Diodes Incorporated ZTX550STZ

Overview

ZTX550STZ from Diodes Incorporated is an 80V PNP medium-power transistor in E-Line (TO-92 compatible) package, rated for -1A continuous collector current, -2A peak pulse current, 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 thermal robustness is required.

For engineers reviewing the ZTX550STZ datasheet, ZTX550STZ pinout, ZTX550STZ application, or ZTX550STZ equivalent, key selection criteria include its -65V V_CEO rating (ZTX551 variant), -1.1V V_BE(sat) at -150mA/-15mA, h_FE of 50–150 at -1A, f_T = 150MHz, and ESD HBM rating of 4kV - all critical for reliable high-temperature switching in industrial power stages.

Technical Context

This PNP bipolar junction transistor is optimized for medium-power linear and switching applications requiring high breakdown voltage and thermal resilience. Its -65V V_CEO (ZTX551-spec) and -80V V_CBO support operation in 48V and higher DC bus environments, while the 175°C/W R_θJA (min pad layout) defines thermal limits under constrained PCB conditions.

The device exhibits a DC current gain (h_FE) of 50–150 at -1A and -10V V_CE, with saturation voltage of -350mV at -150mA/-15mA drive, enabling efficient base-driven switching in low-to-medium frequency (<1 MHz) power control. Its 150MHz f_T confirms usable gain beyond audio frequencies but not RF switching.

Key Specifications

Pinout & Package

E-Line package (TO-92 compatible), molded plastic body with matte tin-plated leads, UL 94V-0 rated, weight ≈0.159 g. Pin configuration confirmed as emitter-collector-base (ECB) when viewed with flat face toward observer and leads pointing downward: left = E, center = C, right = B.

Key Features

Applications

Equivalent & Alternatives

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

Compared with ZTX550STZ, ZTX551STZ offers identical form-factor and improved voltage ratings with active supply, while MJD2955T4G delivers higher power handling at the cost of size and thermal design complexity - making ZTX551STZ the preferred direct upgrade path.

Availability

ZTX550STZ is available at Aetrix Electronics and suitable for LCD backlight converters, emergency lighting drivers, and industrial DC-DC modules requiring stable component supply despite its obsolete status - inventory is held for legacy system support and repair programs.

Supply support for ZTX550STZ 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 medium-power bipolar transistors for industrial, automotive, and consumer power conversion - emphasizing high-voltage capability, thermal resilience, and lead-free compliance in compact through-hole packages.

FAQ

Is ZTX550STZ still in active production?

No, ZTX550STZ is marked obsolete in Diodes' official documentation and should be replaced with ZTX551STZ for new designs. However, Aetrix Electronics maintains limited legacy stock for repair and maintenance of existing equipment where redesign is impractical or cost-prohibitive.

What is the correct pinout orientation for ZTX550STZ in E-Line package?

When viewing the flat face of the E-Line package with leads pointing downward, the left-to-right pin order is Emitter (E), Collector (C), Base (B). This ECB configuration is confirmed in Diodes' DS33273 Rev. 2-2, page 2, "Pinout Configuration" diagram and matches standard TO-92 PNP orientation.

Can ZTX550STZ be used in automotive applications?

ZTX550STZ itself is not AEC-Q101 qualified, but its direct replacement ZTX551STZ-Q is available in automotive-grade versions. For non-safety-critical auxiliary functions in temperature-stable environments, ZTX550STZ may be used with customer-level validation - however, Diodes explicitly recommends the Q-suffix parts for automotive applications per their datasheet note.

How does the joggled lead variant (STZ) differ electrically from the straight-lead version?

The STZ suffix denotes joggled (bent) leads for automated insertion into PCBs with specific height clearance requirements; it has no electrical or thermal performance difference from the straight-lead version. Both share identical maximum ratings, electrical characteristics, package dimensions, and thermal parameters per DS33273.