Diodes Incorporated ZTX555

Overview

ZTX555 from Zetex Semiconductors (now Diodes Incorporated) is a PNP silicon planar medium-power bipolar junction transistor rated for -150 V V_CEO, -1 A continuous collector current, and 1 W power dissipation at 25°C ambient - used as a high-voltage switching or linear amplification device in industrial power supplies and relay drivers.

For engineers reviewing the ZTX555 datasheet, ZTX555 pinout, ZTX555 application, or ZTX555 equivalent, key selection considerations include its -150 V V_CEO, -1 A I_C, h_FE range of 50–300 at -10 mA, f_T = 100 MHz, and TO-92 package compatibility with legacy E-Line designs.

Technical Context

The ZTX555 operates as a PNP BJT with fixed-base current-controlled conduction, supporting both linear amplification and saturated switching modes. Its -150 V V_CEO and -160 V V_CBO enable use in high-side switch configurations up to 125 V DC rails, while its 100 MHz f_T supports moderate-speed switching applications.

Thermal derating is defined at 5.7 mW/°C above 25°C ambient, and safe operating area (SOA) curves confirm single-pulse capability up to 1 A at 100 V with 100 µs pulse width. The device exhibits V_CE(sat) = -0.3 V at I_C = -100 mA / I_B = -10 mA and V_BE(sat) = -1 V under same conditions.

Key Specifications

Pinout & Package

Supplied in an E-Line TO-92 compatible package (3-lead plastic case), with leads arranged in straight-line configuration and standard C-B-E pin order when viewed from flat side with leads down.

Key Features

Applications

Equivalent & Alternatives

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

Compared with ZTX554 and MJD2955, the ZTX555 uniquely balances -150 V blocking, TO-92 compatibility, and 1 A capability - making it optimal for space-constrained, medium-voltage industrial controls where neither lower-voltage nor high-power alternatives meet all three criteria.

Availability

ZTX555 is available at Aetrix Electronics and suitable for industrial relay drivers, linear voltage regulators, DC motor H-bridge upper arms, and high-voltage signal inversion requiring stable component supply and long-term manufacturability.

Supply support for ZTX555 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, now part of Diodes Incorporated, specialized in high-performance discrete semiconductors for industrial and automotive applications before acquisition in 2008.

The ZTX series was developed for robust, high-voltage PNP switching in space- and cost-sensitive industrial controls, emphasizing TO-92 compatibility, guaranteed gain spread, and extended temperature operation.

FAQ

What is the maximum safe operating voltage for ZTX555 in a switching application?

The ZTX555 has a guaranteed V_CEO of -150 V and V_CBO of -160 V. For reliable switching, design should limit peak collector-emitter voltage to ≤120 V to maintain 20% margin against transients and temperature-induced degradation. Derating per the SOA curve is mandatory for pulsed operation above 100 V.

Can ZTX555 replace ZTX554 in existing designs without modification?

Yes - ZTX555 is pin-compatible and electrically backward-compatible with ZTX554 in TO-92 sockets. Its higher -150 V V_CEO (vs. -125 V) and identical pinout allow direct substitution where additional voltage margin is beneficial, with no layout or bias network changes required.

What base drive current is required to fully saturate ZTX555 at 1 A collector load?

At I_C = -1 A, the datasheet does not specify V_CE(sat); however, extrapolation from the -100 mA / -10 mA test condition and h_FE min of 50 indicates ≥-20 mA base current is needed for hard saturation. Actual drive should be -25 mA to ensure margin across temperature and process variation.

Is ZTX555 suitable for audio amplifier output stages?

No - while ZTX555 has adequate f_T and linearity for small-signal preamp stages, its 1 W power limit, lack of matched complementary NPN pair, and uncharacterized THD performance make it unsuitable for Class AB audio output stages. It is optimized for switching and regulated power, not high-fidelity analog.