STF8NK85Z Equivalent & Substitute Parts

Part Overview

The STF8NK85Z is an N-Channel MOSFET manufactured by STMicroelectronics, rated for 850 V drain-to-source voltage with 6.7 A continuous drain current at 25°C. This device is packaged in a Through Hole TO-220FP configuration and is part of the SuperMESH™ series. The STF8NK85Z is classified as obsolete, making equivalent and substitute parts necessary for ongoing design requirements and production continuity.

Key Parameters

Parameter	Value	Unit
FET Type	N-Channel	—
Drain to Source Voltage (Vdss)	850	V
Continuous Drain Current (Id) @ 25°C	6.7	A
On-State Drain Resistance (Rds On Max)	1.4	Ω
Gate Threshold Voltage (Vgs(th) Max)	4.5	V
Power Dissipation (Max)	35	W
Operating Temperature Range	−55 to 150	°C
Mounting Type	Through Hole	—
Package / Case	TO-220-3 Full Pack	—

Substitute Part Grouping Explanation

Substitution of the STF8NK85Z is determined by the following critical parameters:

Voltage Rating Compatibility: Substitute parts must operate at or above the 850 V Vdss specification. The listed substitutes operate at 900 V, providing voltage margin above the original specification.

Current Handling Capability: Substitute parts must support the continuous drain current requirement of 6.7 A or higher at 25°C. All listed substitutes meet or exceed this specification.

On-State Resistance (Rds On): The maximum on-state resistance must not significantly degrade circuit performance. Substitute parts are selected with comparable or superior Rds On characteristics at equivalent gate drive voltages.

Gate Drive Voltage: All substitutes operate with a 10 V gate drive voltage, matching the original part specification.

Thermal Performance: Power dissipation capability and operating temperature range must support the application requirements. Substitutes are rated for −55°C to 150°C operation, consistent with the original part.

Mounting and Packaging: All substitute parts are Through Hole mounted in TO-220 package variants, maintaining mechanical and electrical compatibility with existing PCB designs.

Parameter Comparison

Parameter	STF8NK85Z	FQPF8N90C	FQPF9N90CT	TK9A90E,S4X
Manufacturer	STMicroelectronics	Fairchild Semiconductor	onsemi	Toshiba Semiconductor and Storage
FET Type	N-Channel	N-Channel	N-Channel	N-Channel
Vdss (V)	850	900	900	900
Id @ 25°C (A)	6.7	6.3	8	9
Rds On Max @ 10V (Ω)	1.4	1.9	1.4	1.3
Vgs(th) Max (V)	4.5	5	5	4
Gate Charge Qg @ 10V (nC)	60	45	58	46
Power Dissipation Max (W)	35	60	68	50
Operating Temperature (°C)	−55 to 150	−55 to 150	−55 to 150	−55 to 150
Mounting Type	Through Hole	Through Hole	Through Hole	Through Hole
Package	TO-220FP	TO-220F	TO-220F-3	TO-220SIS
Product Status	Obsolete	Active	Active	Active
RoHS Compliance	ROHS3 Compliant	Not specified	ROHS3 Compliant	ROHS3 Compliant

Engineering Selection Recommendations

FQPF8N90C (Fairchild Semiconductor): This substitute provides a 900 V voltage rating with 6.3 A continuous drain current. The higher on-state resistance of 1.9 Ω compared to the original 1.4 Ω may result in increased power dissipation in high-current applications. This part is suitable for applications where the current requirement does not exceed 6.3 A and where the additional power dissipation can be accommodated. Product status is Active, ensuring long-term availability.

FQPF9N90CT (onsemi): This substitute offers 900 V voltage rating with 8 A continuous drain current and 1.4 Ω on-state resistance, matching the original part's Rds On specification. The higher current rating and increased power dissipation capability (68 W) provide design margin for applications requiring higher current handling. This part is ROHS3 compliant and carries Active product status. The TO-220F-3 package is mechanically compatible with the original TO-220FP configuration.

TK9A90E,S4X (Toshiba Semiconductor and Storage): This substitute provides 900 V voltage rating with 9 A continuous drain current and superior on-state resistance of 1.3 Ω. The lower gate threshold voltage of 4 V and reduced gate charge of 46 nC offer improved switching characteristics. This part is ROHS3 compliant with Active product status. The TO-220SIS package variant maintains Through Hole mounting compatibility.

All substitute parts operate within the −55°C to 150°C temperature range, are REACH Unaffected, and carry EAR99 ECCN classification, matching the regulatory and compliance profile of the original part.

Frequently Asked Questions (FAQ)

Q: Can the FQPF8N90C directly replace the STF8NK85Z in all applications?

A: The FQPF8N90C is electrically compatible for applications where the continuous drain current does not exceed 6.3 A. The higher on-state resistance (1.9 Ω versus 1.4 Ω) will increase power dissipation. Thermal analysis is required to confirm the 60 W power dissipation capability is sufficient for the application. The TO-220F package is mechanically compatible with the original TO-220FP.

Q: What is the primary advantage of the FQPF9N90CT substitute?

A: The FQPF9N90CT provides the same on-state resistance as the original part (1.4 Ω) while offering higher continuous drain current (8 A) and greater power dissipation capability (68 W). This substitute is suitable for applications requiring higher current handling or where design margin is necessary. Active product status ensures long-term availability.

Q: How does the TK9A90E,S4X compare in terms of switching performance?

A: The TK9A90E,S4X features a lower gate threshold voltage (4 V versus 4.5 V) and reduced gate charge (46 nC versus 60 nC), resulting in faster switching transitions and lower gate drive power requirements. The superior on-state resistance of 1.3 Ω provides lower conduction losses compared to the original part.

Q: Are all substitute parts RoHS compliant?

A: The FQPF9N90CT and TK9A90E,S4X are ROHS3 compliant. RoHS compliance status for the FQPF8N90C is not specified in the provided data. Verification with the manufacturer is recommended if RoHS compliance is a design requirement.

Q: What are the package differences among the substitute parts?

A: The FQPF8N90C uses TO-220F packaging, the FQPF9N90CT uses TO-220F-3 packaging, and the TK9A90E,S4X uses TO-220SIS packaging. All are Through Hole mounted variants of the TO-220 family and are mechanically compatible with PCB designs originally specified for the TO-220FP package. Pin configuration and lead spacing remain consistent across these variants.

Q: Which substitute part offers the best thermal performance?

A: The FQPF9N90CT provides the highest power dissipation rating at 68 W, followed by the FQPF8N90C at 60 W. The TK9A90E,S4X is rated for 50 W. Selection depends on the specific thermal requirements and heat dissipation capability of the application circuit.

Q: Can these substitutes be used interchangeably in existing designs?

A: All substitute parts are Through Hole mounted with compatible pin configurations. However, circuit performance may vary due to differences in on-state resistance, gate charge, and threshold voltage. Circuit simulation or prototype testing is recommended to validate performance in critical applications before full production implementation.

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