Circuit topology comparison and design analysis for controllable pulse parameter transcranial magnetic stimulators

We compare half-bridge and full-bridge circuit topologies for controllable pulse parameter transcranial magnetic stimulation (cTMS) devices. The full bridge can generate two more distinct coil voltage levels for enhanced pulse shaping, does not need an active snubber circuit, and requires lower semiconductor switch voltage ratings, at the cost of necessitating four semiconductor switches and associated drivers compared to two in the half bridge. In cTMS devices it may be beneficial to use coils with higher number of turns and, hence, higher inductance than that optimal in conventional TMS, since this reduces the required capacitance, stored energy, coil current, and, potentially, conduction losses and heating. However, increasing the number of coil turns raises the required capacitor voltage which presents practical limits on the number of turns, especially for very brief pulses.