onsemi BC638ZL1

Overview

BC638ZL1 from onsemi is a PNP silicon high-current general-purpose transistor in TO-92 package, rated for −60 V V_CEO, −0.5 A continuous collector current, 625 mW power dissipation at T_A = 25°C, and DC current gain (h_FE) of 25–160 at I_C = −5 mA. It serves as a medium-power switching or linear amplification device in discrete power control stages.

For engineers reviewing the BC638ZL1 datasheet, pinout, applications, or equivalent options, key selection criteria include its −60 V breakdown rating, TO-92 thermal resistance (R_JA = 200°C/W), saturation voltage (V_CE(sat) ≤ −0.5 V at I_C = −500 mA), and guaranteed h_FE range across operating currents - critical for reliable biasing in industrial relay drivers and LED load switches.

Technical Context

The BC638ZL1 operates as a bipolar junction transistor with fixed PNP polarity, requiring reverse-biased base-emitter junction for conduction. Its safe operating area (SOA) is defined up to −500 mA and −60 V, with thermal derating starting above 25°C ambient (5.0 mW/°C) or 25°C case (12 mW/°C).

It exhibits f_T = 150 MHz at I_C = −50 mA, V_CE = −2 V, supporting moderate-frequency switching; input capacitance C_ib = 110 pF and output capacitance C_ob = 9.0 pF further define its small-signal behavior in amplifier or oscillator configurations.

Key Specifications

Pinout & Package

BC638ZL1 uses the standard TO-92 (Case 29, Style 14) plastic package with 3 leads. Pin 1 is Emitter, Pin 2 is Collector, Pin 3 is Base - confirmed by marking diagram and mechanical drawing in ON Semiconductor BC638/D Rev. 2.

Key Features

Applications

Equivalent & Alternatives

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

Compared with BC636ZL1, BC638ZL1 offers +15 V higher V_CEO headroom for 48 V systems; compared with BC640ZL1, it trades −20 V breakdown margin for broader h_FE tolerance (25–160 vs. 40–250), easing bias design in variable-temperature environments.

Availability

BC638ZL1 is available at Aetrix Electronics and suitable for industrial relay drivers, DC motor direction control, LED load switches, and linear voltage regulator pass elements requiring stable component supply and long-term obsolescence management.

Supply support for BC638ZL1 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 focused on energy-efficient electronics, delivering silicon-based solutions for automotive, industrial, cloud, and IoT applications.

The BC638ZL1 belongs to onsemi's legacy general-purpose bipolar transistor product line, designed for cost-sensitive, medium-power discrete switching and amplification in industrial controls and power management circuits.

FAQ

What is the maximum collector-emitter voltage rating for BC638ZL1?

The BC638ZL1 has a maximum collector-emitter voltage (V_CEO) rating of −60 Vdc, verified per ON Semiconductor BC638/D Rev. 2 datasheet. This rating applies at I_C = −10 mA with base open and defines the absolute maximum reverse bias the device can withstand before breakdown. Exceeding this voltage risks permanent damage, even momentarily. The BC638ZL1 must be used in circuits where V_CE remains within this limit under all operating and transient conditions.

Is BC638ZL1 lead-free and RoHS compliant?

Yes, the BC638ZL1 is available in both standard and Pb-free versions: BC638ZL1 (lead-based) and BC638ZL1G (Pb-free). The "G" suffix denotes compliance with J-STD-609 and EU RoHS Directive 2011/65/EU. Both variants share identical electrical specifications and TO-92 mechanical form factor. The BC638ZL1G variant uses matte tin lead finish and meets reflow profile requirements for lead-free assembly processes.

What is the DC current gain (hFE) range for BC638ZL1 at different collector currents?

The BC638ZL1 exhibits h_FE = 25–160, depending on operating point: minimum 25 at I_C = −5 mA, V_CE = −2 V; typical 100 at I_C = −150 mA; maximum 160 at I_C = −500 mA, V_CE = −2 V. This wide gain spread reflects process variation and must be accounted for in base resistor selection. For robust saturation, design using h_FE(min) = 25 at the intended I_C; for linear amplification, verify gain stability across the full I_C range in BC638ZL1.

Can BC638ZL1 be used in switching applications above 100 kHz?

The BC638ZL1 has an f_T of 150 MHz, but practical switching above 100 kHz is limited by storage time (t_s) and fall time (t_f) not specified in the BC638/D datasheet. At I_C = −500 mA, V_CE(sat) ≤ −0.5 V confirms usable saturation, yet lack of published switching waveforms or time parameters means >50 kHz operation requires empirical validation. For reliable high-frequency switching, consider devices with characterized t_on/t_off specs - the BC638ZL1 is best suited for ≤50 kHz PWM or linear control.

What is the thermal resistance from junction-to-ambient for BC638ZL1 in TO-92 package?

The BC638ZL1 in TO-92 package has a junction-to-ambient thermal resistance (R_JA) of 200°C/W, measured under standard JEDEC test conditions (single device on 1-inch² FR-4 board, 1 oz copper). This value assumes no added heatsinking; actual R_JA improves with larger copper areas or thermal vias. For example, doubling PCB copper area reduces R_JA by ~15–20%. At 625 mW dissipation, this yields ΔT = 125°C rise above ambient - confirming need for derating above 25°C or use below 300 mW in sealed enclosures. The BC638ZL1's R_JC = 83.3°C/W also supports case-mounted heatsink use.