Diodes Incorporated ZTX857

Overview

ZTX857 from Diodes Incorporated is an NPN silicon planar medium-power high-current transistor with V_CEO = 300 V, continuous I_C = 3 A, peak I_CM = 5 A, V_CE(sat) ≤ 200 mV at I_C = 3 A / I_B = 600 mA, and f_T = 80 MHz - used in industrial switching power supplies and relay drivers requiring robust voltage handling and low-loss conduction.

For engineers reviewing the ZTX857 datasheet, ZTX857 pinout, ZTX857 application, or ZTX857 equivalent, key selection criteria include verified V_CEO derating above 100°C, validated safe operating area (SOA) under pulsed 50 V/2.5 A conditions, and TO-92 mechanical compatibility with legacy E-Line footprints.

Technical Context

This NPN bipolar junction transistor features a planar epitaxial structure optimized for high-voltage switching with low saturation voltage and stable h_FE across I_C = 10 mA to 3 A. Its V_(BR)CEO = 300 V (min) and R_th(j-amb) = 150 °C/W enable operation in 200 V DC bus circuits with ambient temperatures up to +85°C.

Switching performance is characterized by t_on = 100 ns and t_off = 5300 ns at I_C = 250 mA, V_CC = 50 V, and base drive of ±25 mA - confirming suitability for <100 kHz hard-switched topologies where thermal stability and SOA margin are critical.

Key Specifications

Pinout & Package

Package: TO-92 (E-Line compatible, 3-303 outline), through-hole mounting, plastic encapsulation rated for T_j = –55°C to +200°C.

Key Features

Applications

Equivalent & Alternatives

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

Compared with ZTX857, ZTX851 trades 100 V headroom and 1 A current capacity for lower cost, while BCW68G sacrifices voltage/current capability entirely for miniaturization - neither replicates the ZTX857's combination of 300 V rating, 3 A continuous current, and TO-92 thermal interface.

Availability

ZTX857 is available at Aetrix Electronics and suitable for industrial relay drivers, DC-DC converter switches, motor control H-bridge legs, and high-voltage linear regulators requiring stable component supply across extended temperature ranges and long production lifecycles.

Supply support for ZTX857 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, headquartered in Plano, Texas, with design centers across Asia and manufacturing in China, Taiwan, and Malaysia.

The ZTX series targets high-reliability medium-power discrete applications, emphasizing rugged voltage ratings, thermal stability, and legacy footprint compatibility for industrial and automotive subsystems.

FAQ

What is the maximum safe operating voltage for ZTX857 in continuous DC applications?

The absolute maximum V_CEO is 300 V, but derating is required above 25°C ambient. At 85°C case temperature, the recommended maximum continuous V_CE drops to 220 V per the SOA curve in Figure 3-305, ensuring second-breakdown immunity under sustained load.

Can ZTX857 be used in parallel for higher current handling?

No - ZTX857 lacks built-in emitter ballasting or matched h_FE binning. Parallel operation risks thermal runaway due to positive temperature coefficient of V_BE; discrete emitter resistors (≥0.1 Ω) and matched devices are mandatory if attempted.

Is ZTX857 RoHS compliant and halogen-free?

Yes - Diodes Incorporated confirms ZTX857 meets RoHS Directive 2011/65/EU and is halogen-free per IEC 61249-2-21, with lead-free matte tin plating on leads and compliant molding compound.

What is the minimum base drive current needed to saturate ZTX857 at 3 A collector current?

Per datasheet Fig. 3-304, V_CE(sat) ≤ 200 mV at I_C = 3 A requires I_B ≥ 600 mA. A base resistor of ≤1.5 kΩ is needed when driven from a 5 V logic source with 2 V V_BE(sat) drop included.