1kV SiC FETs Enable 6.6kW Bi-Directional On-Board Charger Design

March 12, 2018 by Paul Shepard

This 6.6kW bi-directional on-board charger (OBC) design targets high-efficiency, high-power-density onboard charger applications. The high voltage rating of Wolfspeed SiC MOSFETs allows the dc bus voltage to vary according to the battery voltage to achieve optimal efficiency.

Wolfspeed SiC MOSFETs in the new low-inductance packaging can cut switching losses and simplify designs as seen below. The 6.6kWOBC features C3M0065100K, a 65mΩ, 1kV MOSFET in a TO-247-4 package.

Optimized for electric-vehicle charging systems, and three-phase industrial power supplies, the 1kV C3M0065100K addresses many power design challenges by providing a unique device with low on-Resistance, very low output capacitance and low source inductance for an optimized blend of low switching losses and low conduction losses.

In addition to the 6.6kW bi-directional on-board charger described here, check out the new 20kW LLC reference design which includes schematics and BOM to reduce development time and get products to the market faster.

(click on schematic to enlarge)

6.6kW bi-directional OCB design summary:

  • New C3M SiC MOSFETs low switching losses and superior body diode ideal for totem pole PFC topology
  • High voltage rating 1000V SiC MOSFET allows new operation (variable dc link) to maximize efficiency
  • High switching and high efficiency operation allows OBC to be smaller, lighter, and overall more cost-effective

A 2.5% efficiency improvement in a 6.6kW system means 150W power loss reduction. (click on graph to enlarge)