onsemi ZTX614

Overview

ZTX614 from Fairchild Semiconductor is an NPN Darlington transistor optimized for high-gain switching at collector currents up to 800 mA and with 100 V collector-emitter breakdown voltage; it features low saturation voltage (1.25 V at IC = 800 mA, IB = 8 mA), high DC current gain (5000–10000), and operates across –55°C to +150°C junction temperature range; used in relay drivers, power supply control, and industrial solid-state switches.

For engineers reviewing the ZTX614 datasheet, pinout, applications, or equivalent options, key selection criteria include verified Darlington gain performance at 500 mA, thermal resistance (RθJA = 125°C/W), TO-226 package compatibility, and safe operating area under continuous 800 mA load conditions.

Technical Context

The ZTX614 implements a monolithic NPN Darlington pair structure, delivering high hFE (>5000) with matched internal base-emitter junctions and integrated emitter resistor for stability. Its breakdown ratings-VCEO = 100 V, VCBO = 120 V-support medium-voltage switching where isolation from transient spikes is required.

Thermal design is constrained by RθJA = 125°C/W and PD = 1000 mW at 25°C, derating linearly at 8 mW/°C above ambient; the device requires heatsinking or board copper area when operating continuously above ~300 mA in still air.

Key Specifications

Pinout & Package

Package: TO-226AE (also designated TO-92 variant), epoxy-molded plastic case with 3-pin vertical leadform; standardized footprint compatible with manual or wave soldering.

Key Features

Applications

Equivalent & Alternatives

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

Compared with MPSA13 and BCX38, the ZTX614 delivers superior combination of breakdown voltage, gain, and saturation performance in TO-226 - making it the preferred choice for 48 V industrial switching where single-transistor simplicity and thermal headroom are critical.

Availability

ZTX614 is available at Aetrix Electronics and suitable for relay drivers, DC motor control, linear power supply regulators, and overcurrent protection circuits requiring stable component supply and long-term industrial availability.

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

Fairchild Semiconductor was a U.S.-based analog and power semiconductor manufacturer, acquired by ON Semiconductor in 2016; known for robust bipolar and MOSFET product lines serving industrial and automotive markets.

The ZTX614 belongs to Fairchild's legacy high-gain Darlington transistor family, designed specifically for cost-effective, high-reliability switching in industrial control, power management, and electromechanical interface applications.

FAQ

What is the maximum continuous collector current rating for ZTX614?

The ZTX614 is rated for 800 mA continuous collector current at TA = 25°C. This rating assumes adequate PCB copper area or heatsinking to maintain junction temperature ≤150°C. Derating is required above 25°C ambient per the 8 mW/°C specification. At 70°C ambient, usable continuous current drops to approximately 620 mA. Always verify thermal design using RθJA = 125°C/W and actual board layout.

Does ZTX614 have built-in base-emitter resistors?

No, the ZTX614 does not integrate base-emitter resistors. It is a standard monolithic NPN Darlington pair without internal biasing networks. External base current limiting and optional base-emitter shunt resistors must be added per application requirements to ensure stable turn-off and prevent leakage-induced false triggering. This differs from digital transistors like the MMBT2222A with integrated resistors.

Can ZTX614 replace BC517 in existing designs?

Yes, ZTX614 can functionally replace BC517 in most applications, as both are NPN Darlington transistors in TO-92 packages with VCEO = 100 V and comparable hFE. However, ZTX614 uses TO-226AE (slightly larger than TO-92), so mechanical fit must be verified. Electrical behavior is nearly identical, but ZTX614 exhibits lower VCE(sat) (1.25 V vs. 1.5 V typical for BC517), improving efficiency in high-current switching.

What is the safe operating area (SOA) limitation for ZTX614 at DC operation?

The ZTX614 SOA at DC is bounded by its 1000 mW power dissipation limit, 100 V VCEO, and 800 mA IC rating. At VCE = 50 V, maximum allowable DC current is ~20 mA to stay within PD; at VCE = 10 V, it supports up to ~100 mA continuously without exceeding thermal limits. Pulse operation (≤300 µs, ≤1% duty cycle) extends SOA beyond these boundaries, but steady-state use must respect the derated power curve.

Is ZTX614 compliant with RoHS and REACH regulations?

Original Fairchild ZTX614 devices manufactured prior to 2006 predate mandatory RoHS compliance and are not RoHS-compliant. Aetrix Electronics supplies only RoHS-compliant re-manufactured or cross-referenced equivalents meeting EU Directive 2011/65/EU and Regulation (EC) No 1907/2006. For new designs, confirm material declaration with current lot documentation before release.