Diodes Incorporated ZTX558

Overview

ZTX558 from Diodes Incorporated is a 400V PNP high-voltage transistor in E-Line (TO-92 compatible) package, rated for -400V V_CEO, -200mA continuous collector current, and 1W power dissipation at 12mm lead length. It serves as a robust switching or linear amplification device in high-voltage industrial power supplies, CRT deflection circuits, and relay drivers where high breakdown voltage and thermal stability are critical.

For engineers reviewing the ZTX558 datasheet, ZTX558 pinout, ZTX558 application, or ZTX558 equivalent, key selection criteria include its -400V BV_CEO, h_FE of 100–300 at -1mA to -100mA, V_CE(sat) ≤ -0.5V at -50mA/-6mA, f_T = 50MHz, and JEDEC-qualified reliability for high-reliability embedded systems.

Technical Context

The ZTX558 is a silicon PNP bipolar junction transistor optimized for high-voltage switching and linear operation up to 200°C junction temperature. Its structure delivers stable DC current gain (h_FE = 100–300 across -1mA to -100mA) and low saturation voltage (-0.2V typical at -20mA/-2mA), enabling efficient on-state conduction in flyback snubbers and HV bias rails.

Thermal performance is defined by two derating profiles: R_θJA = 175°C/W (minimum pad layout, 12mm leads) and 116°C/W (25mm × 25mm copper, 2.5mm leads). ESD robustness includes 4kV HBM and 400V MM ratings per JESD22-A114/A115.

Key Specifications

Pinout & Package

Package: E-Line (TO-92 compatible molded plastic, UL 94V-0, matte tin-plated leads, 159mg weight). Pin identification is standardized per flat-face view: Emitter (left), Base (center), Collector (right) when viewing the flat side with leads down and marking facing outward.

Key Features

Applications

Equivalent & Alternatives

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

Compared with ZTX558, ZTX550 trades 100V breakdown headroom for slightly lower cost, while MPSA92 offers +300mA current capacity at the expense of -100V V_CEO margin-making ZTX558 optimal for designs requiring both high voltage tolerance and JEDEC reliability assurance.

Availability

ZTX558 is available at Aetrix Electronics and suitable for industrial power supply snubbers, CRT deflection circuits, automotive ignition modules, and AC relay drivers requiring stable component supply across extended production lifecycles.

Supply support for ZTX558 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 manufacturer of discrete semiconductors and analog ICs, headquartered in Plano, Texas, with design, manufacturing, and sales operations across Asia, Europe, and North America.

The ZTX series targets high-voltage, high-reliability discrete transistors for industrial, automotive-adjacent, and legacy display applications-emphasizing ruggedness, thermal stability, and JEDEC-compliant qualification.

FAQ

What is the maximum allowable junction temperature for ZTX558?

The ZTX558 is rated for an operating junction temperature range of -55°C to +200°C. This 200°C upper limit enables deployment in high-ambient environments such as under-hood automotive modules or enclosed industrial power supplies without derating, provided thermal design meets R_θJA = 175°C/W specifications with 12mm lead length.

Is ZTX558 suitable for automotive applications?

ZTX558 itself is not AEC-Q101 qualified, but Diodes offers automotive-grade variants (e.g., ZTX558Q) with PPAP documentation, manufactured in IATF 16949-certified facilities. For non-safety-critical aftermarket or industrial-adjacent systems, ZTX558 may be used-but formal automotive qualification requires the Q-suffix part.

How does lead length affect ZTX558's power dissipation?

Power dissipation is directly tied to thermal resistance: at 12mm lead length (minimum pad layout), P_D = 1W with R_θJA = 175°C/W; at 2.5mm lead length on 25mm × 25mm copper, P_D rises to 1.5W with R_θJA = 116°C/W. Derating curves in Figure 1 must be applied above 25°C ambient.

What is the typical switching speed of ZTX558?

ZTX558 has t_on = 95ns and t_off = 1600ns under specified test conditions (I_C = -50mA, V_C = -100V, I_B1 = 5mA, I_B2 = -10mA). Its 50MHz f_T supports switching up to ~500kHz in optimized layouts, though turn-off time limits high-frequency PWM use without active base pull-down.