rusefi.com

3V is generated by the STM32 discovery board. It's not 3.3V because it goes through a diode so you have additional drop, and it ends up being around 3V. the STM32 discovery can handle an external 3.3V if you provide it some how. As for this board, it only generates 5V.

Just came across these: http://www.ti.com/product/tps54340/description

Automotive rated, 3.5A and only half a buck on aliexpress (also available on digikey/mouser etc)

https://www.aliexpress.com/item/TPS54340-SOP8-Conv-DC-DC-4-5V-to-42V-Step-Down-Single-Out-0-8V-to/32857633519.html

Oh, very nice. I like. I see it's typically better then 85% efficient, commonly 90% efficient. That's very nice.

It would be nice if someone made a PCB for that, such that one could experiment with it.