A high-frequency 4-switch GTO speed-up inverter for the generation of fast-changing MRI gradient fields

Magnetic resonance imaging (MRI) systems require stronger gradient coil currents with faster ramp times for high-speed image taking and in order to obtain a smaller field of view or a magnification effect. A new simplified four-switch circuit topology is described which is based not on the parallel but on the series connection of a high-voltage inverter and a low-voltage linear amplifier. It is implemented with gate turn-off thyristors (GTOs). This nonresonant circuit combines the advantages of linear amplifiers with those of high-efficiency switchmode power conversion techniques for the generation of up to megawatt pulses. An order of magnitude increase in available gradient power is achieved with excellent coil current waveforms