I'm making a H-bridge using 20N60 Power MOSFET. The input to the first pair of MOSFET is 300V DC and second pair of MOSFET is 160V DC. The high power DC is obtained from a 3-phase rectifier with the supply from auto transformer. Do I need to isolate the ground of the two high power DC inputs from rectifier to the MOSFETS? Or else is it OK to short them both to the common ground without isolation?