Diodes Incorporated ZTX614STZ

Overview

ZTX614STZ from Diodes Incorporated is an NPN silicon planar medium-power Darlington transistor with V_CEO = 100 V, I_C = 800 mA continuous, h_FE = 10,000 at I_C = 500 mA, and P_tot = 1.0 W at T_amb = 25°C; used in high-gain switching and linear amplification stages of industrial power supplies and relay drivers.

For engineers reviewing the ZTX614STZ datasheet, ZTX614STZ pinout, ZTX614STZ application, or ZTX614STZ equivalent, key selection criteria include verified Darlington gain linearity at 500 mA, V_CE(sat) ≤ 1.25 V under 8 mA base drive, thermal derating slope (5.7 mW/°C), and TO-92-compatible E-line package mechanical compatibility.

Technical Context

This Darlington pair integrates two NPN transistors monolithically to deliver high DC current gain while maintaining single-base control. It operates with a guaranteed minimum h_FE of 5000 at I_C = 100 mA and up to 10,000 at I_C = 500 mA, enabling low-base-drive logic-level interfacing.

V_CEO(sus) = 100 V and V_CBO = 120 V support robust blocking in inductive load switching; V_CE(sat) = 1.25 V at I_C = 800 mA / I_B = 8 mA ensures low conduction loss in medium-power driver stages.

Key Specifications

Pinout & Package

E-line TO-92 compatible package (3-215 outline); molded plastic case with axial leads, standard footprint for through-hole mounting and manual rework.

Key Features

Applications

Equivalent & Alternatives

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

Compared with BCX38, ZTX614STZ offers 25% higher blocking voltage for improved surge margin in 24–48 V industrial systems; versus ZTX615, it provides complementary polarity for low-side switching topologies requiring grounded load return paths.

Availability

ZTX614STZ is available at Aetrix Electronics and suitable for industrial relay drivers, DC motor speed control circuits, linear voltage regulators, and overcurrent protection circuits requiring stable component supply and long-term manufacturability.

Supply support for ZTX614STZ 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 is a global manufacturer of discrete semiconductors and analog ICs, specializing in high-reliability components for industrial, automotive, and computing markets.

ZTX614STZ belongs to the ZTX series of medium-power bipolar transistors designed specifically for ruggedized switching and amplification in space-constrained industrial power interfaces.

FAQ

What is the maximum safe operating collector current for ZTX614STZ in continuous DC mode?

The absolute maximum continuous collector current is 800 mA at T_amb = 25°C. Derating is required above 25°C at 5.7 mW/°C; actual usable current depends on PCB copper area, ambient temperature, and heatsinking. At 70°C ambient with minimal copper, sustained current must be reduced to approximately 550 mA to maintain junction temperature below 200°C.

Does ZTX614STZ require a base resistor when driven from a 3.3 V microcontroller GPIO?

Yes - a base resistor is mandatory. With V_BE(on) = 1.8 V and typical h_FE ≥ 5000, driving 800 mA requires ≥160 µA base current. For a 3.3 V GPIO, a 9.1 kΩ resistor delivers ~165 µA, ensuring saturation while limiting GPIO stress. Lower resistance increases base current margin but raises power dissipation in the resistor.

Can ZTX614STZ replace BCX38 in existing designs without layout changes?

Yes - ZTX614STZ uses the same E-line TO-92 (3-215) package and identical C-B-E pinout as BCX38. However, its higher V_CEO (100 V vs. 80 V) improves surge immunity, and its higher minimum h_FE (5000 vs. 4000) reduces required base drive. No PCB modification is needed, but verify voltage margins in the target application.

Is ZTX614STZ suitable for audio amplifier output stages?

No - ZTX614STZ is optimized for switching and medium-speed linear control, not high-fidelity audio. Its Darlington structure introduces significant V_BE nonlinearity and limited frequency response (f_T not specified in datasheet); crossover distortion and poor slew rate make it unsuitable for Class-A/B audio output stages. Use dedicated audio transistors like BD139/BD140 instead.