2SK3878 MOSFET — Specifications & Equivalents

About the 2SK3878

The 2SK3878 is an N-channel MOSFET with a drain–source voltage (V_DS) rating of 900 V, a continuous drain current (I_D) of 9 A and an on-resistance (R_DS(on)) of 1.3 Ω. It can dissipate up to 150 W and is rated to a junction temperature of 150 °C. It is available in SC65 and TO3P packages, so confirm the pinout of the exact variant you order.

At a glance

• Type: N-channel MOSFET
• Max drain–source voltage (V_DS): 900 V
• Max continuous drain current (I_D): 9 A
• On-resistance (R_DS(on)): 1.3 Ω
• Gate threshold (V_GS(th)): 4 V
• Power dissipation (P_D): 150 W
• Max junction temperature (T_J): 150 °C
• Package: SC65, TO3P
• Manufacturer: Multi-source (JIS registered part number)

Typical applications

With its 900 V drain–source rating the 2SK3878 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.

On-resistance of 1.3 Ω is relatively high, so this part is better suited to low duty-cycle or low-current switching than to continuous high-current conduction.

Gate drive and switching notes

With a gate threshold (V_GS(th)) of 4 V this is not a logic-level device: driving the gate directly from a 3.3 V or 5 V microcontroller pin will leave it only partly on and cause it to overheat. Use a gate driver or level shifter, typically taking V_GS to 10 V.

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

Total gate charge (Q_g) of 60 nC sets the drive current required: average gate current is roughly Q_g × switching frequency, so faster switching needs a stronger driver.

Switching behaviour is characterised by a rise time of 25 ns and an output capacitance (C_oss) of 190 pF, which together with the gate drive determines switching loss and the practical upper frequency limit.

Choosing a replacement for the 2SK3878

A drop-in substitute for the 2SK3878 must be the same N-channel type and offer a drain–source rating of at least 900 V, a continuous drain current rating of at least 9 A, an on-resistance no higher than 1.3 Ω if efficiency and heat matter and a comparable gate threshold, so your existing gate drive still fully enhances the device.

Mechanically, check the replacement against the SC65 and TO3P footprint and confirm the pin order — parts sharing a package outline do not always share a pinout.

Because 2SK3878 is a JIS-registered part number rather than one vendor's proprietary series, it is produced by several manufacturers. Datasheet figures vary slightly between them, so check the datasheet of the brand you actually buy — this also makes like-for-like sourcing easier.

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 2SK3878?

The 2SK3878 is an N-channel MOSFET (metal-oxide-semiconductor field-effect transistor). It is rated for 900 V drain-source and 9 A continuous drain current.

What is the maximum voltage of the 2SK3878?

The 2SK3878 has a maximum drain-source voltage (Vds) of 900 V. Treat this as an absolute maximum and design with margin, especially when switching inductive loads.

How much current can the 2SK3878 handle?

It is rated for 9 A of continuous drain current, with power dissipation limited to 150 W. Real-world capability depends on your heatsinking and ambient temperature.

What is the on-resistance of the 2SK3878?

On-resistance (Rds(on)) is 1.3 Ω. Multiply by the square of your load current to estimate conduction loss.

Is the 2SK3878 logic-level compatible?

No. The gate threshold is 4 V, so a 3.3 V or 5 V logic output cannot fully turn it on. Use a gate driver and take Vgs to around 10 V.

What package does the 2SK3878 come in?

It is listed in SC65 and TO3P. Verify the pinout of the specific variant, as one outline can carry different pin assignments.

What can I use to replace the 2SK3878?

No verified equivalents are listed yet. Choose a part of the same polarity that meets or exceeds every rating above and shares a compatible package and pinout.