STMicroelectronics STF20NK50Z

Overview

STF20NK50Z from STMicroelectronics is an N-channel 500 V, 0.23 Ω (typ), 17 A SuperMESH™ Power MOSFET in TO-220FP package with integrated gate-source Zener protection (±30 V), 100% avalanche tested, and rated for 40 W total dissipation at T_C = 25 °C. It serves as a high-voltage switching device in offline SMPS primary-side circuits.

For engineers reviewing the STF20NK50Z datasheet, STF20NK50Z pinout, STF20NK50Z application, or STF20NK50Z equivalent, key selection criteria include its 4.5 V/ns dv/dt capability, low 85 nC total gate charge, 2600 pF input capacitance, Zener-protected gate, and thermal resistance of 3.1 °C/W (j-case).

Technical Context

This MOSFET employs ST's SuperMESH™ layout optimization to reduce R_DS(on) while maintaining robust dv/dt immunity-critical for hard-switched flyback and resonant converters operating near 500 V bus rails. Its built-in back-to-back gate-source Zener diodes clamp transients up to ±30 V, eliminating external gate protection components.

The device features a 150 °C maximum junction temperature, 2500 V_RMS insulation withstand voltage between leads and heat sink, and 850 mJ single-pulse avalanche energy (E_AS) at V_DD = 50 V-enabling reliable unclamped inductive switching in industrial power supplies.

Key Specifications

Pinout & Package

STF20NK50Z uses the TO-220FP (full-pack) package: insulated plastic case with integral heatsink tab, footprint compatible with standard TO-220 but with reduced thermal resistance (3.1 °C/W j-case) and enhanced creepage/clearance for safety-critical isolation.

Key Features

Applications

Equivalent & Alternatives

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

Compared with STP20NK50Z, STF20NK50Z trades 150 W dissipation headroom for electrical isolation and compact footprint; versus FQP20N50, it adds gate Zener protection and guaranteed avalanche performance at minimal cost premium-critical for certified industrial power supplies.

Availability

STF20NK50Z is available at Aetrix Electronics and suitable for industrial SMPS, AC-DC adapters, LED driver power stages, and UPS inverter stages requiring stable component supply across multi-year production cycles.

Supply support for STF20NK50Z 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

STMicroelectronics is a global semiconductor leader headquartered in Geneva, Switzerland, designing and manufacturing microcontrollers, power devices, sensors, and analog ICs for industrial, automotive, and consumer markets.

This device belongs to ST's SuperMESH™ Power MOSFET product line, engineered specifically for high-efficiency, high-reliability switching in 400–600 V offline power conversion systems where avalanche ruggedness and gate protection are mandatory.

FAQ

What is the maximum continuous drain current at 100 °C case temperature?

The STF20NK50Z supports 10.71 A continuous drain current at T_C = 100 °C, as specified in Table 2 of the datasheet. This derating reflects thermal limits imposed by its 3.1 °C/W junction-to-case thermal resistance and 150 °C maximum junction temperature, making it suitable for thermally constrained designs like sealed LED drivers.

Does STF20NK50Z require external gate protection?

No. The device integrates back-to-back Zener diodes between gate and source with ±30 V breakdown voltage (BVGSO), providing inherent protection against ESD and gate overvoltage transients. External TVS diodes are unnecessary unless system-level surge immunity exceeds 6 kV HBM or involves long gate traces in high-noise environments.

How does its avalanche rating compare to STP20NK50Z?

Both STF20NK50Z and STP20NK50Z share identical avalanche characteristics: 17 A repetitive avalanche current and 850 mJ single-pulse energy at V_DD = 50 V. The difference lies solely in packaging-TO-220FP vs TO-220-not in silicon-level ruggedness. Both are 100% avalanche tested per production test flow.

Can STF20NK50Z be used in synchronous rectification?

No. STF20NK50Z is optimized as a high-voltage primary-side switch, not a low-side synchronous rectifier. Its body diode has relatively high forward voltage (1.6 V at 17 A) and slow reverse recovery (355 ns), making it unsuitable for secondary-side rectification where low V_F and fast t_rr are essential. Use dedicated SR controllers with logic-level MOSFETs instead.