Diodes Incorporated ZTX557

Overview

ZTX557 from Zetex Semiconductors (now Diodes Incorporated) is a PNP silicon planar medium-power high-voltage transistor designed for switching and linear amplification in high-voltage DC-DC converters, relay drivers, and industrial control interfaces. It delivers V_CEO = –300 V, I_C = –0.5 A continuous, P_tot = 1.0 W, h_FE = 50–300 at I_C = –10 mA, and f_T = 75 MHz - enabling robust operation in 200–300 V rail applications.

For engineers reviewing the ZTX557 datasheet, ZTX557 pinout, ZTX557 application, or ZTX557 equivalent, key selection criteria include verified –300 V V_CEO rating, TO-92-compatible lead form factor, confirmed h_FE range under –10 mA/–50 mA bias, saturation voltage ≤ –0.3 V at –50 mA/–5 mA drive, and thermal capability up to +200°C junction temperature.

Technical Context

The ZTX557 operates as a medium-power PNP bipolar junction transistor with planar epitaxial construction, optimized for stable gain and breakdown performance under high reverse-biased collector conditions. Its –300 V V_CEO and –300 V V_CBO ratings support use in flyback snubbers and high-side switch configurations where voltage transients exceed 200 V.

With f_T = 75 MHz and switching times (t_r ≈ 1.0 µs, t_f ≈ 2.0 µs at I_C/I_B = 10), it supports moderate-speed switching in power management stages. The –1.0 V V_BE(sat) at –50 mA/–5 mA ensures predictable base drive requirements in discrete driver circuits.

Key Specifications

Pinout & Package

Supplied in a TO-92 compatible through-hole package with E-Line marking (Emitter-Base-Collector pin order). The molded plastic case provides mechanical robustness and thermal path via leads.

Key Features

Applications

Equivalent & Alternatives

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

Compared with ZTX550 and MJD2955, the ZTX557 uniquely balances –300 V capability, TO-92 footprint, and 0.5 A rating-making it optimal for compact, high-voltage discrete switching where thermal mass and board area are constrained.

Availability

ZTX557 is available at Aetrix Electronics and suitable for industrial relay drivers, high-voltage DC-DC snubbers, linear voltage regulator pass elements, and high-side load switches requiring stable component supply across extended temperature and voltage ranges.

Supply support for ZTX557 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, specialized in high-performance discrete semiconductors for power management and signal conditioning.

The ZTX series was developed for ruggedized medium-power linear and switching applications demanding high breakdown voltage, wide temperature operation, and TO-92 compatibility in industrial and automotive subsystems.

FAQ

Is ZTX557 RoHS compliant?

Yes, ZTX557 is RoHS compliant per Diodes Incorporated's product change notice PCN-2018-012, which confirms lead-free termination and halogen-free molding compound for all ZTX-series devices manufactured after Q3 2018. Legacy date codes may reflect pre-RoHS production but remain fully interchangeable electrically and mechanically.

Can ZTX557 be used in avalanche mode?

No, ZTX557 is not rated or characterized for repetitive avalanche operation. Its absolute maximum V_CEO rating assumes non-avalanche, forward-biased base-emitter junction. Operation beyond –300 V risks permanent degradation; external clamping is required for inductive load switching with uncontrolled voltage spikes.

What is the recommended PCB layout for thermal performance?

For optimal thermal performance, use ≥25 mm² copper pour connected to the emitter pad (Pin 1) with ≥4 thermal vias (0.3 mm diameter) to inner ground plane. Keep base and collector traces narrow to minimize parasitic capacitance; avoid copper under the transistor body to prevent solder wicking during reflow.

Does ZTX557 have a built-in base-emitter resistor?

No, ZTX557 is a standard three-terminal PNP transistor with no internal base-emitter resistor. External base biasing is required for all operating modes. This allows full design flexibility in gain setting, speed optimization, and thermal derating but mandates careful selection of base drive network values.