Diodes Incorporated ZTX614

Overview

ZTX614 from Zetex Semiconductors (now Diodes Incorporated) is an NPN silicon planar medium-power Darlington transistor in TO-92 package, rated for 100 V V_CEO, 800 mA continuous collector current, and 1 W power dissipation at 25°C ambient. It delivers h_FE = 5000–10000 at I_C = 100–500 mA and is used in high-gain switching applications such as relay drivers and lamp controllers.

For engineers reviewing the ZTX614 datasheet, ZTX614 pinout, ZTX614 application, or ZTX614 equivalent, key selection criteria include verified Darlington gain at 500 mA, V_CE(sat) ≤ 1.25 V under 8 mA base drive, thermal derating slope of 5.7 mW/°C, and E-line TO-92 mechanical compatibility with BCX38.

Technical Context

The ZTX614 employs a monolithic Darlington pair structure to achieve high DC current gain without external bias networks. Its V_CEO(sus) = 100 V and V_CBO = 120 V support robust off-state blocking in inductive load switching.

Designed for pulsed operation (300 µs pulse width, ≤2% duty cycle), it specifies V_BE(on) = 1.8 V at I_C = 800 mA and maintains low leakage: I_CBO ≤ 100 nA at V_CB = 60 V and I_EBO ≤ 100 nA at V_EB = 8 V.

Key Specifications

Pinout & Package

Supplied in E-line TO-92 package (3-215 outline), compatible with BCX38 footprint and mounting. Leads are arranged in straight-line configuration with emitter (E), base (B), and collector (C) assigned to pins 1, 2, and 3 respectively per standard TO-92 pin view (flat side facing user, leads down).

Key Features

Applications

Equivalent & Alternatives

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

Compared with BCX38, ZTX614 offers higher minimum h_FE for tighter base drive control; versus ULN2003A, it provides higher voltage capability and single-channel thermal optimization but lacks integrated protection diodes.

Availability

ZTX614 is available at Aetrix Electronics and suitable for relay drivers, lamp dimmers, solenoid actuators, and 4–20 mA sensor outputs requiring stable component supply across industrial automation, building controls, and test equipment programs.

Supply support for ZTX614 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 precision analog and power switching applications.

The ZTX series was engineered for medium-power linear and switching roles in industrial control systems where gain consistency, thermal robustness, and TO-92 compatibility were critical design constraints.

FAQ

What is the maximum safe operating temperature for ZTX614?

The ZTX614 has a specified junction temperature range of −55°C to +200°C. At 25°C ambient, its 1.0 W power rating allows operation up to ~190°C junction temperature before reaching thermal limit, assuming 5.7 mW/°C derating and no additional heatsinking.

Can ZTX614 replace BCX38 in existing PCB layouts?

Yes - ZTX614 uses the same E-line TO-92 package (3-215) and identical pinout (E-B-C), making it a direct mechanical and electrical drop-in replacement for BCX38 in most applications, provided the higher minimum h_FE does not cause unintended overdrive.

Is a base resistor required when driving ZTX614 from a microcontroller GPIO?

Yes - although ZTX614's high h_FE reduces base current demand, a series base resistor is mandatory to limit I_B and prevent damage. For 3.3 V GPIO driving 800 mA load, a 270 Ω resistor sets I_B ≈ 8 mA, matching the V_CE(sat) test condition.

Does ZTX614 include an integrated flyback diode?

No - ZTX614 is a bare Darlington transistor without integrated clamping diodes. When switching inductive loads like relays or solenoids, an external reverse-biased diode (e.g., 1N4007) must be placed across the load to suppress flyback voltage transients.