Abstract: A gradient amplifier arrangement is described that comprises a gradient amplifier power stage. The device may be employed to provide a current to a gradient coil, as in a MRI system. The circuitry disclosed includes a series coupling of a first bridge amplifier operating at a first voltage, a second bridge amplifier operating at a second voltage, a third bridge amplifier operating at a third voltage, and a gradient amplifier control stage. The amplifiers may provide output voltages at different levels, and may be switched at different times and frequencies to provide a range of output voltage and current levels.

Abstract: An optimal phase-shifted control for a series resonant converter involves instantaneous monitoring of state variables (resonant capacitor voltage resonant inductor current and output voltage) and implementation of a control law for providing a quasi-squarewave-with-maximum-coasting (QSWMC) mode of operation. The control law uses the instantaneous resonant inductor current, the instantaneous resonant capacitor voltage and the output voltage to determine the optimal time to perform switching events in order to operate on a desired control trajectory. The QSWMC converter operates at a minimized frequency in a super-resonant mode with zero-voltage switching, minimized electrical stresses, and reduced electromagnetic interference due to nearly sinusoidal resonant tank currents.

Abstract: A plurality of low-voltage, series-connected input dc-dc converters provide the input to a low-frequency, high-voltage dc-ac output bridge converter suitable for driving a gradient coil in an MRI system. The relatively low-voltage, series-connected dc-dc converters, or choppers, control the gradient coil current, while the dc-ac converter bridge steers the current to the proper coil polarity. A binary weighting of the voltage ratings of the input choppers results in the lowest voltage unit doing most of the high-frequency switching. Such an amplifier configuration is modular and allows for different gradient coil requirements to be met with a common approach by applying a predetermined number of choppers and bridges.

Abstract: A partial-voltage buck regulator controls a high-voltage bus to a full-bridge circuit such that overall switching losses are reduced and distributed. Low-voltage buck regulator devices are PWM-switched when high output voltage is needed, and high-voltage bridge devices are PWM-switched when low output voltage is needed. A variable input power supply, which may be operated in a high power factor mode, can adjust the input bus voltages to achieve optimum performance for a given magnetic resonance imaging sequence.

Abstract: An amplification device is provided for driving a gradient coil in an MR system, wherein the gradient coil is required to generate a rapidly changing gradient magnetic field during a first time period, and a substantially constant field during an immediately following second time period. The device includes a adjustable bus, for providing first and second voltage levels, and a switching or PWM amplifier. A switch is coupled between the bus and the switching amplifier for applying the first voltage to the amplifier during the first time period, and the second voltage to the amplifier during the second time period. The switching amplifier comprises an inverter for generating a PWM voltage in response to its input, and an LC filter for converting the PWM wave into a DC voltage. The switching amplifier generates a substantially higher coil driving voltage during the first period, in response to the first voltage level, than during the second period in response to the second voltage level.