Diodes Incorporated ZTX1055ASTOB

Overview

ZTX1055ASTOB from Diodes Incorporated (formerly Zetex) is an NPN silicon planar medium-power high-gain transistor in TO-92 package, rated for 120 V V_CEO, 3 A continuous collector current, and 6 A pulse current, with typical h_FE of 400 at IC = 1 A - used in automotive switching circuits and audio driver stages.

For engineers reviewing the ZTX1055ASTOB datasheet, ZTX1055ASTOB pinout, ZTX1055ASTOB application, or ZTX1055ASTOB equivalent, key selection criteria include V_CEO ≥ 120 V, I_C ≥ 3 A continuous, V_CE(sat) ≤ 160 mV at IC = 1 A / IB = 20 mA, f_T = 130 MHz, and TO-92 thermal derating behavior up to +200°C junction temperature.

Technical Context

This NPN bipolar junction transistor employs a planar silicon structure optimized for medium-power linear and switching operation. Its high h_FE (min 275 at IC = 10 mA, typ 400 at IC = 1 A) enables efficient base drive in low-control-current applications, while low V_CE(sat) (120–160 mV) minimizes conduction loss under load.

The device supports pulsed operation up to 6 A with 2% duty cycle and exhibits robust safe operating area (SOA) up to 100 V and 10 A in single-pulse conditions. Thermal resistance and transient response are characterized across –55°C to +200°C, supporting automotive under-hood deployment.

Key Specifications

Pinout & Package

Package: TO-92 (standard through-hole plastic package, 3-pin, lead pitch 1.27 mm, body height ~4.5 mm). Compatible with E-Line mounting and manual soldering processes.

Key Features

Applications

Equivalent & Alternatives

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

Compared with ZTX1055ASTOB, ZTX1048ASTOB trades voltage headroom and current capacity for cost reduction in low-voltage designs, while MJD127G offers higher current capability at the expense of efficiency and board space - making ZTX1055ASTOB optimal for 12–24 V, 1–3 A saturated switching where thermal and size constraints apply.

Availability

ZTX1055ASTOB is available at Aetrix Electronics and suitable for automotive relay drivers, audio power stages, industrial solenoid interfaces, and DC motor speed control requiring stable component supply and long-term manufacturability.

Supply support for ZTX1055ASTOB 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 acquired Zetex Semiconductors in 2008 and maintains its legacy high-performance bipolar and analog product lines for industrial and automotive markets.

The ZTX series was developed specifically for medium-power discrete switching and amplification applications demanding high h_FE, low V_CE(sat), and extended temperature reliability - especially in automotive and industrial control subsystems.

FAQ

Is ZTX1055ASTOB RoHS compliant?

Yes, ZTX1055ASTOB is RoHS compliant and halogen-free per Diodes Incorporated's standard qualification for legacy Zetex products manufactured post-2010. The TO-92 package uses lead-free matte tin plating on leads and meets JEDEC J-STD-020 reflow profiles.

What is the maximum safe base current for continuous operation?

The absolute maximum base current is 500 mA, but continuous operation above 150 mA is not recommended due to thermal stress on the bond wire and internal junction. For 3 A collector current, IB = 150 mA (h_FE ≈ 20) ensures robust saturation while maintaining reliability.

Can ZTX1055ASTOB replace BC337 in existing designs?

No - BC337 has V_CEO = 45 V and I_C = 0.5 A, making it unsuitable as a direct replacement. ZTX1055ASTOB's 120 V/3 A rating requires PCB layout review for trace width, thermal relief, and flyback protection, especially in inductive load applications.

Does this transistor support linear (Class-A) operation?

Yes, ZTX1055ASTOB is characterized for linear use with specified V_BE(on), h_FE, and f_T. However, its 1 W P_tot at 25°C limits Class-A dissipation to ~300 mW at elevated ambient temperatures; proper heatsinking or derating per the published thermal curve is required.