FQD6N40CTF N-Channel MOSFET Equivalent & Substitute Parts

Part Overview

The FQD6N40CTF is an N-Channel MOSFET manufactured by onsemi, rated for 400V drain-to-source voltage with 4.5A continuous drain current. This device is housed in a TO-252AA (DPAK) surface mount package and is part of the QFET® series. The FQD6N40CTF is classified as obsolete, making identification of equivalent and substitute parts necessary for ongoing design support and production continuity. Equivalent parts maintain identical electrical and mechanical specifications, while substitute parts provide functional alternatives with comparable performance characteristics within defined parameter tolerances.

Key Parameters

Parameter	Value	Unit
Drain to Source Voltage (Vdss)	400	V
Continuous Drain Current (Id) @ 25°C	4.5	A (Tc)
On-State Resistance (Rds On Max) @ Id, Vgs	1	Ohm @ 2.25A, 10V
Gate Threshold Voltage (Vgs(th) Max) @ Id	4	V @ 250µA
Gate Charge (Qg Max) @ Vgs	20	nC @ 10V
Input Capacitance (Ciss Max) @ Vds	625	pF @ 25V
Power Dissipation (Max)	2.5 / 48	W (Ta) / W (Tc)
Operating Temperature Range	-55 to 150	°C (TJ)
Package Type	TO-252-3, DPAK	Surface Mount
Gate Voltage (Vgs Max)	±30	V

Substitute Part Grouping Explanation

Substitute parts for the FQD6N40CTF are classified based on electrical parameter compatibility within the following criteria:

Parametric Equivalent Classification: Parts maintaining identical specifications across all critical parameters including Vdss (400V), Id (4.5A), Rds On (1 Ohm @ 2.25A, 10V), Vgs(th) (4V @ 250µA), and Gate Charge (20 nC @ 10V). These parts are direct functional replacements with no performance trade-offs.

Similar Substitute Classification: Parts with comparable but not identical electrical characteristics. Substitution is valid when the following conditions are met:

Drain-to-source voltage rating equal to or greater than the original specification
Continuous drain current rating equal to or greater than the original specification
On-state resistance within acceptable operating parameters
Gate threshold voltage within compatible range
Operating temperature range encompassing the original specification
Identical package type (TO-252-3, DPAK surface mount)

The following parts meet these criteria for substitution:

FQD6N40CTM: Parametric equivalent with identical electrical specifications and active product status
STD5NK40ZT4: Similar substitute with 400V Vdss, reduced Id (3A), increased Rds On (1.8 Ohm), active status
STD6NK50ZT4: Similar substitute with elevated Vdss (500V), increased Id (5.6A), reduced Rds On (1.2 Ohm), not for new designs status
STD7NK40ZT4: Similar substitute with 400V Vdss, increased Id (5.4A), maintained Rds On (1 Ohm), active status

Parameter Comparison

Parameter	FQD6N40CTF	FQD6N40CTM	STD5NK40ZT4	STD6NK50ZT4	STD7NK40ZT4
Manufacturer	onsemi	onsemi	STMicroelectronics	STMicroelectronics	STMicroelectronics
Vdss (V)	400	400	400	500	400
Id @ 25°C (A)	4.5	4.5	3	5.6	5.4
Rds On Max @ Id, Vgs (Ohm)	1 @ 2.25A, 10V	1 @ 2.25A, 10V	1.8 @ 1.5A, 10V	1.2 @ 2.8A, 10V	1 @ 2.7A, 10V
Vgs(th) Max @ Id (V)	4 @ 250µA	4 @ 250µA	4.5 @ 50µA	4.5 @ 50µA	4.5 @ 50µA
Gate Charge Qg Max @ Vgs (nC)	20 @ 10V	20 @ 10V	17 @ 10V	24.6 @ 10V	26 @ 10V
Ciss Max @ Vds (pF)	625 @ 25V	625 @ 25V	305 @ 25V	690 @ 25V	535 @ 25V
Power Dissipation Max (W)	2.5 (Ta) / 48 (Tc)	2.5 (Ta) / 48 (Tc)	45 (Tc)	90 (Tc)	70 (Tc)
Operating Temperature (°C)	-55 to 150	-55 to 150	-55 to 150	-55 to 150	-55 to 150
Package	TO-252-3, DPAK	TO-252-3, DPAK	TO-252-3, DPAK	TO-252-3, DPAK	TO-252-3, DPAK
Product Status	Obsolete	Active	Active	Not For New Designs	Active
RoHS Status	Not specified	ROHS3 Compliant	ROHS3 Compliant	ROHS3 Compliant	ROHS3 Compliant

Engineering Selection Recommendations

Primary Recommendation: FQD6N40CTM

The FQD6N40CTM is the preferred substitute for the obsolete FQD6N40CTF. This part is a parametric equivalent manufactured by onsemi with identical electrical specifications across all critical parameters. The FQD6N40CTM maintains active product status and is ROHS3 compliant, ensuring long-term availability and regulatory compliance. The identical TO-252-3 DPAK package enables direct board-level substitution without layout modifications. Inventory availability of 35,100 pieces supports production requirements.

Secondary Recommendation: STD7NK40ZT4

The STD7NK40ZT4 manufactured by STMicroelectronics provides a functional alternative with maintained 400V Vdss rating and improved continuous drain current (5.4A versus 4.5A). The on-state resistance remains at 1 Ohm, ensuring equivalent switching performance. This part is active and ROHS3 compliant. The increased current rating provides design margin for applications requiring higher current capacity. The TO-252-3 DPAK package is identical to the original specification.

Tertiary Recommendation: STD5NK40ZT4

The STD5NK40ZT4 is suitable for applications where reduced current requirements (3A) are acceptable. This part maintains the 400V Vdss rating and is active with ROHS3 compliance. The increased on-state resistance (1.8 Ohm) results in higher conduction losses and should be evaluated against thermal design constraints. The reduced gate charge (17 nC) provides faster switching characteristics. This part is appropriate for lower-power applications within the 400V class.

Not Recommended: STD6NK50ZT4

The STD6NK50ZT4 carries a "Not For New Designs" product status and should not be selected for new development. While this part offers elevated voltage (500V) and current (5.6A) ratings, the obsolescence trajectory and regulatory uncertainty make it unsuitable for long-term production support.

Frequently Asked Questions (FAQ)

Q: Can the FQD6N40CTM be used as a direct replacement for the FQD6N40CTF?

A: Yes. The FQD6N40CTM is a parametric equivalent with identical electrical specifications including Vdss (400V), Id (4.5A), Rds On (1 Ohm @ 2.25A, 10V), and gate charge (20 nC @ 10V). The package type is identical (TO-252-3, DPAK). Direct substitution is valid without circuit modifications.

Q: What is the difference between the FQD6N40CTF and STD7NK40ZT4?

A: Both parts maintain 400V Vdss and 1 Ohm on-state resistance. The STD7NK40ZT4 provides higher continuous drain current (5.4A versus 4.5A), making it suitable for applications requiring additional current capacity. The STD7NK40ZT4 is active and ROHS3 compliant, whereas the FQD6N40CTF is obsolete. The package type is identical.

Q: Why is the STD6NK50ZT4 not recommended despite superior electrical ratings?

A: The STD6NK50ZT4 carries a "Not For New Designs" product status, indicating the manufacturer is discontinuing this part. While electrical specifications are superior (500V, 5.6A, 1.2 Ohm Rds On), the obsolescence trajectory creates supply chain risk and limits long-term production support. Active alternatives are preferred.

Q: Are all substitute parts available in the same package type?

A: Yes. All substitute parts listed are housed in the TO-252-3 DPAK surface mount package, identical to the FQD6N40CTF. No PCB layout modifications are required for substitution.

Q: What is the significance of the gate charge (Qg) parameter in substitution?

A: Gate charge determines the energy required to switch the MOSFET and affects switching speed and driver circuit design. The FQD6N40CTF and FQD6N40CTM both specify 20 nC @ 10V. The STD5NK40ZT4 (17 nC) provides faster switching, while STD7NK40ZT4 (26 nC) requires slightly more gate drive energy. These differences are within acceptable design margins for most applications.

Q: Can the STD5NK40ZT4 be used in applications designed for 4.5A continuous current?

A: The STD5NK40ZT4 is rated for 3A continuous drain current, which is below the original 4.5A specification. This part is suitable only for applications where the actual operating current does not exceed 3A. Thermal analysis is required to confirm safe operation within the 45W (Tc) power dissipation limit.

Q: What compliance certifications should be verified for new designs?

A: All active substitute parts (FQD6N40CTM, STD5NK40ZT4, STD7NK40ZT4) are ROHS3 compliant and REACH unaffected. These certifications ensure regulatory compliance for commercial and industrial applications. The original FQD6N40CTF compliance status is not specified; verification with the manufacturer is recommended for legacy designs.

Q: Is the input capacitance (Ciss) parameter important for substitution?

A: Input capacitance affects gate drive circuit design and switching transient behavior. The FQD6N40CTF specifies 625 pF @ 25V. Substitute parts vary: STD5NK40ZT4 (305 pF), STD7NK40ZT4 (535 pF), and STD6NK50ZT4 (690 pF). Lower capacitance enables faster switching; higher capacitance requires more gate drive energy. Circuit-level evaluation is necessary if switching frequency or gate driver current limits are critical design constraints.

Request Quote (Ships tomorrow)

Part Number

Quantity

Company

Contact Name

E-mail

Message