Diodes Incorporated ZTX458

Overview

ZTX458 from Diodes Incorporated is an NPN silicon planar medium-power high-voltage transistor with 400 V V_CEO, 300 mA continuous collector current, and 1 W power dissipation at 25°C - used in flyback snubber circuits, relay drivers, and industrial switch-mode power supply (SMPS) auxiliary supplies.

For engineers reviewing the ZTX458 datasheet, ZTX458 pinout, ZTX458 application, or ZTX458 equivalent, key selection criteria include breakdown voltage margin at elevated temperature, h_FE stability across 1–100 mA I_C, V_CE(sat) at I_B/I_C = 1/10, and TO-92 thermal derating behavior in sealed enclosures.

Technical Context

This transistor employs a planar epitaxial structure optimized for high-voltage blocking and stable gain under pulsed switching conditions. Its 400 V V_CEO rating supports operation in 380 V DC bus applications with 5% safety margin, while f_T = 50 MHz enables use in low-duty-cycle, high-frequency snubbers up to 2 MHz.

The device exhibits V_BE(sat) = 0.9 V at I_C = 50 mA / I_B = 5 mA and maintains h_FE ≥ 100 from I_C = 1 mA to 50 mA at V_CE = 10 V - enabling reliable base drive design without active current limiting in discrete driver stages.

Key Specifications

Pinout & Package

Supplied in E-Line TO-92 compatible package (3-182 outline), with standard C-B-E lead assignment and 1.5 mm lead pitch. Thermal resistance R_θJA = 200°C/W typical in free air.

Key Features

Applications

Equivalent & Alternatives

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

Compared with ZTX450 and BCV46, the ZTX458 uniquely delivers 400 V blocking with 1 W dissipation in TO-92 - making it the only option among the three for 380 V DC auxiliary supplies requiring >300 mA pulsed current and >100°C ambient operation.

Availability

ZTX458 is available at Aetrix Electronics and suitable for relay driver stages, flyback snubber circuits, and industrial auxiliary supplies requiring stable component supply across extended temperature and high-voltage stress conditions.

Supply support for ZTX458 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 semiconductor company specializing in discrete, analog, and mixed-signal devices for industrial, computing, and consumer markets.

The ZTX series targets high-reliability medium-power switching applications, with emphasis on voltage robustness, thermal stability, and TO-92 manufacturability for cost-sensitive industrial controls.

FAQ

Is ZTX458 suitable for avalanche operation?

No. The ZTX458 is not rated for repetitive avalanche energy. Its 400 V V_CEO is a DC blocking specification - operation beyond this voltage risks irreversible breakdown. For avalanche-tolerant designs, consider purpose-built parts like the MJD122 or FMMT417 with specified E_AS.

What is the maximum safe continuous collector current at 100°C ambient?

At T_amb = 100°C, derating requires limiting P_tot to ~300 mW. With V_CE(sat) ≈ 0.4 V at I_C = 300 mA, power dissipation would exceed 120 mW - allowing I_C up to ~250 mA continuously in still air with minimal PCB copper.

Does ZTX458 have built-in base-emitter resistor?

No. The ZTX458 is a bare-die NPN transistor with no integrated base resistors. External base biasing - either fixed-resistor or active current source - must be provided per application requirements and h_FE variation.

Can ZTX458 replace BC337 in high-voltage applications?

No. The BC337 has V_CEO = 45 V and is unsuitable above 50 V. ZTX458 provides 400 V capability but differs in gain profile, saturation voltage, and thermal characteristics - direct substitution requires full revalidation of base drive, thermal margin, and switching timing.