cute-qcw: an FPGA QCW Tesla coil controller with a RISC-V core

The only FPGA-based controller in the tree. Weston Braun published the whole system (four boards, their schematics, gerbers, stencils and the firmware) while it was still being built: “system design and construction are in progress”. Boards photographed on his own bench carry the repository address on the silkscreen (“Cute QCW Power input Board: github.com/westonb/cute-qcw”), so the attribution is clear.

The controller is a Xilinx Spartan-7 XC7S25 with an S25FL127S config flash, a 74AVC4T245 level shifter, JTAG, fibre TX/RX, four gate outputs, ten ADC channels, ZCS_DETECT, UVLO, relay drives and RS485. The firmware runs it as a system on chip, not a plain state machine. A PicoRV32 RISC-V core sits on a Wishbone bus (GPIO, SPI, UART, memory, a power interface) alongside hardware blocks written for the job (qcw_pll.v, qcw_osc.v, qcw_fsm.v, qcw_ocd.v).

The repository does not say how the ramp is made, so it has to be read off the sheets. The inverter is eight IRG4PF50W IGBTs in two groups of four, VSW+ from one and VSW- from the other, with eight separate gate inputs on four headers. That is a full bridge whose halves are driven independently, which phase shifting needs. The power board is input-side only (fuse, common-mode filter, safety and precharge relays, a voltage doubler, discharge resistor), with no buck stage anywhere. So the card sits here and not under the buck milestone.

Every title block in the seven-page controller schematic is blank: no title, no date, no revision, only KiCad 5.0.2 and the file name. The repository carries no licence at all.

Schematics and photos

Sources

• github.com/westonb/cute-qcw: schematics, gerbers, FPGA firmware, stencils
• build photographs (Flickr set)

This is the card from the driver tree, written from what the builder published. Send corrections through the forum.