Diodes Incorporated ZTX450STZ

Overview

ZTX450STZ from Diodes Incorporated is an NPN silicon planar medium-power bipolar junction transistor (BJT) designed for general-purpose switching and linear amplification in industrial control, power supply regulation, and relay driver circuits. It features a 45 V V_CEO, 1 A continuous collector current, 1 W power dissipation at 25°C, and a minimum DC current gain (h_FE) of 100 at I_C = 150 mA and V_CE = 10 V.

For engineers reviewing the ZTX450STZ datasheet, ZTX450STZ pinout, ZTX450STZ application, or ZTX450STZ equivalent, key selection criteria include its 45 V V_CEO rating, 0.25 V V_CE(sat) at I_C = 150 mA / I_B = 15 mA, 150 MHz f_T, TO-92 package compatibility, and suitability for medium-speed switching (<100 ns turn-off time) in discrete power interface stages.

Technical Context

The ZTX450STZ operates as a standard NPN BJT with fixed base-emitter junction architecture and no integrated biasing or protection circuitry. Its 150 MHz transition frequency supports operation up to low RF frequencies, while its 0.25 V saturation voltage enables efficient switching in 5–24 V logic-driven loads.

Thermal performance is defined by a maximum junction temperature of +200°C and a thermal resistance R_θJA of ~200°C/W (typical for TO-92), requiring heatsinking only above ~300 mW sustained dissipation. The device exhibits stable h_FE across I_C = 10 mA to 1 A under specified V_CE conditions.

Key Specifications

Pinout & Package

Supplied in an E-Line TO-92 compatible package - a 3-lead through-hole plastic case with standardized lead spacing and mechanical footprint matching JEDEC TO-92. Leads are arranged in straight-line configuration with emitter (E), base (B), and collector (C) assigned per standard orientation.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar NPN medium-power switching applications.

Compared with ZTX450STZ, ZTX451STZ offers higher voltage headroom without trade-offs in speed or gain, while BC337-40 trades off f_T and h_FE consistency for broader availability and lower unit cost in non-demanding applications.

Availability

ZTX450STZ is available at Aetrix Electronics and suitable for industrial relay drivers, linear voltage regulator pass elements, DC motor speed control stages, and audio preamp gain stages requiring stable component supply and long-term manufacturability.

Supply support for ZTX450STZ 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 industrial, automotive, and computing applications.

ZTX450STZ belongs to the ZTX series of medium-power silicon BJTs, engineered for robustness in industrial control interfaces and legacy-compatible replacements where TO-92 form factor and proven reliability are essential.

FAQ

Is ZTX450STZ RoHS compliant?

Yes, ZTX450STZ is RoHS compliant and meets EU Directive 2011/65/EU requirements, including exemption 7a for lead in high-melting-temperature solder. Lead finish is matte tin, and packaging uses halogen-free molding compound per Diodes Incorporated's product change notice PCN-2019-003.

What is the typical thermal resistance R_θJA for ZTX450STZ in TO-92?

The typical junction-to-ambient thermal resistance (R_θJA) for ZTX450STZ in standard TO-92 mounting on FR-4 PCB with 1-inch² copper pad is 200°C/W. This value assumes no additional heatsinking and defines the maximum allowable power dissipation before exceeding 200°C junction temperature at 25°C ambient.

Can ZTX450STZ replace BC548 in a 5 V logic interface?

ZTX450STZ can replace BC548 in 5 V logic interfaces only if collector load voltage remains ≤45 V and current stays ≤1 A. However, its higher V_BE(sat) (1.1 V vs. ~0.7 V for BC548) may reduce noise margin in TTL-level circuits, and its higher h_FE spread requires careful base resistor selection to avoid overdrive.

Does ZTX450STZ have built-in ESD protection?

No, ZTX450STZ does not include on-chip ESD protection diodes. Its absolute maximum rating for V_EB0 is 5 V, and exposure to >2 kV HBM without external clamping risks permanent junction damage. External 5.1 V Zener or TVS diode across base-emitter is recommended in handling-sensitive or field-deployed designs.