Diodes Incorporated ZTX605STOB

Overview

ZTX605STOB from Diodes Incorporated is an NPN silicon planar medium-power Darlington transistor with V_CEO = 120 V, I_C = 1 A continuous, h_FE ≥ 2000 at I_C = 1 A, P_tot = 1 W at T_amb = 25°C, and TO-92 compatible E-line package - used in high-gain switching and linear amplification stages of industrial power supplies and relay drivers.

For engineers reviewing the ZTX605STOB datasheet, ZTX605STOB pinout, ZTX605STOB application, or ZTX605STOB equivalent, key selection criteria include verified Darlington gain stability at 1 A, V_CEO derating behavior above 25°C, safe operating area (SOA) compliance under pulsed 1 A loads, and thermal resistance validation for PCB-mounted TO-92 thermal management.

Technical Context

This Darlington pair integrates a high-gain input transistor and a power output transistor on a single silicon die, enabling low base drive current (I_B = 1 mA) to switch 1 A collector current while maintaining V_CE(sat) ≤ 1.5 V. Its f_T = 150 MHz supports fast switching up to ~100 kHz with controlled turn-on/turn-off times (t_on = 0.5 µs, t_off = 1.6 µs).

The device operates across –55°C to +200°C junction temperature range and features V_CB0 = 140 V, V_EBO = 10 V, and C_ibo = 90 pF / C_obo = 15 pF - critical for noise-sensitive analog amplifiers and EMI-limited relay interface circuits requiring low capacitance and high breakdown margins.

Key Specifications

Pinout & Package

Package: TO-92 compatible E-line (3-lead plastic case, JEDEC TO-92 outline), lead-free and RoHS compliant, designed for through-hole mounting with standard PCB footprint.

Key Features

Applications

Equivalent & Alternatives

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

Compared with ZTX604STOB, ZTX605STOB provides 20 V higher V_CEO headroom for industrial transient immunity; versus MJD127G, it trades thermal capacity and package size for compact TO-92 integration in space-constrained control modules.

Availability

ZTX605STOB is available at Aetrix Electronics and suitable for industrial relay drivers, DC motor start/stop control, linear audio pre-amplifiers, and overvoltage-protected power supplies requiring stable component supply and long-term manufacturability.

Supply support for ZTX605STOB 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.

ZTX605STOB belongs to the ZTX series of medium-power bipolar transistors engineered for ruggedized switching and linear amplification in harsh-temperature industrial environments.

FAQ

What is the maximum safe operating temperature for ZTX605STOB?

The junction temperature range is –55°C to +200°C. Maximum ambient temperature depends on actual power dissipation and PCB thermal design. Using the derating factor of 5.7 mW/°C, T_amb(max) = (1000 mW − P_act) / 5.7 + 25°C. For example, at 500 mW dissipation, max ambient is ≈114°C.

Can ZTX605STOB replace ZTX604STOB in existing designs?

Yes, with verification of V_CE stress margins. ZTX605STOB has identical pinout, package, and gain but offers 20 V higher V_CEO (120 V vs. 100 V). If the original design operates below 80 V collector-emitter voltage, ZTX605STOB provides improved transient tolerance without layout changes.

Is ZTX605STOB suitable for PWM motor control at 20 kHz?

Yes - its f_T = 150 MHz and t_on/t_off = 0.5 µs / 1.6 µs support clean switching at 20 kHz. However, ensure base drive strength (≥1 mA peak) and minimize trace inductance to avoid oscillation, especially given its Darlington Miller capacitance (C_obo = 15 pF).

Does ZTX605STOB require a base resistor, and what value is recommended?

Yes - a base resistor is mandatory to limit I_B and prevent thermal runaway. For 1 A I_C and h_FE ≥ 2000, I_B ≥ 0.5 mA suffices. With 5 V drive, R_B = (5 V − V_BE(sat)) / 0.5 mA ≈ (5 − 1.8) V / 0.5 mA = 6.4 kΩ; use 4.7 kΩ standard value for margin.