STF21NM50N Equivalent & Substitute Parts

Part Overview

The STF21NM50N is an N-Channel MOSFET manufactured by STMicroelectronics, rated for 500V drain-to-source voltage with 18A continuous drain current at 25°C. This device is packaged in a TO-220FP through-hole configuration and is part of the MDmesh™ II series. The part is currently classified as obsolete, necessitating identification of functionally equivalent alternatives for ongoing design support and procurement requirements. Substitute parts must maintain electrical compatibility across critical parameters including voltage rating, current capacity, and thermal characteristics while accommodating packaging variations.

Substiute Parts

STF21NM50N

STMicroelectronicsIn Stock: 2154STF21NM50N Datasheet

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FDPF20N50FT

onsemiIn Stock: 20444FDPF20N50FT Datasheet

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FDPF20N50T

onsemiIn Stock: 1915FDPF20N50T Datasheet

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Key Parameters

Substitute Part Grouping Explanation

Substitution of the STF21NM50N is determined by strict equivalence across the following critical parameters:

Voltage Rating Compatibility: All substitute parts must maintain a Drain to Source Voltage (Vdss) rating of 500V or greater to ensure safe operation in the original application circuit.

Current Capacity: Substitute parts must support a continuous drain current (Id) at 25°C equal to or exceeding 18A to handle the design load without thermal derating.

Gate Drive Voltage: The drive voltage specification at maximum Rds On must be 10V to ensure compatibility with existing gate driver circuits.

Thermal Performance: Power dissipation capability and maximum junction temperature must support the thermal requirements of the application.

Packaging and Mounting: Through-hole TO-220 package variants (TO-220F, TO-220FP) are mechanically compatible with the original PCB layout.

Regulatory Compliance: All substitute parts must maintain ROHS3 compliance and REACH unaffected status to satisfy procurement and environmental requirements.

The identified substitute parts FDPF20N50FT and FDPF20N50T, both manufactured by onsemi under the UniFET™ series, meet these substitution criteria with enhanced current ratings (20A) and improved thermal performance (38.5W), while maintaining the 500V voltage rating and 10V gate drive specification.

Parameter Comparison

Engineering Selection Recommendations

Primary Substitutes: FDPF20N50FT and FDPF20N50T are direct functional equivalents for the STF21NM50N. Both parts are manufactured by onsemi and maintain active product status, ensuring long-term availability and supply chain continuity. These devices exceed the original part's current rating (20A versus 18A) and thermal performance (38.5W versus 30W), providing design margin for thermal management.

Compliance Alignment: All substitute parts maintain ROHS3 compliance and REACH unaffected status, satisfying regulatory requirements equivalent to the original device. The extended operating temperature range (-55°C to 150°C) of the substitute parts provides broader environmental operating capability compared to the STF21NM50N.

Packaging Compatibility: The TO-220-3 Full Pack configuration is consistent across all three parts, ensuring mechanical compatibility with existing PCB layouts and thermal management solutions. Minor package designation variations (TO-220F versus TO-220FP) do not affect electrical performance or mounting compatibility.

Performance Considerations: The FDPF20N50T exhibits lower on-resistance (230 mOhm @ 10A, 10V) and reduced gate charge (59.5 nC @ 10V) compared to the STF21NM50N, resulting in improved switching efficiency and reduced gate drive power requirements. The FDPF20N50FT maintains equivalent gate charge specifications (65 nC @ 10V) with slightly higher on-resistance (260 mOhm @ 10A, 10V), offering alternative performance trade-offs depending on application requirements.

Frequently Asked Questions (FAQ)

Q: Can FDPF20N50FT and FDPF20N50T be used interchangeably with STF21NM50N?

A: Both onsemi parts are functionally equivalent substitutes for the STF21NM50N. They maintain the same 500V voltage rating, 10V gate drive specification, and TO-220-3 package configuration. The primary differences are enhanced current ratings (20A versus 18A) and improved thermal performance (38.5W versus 30W). Selection between the two onsemi variants depends on specific on-resistance and gate charge requirements for the application.

Q: What are the key electrical parameters that determine substitution compatibility?

A: Substitution compatibility is determined by: (1) Drain to Source Voltage rating of 500V or greater, (2) Continuous drain current capacity of 18A or higher at 25°C, (3) Gate drive voltage specification of 10V, (4) Through-hole TO-220 package configuration, and (5) ROHS3 compliance and REACH unaffected status. All identified substitute parts satisfy these criteria.

Q: Are there packaging differences between TO-220F and TO-220FP?

A: TO-220F and TO-220FP are both three-lead through-hole packages with identical mechanical footprints and mounting compatibility. The designations reflect minor manufacturing variations that do not affect electrical performance or PCB layout requirements. Both package types are suitable for direct substitution in existing designs.

Q: How do the on-resistance specifications compare between the three parts?

A: The STF21NM50N specifies 190 mOhm maximum on-resistance at 9A and 10V gate voltage. The FDPF20N50T specifies 230 mOhm at 10A and 10V, while the FDPF20N50FT specifies 260 mOhm at 10A and 10V. The FDPF20N50T provides the closest on-resistance performance to the original part. Higher on-resistance in substitute parts is offset by increased current capacity and thermal performance.

Q: What is the significance of the extended operating temperature range in the substitute parts?

A: The FDPF20N50FT and FDPF20N50T specify an operating temperature range of -55°C to 150°C, compared to the STF21NM50N maximum of 150°C. This extended lower temperature limit provides design flexibility for applications requiring operation in cold environments, though the maximum junction temperature remains equivalent at 150°C.

Q: Are the substitute parts available in the same packaging format?

A: Yes. All three parts are supplied in TO-220-3 Full Pack through-hole configuration. The FDPF20N50FT is supplied in tube packaging, while the FDPF20N50T is also supplied in tube packaging. Both formats are compatible with standard PCB assembly processes and thermal management solutions designed for the original STF21NM50N.

Q: What is the product status significance for long-term design support?

A: The STF21NM50N is classified as obsolete, indicating discontinued manufacturing and limited future availability. The substitute parts FDPF20N50FT and FDPF20N50T are both classified as active products, ensuring continued manufacturing, supply chain availability, and technical support from onsemi for ongoing design requirements and production needs.