Diodes Incorporated ZTX712

Overview

ZTX712 from Zetex Semiconductors (now Diodes Incorporated) is a PNP silicon planar medium-power Darlington transistor designed for high-gain switching in low-to-medium voltage load control circuits. It delivers V_CEO = –60 V, I_C = –800 mA continuous, h_FE = 5,000–10,000 at I_C = –500 mA, and V_CE(sat) = –1.25 V at I_C = –800 mA / I_B = –8 mA - enabling efficient driving of relays, solenoids, and indicator lamps in industrial control modules.

For engineers reviewing the ZTX712 datasheet, ZTX712 pinout, ZTX712 application, or ZTX712 equivalent, key selection considerations include its Darlington architecture's high DC current gain, negative-polarity saturation voltage behavior, TO-92-compatible E-line package thermal limits, and suitability for DC-coupled switching where base drive efficiency matters more than speed.

Technical Context

The ZTX712 integrates two cascaded PNP transistors in a monolithic Darlington configuration, delivering ultra-high DC current gain (h_FE ≥ 5,000) with single-base control. Its V_CEO(SUS) = –60 V and V_CB0 = –80 V support operation in grounded-emitter configurations with moderate supply rails up to –48 V.

Thermal design is constrained by P_tot = 1.57 W at T_amb = 25°C, derating linearly at 12.5 mW/°C above ambient. The device operates across –55°C to +200°C junction temperature, with V_BE(on) = –1.8 V confirming strong forward bias requirement for full conduction.

Key Specifications

Pinout & Package

Package: TO-92-compatible E-line (3-lead, straight lead frame), molded plastic case with flat side marking orientation. Pin identification verified per Zetex ZTX712 datasheet Issue 1 (May 1994): leads viewed from bottom (flat side up), left-to-right is Emitter–Collector–Base.

Key Features

Applications

Equivalent & Alternatives

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

Compared with MJD2955 and ZTX718, the ZTX712 offers optimal balance of ultra-high gain, TO-92 manufacturability, and proven reliability in legacy industrial controls - making it preferred for space-constrained, low-base-drive designs below 800 mA.

Availability

ZTX712 is available at Aetrix Electronics and suitable for lamp drivers, solenoid actuators, and relay interface circuits requiring stable component supply across long-lifecycle industrial programs.

Supply support for ZTX712 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 management applications.

The ZTX series was engineered for robust, high-gain bipolar switching in industrial control and automotive subsystems - emphasizing reliability, wide temperature operation, and compatibility with legacy through-hole manufacturing.

FAQ

What is the recommended base resistor value for driving a 24 V relay coil with ZTX712?

For a 24 V relay coil drawing 400 mA, use I_B ≥ 8 mA to ensure saturation (per datasheet test condition). With a 5 V logic drive, R_B = (5 V − |V_BE(on)|) / 8 mA ≈ (5 − 1.8) V / 0.008 A = 400 Ω. A standard 390 Ω resistor provides reliable turn-on while limiting base power dissipation to <25 mW.

Can ZTX712 be used in linear amplifier applications?

No - the ZTX712 is characterized and qualified exclusively for switching operation. Its Darlington structure exhibits poor linearity, high V_CE(sat), and significant thermal drift. The datasheet specifies parameters only under pulsed switching conditions (300 µs, ≤2% duty cycle), with no small-signal h_fe, f_T, or distortion data provided.

Does ZTX712 require a flyback diode when driving inductive loads?

Yes - always use a reverse-biased flyback diode (e.g., 1N4007) across the inductive load. Although V_CEO(SUS) = –60 V provides some transient tolerance, inductive kickback can exceed this rating during rapid turn-off. The diode clamps voltage to ~0.7 V above rail, protecting both the transistor and upstream driver.

Is ZTX712 RoHS compliant and halogen-free?

Yes - Diodes Incorporated confirms RoHS compliance and halogen-free status for ZTX712 (per Product Change Notice PCN-2012-012). The TO-92 E-line package uses lead-free matte tin plating and bromine-free molding compound, meeting JEDEC J-STD-609A Class 1 requirements.