20N40 MOSFET — Specifications & Equivalents

About the 20N40

The 20N40 is a MOSFET with a drain–source voltage (V_DS) rating of 400 V and a continuous drain current (I_D) of 23 A. It can dissipate up to 235 W and is rated to a junction temperature of 150 °C. It is supplied in the TO-247 package.

At a glance

• Type: MOSFET
• Max drain–source voltage (V_DS): 400 V
• Max continuous drain current (I_D): 23 A
• Power dissipation (P_D): 235 W
• Max junction temperature (T_J): 150 °C
• Package: TO-247

Typical applications

With its 400 V drain–source rating the 20N40 sits in the medium-high-voltage class of switching MOSFETs, typically found in telecom and industrial DC rails, boost and flyback converters, LED and backlight drivers and power-factor-correction stages. Common where the bus sits well above 100 V but below rectified mains.

Gate drive and switching notes

Keep gate–source voltage within the ±30 V maximum; exceeding it punctures the gate oxide and destroys the device permanently.

Switching behaviour is characterised by an output capacitance (C_oss) of 370 pF, which together with the gate drive determines switching loss and the practical upper frequency limit.

Choosing a replacement for the 20N40

A drop-in substitute for the 20N40 should match its polarity and offer a drain–source rating of at least 400 V and a continuous drain current rating of at least 23 A.

Mechanically, check the replacement against the TO-247 footprint and confirm the pin order — parts sharing a package outline do not always share a pinout.

Where the application switches inductive loads or runs near the voltage limit, keep extra headroom rather than choosing a part that only just meets the original numbers.

Frequently asked questions

What is the 20N40?

The 20N40 is a MOSFET (metal-oxide-semiconductor field-effect transistor). It is rated for 400 V drain-source and 23 A continuous drain current.

What is the maximum voltage of the 20N40?

The 20N40 has a maximum drain-source voltage (Vds) of 400 V. Treat this as an absolute maximum and design with margin, especially when switching inductive loads.

How much current can the 20N40 handle?

It is rated for 23 A of continuous drain current, with power dissipation limited to 235 W. Real-world capability depends on your heatsinking and ambient temperature.

What package does the 20N40 come in?

It is listed in TO-247. Verify the pinout of the specific variant, as one outline can carry different pin assignments.

What can I use to replace the 20N40?

This page lists 17 candidate equivalents matched on electrical ratings and package. Any replacement should meet or exceed the original voltage, current and dissipation figures and use a compatible drive level.