onsemi BC638

Overview

BC638 from onsemi is a PNP epitaxial silicon transistor rated for −60 V V_CEO, −1 A continuous collector current, and 1 W power dissipation in TO-92-3 package; it delivers h_FE = 25–160 across 5 mA to 500 mA, with f_T = 100 MHz, and is used in low-voltage switching and linear amplification stages of consumer power supplies and signal conditioning circuits.

For engineers reviewing the BC638 datasheet, pinout, applications, or equivalent options, key selection criteria include its −60 V breakdown rating, −1 A DC current capability, TO-92-3 mechanical compatibility, saturation voltage of −0.5 V at −500 mA/−50 mA drive, and complementarity to BC637 in push-pull configurations.

Technical Context

This PNP bipolar junction transistor operates with emitter-grounded configuration in common-emitter mode, supporting both active-region amplification (V_CE = −2 V, I_C = −5 mA to −500 mA) and saturated switching (V_CE(sat) ≤ −0.5 V). Its f_T = 100 MHz enables RF-capable small-signal use up to mid-VHF band.

Thermal design requires attention to R_JA = 125 °C/W on standard FR-4 PCB; derating begins above 25 °C at 8 mW/°C. Junction temperature must remain ≤150 °C under all operating conditions, with storage range spanning −65 to 150 °C.

Key Specifications

Pinout & Package

BC638 is housed in TO-92-3 package (Case 135AR), with standardized leadform: Emitter (pin 1), Collector (pin 2), Base (pin 3), as marked on device body and confirmed in onsemi mechanical drawings.

Key Features

Applications

Equivalent & Alternatives

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

Compared with BC636 and MPSA92, BC638 uniquely balances 60 V rating, 1 A current, and 100 MHz f_T in TO-92-making it optimal for general-purpose medium-voltage switching and mid-band amplification where neither extreme HV nor ultra-low noise is needed.

Availability

BC638 is available at Aetrix Electronics and suitable for DC power regulation, relay driving, audio pre-amplification, and LED current control requiring stable component supply across industrial, consumer, and embedded design cycles.

Supply support for BC638 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

onsemi (formerly ON Semiconductor) is a global semiconductor supplier delivering energy-efficient, intelligent power and sensing solutions for automotive, industrial, cloud, medical, and IoT applications.

The BC638 belongs to onsemi's legacy discrete bipolar transistor family, engineered for cost-sensitive, high-reliability linear and switching applications in consumer electronics and industrial controls where TO-92 form factor and proven PNP performance are essential.

FAQ

What is the maximum collector-emitter voltage rating for BC638?

The BC638 has a guaranteed minimum collector-emitter breakdown voltage (V_CEO) of −60 V at I_C = −10 mA and I_B = 0. This rating applies under open-base conditions and defines the absolute upper limit for safe DC or peak AC voltage across collector and emitter terminals in the BC638.

Is BC638 pin-compatible with BC637?

No, BC638 is not pin-compatible with BC637. While BC638 (PNP) and BC637 (NPN) are complementary devices intended for matched circuit design, they share identical TO-92-3 package outline and pin numbering (Emitter-Collector-Base), but their polarity and biasing requirements differ fundamentally-requiring separate PCB layouts for each type.

What is the typical DC current gain (h_FE) of BC638 at 150 mA collector current?

At V_CE = −2 V and I_C = −150 mA, the BC638 exhibits h_FE ranging from 40 (minimum) to 160 (maximum), with typical performance centered near 100. This wide spread reflects process variation and must be accounted for in gain-critical linear designs using the BC638.

Can BC638 be used in RF amplifier applications?

Yes, BC638 can be used in RF amplifier applications up to approximately 50–80 MHz. Its f_T = 100 MHz-measured at V_CE = −5 V, I_C = −10 mA-supports small-signal amplification in VHF front-ends, FM transmitters, and local oscillator buffers where moderate gain and low cost are prioritized over ultra-low noise or high linearity.

Does BC638 require a heatsink in 1 W continuous operation?

Yes, BC638 requires thermal management for sustained 1 W dissipation. With R_JA = 125 °C/W on standard FR-4 PCB, 1 W power leads to ~125 °C junction rise above ambient-exceeding the 150 °C max rating unless ambient stays below 25 °C. Derating or a small copper pad heatsink is recommended for reliable long-term operation at full power.