Diodes Incorporated ZTX558STOA

Overview

ZTX558STOA 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, relay drivers, and flyback snubber circuits.

For engineers reviewing the ZTX558STOA datasheet, ZTX558STOA pinout, ZTX558STOA application, or ZTX558STOA equivalent, key selection criteria include its -400V breakdown rating, h_FE of 100–300 across -1mA to -100mA, -0.5V V_CE(sat) at -50mA/-6mA drive, 50MHz f_T, and ESD HBM rating of 4kV - all critical for reliable high-voltage switching in constrained thermal environments.

Technical Context

The ZTX558STOA is a silicon PNP bipolar junction transistor optimized for high-voltage switching with low saturation voltage and stable DC current gain over wide collector current range (-1mA to -100mA). Its BV_CEO = -400V and BV_CBO = -400V enable operation in circuits with elevated rail voltages, while its 50MHz f_T supports moderate-speed switching up to ~100kHz with controlled turn-on/turn-off times (t_on = 95ns, t_off = 1600ns).

Thermal performance is defined by two derating profiles: 1W at 175°C/W R_θJA (minimum pad layout, 12mm leads) and 1.5W at 116°C/W R_θJA (25mm × 25mm copper, 2.5mm leads). Junction-to-lead thermal resistance is 63.75°C/W, confirming effective heat conduction through the collector lead - essential for through-hole mounting in thermally demanding applications.

Key Specifications

Pinout & Package

Package: E-Line (TO-92 compatible), molded plastic with matte tin-plated leads, UL 94V-0 flammability rating, 159mg weight. Lead configuration: straight leads, 4000 pcs/box.

Key Features

Applications

Equivalent & Alternatives

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

Compared with ZTX558STOA, ZTX550STOA offers identical packaging and gain but half the voltage rating, limiting safe operating area in high-BUS applications; MJD2955T4G delivers 50× higher current but cannot replace ZTX558STOA in 400V circuits due to catastrophic V_CEO mismatch and TO-220 mechanical incompatibility.

Availability

ZTX558STOA is available at Aetrix Electronics and suitable for industrial power supplies, relay driver modules, and high-voltage snubber networks requiring stable component supply, RoHS-compliant manufacturing, and long-term obsolescence management.

Supply support for ZTX558STOA 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, specializing in high-reliability components for automotive, industrial, and computing markets.

The ZTX series targets high-voltage bipolar transistors for ruggedized switching and amplification, emphasizing breakdown robustness, thermal stability, and JEDEC-compliant reliability in through-hole packages.

FAQ

What is the maximum safe collector-emitter voltage for continuous operation?

The ZTX558STOA is rated for V_CEO = -400V at T_A = +25°C, meaning it can sustain up to 400V reverse bias between collector and emitter without breakdown. Derating applies above 25°C ambient; consult Figure 1 in DS33275 for linear thermal derating curves based on PCB layout and lead length.

Can ZTX558STOA be used in surface-mount designs?

No - ZTX558STOA uses the through-hole E-Line (TO-92 compatible) package with straight leads intended for axial insertion and soldering. It lacks SMD-compatible terminations or thermal pads. For surface-mount equivalents, consider Diodes' DXT558 series in SOT-23 or SOT-89 packages, which share similar electrical specs but differ in pinout and thermal behavior.

How does the 12mm lead length affect thermal performance?

With 12mm leads mounted per minimum recommended pad layout, ZTX558STOA achieves R_θJA = 175°C/W and P_D = 1W. This configuration reflects typical production assembly and defines the conservative thermal limit for steady-state operation. Shorter leads or enhanced copper reduce R_θJA to 116°C/W (P_D = 1.5W), but require specific PCB land patterns per Diodes' package outline documentation.

Is ZTX558STOA qualified for automotive applications?

ZTX558STOA itself is not AEC-Q101 qualified. However, Diodes offers the ZTX558Q series - identical electrically and mechanically but manufactured in IATF 16949-certified facilities, PPAP-capable, and fully qualified to AEC-Q101. Customers requiring automotive-grade assurance must specify the Q-suffix part number and follow Diodes' automotive change control process.