Diodes Incorporated ZTX789A

Overview

ZTX789A from Zetex Semiconductors (now Diodes Incorporated) is a PNP silicon planar medium-power high-gain bipolar junction transistor, designed for switching and linear amplification in low-voltage DC circuits. It delivers V_CEO = –25 V, h_FE = 200 at I_C = –2 A, V_CE(sat) = –0.45 V at I_C = –2 A / I_B = –20 mA, and f_T = 100 MHz - enabling use in battery-powered motor drivers and Darlington pair emitter followers.

For engineers reviewing the ZTX789A datasheet, ZTX789A pinout, ZTX789A application, or ZTX789A equivalent, key selection considerations include its TO-92-compatible E-Line package, low saturation voltage under high current, gain stability across –10 mA to –6 A, thermal resistance of 116 °C/W (PCB-mounted), and suitability for pulsed switching with t_on/t_off ≤ 400 ns.

Technical Context

This PNP BJT operates with reverse-polarity biasing: collector and emitter voltages are negative relative to base, supporting sink-switching topologies. Its high h_FE (up to 800 at I_C = –10 mA) and low V_CE(sat) (–0.25 V min at I_C = –1 A) reduce drive current requirements and conduction losses in discrete power stages.

The device's f_T = 100 MHz and C_ibo = 225 pF indicate usable bandwidth for audio-frequency switching and moderate-speed digital control. Thermal design must account for R_th(j–amb) = 116 °C/W on 1-inch² copper, with safe operating area limited to I_C ≤ –3 A and V_CE ≤ –25 V under DC conditions.

Key Specifications

Pinout & Package

Package: TO-92-compatible E-Line (3-lead, plastic, through-hole). Standard lead configuration: Emitter (E), Base (B), Collector (C) - left-to-right when viewing flat side with leads down.

Key Features

Applications

Equivalent & Alternatives

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

Compared with MJD2955 and ZTX753, the ZTX789A uniquely balances TO-92 mountability, 200 h_FE at 2 A, and sub-0.5 V saturation - making it optimal for compact, battery-fed motor and relay drivers where thermal budget and board space are tightly constrained.

Availability

ZTX789A is available at Aetrix Electronics and suitable for battery-powered load switches, DC motor driver stages, Darlington emitter followers, and linear regulator pass elements requiring stable component supply and consistent parametric performance across production batches.

Supply support for ZTX789A 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 was a UK-based analog and discrete semiconductor specialist, acquired by Diodes Incorporated in 2008; known for high-performance BJTs, MOSFETs, and interface ICs targeting industrial and automotive markets.

The ZTX series comprises medium-power silicon transistors optimized for robust switching and linear operation in space- and thermally-constrained applications - emphasizing gain consistency, low saturation, and rugged SOA performance.

FAQ

Is ZTX789A suitable for surface-mount assembly?

No - ZTX789A uses a through-hole TO-92-compatible E-Line package with axial leads. It is not designed for reflow soldering or pick-and-place automation. For SMT equivalents, consider Diodes Incorporated's DXT789A (SOT-23) or DMJ789A (SOT-89), which share similar electrical specs but differ in package and thermal behavior.

What is the maximum safe continuous collector current at 70°C ambient?

At T_amb = 70°C, derating from 5.7 W at 25°C applies at 5.7 mW/°C (per R_th(j–amb) = 116 °C/W). Available power drops to ~3.2 W. Using V_CE(sat) ≈ –0.45 V, max continuous I_C ≈ 3.2 W / 0.45 V ≈ 7.1 A - but absolute max rating limits I_C to –3 A regardless of thermal headroom.

Can ZTX789A replace BC557 in existing designs?

Only with circuit review: BC557 is a general-purpose PNP (I_C = –100 mA, h_FE = 125–800), while ZTX789A handles –3 A and requires significantly higher base drive. Direct substitution may overdrive base resistors or exceed SOA in small-signal nodes. Use only where load current and gain requirements align.

Does ZTX789A have built-in ESD protection?

No - ZTX789A is an unprotected bipolar transistor. Its ESD sensitivity is typical for silicon planar BJTs (HBM Class 1A, <250 V). System-level ESD protection (e.g., series resistors, TVS diodes) must be implemented externally in handling and PCB layout per IEC 61000-4-2 Level 2 requirements.