Diodes Incorporated BCX38CSTZ

Overview

BCX38CSTZ from ON Semiconductor is an NPN silicon planar medium-power Darlington transistor in TO-92 package, rated for 60 V V_CEO, 800 mA continuous collector current, and 1 W power dissipation at 25°C ambient. It delivers DC current gain (h_FE) of 5000–10000 at I_C = 500 mA and V_CE = 5 V, and is used in low-frequency switching and linear amplification stages in industrial control interfaces.

For engineers reviewing the BCX38CSTZ datasheet, BCX38CSTZ pinout, BCX38CSTZ application, or BCX38CSTZ equivalent, key selection criteria include verified Darlington gain linearity at 500 mA, V_CE(sat) ≤ 1.25 V under 8 mA base drive, thermal derating behavior up to +200°C junction temperature, and TO-92 mechanical compatibility with legacy E-line footprints.

Technical Context

This Darlington pair integrates two NPN transistors monolithically to achieve high current gain while maintaining single-package simplicity. Its structure supports base-emitter turn-on voltage (V_BE(on)) of 1.8 V at I_C = 800 mA and exhibits safe operating area (SOA) compliance up to 1 A pulsed with 10 ms duration at 25°C ambient.

The device operates across –55°C to +200°C junction temperature range and sustains V_CEO(sus) = 60 V under zero-base-drive conditions. Its 100 nA I_CBO and I_EBO ratings confirm low leakage performance suitable for stable bias networks in analog front-ends.

Key Specifications

Pinout & Package

BCX38CSTZ is housed in a standard TO-92 plastic package with E-Line footprint compatibility (3-lead, straight lead form). Pin assignment follows 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 Darlington transistor applications.

Compared with BCX38BSTZ and MJD127G, BCX38CSTZ offers the highest gain in TO-92 format-critical for space-constrained, low-drive applications-while maintaining full compatibility with legacy E-line layouts and proven thermal performance up to +200°C.

Availability

BCX38CSTZ is available at Aetrix Electronics and suitable for industrial relay drivers, linear voltage regulator pass elements, and DC motor speed controllers requiring stable component supply and long-term manufacturability.

Supply support for BCX38CSTZ 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

ON Semiconductor is a global semiconductor supplier focused on energy-efficient electronics, delivering power management, analog, sensing, and connectivity solutions for automotive, industrial, and cloud infrastructure markets.

BCX38CSTZ belongs to ON Semiconductor's legacy bipolar transistor portfolio designed for cost-sensitive, high-reliability industrial control and power interface applications where TO-92 compatibility and extended temperature operation are essential.

FAQ

What is the maximum base current required to saturate BCX38CSTZ at 800 mA collector current?

BCX38CSTZ requires 8 mA base current to achieve V_CE(sat) ≤ 1.25 V at I_C = 800 mA, per the Electrical Characteristics table. This corresponds to a forced beta (I_C/I_B) of 100, ensuring reliable saturation even with minimum h_FE of 5000. Exceeding 8 mA provides no significant V_CE(sat) improvement and increases base drive power loss.

Can BCX38CSTZ replace BCX38ASTZ in existing designs?

Yes, BCX38CSTZ is pin-compatible and electrically substitutable for BCX38ASTZ, but with significantly higher h_FE (5000–10000 vs. 500–1000). Designers should verify that increased gain does not cause instability in feedback-controlled circuits or excessive base current in high-impedance drive networks.

Is BCX38CSTZ suitable for switching 24 V inductive loads?

Yes-BCX38CSTZ supports V_CEO = 60 V and features built-in safe operating area (SOA) curves validated for inductive switching. When driving 24 V relays or solenoids, a flyback diode must be placed across the load to clamp inductive kickback and prevent V_CE overshoot beyond 60 V.

How does thermal derating affect BCX38CSTZ's power handling above 25°C ambient?

BCX38CSTZ's P_tot decreases linearly above 25°C ambient: 1 W at 25°C, 0.5 W at 100°C, and 0 W at 175°C (per the thermal resistance curve). The maximum allowable ambient temperature is calculated using Tamb(max) = (P_max − P_actual)/0.0057 + 25°C, where P_max depends on V_CE and source resistance.