STF20NK50Z Equivalent & Substitute Parts

Part Overview

The STF20NK50Z is an N-Channel 500V 17A MOSFET manufactured by STMicroelectronics in the SuperMESH™ series, housed in a TO-220FP through-hole package. This device is classified as obsolete, indicating discontinuation from the manufacturer. Identifying equivalent and substitute parts is necessary to maintain design continuity, ensure supply chain availability, and support ongoing production or maintenance requirements for applications utilizing this component.

Key Parameters

Parameter	Value	Unit
Drain to Source Voltage (Vdss)	500	V
Continuous Drain Current (Id) @ 25°C	17	A
On-State Resistance (Rds On Max) @ 10V	270	mOhm
Gate Threshold Voltage (Vgs th) Max	4.5	V @ 100µA
Gate Charge (Qg) Max @ 10V	119	nC
Power Dissipation (Max)	40	W
Operating Temperature Range	-55 to 150	°C (TJ)
Package Type	TO-220-3	Through Hole
FET Type	N-Channel	—
Technology	MOSFET (Metal Oxide)	—

Substitute Part Grouping Explanation

Substitution of the STF20NK50Z is determined by electrical and mechanical compatibility across the following critical parameters:

Primary Substitution Criteria:

Drain to Source Voltage (Vdss): Must equal or exceed 500V
Continuous Drain Current (Id): Must equal or exceed 17A at 25°C
On-State Resistance (Rds On): Must not significantly exceed 270mOhm at rated conditions
Gate Threshold Voltage (Vgs th): Must be compatible with 10V drive voltage
Package Type: Must be TO-220-3 through-hole configuration
FET Type: Must be N-Channel MOSFET (Metal Oxide)

Substitution Logic: Parts are grouped into two categories based on electrical performance alignment:

Direct Substitutes – Parts meeting or exceeding all primary electrical parameters with minimal deviation in Rds On and gate charge characteristics
Similar Substitutes – Parts with comparable voltage and current ratings but with trade-offs in secondary parameters such as power dissipation, gate charge, or current rating

The following substitute parts are evaluated against these criteria.

Parameter Comparison

Parameter	STF20NK50Z (Main)	FDPF18N50T	FDPF20N50T	FQPF17N40T	IPA50R280CEXKSA2	SPA16N50C3XKSA1
Manufacturer	STMicroelectronics	onsemi	onsemi	Fairchild Semiconductor	Infineon Technologies	Infineon Technologies
Vdss (V)	500	500	500	400	500	560
Id @ 25°C (A)	17	18	20	9.5	7.5	16
Rds On Max @ 10V (mOhm)	270	265	230	270	280	280
Vgs th Max (V)	4.5 @ 100µA	5 @ 250µA	5 @ 250µA	5 @ 250µA	3.5 @ 350µA	3.9 @ 675µA
Gate Charge Qg Max @ 10V (nC)	119	60	59.5	60	32.6	66
Power Dissipation Max (W)	40	38.5	38.5	56	30.4	34
Operating Temperature (°C)	-55 to 150	-55 to 150	-55 to 150	-55 to 150	-40 to 150	-55 to 150
Package	TO-220FP	TO-220F-3	TO-220F-3	TO-220F-3	PG-TO220-3-FP	PG-TO220-3-31
Product Status	Obsolete	Active	Active	Active	Active	Last Time Buy
RoHS Compliance	ROHS3	ROHS3	ROHS3	Not specified	ROHS3	ROHS3

Engineering Selection Recommendations

FDPF18N50T (onsemi UniFET™)

This part is the primary direct substitute for the STF20NK50Z. It maintains 500V Vdss rating and provides 18A continuous drain current, exceeding the original 17A specification. On-state resistance of 265mOhm at 9A, 10V is marginally lower than the original 270mOhm specification. Gate charge is significantly reduced to 60nC, improving switching performance. The device is in active production status with full ROHS3 compliance, ensuring long-term availability and regulatory alignment.

FDPF20N50T (onsemi UniFET™)

This part offers enhanced current capability at 20A continuous drain current with improved on-state resistance of 230mOhm at 10A, 10V. Vdss rating remains at 500V. Gate charge is 59.5nC, providing superior switching characteristics compared to the original part. Active production status and ROHS3 compliance support sustained supply chain availability. This substitute is suitable for applications where improved thermal performance and lower switching losses are beneficial.

SPA16N50C3XKSA1 (Infineon CoolMOS™)

This part provides 500V+ voltage rating (560V Vdss) with 16A continuous drain current, closely matching the original 17A specification. On-state resistance of 280mOhm at 10A, 10V is within acceptable tolerance of the original specification. The device features lower gate charge at 66nC and reduced input capacitance, supporting efficient switching operation. However, this part is classified as Last Time Buy, indicating limited future availability. ROHS3 compliance is maintained.

FQPF17N40T (Fairchild QFET®)

This part is not recommended as a primary substitute due to reduced voltage rating of 400V Vdss, which is below the original 500V specification. Continuous drain current is limited to 9.5A, significantly below the 17A requirement. This part is suitable only for applications with reduced voltage and current demands.

IPA50R280CEXKSA2 (Infineon CoolMOS™ CE)

This part is not recommended as a primary substitute due to reduced continuous drain current of 7.5A, which is substantially below the original 17A specification. Although Vdss rating is maintained at 500V, the current limitation restricts its application scope. Operating temperature minimum of -40°C is also narrower than the original -55°C specification.

Frequently Asked Questions (FAQ)

Q: Can FDPF18N50T directly replace STF20NK50Z in existing designs?

A: Yes. FDPF18N50T maintains the same 500V Vdss rating and exceeds the 17A continuous drain current requirement with 18A capability. On-state resistance is comparable at 265mOhm versus 270mOhm. The TO-220F-3 package is mechanically and electrically compatible with the original TO-220FP package. Gate charge reduction to 60nC from 119nC improves switching performance without requiring circuit modifications.

Q: What is the primary advantage of FDPF20N50T over FDPF18N50T?

A: FDPF20N50T provides higher continuous drain current at 20A and lower on-state resistance at 230mOhm, resulting in reduced power dissipation and improved thermal performance. This makes it suitable for applications operating near the thermal limits of the original design or requiring enhanced current capacity.

Q: Why is SPA16N50C3XKSA1 classified as a similar substitute rather than a direct substitute?

A: SPA16N50C3XKSA1 is classified as similar because it is designated Last Time Buy, indicating limited future availability. While electrical parameters are acceptable, the supply status creates long-term sourcing risk. Additionally, the higher Vdss rating of 560V versus 500V may introduce unnecessary cost and component size considerations.

Q: Are there package compatibility concerns between TO-220FP and TO-220F-3?

A: Both packages are TO-220-3 through-hole configurations with identical pin assignments and mechanical footprints. The FP designation indicates full pack variant, while F-3 indicates standard variant. Both are compatible with standard TO-220 PCB layouts and mounting hardware.

Q: What is the impact of reduced gate charge in substitute parts?

A: Reduced gate charge (60nC in FDPF18N50T and FDPF20N50T versus 119nC in STF20NK50Z) decreases switching time and reduces gate drive power requirements. This improves overall circuit efficiency and reduces electromagnetic interference. No circuit modifications are required; the benefit is automatic upon substitution.

Q: Should FQPF17N40T be considered for this application?

A: No. FQPF17N40T has a 400V Vdss rating, which is below the 500V requirement of the original design. Using this part in a 500V application creates risk of device failure. Additionally, the 9.5A current rating is insufficient for the 17A requirement.

Q: What is the significance of product status (Active, Last Time Buy, Obsolete)?

A: Product status indicates supply chain availability and manufacturer support. Active status ensures continued production and long-term availability. Last Time Buy indicates the manufacturer will cease production after a specified date, requiring transition planning. Obsolete status means the part is no longer manufactured, necessitating substitution.

Q: Are all substitute parts ROHS3 compliant?

A: FDPF18N50T, FDPF20N50T, IPA50R280CEXKSA2, and SPA16N50C3XKSA1 are all ROHS3 compliant. FQPF17N40T compliance status is not specified in available documentation. For applications requiring ROHS3 certification, FQPF17N40T should not be selected without verification from the manufacturer.

Q: Can multiple substitute parts be used interchangeably in production?

A: FDPF18N50T and FDPF20N50T are interchangeable from electrical and mechanical perspectives. However, design validation should confirm that the reduced gate charge and improved thermal characteristics do not introduce unintended circuit behavior. SPA16N50C3XKSA1 is interchangeable but should be avoided due to Last Time Buy status. FQPF17N40T and IPA50R280CEXKSA2 are not suitable for this application.

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