Diodes Incorporated ZTX551

Overview

ZTX551 from Diodes Incorporated is an 80V PNP medium-power bipolar junction transistor in E-Line (TO-92 compatible) package, rated for -1A continuous collector current, -65V V_CEO, and 1W power dissipation at +25°C ambient. It operates up to +200°C junction temperature and is used in DC-DC converters, LCD backlight drivers, and emergency lighting circuits where high-voltage PNP switching with robust thermal capability is required.

For engineers reviewing the ZTX551 datasheet, ZTX551 pinout, ZTX551 application, or ZTX551 equivalent, key selection criteria include verified BV_CEO = -65V, h_FE = 50–150 at I_C = -150mA, V_CE(sat) = -350mV, R_θJA = 175°C/W on minimum pad layout, and JEDEC-qualified reliability for industrial power control designs.

Technical Context

The ZTX551 is a silicon PNP BJT optimized for medium-power linear and switching applications. Its -80V V_CBO and -65V V_CEO support operation in higher-voltage rails than standard low-voltage PNP transistors, while its 150MHz f_T enables use in moderate-frequency switching converters.

Thermal design is enabled by dual R_θJA ratings: 116°C/W (25mm² copper pad) and 175°C/W (minimum recommended layout), with R_θJL = 63.75°C/W confirming effective heat conduction through the collector lead - critical for through-hole power handling without heatsinks.

Key Specifications

Pinout & Package

E-Line package (TO-92 compatible) with molded plastic body, matte tin-plated leads, and 0.159g mass. Pin configuration confirmed as emitter (E), collector (C), base (B) in left-to-right order when flat face is oriented toward viewer and leads point downward.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar PNP medium-power transistor applications.

Compared with ZTX550 and MJD2955, the ZTX551 uniquely balances 65V blocking, 1A capability, and TO-92-compatible form factor - making it optimal for cost-sensitive, thermally constrained, medium-voltage PNP switching where drop-in replacement and board-level reliability are prioritized over extreme current or package interchangeability.

Availability

ZTX551 is available at Aetrix Electronics and suitable for LCD backlight converters, emergency lighting drivers, and industrial DC-DC modules requiring stable component supply, long-term manufacturability, and JEDEC-qualified reliability.

Supply support for ZTX551 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 distribution operations across Asia, Europe, and the Americas.

The ZTX series targets industrial and automotive power control applications, emphasizing high-voltage PNP performance, thermal resilience, and compliance with AEC-Q101 and RoHS 3 standards in through-hole packages.

FAQ

Is the ZTX551 pin-compatible with the ZTX550?

Yes - both use identical E-Line (TO-92 compatible) package with emitter-collector-base (E-C-B) pinout in left-to-right order when viewed from the flat face with leads down. Mechanical dimensions, lead pitch, and soldering profiles match exactly, enabling direct PCB replacement.

What is the maximum allowable base current for reliable operation?

The datasheet specifies V_BE(sat) = -1.1V at I_C = -150mA and I_B = -15mA. For -1A continuous operation, base current must be ≥ -100mA to ensure saturation; however, practical design limits I_B to ≤ -200mA to avoid bond-wire overheating and maintain h_FE stability.

Does the ZTX551 require a heatsink in 1W operation?

No - at 1W dissipation on minimum recommended PCB pad layout (R_θJA = 175°C/W), junction temperature rise is 175°C above ambient. With T_A ≤ +25°C, T_J reaches +200°C, matching its absolute maximum rating. Derating is required above +25°C ambient; no external heatsink is needed below that threshold.

Can the ZTX551 be used in automotive applications?

Yes - it is qualified to AEC-Q101 standards and manufactured in IATF 16949-certified facilities. While the base ZTX551 is not automotive-grade by default, Diodes offers Q-suffix variants (e.g., ZTX551Q) with full PPAP documentation and enhanced change control for automotive use.