FQL40N50F Equivalent & Substitute Parts

Part Overview

The FQL40N50F is an N-Channel 500V 40A MOSFET manufactured by onsemi in the FRFET® series, housed in a TO-264-3 through-hole package. This device is classified as obsolete, making identification of equivalent and substitute parts essential for ongoing design support and procurement continuity. The FQL40N50F serves applications requiring high-voltage switching with moderate current handling in industrial and power conversion circuits. Due to its obsolete status, active equivalent devices from alternative manufacturers provide viable substitution pathways while maintaining electrical and mechanical compatibility within specified parameter ranges.

Key Parameters

Parameter	Value	Unit
Drain to Source Voltage (Vdss)	500	V
Continuous Drain Current (Id) @ 25°C	40	A
On-State Resistance (Rds On) @ 20A, 10V	110	mOhm
Gate Threshold Voltage (Vgs(th)) @ 250µA	5	V
Gate Charge (Qg) @ 10V	200	nC
Input Capacitance (Ciss) @ 25V	7500	pF
Power Dissipation (Max)	460	W
Operating Temperature Range	-55 to 150	°C
Package Type	TO-264-3	—
Mounting Type	Through Hole	—

Substitute Part Grouping Explanation

Substitution of the FQL40N50F is determined by strict alignment of electrical and mechanical parameters within the following criteria:

Primary Substitution Parameters:

Drain to Source Voltage (Vdss): Must equal 500V
Continuous Drain Current (Id): Must meet or exceed 40A at 25°C
Package Type: Must be TO-264-3 or TO-264AA (mechanically compatible)
Mounting Type: Must be through-hole
Operating Temperature Range: Must span -55°C to 150°C minimum
Gate Drive Voltage: Must support 10V operation

Secondary Compatibility Parameters:

On-State Resistance (Rds On): Lower values indicate improved performance
Gate Charge (Qg): Lower values reduce drive circuit requirements
Input Capacitance (Ciss): Affects switching speed and gate drive design

The substitute parts identified below satisfy the primary substitution parameters. Parts with Vdss ratings exceeding 500V or current ratings below 40A are excluded from direct substitution classification.

Parameter Comparison

Parameter	FQL40N50F	IXFK44N50P	IXFK48N50	IXFK48N50Q	IXFK80N50P
Manufacturer	onsemi	IXYS	IXYS	IXYS	IXYS
Vdss (V)	500	500	500	500	500
Id @ 25°C (A)	40	44	48	48	80
Rds On (mOhm)	110 @ 20A	140 @ 22A	100 @ 24A	100 @ 24A	65 @ 40A
Vgs(th) (V)	5 @ 250µA	5 @ 4mA	4 @ 8mA	4 @ 4mA	5 @ 8mA
Qg @ 10V (nC)	200	98	270	190	197
Ciss @ 25V (pF)	7500	5440	8400	7000	12700
Power Dissipation (W)	460	658	500	500	1040
Operating Temperature (°C)	-55 to 150	-55 to 150	-55 to 150	-55 to 150	-55 to 150
Package	TO-264-3	TO-264AA	TO-264AA	TO-264AA	TO-264AA
Product Status	Obsolete	Active	Active	Active	Active
RoHS Status	ROHS3 Compliant	ROHS3 Compliant	ROHS3 Compliant	ROHS3 Compliant	ROHS3 Compliant

Engineering Selection Recommendations

IXFK44N50P is suitable for applications requiring current ratings at or above 40A with 500V blocking capability. This device maintains active product status and ROHS3 compliance. The 44A rating provides minimal current margin above the FQL40N50F specification. Gate charge of 98 nC is significantly lower than the original part, reducing gate drive circuit power dissipation. The 140 mOhm on-state resistance is higher than the FQL40N50F, resulting in increased conduction losses.

IXFK48N50 and IXFK48N50Q both provide 48A continuous drain current with improved on-state resistance of 100 mOhm compared to the FQL40N50F. Both devices are active products with ROHS3 compliance. The IXFK48N50Q variant includes Q Class designation and exhibits lower gate charge (190 nC) relative to the standard IXFK48N50 (270 nC), making it preferable for gate drive efficiency. Input capacitance differs between variants, affecting switching transient behavior.

IXFK80N50P provides the highest current rating at 80A with superior on-state resistance of 65 mOhm. This device is recommended for applications where thermal management and conduction loss minimization are critical design factors. The significantly higher power dissipation rating (1040W) accommodates higher current operation. Gate charge remains comparable to other substitutes at 197 nC. Input capacitance of 12700 pF is the highest among substitutes, requiring consideration in high-frequency switching applications.

All identified substitutes are mechanically compatible with TO-264-3 footprints through TO-264AA package equivalence and maintain the required -55°C to 150°C operating temperature range.

Frequently Asked Questions (FAQ)

Q: Can the IXFK44N50P directly replace the FQL40N50F in existing PCB designs?

A: The IXFK44N50P is mechanically compatible with TO-264-3 footprints through TO-264AA package equivalence. Electrical parameters align with substitution criteria. However, the higher on-state resistance (140 mOhm vs. 110 mOhm) increases conduction losses. Gate drive circuits must accommodate the lower gate charge (98 nC vs. 200 nC), which may reduce drive circuit stress but requires verification of gate voltage rise time compatibility.

Q: What is the difference between IXFK48N50 and IXFK48N50Q?

A: Both devices share identical electrical ratings for Vdss, Id, Rds On, and power dissipation. The IXFK48N50Q is designated as Q Class and exhibits lower gate charge (190 nC vs. 270 nC) and reduced input capacitance (7000 pF vs. 8400 pF). The Q Class variant is preferable for applications prioritizing gate drive efficiency and switching speed consistency.

Q: Is the IXFK80N50P suitable for direct substitution if my application only requires 40A?

A: The IXFK80N50P exceeds the 40A requirement with an 80A rating and provides superior on-state resistance (65 mOhm). This device is electrically compatible and mechanically interchangeable. The higher current capability and lower on-state resistance result in reduced conduction losses and improved thermal performance. No electrical incompatibility exists for 40A operation.

Q: Why is the IXTK21N100 not listed as a direct substitute?

A: The IXTK21N100 has a Drain to Source Voltage rating of 1000V, which exceeds the FQL40N50F specification of 500V. While the device is mechanically compatible and shares the through-hole TO-264 package family, the higher voltage rating places it outside the primary substitution parameter criteria. This device is classified as a non-equivalent alternative for different voltage class applications.

Q: Are all substitute parts RoHS3 compliant?

A: Yes. All identified substitute parts (IXFK44N50P, IXFK48N50, IXFK48N50Q, and IXFK80N50P) are ROHS3 compliant, matching the compliance status of the FQL40N50F. All devices are REACH unaffected and classified under ECCN EAR99.

Q: How does gate charge affect circuit design when substituting parts?

A: Gate charge (Qg) determines the total charge required to switch the MOSFET from off to on state. The FQL40N50F requires 200 nC, while substitutes range from 98 nC (IXFK44N50P) to 270 nC (IXFK48N50). Lower gate charge reduces gate drive circuit power dissipation and enables faster switching transitions. Gate drive circuits must supply sufficient current to achieve the required gate voltage rise time within the application's switching frequency constraints.

Q: What thermal considerations apply when selecting between substitute parts?

A: Power dissipation ratings vary significantly: FQL40N50F (460W), IXFK44N50P (658W), IXFK48N50/Q (500W), and IXFK80N50P (1040W). Higher power dissipation ratings indicate greater thermal capacity. On-state resistance directly affects conduction losses; lower Rds On values (IXFK80N50P at 65 mOhm) reduce heat generation at rated current. Thermal management design must account for both the device's power dissipation capability and the application's actual operating current and duty cycle.

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