Diodes Incorporated ZTX658

Overview

ZTX658 from Zetex Semiconductors (now Diodes Incorporated) is an NPN silicon planar medium-power high-voltage transistor designed for switching and amplification in high-voltage analog and pulse circuits. It delivers 400 V V_CEO, 500 mA continuous collector current, 1 W power dissipation at 25°C, and operates across –55°C to +200°C junction temperature. It is commonly used in telephone dialler circuits where high-voltage isolation and reliable saturation switching are required.

For engineers reviewing the ZTX658 datasheet, ZTX658 pinout, ZTX658 application, or ZTX658 equivalent, key selection criteria include its 400 V breakdown rating, low V_CE(sat) of 0.25 V at IC=50 mA/IB=5 mA, h_FE range of 50–400, TO-92 package compatibility, and thermal resistance of 175°C/W (junction-to-ambient, free air).

Technical Context

The ZTX658 is a discrete bipolar junction transistor optimized for medium-power, high-voltage DC and pulsed switching. Its 400 V V_CBO and V_CEO ratings enable operation in off-hook telephone line interfaces and relay drivers. The device exhibits f_T = 50 MHz at IC = 20 mA/V_CE = 20 V, supporting moderate-speed switching with ton/toff of 130 ns/3300 ns under specified pulsed conditions.

Thermal design is critical: R_th(j-amb) = 175°C/W (free air), reduced to 116°C/W on PCB with ≥1 in² copper, and R_th(j-case) = 70°C/W. Safe operating area (SOA) curves confirm single-pulse capability up to 100 V and 100 mA with t_P ≤ 1 ms and duty cycle ≤ 2%.

Key Specifications

Pinout & Package

Package: TO-92 (E-Line compatible, 3-229 outline), epoxy-molded, through-hole mounting. Pin identification is standardized as Emitter (E), Base (B), Collector (C) - left-to-right when viewing flat side with leads down.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar high-voltage NPN switching applications.

Compared with ZTX653 and BCV61B, the ZTX658 uniquely balances 400 V capability, 500 mA current, and TO-92 usability-making it irreplaceable in legacy telecom hardware, high-voltage relay drivers, and pulse generators requiring robust through-hole mounting and wide SOA.

Availability

ZTX658 is available at Aetrix Electronics and suitable for telephone dialler circuits, off-hook line interfaces, relay driver stages, and high-voltage pulse generators requiring stable component supply across extended temperature and voltage ranges.

Supply support for ZTX658 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, acquired by Diodes Incorporated in 2008, specialized in high-performance discrete semiconductors for analog, power, and interface applications.

The ZTX series was engineered for ruggedized medium-power switching in telecom, industrial control, and instrumentation-emphasizing high-voltage tolerance, thermal resilience, and TO-92 reliability.

FAQ

What is the maximum safe continuous collector current for ZTX658 at 70°C ambient?

At 70°C ambient, the ZTX658's power dissipation must be derated from 1 W using 5.7 mW/°C. With 45°C rise above ambient, allowable power drops to ~744 mW. Assuming V_CE(sat) ≈ 0.3 V, max continuous I_C ≈ 2.5 A × (744 mW / 1 W) ≈ 1.86 A - but absolute I_C rating remains 500 mA. Therefore, 500 mA is the hard limit regardless of temperature.

Can ZTX658 be used in linear amplifier mode?

Yes - its h_FE stability (50–400 across I_C = 1–200 mA) and low V_CE(sat) support Class-A and AB amplification. However, thermal resistance (175°C/W) limits usable quiescent power to ~300 mW in free air, restricting output swing in high-fidelity applications.

Is ZTX658 RoHS compliant?

Yes - Diodes Incorporated confirms RoHS compliance for ZTX658 (per Diodes Inc. Product Change Notice PCN-2011-001). Lead-free termination and halogen-free molding compound meet EU Directive 2011/65/EU, with exemptions applied only where technically necessary per Annex III.

What is the recommended PCB layout for thermal performance?

Mount ZTX658 on FR-4 with ≥1 in² (6.45 cm²) copper pour connected directly to the collector pad. Use thermal vias (≥4× 0.3 mm) under the pad to inner-layer ground planes. Keep emitter/base traces short and avoid routing high-voltage traces near base to prevent coupling-induced false triggering.