4N70 MOSFET — Specifications & Equivalents

About the 4N70

The 4N70 is a MOSFET with a drain–source voltage (V_DS) rating of 700 V and a continuous drain current (I_D) of 4.4 A. It can dissipate up to 49 W and is rated to a junction temperature of 150 °C. It is available in TO-251, TO-252, TO-220F and TO-220F1 packages, so confirm the pinout of the exact variant you order.

At a glance

• Type: MOSFET
• Max drain–source voltage (V_DS): 700 V
• Max continuous drain current (I_D): 4.4 A
• Power dissipation (P_D): 49 W
• Max junction temperature (T_J): 150 °C
• Package: TO-251, TO-252, TO-220F, TO-220F1

Typical applications

With its 700 V drain–source rating the 4N70 sits in the high-voltage (offline) class of switching MOSFETs, typically found in primary-side switching in offline SMPS (flyback, forward and quasi-resonant), active PFC boost stages, half-bridge and full-bridge inverters, induction heating and electronic ballasts and BLDC and AC motor drives. The rating leaves usable margin above the ~325 V DC bus obtained by rectifying 230 VAC mains, which is why this class dominates offline power supplies.

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 70 pF, which together with the gate drive determines switching loss and the practical upper frequency limit.

Choosing a replacement for the 4N70

A drop-in substitute for the 4N70 should match its polarity and offer a drain–source rating of at least 700 V and a continuous drain current rating of at least 4.4 A.

Mechanically, check the replacement against the TO-251, TO-252, TO-220F and TO-220F1 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 4N70?

The 4N70 is a MOSFET (metal-oxide-semiconductor field-effect transistor). It is rated for 700 V drain-source and 4.4 A continuous drain current.

What is the maximum voltage of the 4N70?

The 4N70 has a maximum drain-source voltage (Vds) of 700 V. Treat this as an absolute maximum and design with margin, especially when switching inductive loads.

How much current can the 4N70 handle?

It is rated for 4.4 A of continuous drain current, with power dissipation limited to 49 W. Real-world capability depends on your heatsinking and ambient temperature.

What package does the 4N70 come in?

It is listed in TO-251, TO-252, TO-220F and TO-220F1. Verify the pinout of the specific variant, as one outline can carry different pin assignments.

What can I use to replace the 4N70?

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.