Diodes Incorporated ZTX657STOA

Overview

ZTX657STOA from Diodes Incorporated is an NPN silicon planar medium-power high-voltage transistor with V_CEO = 300 V, I_C = 0.5 A continuous, P_tot = 1 W at T_amb = 25°C, h_FE ≥ 40 at I_C = 10 mA, and f_T = 30 MHz - used in flyback switch-mode power supply (SMPS) primary-side switching and industrial relay drivers.

For engineers reviewing the ZTX657STOA datasheet, ZTX657STOA pinout, ZTX657STOA application, or ZTX657STOA equivalent, key selection criteria include verified 300 V V_CEO rating, TO-92-compatible E-Line package thermal performance, confirmed h_FE min of 40 at low I_C, and documented switching times (t_r/t_f ≤ 1.2 µs) for hard-switched DC-DC stages.

Technical Context

This transistor operates as a medium-power NPN switch in linear or saturated mode, supporting DC collector currents up to 0.5 A with guaranteed V_CE(sat) ≤ 0.5 V at I_C = 100 mA and I_B = 10 mA. Its 300 V V_CEO and 200 V V_CBO ratings enable use in off-line 230 V AC-derived supplies where voltage transients exceed 200 V.

The device features a transition frequency f_T of 30 MHz at I_C = 10 mA and V_CE = 20 V, confirming suitability for moderate-speed switching (≤ 500 kHz) rather than RF amplification. Safe operating area (SOA) curves are validated for single-pulse and 1 ms–1 s duty-cycle operation up to 300 V and 1 A peak.

Key Specifications

Pinout & Package

Package: TO-92-compatible E-Line (3-227), through-hole, epoxy-molded, lead-form compatible with standard TO-92 sockets and wave-soldering profiles.

Key Features

Applications

Equivalent & Alternatives

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

Compared with ZTX657STOA, ZTX656STOA trades voltage headroom for identical gain and speed in lower-voltage systems, while BCV46 offers same voltage rating in miniature SOT-23 but lacks current capability - making ZTX657STOA the sole option for 300 V / 0.5 A through-hole switching.

Availability

ZTX657STOA is available at Aetrix Electronics and suitable for industrial relay drivers, off-line SMPS primary switches, DC motor brake circuits, and high-voltage LED string drivers requiring stable component supply across multi-year production cycles.

Supply support for ZTX657STOA 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 Taiwan and China.

ZTX657STOA belongs to the ZTX series of high-voltage bipolar transistors, designed specifically for industrial power switching where reliability at elevated voltage and temperature is critical.

FAQ

Is ZTX657STOA RoHS compliant and halogen-free?

Yes, ZTX657STOA meets RoHS Directive 2011/65/EU and is certified halogen-free per IEC 61249-2-21. The device uses lead-free matte tin plating on leads and complies with JEDEC J-STD-020 moisture sensitivity level 1 (MSL-1) for unlimited floor life at ≤30°C/60% RH.

What is the maximum allowable base resistor value when driving ZTX657STOA from a 5 V MCU GPIO?

With I_C = 0.5 A and minimum h_FE = 40, required I_B ≥ 12.5 mA. Accounting for V_BE(sat) ≈ 1 V, R_B ≤ (5 V − 1 V) / 12.5 mA = 320 Ω. A 270 Ω resistor ensures reliable saturation across temperature and process variation.

Can ZTX657STOA be used in avalanche mode?

No - ZTX657STOA is not rated or characterized for controlled avalanche operation. Its SOA curve covers single-pulse and repetitive conditions up to 300 V, but no energy rating (E_AS) or ruggedness data is provided. Use only within specified V_CEO, I_C, and P_tot limits.

Does ZTX657STOA require a heatsink in continuous 0.4 A operation?

At I_C = 0.4 A and V_CE(sat) ≈ 0.45 V, power dissipation is ~180 mW. With TO-92 thermal resistance R_θJA ≈ 200°C/W, junction rise is ~36°C above ambient. Heatsinking is unnecessary below 0.45 A in open-air, but recommended above 0.4 A in sealed enclosures >50°C ambient.