Diodes Incorporated ZTX605STOA

Overview

ZTX605STOA from Zetex Semiconductors (now Diodes Incorporated) is an NPN silicon planar medium-power Darlington transistor designed for high-voltage switching and amplification in industrial control and power interface circuits. It delivers 120 V_CEO, 1 A continuous collector current, DC current gain of 2000 at I_C = 1 A, 1 W power dissipation at T_amb = 25°C, and V_CE(sat) ≤ 1.5 V under I_C = 1 A / I_B = 1 mA - enabling robust relay driving and solenoid control.

For engineers reviewing the ZTX605STOA datasheet, ZTX605STOA pinout, ZTX605STOA application, or ZTX605STOA equivalent, key selection criteria include verified V_CEO derating behavior above 25°C, Darlington-specific base drive requirements (V_BE(sat) = 1.8 V), safe operating area (SOA) limits at pulse widths down to 100 µs, and thermal resistance (R_thJA ≈ 175 K/W) for TO-92 package layout planning.

Technical Context

This Darlington pair integrates two NPN transistors monolithically to achieve high DC current gain (h_FE ≥ 2000 at I_C = 1 A) while maintaining V_CEO = 120 V and low saturation voltage. Its structure supports linear operation up to f_T = 150 MHz at I_C = 100 mA / V_CE = 10 V, with C_ibo = 90 pF and C_obo = 15 pF enabling predictable high-frequency turn-off behavior.

Switching performance is characterized by t_on = 0.5 µs and t_off = 1.6 µs under pulsed conditions (300 µs width, ≤2% duty cycle), with V_BE(on) = 1.7 V at I_C = 1 A / V_CE = 5 V. The device operates across –55°C to +200°C junction temperature range and requires explicit thermal derating per the published voltage derating graph.

Key Specifications

Pinout & Package

Package: TO-92 compatible (E-Line), through-hole, 3-lead plastic case with emitter (E), base (B), collector (C) arranged in standard linear configuration.

Key Features

Applications

Equivalent & Alternatives

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

Compared with MJD127G and BD679A, ZTX605STOA uniquely combines 120 V_CEO, TO-92 mountability, and 2000× DC gain - making it optimal for new designs requiring high-voltage discrete switching in compact through-hole layouts.

Availability

ZTX605STOA is available at Aetrix Electronics and suitable for industrial relay drivers, solenoid actuator interfaces, DC motor control circuits, and high-voltage sensor conditioning requiring stable component supply and long-term manufacturability.

Supply support for ZTX605STOA 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 industrial, automotive, and power management applications.

ZTX605STOA belongs to the ZTX series of medium-power bipolar transistors engineered for ruggedized switching and linear amplification in harsh-temperature environments and high-reliability control systems.

FAQ

What is the maximum allowable base current for ZTX605STOA?

The absolute maximum base current is not explicitly specified, but electrical characteristics confirm reliable operation at I_B = 1 mA for I_C = 1 A. Exceeding 2 mA risks thermal runaway due to Darlington internal gain; design practice limits I_B to ≤1.2 mA with 10 kΩ series resistor from 5 V logic.

Can ZTX605STOA replace ZTX604 in existing designs?

Yes, with verification of V_CEO margin: ZTX605STOA offers 120 V_CEO versus ZTX604's 100 V, identical pinout and package, and matching V_CE(sat) and h_FE curves. No circuit changes are needed unless operating near ZTX604's 100 V limit.

Is heatsinking required for 1 A continuous operation?

At T_amb = 25°C, no heatsink is required - P_tot = 1 W yields ~175°C junction rise. However, at T_amb = 60°C, derated power is ~0.8 W; sustained 1 A demands either ambient reduction or minimal copper pad heatsinking (≥1 cm² 2 oz Cu) to maintain T_j < 150°C.

Does ZTX605STOA support PWM switching at 20 kHz?

Yes: with t_on = 0.5 µs and t_off = 1.6 µs, total switching time is <2.2 µs - well below 50 µs period of 20 kHz. Verified SOA data supports repetitive 100 µs pulses, confirming suitability for PWM-driven solenoids and motor enable signals.