Diodes Incorporated ZTX603STZ

Overview

ZTX603STZ from Zetex Semiconductors (now Diodes Incorporated) is an NPN silicon planar medium-power Darlington transistor designed for high-gain switching and linear amplification in industrial control and power interface circuits. It delivers 80 V V_CEO, 1 A continuous collector current, 2 k minimum h_FE at I_C = 1 A, 1 W power dissipation at 25°C, and operates across –55°C to +200°C junction temperature range.

For engineers reviewing the ZTX603STZ datasheet, ZTX603STZ pinout, ZTX603STZ application, or ZTX603STZ equivalent, key selection criteria include verified Darlington gain linearity at 1 A, V_CE(sat) ≤ 1.0 V under I_C = 1 A / I_B = 1 mA drive, thermal derating capability up to 200°C, and TO-92 package compatibility with legacy E-line footprints.

Technical Context

The ZTX603STZ implements a monolithic Darlington pair architecture with integrated base-emitter resistor network optimized for low-drive switching. Its h_FE of 2 k–5 k at I_C = 1 A and V_CE = 5 V enables direct microcontroller GPIO drive without external base resistors in many applications.

It features V_(BR)CEO = 80 V, V_(BR)CBO = 100 V, and V_(BR)EBO = 10 V - supporting robust operation in inductive load switching where voltage transients exceed 60 V. Safe operating area (SOA) curves confirm single-pulse capability up to 10 A at 100 µs with V_CE ≤ 40 V.

Key Specifications

Pinout & Package

Package: TO-92 (E-Line compatible), 3-lead plastic through-hole package with standard C-B-E terminal assignment (viewed from flat side, leads down).

Key Features

Applications

Equivalent & Alternatives

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

Compared with ZTX602STZ, the ZTX603STZ provides critical 20 V higher V_CEO headroom for 48 V systems; versus MJD127G, it offers identical electrical performance in a space-saving through-hole package but with lower absolute power handling.

Availability

ZTX603STZ is available at Aetrix Electronics and suitable for industrial relay drivers, DC motor speed control, thermal cut-off circuits, and power supply feedback switches requiring stable component supply across extended temperature ranges and long production lifecycles.

Supply support for ZTX603STZ 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

Zetex Semiconductors was a UK-based analog and discrete semiconductor specialist acquired by Diodes Incorporated in 2008; known for high-reliability bipolar transistors and precision analog products.

The ZTX603STZ belongs to the ZTX600 series of medium-power Darlington transistors engineered specifically for industrial control, power interface, and high-temperature switching applications where gain stability and ruggedness are prioritized over RF performance.

FAQ

What is the maximum safe continuous collector current for ZTX603STZ at 70°C ambient?

At T_amb = 70°C, the device derates at 5.7 mW/°C from its 1 W rating at 25°C. This yields 1 W − (45°C × 0.0057 W/°C) = 0.74 W max dissipation. With V_CE(sat) ≈ 1.0 V, I_C ≤ 0.74 A continuous is recommended for reliable long-term operation without forced cooling.

Can ZTX603STZ replace ZTX602STZ without circuit modification?

Yes - both share identical TO-92 package, pinout (C-B-E), and base drive requirements. The ZTX603STZ's higher 80 V V_CEO improves safety margin in existing ZTX602 designs, especially those exposed to voltage transients or operating near 60 V limits. No schematic or layout changes are needed.

Is ZTX603STZ suitable for PWM switching at 20 kHz?

Yes - measured t_on = 0.5 µs and t_off = 1.1 µs support clean 20 kHz PWM operation with minimal dead-time distortion. Its Darlington structure introduces slight storage delay versus single BJTs, but SOA curves confirm safe operation at this frequency with I_C ≤ 1 A and V_CE ≤ 40 V.

Does ZTX603STZ require an external base resistor when driven by a 3.3 V microcontroller?

No - the Darlington configuration provides sufficient current gain (h_FE ≥ 2 k at I_C = 1 A) to saturate with ≤1 mA base current. A 3.3 V GPIO can directly drive the base via a 2.2 kΩ series resistor to limit peak current during turn-on, but no additional biasing network is required for basic on/off control.