Diodes Incorporated BCX38CSTOA

Overview

BCX38CSTOA from Diodes Incorporated is an NPN silicon planar medium-power Darlington transistor with V_CEO = 60 V, h_FE = 5000–10000 at I_C = 500 mA, P_tot = 1 W, and TO-92 compatible E-Line package. It serves as a high-gain switching or linear amplification device in low-frequency power control circuits, such as relay drivers and lamp dimmers.

For engineers reviewing the BCX38CSTOA datasheet, BCX38CSTOA pinout, BCX38CSTOA application, or BCX38CSTOA equivalent, key selection criteria include verified DC current gain at 500 mA, V_CE(sat) ≤ 1.25 V under 800 mA/8 mA drive, thermal derating above 25°C ambient, and TO-92 mechanical compatibility with legacy designs.

Technical Context

This Darlington pair integrates two NPN transistors monolithically to achieve high current gain without external bias networks. Its base-emitter turn-on voltage is 1.8 V at I_C = 800 mA, and it sustains 60 V between collector and emitter with zero base current.

The device operates across –55°C to +200°C junction temperature range and supports pulsed peak currents up to 2 A. Safe operating area (SOA) curves confirm stable operation at V_CE = 10 V / I_C = 0.5 A for 10 ms pulses, with DC derating governed by 0.0057 °C/mW thermal resistance.

Key Specifications

Pinout & Package

BCX38CSTOA uses a 3-pin TO-92 compatible E-Line plastic package with lead finish matte tin over copper. Pin assignment follows standard C-B-E configuration when viewed with flat side facing outward and leads downward.

Key Features

Applications

Equivalent & Alternatives

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

Compared with BCX38BSTOA, BCX38CSTOA delivers 2.5× higher minimum h_FE, enabling simpler base drive in high-side relay interfaces; versus BC879-25, it offers 2.3× higher V_CEO, 2.9× higher P_tot, and through-hole mounting for ruggedized industrial assemblies.

Availability

BCX38CSTOA is available at Aetrix Electronics and suitable for relay drivers, lamp dimmers, motor speed controllers, and industrial sensor interfaces requiring stable component supply across extended temperature ranges and long production lifecycles.

Supply support for BCX38CSTOA 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

Diodes Incorporated is a global manufacturer of discrete semiconductors and analog ICs, headquartered in Plano, Texas, with design centers across Asia and manufacturing in Taiwan and China.

BCX38CSTOA belongs to the BCX38 series of medium-power Darlington transistors designed specifically for cost-sensitive, high-reliability industrial control and power interface applications where robust TO-92 packaging and wide temperature operation are essential.

FAQ

What is the maximum safe continuous collector current for BCX38CSTOA?

The absolute maximum continuous collector current is 800 mA at T_amb = 25°C. Derating is required above this ambient temperature per the datasheet's thermal resistance curve: power dissipation must be reduced by 0.0057 W/°C rise. At 75°C ambient, maximum usable I_C drops to approximately 550 mA to maintain junction temperature below 200°C.

Does BCX38CSTOA require a base resistor in switching applications?

Yes - a base resistor is mandatory to limit base current and prevent damage. For 800 mA collector current with h_FE ≥ 5000, minimum base drive is ~160 µA, but typical design uses 8 mA (per datasheet test condition), requiring a 470 Ω resistor from a 5 V logic source. Omitting this resistor risks thermal runaway and permanent failure.

Can BCX38CSTOA replace BCX38ASTOA in an existing design?

Yes - BCX38CSTOA is pin-compatible and electrically backward-compatible with BCX38ASTOA. Its higher minimum h_FE (500 vs. 500) and identical V_CEO, V_CE(sat), and package allow direct substitution. No layout or schematic changes are needed, though base drive may be reduced if gain margin permits.

Is BCX38CSTOA suitable for automotive under-hood use?

Yes - its validated T_j range of –55°C to +200°C meets AEC-Q101 stress test requirements for discrete transistors. However, qualification documentation must be obtained separately from Diodes Incorporated; the part itself is widely used in engine control modules, fan drivers, and body electronics where ambient temperatures exceed 105°C.