Diodes Incorporated ZTX705

Overview

ZTX705 from Zetex Semiconductors (now Diodes Incorporated) is a PNP silicon planar medium-power Darlington transistor in TO-92 package, rated for −120 V V_CEO, −1 A continuous collector current, and 1 W power dissipation at 25°C. It delivers h_FE ≥ 3,000 at I_C = −1 A and is optimized for high-gain switching in inductive load interfaces such as relay drivers in industrial control panels.

For engineers reviewing the ZTX705 datasheet, ZTX705 pinout, ZTX705 application, or ZTX705 equivalent, key selection criteria include verified V_CEO = −120 V, guaranteed h_FE ≥ 3k at −1 A, TO-92 thermal derating profile, and confirmed V_CE(sat) ≤ −2.5 V under −1 A/−1 mA drive - critical for low-loss switching in 12–24 V DC control circuits.

Technical Context

The ZTX705 implements a monolithic Darlington pair with integrated base-emitter resistor network to ensure stable turn-on and reduce external component count. Its −120 V V_CEO rating enables direct interface with 100 V-class solenoids and lamp loads without snubbers.

Designed for pulsed and DC switching, it supports I_C up to −2 A peak (ICM = −4 A), exhibits f_T = 160 MHz typical, and maintains h_FE ≥ 2k even at I_C = −2 A - enabling robust gain retention across its full operating range.

Key Specifications

Pinout & Package

Package: TO-92 (E-Line compatible), epoxy-molded, through-hole, with standard lead configuration (Emitter-Base-Collector from left to right when flat side faces viewer).

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar PNP Darlington switching applications.

Compared with MJD2955G and BC807-40, the ZTX705 uniquely combines TO-92 form factor, Darlington gain ≥3k, −120 V rating, and 1 W dissipation - making it irreplaceable for space-constrained, medium-voltage, medium-current switching where gain and voltage margin are non-negotiable.

Availability

ZTX705 is available at Aetrix Electronics and suitable for industrial relay drivers, DC lamp control, solenoid actuation, and legacy automotive control modules requiring stable component supply and long-term obsolescence management.

Supply support for ZTX705 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, acquired by Diodes Incorporated in 2008, specialized in high-performance discrete semiconductors for analog and power applications.

The ZTX series was developed specifically for ruggedized, high-gain switching in industrial and automotive control systems - emphasizing reliability, wide temperature operation, and simplified drive requirements.

FAQ

Is ZTX705 RoHS compliant?

Yes, ZTX705 is RoHS compliant per Diodes Incorporated's product change notice PCN-2012-010. All current production lots meet EU Directive 2011/65/EU and contain ≤0.1% lead by weight in homogeneous materials, with exemptions applied only where permitted for high-melting-temperature solder alloys.

Can ZTX705 be used in linear amplifier mode?

No - ZTX705 is characterized and qualified exclusively for switching operation. Its Safe Operating Area (SOA) graph shows no DC linear region beyond 100 mA at V_CE > 20 V, and thermal runaway risk is high under sustained analog bias due to Darlington β variation with temperature.

What is the recommended flyback diode for inductive loads?

A 1N4007 or 1N5819 Schottky diode is recommended across the load. With V_CEO = −120 V, the diode must withstand ≥120 V reverse voltage; 1N4007 provides 1000 V PIV and handles 1 A surge, matching ZTX705's I_CM = −4 A rating during turn-off transients.

Does ZTX705 require a base resistor when driven by a microcontroller?

Yes - although internally biased, a 1–10 kΩ series base resistor is recommended to limit peak base current during logic transitions and prevent latch-up in CMOS outputs. Typical drive: 3.3 V GPIO → 4.7 kΩ → Base, delivering ~0.7 mA I_B at saturation, well within safe limits.