Diodes Incorporated ZTX557STOA

Overview

ZTX557STOA from Diodes Incorporated is a PNP silicon planar medium-power high-voltage transistor with V_CEO = −300 V, I_C = −0.5 A continuous, P_tot = 1.0 W, h_FE = 50–300 at I_C = −10 mA, and f_T = 75 MHz - used in high-voltage switching and linear regulation stages of industrial power supplies and relay drivers.

For engineers reviewing the ZTX557STOA datasheet, ZTX557STOA pinout, ZTX557STOA application, or ZTX557STOA equivalent, key selection criteria include verified −300 V V_CEO rating, −0.3 V V_CE(sat) at −50 mA/−5 mA drive, TO-92-compatible leadform, and safe operating area validated for single-pulse and DC operation up to +200°C junction temperature.

Technical Context

This PNP bipolar junction transistor operates in common-emitter configuration with guaranteed breakdown margins: V_(BR)CBO = −300 V (I_C = −100 µA), V_(BR)CEO = −300 V (I_C = −10 mA), and V_(BR)EBO = −5 V (I_E = −100 µA). Its f_T = 75 MHz supports moderate-speed switching in analog and digital interface circuits.

Switching performance is characterized with defined test conditions: t_r = 1.0 µs, t_d = 100 ns, t_f = 2.0 µs, t_s = 14 µs at V_CE = −10 V, I_C/I_B = 10, confirming suitability for <100 kHz hard-switched applications where voltage headroom and thermal robustness are prioritized over ultrafast transitions.

Key Specifications

Pinout & Package

Supplied in an E-Line TO-92 compatible package (3-lead, straight-lead variant), with standard emitter-base-collector (E-B-C) terminal assignment matching JEDEC TO-92 outline.

Key Features

Applications

Equivalent & Alternatives

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

Compared with ZTX557STOA, ZTX550STZ trades voltage margin for higher minimum h_FE, while MPSA92 matches V_CEO but sacrifices 37.5% power capability and gain consistency - making ZTX557STOA optimal for thermally constrained, high-reliability 300 V applications.

Availability

ZTX557STOA is available at Aetrix Electronics and suitable for industrial relay drivers, high-voltage linear regulators, AC mains-sensing interfaces, and overvoltage protection circuits requiring stable component supply across extended temperature and voltage ranges.

Supply support for ZTX557STOA 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, Malaysia, and Taiwan.

ZTX557STOA belongs to the ZTX series of high-voltage bipolar transistors, engineered specifically for industrial control, power conversion, and ruggedized signal conditioning where reliability at elevated voltage and temperature is non-negotiable.

FAQ

Is ZTX557STOA RoHS compliant and halogen-free?

Yes, ZTX557STOA meets RoHS Directive 2011/65/EU and is certified halogen-free per IEC 61249-2-21. The device carries the "HF" suffix designation in Diodes Incorporated's compliance documentation and uses matte tin lead finish on all three terminals.

What is the maximum allowable base current for continuous operation?

The absolute maximum base current is not explicitly specified, but I_B must be limited to ensure I_C ≤ −0.5 A and P_tot ≤ 1.0 W. At V_BE(sat) ≈ −1.0 V and h_FE ≥ 50, I_B should not exceed −10 mA continuously to maintain safe junction temperature.

Can ZTX557STOA replace ZTX556 in existing designs?

Yes - ZTX557STOA shares identical pinout, package, and thermal characteristics with ZTX556, but offers −300 V V_CEO vs. −200 V. No layout change is needed; the upgrade improves voltage margin without altering base drive or heatsinking requirements.

Does ZTX557STOA require a base-emitter resistor for stability?

Yes - a base-emitter resistor (typically 10 kΩ to 100 kΩ) is recommended to prevent leakage-induced turn-on during high-temperature operation or when driven by open-collector logic. This ensures reliable cutoff when base drive is removed, especially near T_j = +200°C.