IRF840AS N-Channel MOSFET 500V 8A Equivalent & Substitute Parts

Part Overview

The IRF840AS is an N-Channel MOSFET manufactured by Vishay Siliconix, rated for 500V drain-to-source voltage with 8A continuous drain current in a surface mount TO-263 (D2PAK) package. This device is classified as obsolete, making equivalent and substitute parts necessary for ongoing design support and procurement.

The IRF840AS is designed for high-voltage switching applications requiring moderate current handling in a compact surface mount form factor. Due to its obsolete status, active alternatives with equivalent or superior electrical characteristics are available from multiple manufacturers.

Substiute Parts

IRF840AS

Vishay SiliconixIn Stock: 2522IRF840AS Datasheet

Current PartRFQ

IRF840ASPBF

Vishay SiliconixIn Stock: 1401IRF840ASPBF Datasheet

DirectRFQ

FDB12N50TM

onsemiIn Stock: 18284FDB12N50TM Datasheet

MFR RecommendedRFQ

STB11NK50ZT4

STMicroelectronicsIn Stock: 4404STB11NK50ZT4 Datasheet

MFR RecommendedRFQ

Key Parameters

Substitute Part Grouping Explanation

Substitution of the IRF840AS is determined by the following critical parameters:

Electrical Compatibility Requirements:

• Drain-to-Source Voltage (Vdss): Must equal or exceed 500V
• Continuous Drain Current (Id): Must equal or exceed 8A at 25°C
• Gate Drive Voltage: Must operate at 10V maximum Rds On specification
• Operating Temperature Range: Must span -55°C to 150°C
• Gate Threshold Voltage (Vgs(th)): Must be compatible with 4V nominal specification

Mechanical Compatibility Requirements:

• Package Type: TO-263 (D2PAK) surface mount configuration
• Pin Configuration: 2 Leads + Tab standard D2PAK footprint
• Mounting Type: Surface mount only

Regulatory and Compliance Considerations:

• RoHS Status: Preference for RoHS3 compliant alternatives
• Moisture Sensitivity Level: MSL 1 (Unlimited) required
• REACH Status: Compliance status documented

Substitute parts are grouped into two categories: direct equivalents (identical electrical and mechanical specifications) and performance-enhanced alternatives (superior current rating or on-state resistance while maintaining voltage and package compatibility).

Parameter Comparison

Engineering Selection Recommendations

IRF840ASPBF (Vishay Siliconix) – Direct Equivalent

The IRF840ASPBF is the direct active equivalent of the IRF840AS. It maintains identical electrical specifications including 500V Vdss, 8A continuous drain current, 850mOhm on-state resistance, and 38nC gate charge. The primary distinction is product status: IRF840ASPBF is active and RoHS3 compliant, whereas the IRF840AS is obsolete and non-compliant. Packaging differs only in format (Tube vs. unspecified for IRF840AS). This part is the preferred direct replacement for existing IRF840AS designs requiring no circuit modification.

FDB12N50TM (onsemi UniFET™) – Performance-Enhanced Alternative

The FDB12N50TM provides enhanced electrical performance while maintaining 500V Vdss compatibility. It offers 11.5A continuous drain current (44% higher than IRF840AS), reduced on-state resistance of 650mOhm (24% lower), and lower gate charge of 30nC (21% lower). Power dissipation capability increases to 165W at Tc. The gate threshold voltage increases to 5V at 250µA. This part is suitable for designs requiring improved thermal performance or higher current capacity within the same 500V voltage class and D2PAK package. FDB12N50TM is active and RoHS3 compliant.

STB11NK50ZT4 (STMicroelectronics SuperMESH™) – Performance-Enhanced Alternative

The STB11NK50ZT4 offers intermediate performance enhancement with 500V Vdss and 10A continuous drain current (25% higher than IRF840AS). On-state resistance is significantly reduced to 520mOhm (39% lower than IRF840AS). Gate charge increases to 68nC, and gate threshold voltage is 4.5V at 100µA. Power dissipation is rated at 125W at Tc. This part provides a balanced alternative with improved on-state resistance and current capacity. STB11NK50ZT4 is active and RoHS3 compliant.

All substitute parts maintain the required -55°C to 150°C operating temperature range, MSL 1 moisture sensitivity level, and D2PAK surface mount package compatibility. Selection between alternatives depends on thermal design requirements, current capacity needs, and gate drive circuit characteristics.

Frequently Asked Questions (FAQ)

Q: Can IRF840ASPBF be used as a direct replacement for IRF840AS without circuit modification?

A: Yes. IRF840ASPBF maintains identical electrical specifications: 500V Vdss, 8A continuous drain current, 850mOhm on-state resistance at 10V gate drive, 4V gate threshold voltage, and 38nC gate charge. The D2PAK footprint and pin configuration are identical. No circuit changes are required. The primary advantage is that IRF840ASPBF is active and RoHS3 compliant, whereas IRF840AS is obsolete.

Q: What are the key differences between FDB12N50TM and STB11NK50ZT4 as alternatives to IRF840AS?

A: Both parts maintain 500V Vdss and D2PAK packaging. FDB12N50TM provides higher current capacity (11.5A vs. 10A) and lower on-state resistance (650mOhm vs. 520mOhm), but with higher gate charge (30nC vs. 68nC). STB11NK50ZT4 offers the lowest on-state resistance (520mOhm) and moderate current increase (10A). FDB12N50TM is better for applications prioritizing thermal performance; STB11NK50ZT4 is better for applications prioritizing on-state resistance minimization.

Q: Are all substitute parts compatible with the same PCB footprint as IRF840AS?

A: Yes. All substitute parts use the TO-263 (D2PAK) package with identical 2 Leads + Tab configuration. PCB footprints are mechanically compatible without modification.

Q: What is the significance of the gate charge (Qg) differences between substitute parts?

A: Gate charge affects gate drive circuit design and switching speed. IRF840AS and IRF840ASPBF both have 38nC gate charge. FDB12N50TM has lower gate charge (30nC), enabling faster switching with lower gate drive power. STB11NK50ZT4 has higher gate charge (68nC), requiring more gate drive current but potentially offering better noise immunity. Gate drive circuit design must accommodate the selected part's gate charge specification.

Q: Why is on-state resistance (Rds On) important for substitution?

A: On-state resistance directly determines power dissipation during conduction: P = I²R. Lower Rds On reduces heat generation and improves efficiency. IRF840AS has 850mOhm; FDB12N50TM has 650mOhm (24% reduction); STB11NK50ZT4 has 520mOhm (39% reduction). Applications with high continuous current or thermal constraints benefit from lower Rds On alternatives.

Q: Are all substitute parts RoHS3 compliant?

A: IRF840ASPBF, FDB12N50TM, and STB11NK50ZT4 are all RoHS3 compliant. The original IRF840AS is non-compliant. For applications requiring RoHS compliance, any of the three active alternatives are suitable.

Q: What is the difference between continuous drain current (Id) ratings?

A: Continuous drain current specifies the maximum DC current the device can conduct indefinitely at 25°C case temperature without exceeding maximum junction temperature. IRF840AS is rated 8A; FDB12N50TM is rated 11.5A; STB11NK50ZT4 is rated 10A. Higher ratings allow the device to handle greater current loads. Selection depends on application current requirements and thermal management capability.

Q: Can FDB12N50TM or STB11NK50ZT4 be used in applications designed for 8A operation?

A: Yes. Both parts exceed the 8A requirement and are backward compatible in applications designed for IRF840AS. The higher current ratings and improved on-state resistance provide margin and improved performance. No circuit modification is required. Gate charge differences may affect switching characteristics but do not prevent substitution.