I have used isolated supplies while making optocouplers based drive circuitry for driving 6 IGBT switches in 3-phase VSI in my undergrad projects. I remember my professor kind of explained why exactly it was required but I kind of forgot the complete reason. I also remember at first using 6 isolated supplies for 6 switches and then reducing them to 4 as I learned from some application note which was probably from TI. Can anyone tell me what happens if I don't use isolated supply? Thanks in advance!
PS : I know there are other ways such as bootstrap drivers, but I'd really like to know what would happen if I supplied all optocouplers by deriving supply from a same transformer.