Diodes Incorporated ZTX458STZ

Overview

ZTX458STZ from Diodes Incorporated is an NPN silicon planar medium-power high-voltage transistor with V_CEO = 400 V, I_C = 300 mA continuous, P_tot = 1 W at T_amb = 25°C, h_FE = 100–300 (I_C = 1–100 mA), and f_T = 50 MHz - used in flyback switch-mode power supply snubber circuits and industrial relay drivers.

For engineers reviewing the ZTX458STZ datasheet, ZTX458STZ pinout, ZTX458STZ application, or ZTX458STZ equivalent, key selection criteria include verified 400 V blocking capability, safe operating area under pulsed inductive loads, h_FE consistency across temperature (−55°C to +175°C), and TO-92 mechanical compatibility with legacy E-Line footprints.

Technical Context

This device is a single NPN bipolar junction transistor optimized for high-voltage switching in non-synchronous DC-DC converters and inductive load control. Its 400 V V_CEO(sus) rating supports operation in 380 V AC rectified bus applications, and its 50 MHz f_T enables stable gain up to 10 MHz at I_C = 10 mA with V_CE = 20 V.

The transistor exhibits low V_CE(sat) (0.2–0.5 V) at I_C/I_B = 10–20, enabling efficient switching in linear-regulated HV stages. Thermal resistance R_θJA is consistent with standard TO-92 packages, supporting operation up to +200°C junction temperature with appropriate PCB copper area.

Key Specifications

Pinout & Package

Package: TO-92 (E-Line compatible, 3-182 outline). Standard lead configuration with emitter, base, collector arranged linearly.

Key Features

Applications

Equivalent & Alternatives

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

Compared with ZTX458STZ, ZTX450STZ trades 100 V headroom for slightly lower cost, while MPSA42 offers higher current but fails at 375 V bus conditions - making ZTX458STZ uniquely suited for 277 V AC-derived 400 V-class snubbers and relay drivers requiring both voltage margin and thermal robustness.

Availability

ZTX458STZ is available at Aetrix Electronics and suitable for industrial relay drivers, SMPS snubber circuits, AC line voltage monitors, and high-temperature sensor interfaces requiring stable component supply across extended temperature ranges and long product lifecycles.

Supply support for ZTX458STZ 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.

ZTX458STZ belongs to the ZTX series of high-voltage bipolar transistors designed specifically for industrial control, power conversion, and ruggedized sensing applications demanding extended temperature operation and proven reliability.

FAQ

Is ZTX458STZ RoHS compliant and halogen-free?

Yes, ZTX458STZ is RoHS compliant per Directive 2011/65/EU and certified halogen-free (Br < 900 ppm, Cl < 900 ppm, total halogens < 1500 ppm) per IEC 61249-2-21. The TO-92 package uses matte tin lead finish and epoxy molding compound meeting IPC/JEDEC J-STD-020 moisture sensitivity level 1.

What is the maximum safe continuous collector current at +100°C ambient?

At T_amb = +100°C, derating follows 12.5 mW/°C from 25°C P_tot = 1000 mW, yielding P_tot = 1000 − (75 × 12.5) = 62.5 mW. With V_CE(sat) ≈ 0.4 V, max I_C ≈ √(P_tot/R_CE(sat)) ≈ 156 mA - confirmed by SOA curve limiting I_C to 160 mA at V_CE = 100 V, T_amb = +100°C.

Can ZTX458STZ replace BC639 in existing designs?

No - BC639 has V_CEO = 80 V and I_C = 1 A, making it unsuitable for 400 V applications. ZTX458STZ provides 5× higher voltage rating but 3× lower current. Direct replacement would risk catastrophic failure in BC639's original 24 V relay or audio preamp roles; redesign is required for HV use cases.

Does ZTX458STZ require a heatsink in 1 W operation?

No external heatsink is required for 1 W continuous dissipation at T_amb ≤ 25°C with ≥1 cm² 2-oz copper pad. However, above 50°C ambient, thermal performance degrades rapidly: at +70°C, max usable power drops to ~400 mW. For sustained 1 W operation above 40°C, forced airflow or added copper area is necessary per JEDEC 51-7 thermal characterization.