Abstract: A resonant power converter includes a full bridge configuration of switching devices and a resonant tank circuit coupled between the full bridge and an isolation transformer having a primary winding and a secondary winding. A full bridge rectifier is coupled between the isolation transformer and a load. A converter controller for generating switching signals for the switching devices includes an outer controller to generate a tank command signal based on a voltage error signal between an output voltage command signal and an actual output voltage signal and an inner controller to generate an actual tank signal based on a secondary winding current and the output voltage command signal. The converter controller also includes a signal generator for generating the switching signals for the switching devices based on a tank error signal between the tank command signal and the actual tank signal.

Abstract: A gradient amplifier for an MRI system includes a low voltage amplifier and high voltage amplifier connected in series circuit with a gradient coil. A gradient current command pulse causes the low voltage amplifier to produce the desired coil current and the same command is differentiated to provide a voltage command for the high voltage amplifier which causes it to deliver power to rapidly build the gradient field at the beginning of the pulse and to remove power at the conclusion of the pulse. Two embodiments disclose different strategies for maintaining the high voltage power supply fully charged throughout a scan.

Abstract: A gradient amplifier for use in magnetic resonance imaging equipment employs a low voltage DC power supply connected in series between a pair of higher voltage DC power supplies, the latter supplies serving to provide increased power for rapid gradient switching and the former supply providing correction current to produce the desired voltage output. The high voltage DC power supplies preferably comprise multiple DC units which can be combined to provide finer steps of control prior to correction by the lower voltage supply. The low voltage DC power supply preferably comprise one or more linear amplifiers connected in series, or one or more switchmode amplifiers connected in series. The DC power supplies are controlled in an open loop manner from a gradient signal that designates the desired current for the gradient coil and the amplifiers are operated in a closed loop responding to to a feedback signal from the gradient coil.

Abstract: A compact local gradient coil is combined with a local RF coil to provide lower powered, higher strength gradient fields and faster gradient response as is useful in magnetic resonance imaging. Interference between the RF coil and gradient coil is minimized by placement of the gradient coil external to the RF coil and by gradient coils that are axially symmetric and/or have conductors substantially orthogonal to the RF coil conductors. Acoustic noise in these smaller, stronger coils is reduced with ports cut into the coil forms.

Abstract: A magnetic resonance imaging system uses a pool of amplifiers to generate gradient signals. Each amplifier within the pool may be switched among any of the gradient axes, so as to efficiently allocate amplifier power among the gradients. In one embodiment, the amplifiers of the pools are connected in stacks by an input and output matrix comprised of mechanical switches driven in tandem by interlocked motors. The switches connect the outputs of the amplifiers in series. The input signal is "boot strapped" through the amplifier stack to provide proper signal level.