Diodes Incorporated ZTX603

Overview

ZTX603 from Zetex Semiconductors (now Diodes Incorporated) is an NPN silicon planar medium-power Darlington transistor in TO-92 package, rated for 80 V V_CEO, 1 A continuous collector current, and 1 W power dissipation at 25°C ambient. It delivers h_FE ≥2000 at I_C = 1 A, V_CE = 5 V, with V_CE(sat) ≤ 1.0 V and V_BE(sat) ≤ 1.8 V under same conditions-used in industrial relay drivers and linear power supply pass elements.

For engineers reviewing the ZTX603 datasheet, ZTX603 pinout, ZTX603 application, or ZTX603 equivalent, key selection criteria include verified Darlington gain stability at 1 A, safe operating area under pulsed switching (t_on = 0.5 µs, t_off = 1.1 µs), thermal derating capability to +200°C junction, and TO-92 mechanical compatibility with legacy E-line footprints.

Technical Context

The ZTX603 implements a monolithic Darlington pair with integrated base-emitter resistor network optimized for high DC current gain and low saturation voltage. Its structure supports direct drive from TTL/CMOS logic without external base resistors when I_B/I_C ≤ 0.001, enabling simplified interface in discrete power control stages.

It operates across –55°C to +200°C junction temperature range, with voltage derating governed by fixed thermal resistance (5.7 mW/°C above 25°C) and defined safe operating area curves for single-pulse and DC conditions up to 100 ms. Output capacitance C_obo = 15 pF and f_T = 150 MHz support moderate-speed switching in analog and digital load interfaces.

Key Specifications

Pinout & Package

Package: TO-92 (E-Line compatible, 3-lead plastic case). Lead identification follows standard emitter-base-collector (E-B-C) sequence when viewing flat side with leads downward.

Key Features

Applications

Equivalent & Alternatives

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

Compared with ZTX602 and BCX38, the ZTX603 uniquely balances 80 V blocking, ≥2000 gain at 1 A, and TO-92 form factor-making it optimal for space-constrained, high-reliability industrial switches where both voltage headroom and drive simplicity are critical.

Availability

ZTX603 is available at Aetrix Electronics and suitable for industrial relay drivers, linear power supply pass elements, motor start assist circuits, and overcurrent protection latches requiring stable component supply across extended temperature ranges.

Supply support for ZTX603 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, now part of Diodes Incorporated, specializes in high-performance discrete semiconductors for industrial, automotive, and power management applications.

The ZTX series was developed specifically for medium-power linear and switching applications demanding robust SOA, high DC gain, and extended temperature operation in TO-92 packages.

FAQ

What is the maximum allowable base current for continuous operation?

The ZTX603 does not specify a maximum continuous base current in its absolute maximum ratings. However, based on thermal limits and typical V_BE(sat) = 1.8 V at I_C = 1 A, sustained base current should remain below 2 mA to avoid localized heating at the base-emitter junction. For reliable long-term operation, design base drive to deliver ≤1 mA under worst-case gain conditions (h_FE = 2000).

Can ZTX603 be used in avalanche mode?

No-the ZTX603 is not rated or characterized for controlled avalanche operation. Its V_(BR)CEO = 80 V is a breakdown limit, not an energy-rated avalanche voltage. The device lacks specified avalanche energy (E_AS) or ruggedness testing. Use only within safe operating area boundaries; add external clamping (e.g., TVS diode) for inductive load switching.

Is the TO-92 package lead-free and RoHS compliant?

Yes-ZTX603 devices manufactured after Diodes Incorporated's 2006 RoHS transition meet EU Directive 2011/65/EU. The TO-92 package uses matte tin-plated leads with no lead content, and all internal die attach and molding compounds comply with RoHS substance restrictions. Full compliance documentation is available under Diodes Inc. part number ZTX603STZ.

How does thermal derating work above 25°C ambient?

Power dissipation must be reduced linearly above 25°C at 5.7 mW/°C, per the datasheet's derating curve. At 75°C ambient, maximum allowed P_tot = 1 W − (50 × 0.0057) = 0.715 W. This assumes no heatsink; adding a 20°C/W heatsink extends usable ambient range by ~14°C at 1 W. Junction temperature must stay ≤+200°C.