Hello Gangi Anandkumar Reddy ,

MRI (Magnetic Resonance Imaging) is not my field of expertise, but the reason people usually use DC-DC converters is that it is easier and uses less bulky components to get low ripple DC voltages from DC-DC converters than from a standard AC-DC power supply. The MRI gradient coil system usually employs an AC-DC power supply, a DC-DC switching power supply, and a phase shift, dual H-bridge driver for each x, y, and z gradient coils. One could simply use a H-bridge driver, but there are two problems with this approach: 1) inefficient driving of the gradient coil due to the hard starting of the coil with such an arrangment, and 2) the generation of EMI (Electro-Magnetic Interference), again, due to the hard starting of the coil resulting from large back EMF (Electro-Magnetic Force). Using a phase shift, dual H-bridge driver for each x, y, ad z gradient coil allows for soft starting of the coils. For a complete discussion with diagrams, see the attached US Patent 9,389,288.

Regards,

Thomas Cuff