IRF840B N-Channel 500V 8A MOSFET Equivalent & Substitute Parts

Part Overview

The IRF840B is an N-Channel metal oxide semiconductor field-effect transistor (MOSFET) manufactured by onsemi, rated for 500V drain-to-source voltage and 8A continuous drain current in a through-hole TO-220-3 package. This device is classified as obsolete, necessitating identification of equivalent and substitute components for ongoing applications and new designs. Equivalent parts maintain identical electrical and mechanical specifications, while substitute parts provide functional alternatives within defined parameter tolerances suitable for the same circuit applications.

Key Parameters

Parameter	Value	Unit
FET Type	N-Channel	—
Drain to Source Voltage (Vdss)	500	V
Continuous Drain Current (Id) @ 25°C	8	A
Drive Voltage (Max Rds On)	10	V
Rds On (Max) @ Id, Vgs	800 mOhm @ 4A, 10V	—
Gate Threshold Voltage Vgs(th) (Max) @ Id	4	V @ 250µA
Gate Charge (Qg) (Max) @ Vgs	53	nC @ 10V
Vgs (Max)	±30	V
Input Capacitance (Ciss) (Max) @ Vds	1800	pF @ 25V
Power Dissipation (Max)	134	W
Operating Temperature Range	-55 to 150	°C (TJ)
Mounting Type	Through Hole	—
Package / Case	TO-220-3	—
Moisture Sensitivity Level (MSL)	1 (Unlimited)	—

Substitute Part Grouping Explanation

Substitution of the IRF840B is determined by strict equivalence in the following critical parameters:

Primary Substitution Criteria:

FET Type: N-Channel
Drain to Source Voltage (Vdss): 500V minimum
Continuous Drain Current (Id): 8A or greater at 25°C
Drive Voltage: 10V
Package / Case: TO-220-3 compatible through-hole mounting
Operating Temperature Range: -55°C to 150°C minimum
Gate Threshold Voltage (Vgs(th)): 4V to 4.5V @ 250µA

Secondary Compatibility Parameters:

Rds On (Max): 800 mOhm to 850 mOhm @ specified Id and Vgs
Vgs (Max): ±30V
Gate Charge (Qg): 28 nC to 63 nC @ 10V
Input Capacitance (Ciss): 535 pF to 1800 pF @ 25V
Power Dissipation: 70W or greater

Substitute parts are grouped into two categories: direct equivalents (matching all primary criteria) and functional alternatives (meeting primary criteria with minor variations in secondary parameters that do not affect circuit operation within standard application ranges).

Parameter Comparison

Part Number	Manufacturer	Vdss (V)	Id @ 25°C (A)	Rds On (mOhm)	Vgs(th) (V)	Qg (nC)	Ciss (pF)	Power Diss. (W)	Package	Product Status
IRF840B	onsemi	500	8	800 @ 4A	4 @ 250µA	53 @ 10V	1800 @ 25V	134	TO-220-3	Obsolete
IRF840LCPBF	Vishay Siliconix	500	8	850 @ 4.8A	4 @ 250µA	39 @ 10V	1100 @ 25V	125	TO-220-3	Active
IRF840APBF	Vishay Siliconix	500	8	850 @ 4.8A	4 @ 250µA	38 @ 10V	1018 @ 25V	125	TO-220-3	Active
IRF840PBF	Vishay Siliconix	500	8	850 @ 4.8A	4 @ 250µA	63 @ 10V	1300 @ 25V	125	TO-220-3	Active
AOT8N50	Alpha & Omega Semiconductor Inc.	500	8	850 @ 4A	4.5 @ 250µA	28 @ 10V	1042 @ 25V	192	TO-220-3	Not For New Designs
AOT9N50	Alpha & Omega Semiconductor Inc.	500	9	850 @ 4.5A	4.5 @ 250µA	28 @ 10V	1042 @ 25V	192	TO-220-3	Not For New Designs
STP9NK50Z	STMicroelectronics	500	7.2	850 @ 3.6A	4.5 @ 100µA	32 @ 10V	910 @ 25V	110	TO-220-3	Active
AOT9N40	Alpha & Omega Semiconductor Inc.	400	8	800 @ 4A	4.5 @ 250µA	16 @ 10V	760 @ 25V	132	TO-220-3	Active
STP5NK50Z	STMicroelectronics	500	4.4	1500 @ 2.2A	4.5 @ 50µA	28 @ 10V	535 @ 25V	70	TO-220-3	Active

Engineering Selection Recommendations

Direct Equivalents (Recommended for Replacement):

The IRF840LCPBF and IRF840APBF from Vishay Siliconix are direct functional equivalents to the IRF840B. Both devices maintain 500V Vdss, 8A continuous drain current, and TO-220-3 packaging. These parts are in active production status with RoHS3 compliance. IRF840LCPBF carries REACH Unaffected status, while IRF840APBF is REACH Affected. Both exhibit slightly lower on-resistance (850 mOhm vs. 800 mOhm) and reduced power dissipation (125W vs. 134W), representing improved thermal performance. Gate charge is reduced (38–39 nC vs. 53 nC), resulting in faster switching characteristics.

Primary Substitutes (Full Parameter Compatibility):

The IRF840PBF from Vishay Siliconix maintains identical voltage and current ratings with the same TO-220-3 package. This part is in active production with RoHS3 compliance but carries REACH Affected status. Gate charge is elevated to 63 nC and input capacitance to 1300 pF, resulting in slower switching compared to the original IRF840B. This part is suitable for applications where switching speed is not critical.

Functional Alternatives (Reduced Current Rating):

The STP9NK50Z from STMicroelectronics provides 500V Vdss in TO-220-3 packaging with active production status and RoHS3 compliance. Continuous drain current is reduced to 7.2A (90% of IRF840B rating). This device is suitable for applications where the full 8A rating is not required. Power dissipation is 110W, and gate charge is 32 nC, providing improved switching performance.

Functional Alternatives (Reduced Voltage Rating):

The AOT9N40 from Alpha & Omega Semiconductor Inc. provides 400V Vdss (80% of IRF840B rating) with 8A continuous drain current and active production status. This part is suitable only for applications where the circuit voltage does not exceed 400V. RoHS3 compliance is confirmed.

Not Recommended for New Designs:

The AOT8N50 and AOT9N50 from Alpha & Omega Semiconductor Inc. are classified as "Not For New Designs" despite meeting electrical specifications. These parts should be used only for legacy system maintenance and repair.

Not Suitable:

The STP5NK50Z from STMicroelectronics provides only 4.4A continuous drain current, insufficient for applications requiring the full 8A rating of the IRF840B.

Frequently Asked Questions (FAQ)

Q: Can I use IRF840LCPBF as a direct replacement for IRF840B?

A: Yes. The IRF840LCPBF maintains identical voltage (500V), current (8A), and package (TO-220-3) specifications. The reduced on-resistance (850 mOhm vs. 800 mOhm) and lower gate charge (39 nC vs. 53 nC) represent improvements in thermal performance and switching speed. This part is in active production with RoHS3 compliance.

Q: What is the difference between IRF840LCPBF and IRF840APBF?

A: Both parts are functionally equivalent with 500V, 8A, and TO-220-3 specifications. IRF840LCPBF has gate charge of 39 nC and input capacitance of 1100 pF. IRF840APBF has gate charge of 38 nC and input capacitance of 1018 pF. The difference is negligible for most applications. IRF840LCPBF carries REACH Unaffected status, while IRF840APBF is REACH Affected.

Q: Can I use STP9NK50Z instead of IRF840B?

A: The STP9NK50Z is a functional alternative with 500V Vdss and TO-220-3 packaging. However, continuous drain current is 7.2A, which is 90% of the IRF840B rating. This part is suitable only if your application does not require the full 8A continuous current. Verify circuit current requirements before substitution.

Q: Why is AOT9N40 not suitable for my application?

A: The AOT9N40 provides only 400V Vdss compared to the IRF840B's 500V rating. This part is suitable only for circuits operating at 400V or below. If your circuit requires 500V operation, this part will not provide adequate voltage margin and must not be used.

Q: What does "Not For New Designs" mean for AOT8N50 and AOT9N50?

A: This designation indicates that these parts are in production but the manufacturer does not recommend their use in new circuit designs. These parts should be used only for maintenance and repair of existing systems. For new designs, select from parts with "Active" production status.

Q: Are all substitute parts RoHS3 compliant?

A: All substitute parts listed carry RoHS3 compliance. The IRF840B itself does not specify RoHS status. Verify RoHS compliance requirements for your specific application and regulatory jurisdiction.

Q: What is the difference between TO-220 and TO-220-3 packaging?

A: TO-220-3 is the standard three-lead through-hole package for power MOSFETs, with leads for Gate, Drain, and Source. All substitute parts listed use TO-220-3 or compatible TO-220 packaging with identical pin configuration and mounting footprint. These packages are mechanically and electrically interchangeable.

Q: Can I use IRF840PBF if switching speed is important in my circuit?

A: The IRF840PBF has elevated gate charge (63 nC vs. 53 nC in IRF840B) and higher input capacitance (1300 pF vs. 1800 pF), resulting in slower switching characteristics. If your circuit requires fast switching, select IRF840LCPBF or IRF840APBF instead, which have reduced gate charge (38–39 nC).

Q: What is REACH Affected status and does it matter?

A: REACH Affected status indicates that the part contains substances of concern under European REACH regulations. If your application is subject to REACH compliance requirements, select parts with REACH Unaffected status. IRF840LCPBF carries REACH Unaffected status and is suitable for REACH-regulated applications.

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