650V / 60mΩ SiC FETs in 6.6kW High-Frequency DC-DC Converter Reference DesignApril 16, 2020 by Paul Shepard
The CRD06600DD06N reference design from Cree is used to demonstrate the performance of the Cree C3M0060065D (60mΩ/650V, TO-247-3) SiC MOSFET and the Cree C6D10065A (10A/650V, TO-220-2) SiC diode in a 6.6kW high-frequency dc-dc LLC converter with an output voltage of 400Vdc and with a maximum output current of 16.5A.
Thanks to the low switching loss of these Cree SiC devices, the converter can be operated at high frequencies. The converter operates between 500kHz and 1MHz with soft-startup at 1.5MHz and an operating frequency of 625kHz at 400V input and full load. The main benefits of high-frequency converter operation are smaller transformer and EMI filters, plus integrating resonant inductors into the transformer, and further size reduction of the converter.
Measuring approximately 190mm x 125mm x 35mm, the board allows an input voltage range of 380- to 420-Vdc and can operate in either open-loop or closed-loop mode, depending on the operation mode selection of the user. In closed-loop operation, the converter regulates the output voltage to 400Vdc.
Four Cree SiC MOSFETs are used for the primary switches which are turned on at zero-voltage (ZVS) which results in high efficiency and low EMI. Four Cree SiC diodes are used for secondary-side rectifiers.
The board accepts an optional daughter card (a Cree CRD-15DD17P 15W Flyback, which must be purchased separately) for the bias power needed for the control circuit including the optional Texas Instruments (TI) control card (P/N TMDSCNCD280049C, which must also be purchased separately for the closed loop operation) and the primary-side bias needed for the four isolated dc-dc modules for the two gate drivers. With the Cree daughter card, the board doesn't need an external 12Vdc power supply for the control circuit.
The optional TI control card can generate the desired control signals to turn on or turn off the four SiC MOSFETs, therefore, no external signal generator is needed if it is installed.
Summary of Features:
- Demonstration of Cree's 650V, 60mΩ (C3M™) SiC MOSFETs in a 6.6kW high frequency dc-dc converter targeting high power density applications
- The demo board consist of a dc-dc LLC topology in which primary side is based on a Full bridge stage while the secondary side is based on an asynchronous rectification stage
- Utilization of high frequency operation allow the demo board to be smaller, lighter and overall more cost effective
- Cree's 6.6kW high frequency board can accept 380Vdc to 420Vdc as an input and provide 400Vdc at the output with >96 % efficiency
- Main target application of this demo board include industrial power supplies and EV chargers
- Documentation includes a bill of materials (BOM), schematic, board layout and the application note