New SiC FET Option for EV Charging Applications from UnitedSiC Adds 4-Lead Kelvin Device

June 24, 2019 by Gary Elinoff

Designing an EV charging power system? UnitedSiC just served up an SiC FET option with you in mind.

Designing an EV charging power system? UnitedSiC just served up an SiC FET option with you in mind.

The advent of the UF3C120150K4S marks the sixth member of UnitedSiC's line of 4-leaded “FAST” devices. This offering is aimed for several applications:

  • EV charging
  • Photovoltaic inverters
  • Switch mode power supplies
  • Power factor correction (PFC) modules
  • Motor drives
  • Induction heating

The UF3C120150K4S is a 1200-volt silicon carbide (SiC) FET that offers a typical on-resistance (RDS(on)) of 150 mΩ and a maximum operating temperature of 175°C. SiC's high junction temperatures are also leveraged in the device's screw or clamp mounting, which offer low junction-to-case thermal resistance.

Offered in a TO-247-4L package, the device can offer faster switching times and much cleaner gate waveforms when compared to a standard 3-leaded TO-247.

Members of UnitedSiC’s new UF3C FAST SiC series, which now totals 13 devices, are available in TO-247-3L packages as well as in TO-247-4L packages. There are both 1200V and 650V options.


The UF3C120150K4S. Image from UnitedSiC

Why the Fourth Lead? A Kelvin Connection

Dr. Anup Bhalla, VP Engineering at UnitedSiC, describes the efficacy of Kevin connections in his article, “Using Kelvin connections to enhance switching efficiency in SiC FETs.”

He points out that SiC devices are best offered in packages such as the TO-247, so that the heat they generate can be carried away. But the problem, as he goes on to describe, is that “connections to the TO-247 package often have high inductances, which can limit switching speeds.” But, by using a technique called a Kelvin Connection, this problem can be controlled.


The UF3C120150K4S includes a Kelvin connection to manage lead inductances. Image from UnitedSiC


The effect of these troublesome inductances can be overcome by driving the gate to a negative voltage when the device is to be turned off. This requires extra circuitry.

However, by using Kelvin connections to control lead inductances, designers can avoid this issue. By exploiting this technique, UnitedSiC’s devices are able to run at their greatest potential switching speeds without the need for complex drive circuitry. This reduces time to market for OEMs and reduces manufacturing costs.

Cascode Devices

The UF3C120150K4S is a cascode device. In this arrangement, a SiC fast JFET is co-packaged with silicon MOSFET. The advantage here is that the MOSFET, which is controlled with a very low input voltage, can itself control a very high-voltage JFET.


Low-voltage MOSFET controls a high voltage JFET. Image from UnitedSiC


If you'd like to learn more about cascode devices, check out my article on UnitedSiC's 650V SiC FET, introduced in May.

Drop-In Replacement Functionality

Members of UnitedSiC’s UF3C family employ what the company describes as its true “drop-in replacement” functionality. What this means is that designers can significantly enhance system performance without the need to change gate drive voltage by simply replacing their existing Si IGBTs, Si FETs, SiC MOSFETs or Si superjunction devices with the UnitedSiC FETs.

The same can be said of the UJ3C the sister family to the UF3C. The variations between the families relate to the difference between hard switching and soft switching, and are described on UnitedSiC’s site, along with a selection guide for both the UJ3C and the UF3C families.

What Other Manufacturers Have on Offer

With today’s emphasis on power electronics, there are other participants in this field. Here are two of the many available choices:

  • SSDI’s SGF46E70 and SGF15E100 families are cascode devices combining a GaN HEMT (high-electron-mobility transistor) with a low-voltage silicon MOSFET. These devices are designed for demanding aerospace and defense applications.
  • The TP65H035WS from Transphorm is a 650 V device combining a high-voltage GaN HEMT with a low-voltage silicon MOSFET. It is designed for service in datacom, solar inverter, and servo motor devices, as well as in a broad range of industrial applications.

It does appear, however, that UnitedSiC is alone in offering GaN or SiC-based Kelvin power FETS.



What's your experience with SiC FETs? Are you making the switch from silicon? Share your thoughts in the comments below.