25 at I_C = 5 mA - used in low-voltage DC-DC converter control stages and audio preamplifier gain blocks.

For engineers reviewing the BC635 datasheet, pinout, applications, or equivalent options, key selection considerations include its TO-92 package compatibility, 45 V V_CEO rating, 100 MHz f_T, saturation voltage of 0.5 V at 500 mA, and complementary pairing with BC636 in push-pull configurations.

Technical Context

The BC635 operates as a general-purpose bipolar junction transistor with fixed NPN polarity and epitaxial base construction, supporting linear amplification (V_CE = 2 V, I_C = 5–500 mA) and saturated switching (I_C = 500 mA, I_B = 50 mA). Its h_FE range (25–250) and f_T = 100 MHz enable mid-frequency signal handling up to ~10 MHz in Class-A amplifiers.

Thermal limits are defined by T_J = 150°C maximum junction temperature and T_STG = –65 to 150°C storage range, with absolute ratings including V_CER = 45 V (R_BE = 1 kΩ), V_CES = 45 V, and V_EBO = 5 V - confirming suitability for 24 V rail logic interfacing and relay driver circuits.

Key Specifications

Pinout & Package

BC635 is housed in a through-hole TO-92 package with standardized lead configuration: Emitter (Pin 1), Collector (Pin 2), Base (Pin 3).

Key Features

Applications

Equivalent & Alternatives

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

Compared with BC547B and 2N2222A, the BC635 uniquely balances 45 V V_CEO, 1 A I_C, and 1 W P_C in TO-92 - making it optimal for medium-power switching where both voltage margin and thermal robustness matter.

Availability

BC635 is available at Aetrix Electronics and suitable for relay driver circuits, audio preamplifier stages, DC-DC converter control, LED constant-current sinks, and industrial sensor interface modules requiring stable component supply across long-lifecycle production programs.

Supply support for BC635 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 analog, discrete, and power management ICs before its acquisition by ON Semiconductor in 2016.

The BC635 belongs to Fairchild's general-purpose bipolar transistor family, engineered for cost-sensitive, medium-power linear and switching applications in industrial controls, consumer audio, and power supply subsystems.

FAQ

What is the maximum collector-emitter voltage rating for BC635?

The BC635 has a V_CEO rating of 45 V at T_A = 25°C, meaning it can safely block up to 45 V between collector and emitter with the base open. This rating is confirmed in the Absolute Maximum Ratings table and applies specifically to the BC635 variant - distinct from BC637 (60 V) and BC639 (80 V). Exceeding this voltage risks avalanche breakdown and permanent device failure.

Is BC635 pin-compatible with BC547 or 2N2222A?

Yes, BC635 uses the standard TO-92 package with Emitter–Collector–Base pinout (1–2–3), matching BC547 and 2N2222A physical layout. However, electrical differences exist: BC635 supports 1 A I_C and 1 W P_C, while BC547 is rated for 100 mA and 500 mW. Direct substitution requires verification of current, power, and gain requirements in the target circuit.

What is the typical DC current gain (hFE) of BC635 at 500 mA collector current?

At V_CE = 2 V and I_C = 500 mA, the BC635 exhibits h_FE ≥ 40 (minimum) per the datasheet's "hFE3" specification. Typical values range up to 160 under those conditions. This gain level ensures sufficient base drive efficiency for medium-power switching without excessive base current overhead.

Does BC635 have a specified current gain bandwidth product (fT)?

Yes, the BC635 has a guaranteed f_T of 100 MHz, measured at V_CE = 5 V, I_C = 10 mA, and f = 50 MHz test frequency. This parameter confirms its capability for RF amplification and fast-switching applications up to ~10 MHz, distinguishing it from lower-frequency general-purpose transistors like BC546.

What is the collector-emitter saturation voltage (VCE(sat)) for BC635 under standard switching conditions?

The BC635 specifies V_CE(sat) = 0.5 V maximum at I_C = 500 mA and I_B = 50 mA. This low saturation voltage reduces conduction losses to under 250 mW in switching applications, enabling efficient operation in relay drivers and LED current sinks without additional heatsinking at ambient temperatures ≤ 50°C.