Diodes Incorporated ZTX601B

Overview

ZTX601B from Zetex Semiconductors (now Diodes Incorporated) is an NPN silicon planar medium-power Darlington transistor designed for high-voltage switching and linear amplification in industrial control and power interface circuits. It delivers 160 V_CEO, 1 A continuous collector current, DC current gain up to 100k at I_C = 50 mA, 1 W power dissipation at 25°C ambient, and V_CE(sat) ≤ 1.2 V at I_C = 1 A / I_B = 10 mA - used in relay drivers and solid-state output modules.

For engineers reviewing the ZTX601B datasheet, ZTX601B pinout, ZTX601B application, or ZTX601B equivalent, key selection criteria include verified V_CEO = 160 V, guaranteed h_FE ≥ 5k at I_C = 1 A, TO-92-compatible E-Line package thermal derating (5.7 mW/°C), and confirmed switching times (t_on = 0.75 µs, t_off = 2.2 µs under pulsed conditions).

Technical Context

The ZTX601B implements a monolithic Darlington pair architecture with integrated base-emitter resistor network absent - requiring external base drive control. Its high h_FE (up to 100k) enables low-base-current switching of inductive loads, while V_CEO = 160 V and V_CBO = 180 V support operation across 120 V AC line-referenced circuits and 48 V industrial bus systems.

Thermal design relies on its TO-92 package's 5.7 mW/°C derating slope above 25°C, and safe operating area (SOA) is defined for single-pulse conditions up to 1000 V•A with 1 ms pulse width. f_T = 250 MHz at I_C = 100 mA / V_CE = 10 V confirms suitability for moderate-speed switching, not RF amplification.

Key Specifications

Pinout & Package

Supplied in an E-Line TO-92-compatible package (3-206 outline), lead-forming matches standard TO-92 footprint with emitter (E), base (B), and collector (C) arranged in linear C–B–E configuration when viewed from front (flat side), enabling drop-in replacement in legacy through-hole designs.

Key Features

Applications

Equivalent & Alternatives

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

Compared with MMBT6427 and BC879-25, the ZTX601B uniquely combines 160 V blocking capability, TO-92 through-hole compatibility, and guaranteed 5k h_FE at 1 A - making it irreplaceable in legacy industrial controls requiring robust 120 V AC interfacing without redesign.

Availability

ZTX601B is available at Aetrix Electronics and suitable for industrial relay drivers, solid-state output modules, DC motor on/off controllers, and AC line-switched indicators requiring stable component supply across extended product lifecycles.

Supply support for ZTX601B 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 and automotive signal conditioning and power interface applications.

The ZTX series was engineered specifically for ruggedized medium-power switching in programmable logic controllers, factory automation I/O modules, and power supply protection circuits - emphasizing voltage robustness, gain consistency, and thermal reliability in TO-92 form factor.

FAQ

What is the maximum safe continuous collector current for ZTX601B at 70°C ambient?

At 70°C ambient, derating begins at 25°C using 5.7 mW/°C. With P_tot = 1 W at 25°C, allowable power drops to 1 W − (45 × 0.0057) = 0.74 W. Using V_CE(sat) ≈ 1.0 V at I_C = 1 A, max continuous I_C ≈ 0.74 A. This assumes no heatsink and natural convection cooling.

Does ZTX601B include an internal base-emitter resistor?

No, ZTX601B is a bare Darlington transistor without integrated biasing resistors. External base drive must be provided - typically via a series resistor from a logic output or microcontroller GPIO. The device requires ~10 mA base current to fully saturate at 1 A collector current.

Can ZTX601B replace ZTX600 in existing designs?

Yes, ZTX601B is a direct upgrade to ZTX600 with higher V_CEO (160 V vs. 140 V) and V_CBO (180 V vs. 160 V), identical pinout, package, and thermal characteristics. All electrical parameters meet or exceed ZTX600 specs, enabling drop-in replacement without circuit modification.

Is ZTX601B suitable for PWM motor speed control?

ZTX601B supports PWM operation up to ~200 kHz based on t_on/t_off values, but its 1.2 V V_CE(sat) causes significant conduction loss at high duty cycles. It is appropriate for on/off control and low-frequency (<5 kHz) PWM, but not recommended for high-efficiency variable-speed drives where MOSFETs or dedicated motor drivers offer superior performance.