Resonant converters

Claim 2

A resonant converter arrangement comprising: a first resonant converter having a resonant circuit through which current is switched alternately in opposite directions, the converter providing a first signal; a second resonant converter having a resonant circuit through which current is switched alternately in opposite directions, the converter providing a second signal; first switching means for controlling the switching frequency of the current in the first resonant converter at a fixed frequency; second switching means for controlling the switching frequency of the current in the second resonant converter at a fixed frequency; signal combining means for combining the first and second signals to provide an output signal; and a switch controller for controlling the second switching means in accordance with relative phase of said first and second signals to control the amplitude of the output signal.

Claim 3

A resonant converter arrangement as claimed in claim 1, wherein the phase of one of said first and second resonant converters is phase-locked to the other of said first and second resonant converters by means of a phase-locked loop.

Claim 4

A resonant converter arrangement as claimed in claim 2, wherein the phase-locked loop comprises a phase detector responsive to said first and second signals from said first and second resonant converters for providing a feedback signal in dependence upon the phase difference therebetween, which feedback signal is fed back via said signal combining means to control the phase of said second resonant converter so that it bears a predetermined phase relationship to the phase of said first resonant converter as determined by the amplitude of a demand signal fed into the signal combining means.

Claim 5

A resonant converter arrangement as claimed in claim 3, wherein the signal combining means comprises a first combiner in which a control signal is combined with said output signal of said resonant converter arrangement thereby to provide a resultant signal, and a second combiner in which the resultant signal and the feedback signal are combined to provide a control signal effective to control the phase of said second resonant converter.

Claim 6

A resonant converter arrangement as claimed in claim 1, wherein said first and second signals from said first and second resonant converters are combined in a transformer and fed via a bridge rectifier to provide a d.c. output.

Claim 7

An MRI system including a resonant converter arrangement as claimed in claim 1.

Claim 8

A resonant converter arrangement comprising two resonant converters, each having a resonant circuit through which current is switched alternately in opposite directions by respective switch means which are responsive to a switch controller, the outputs of the two resonant converters being mutually combined to provide an output of the arrangement the amplitude of which is controlled in dependence upon the relative phase of the outputs of the two resonant converters, wherein: the phase of one of the two resonant converters is phase-locked to the other of the two resonant converters by means of a phase-locked loop; and the phase-locked loop comprises a phase detector responsive to the outputs of the two converters for providing a feedback signal in dependence upon the phase difference therebetween, which feedback signal is fed back via signal combining means to control the phase of one of the two converters so that it bears a predetermined phase relationship to the phase of the other of the two converters as determined by the amplitude of a demand signal contribution fed into the signal combining means.

Claim 9

A resonant converter arrangement comprising two resonant converters, each having a resonant circuit through which current is switched alternately in opposite directions by respective switch means which are responsive to a switch controller, the outputs of the two resonant converters being mutually combined to provide an output of the arrangement the amplitude of which is controlled in dependence upon the relative phase of the outputs of the two resonant converters, wherein: the phase of one of the two resonant converters is phase-locked to the other of the two resonant converters by means of a phase-locked loop; and the phase-locked loop comprises a phase detector responsive to the outputs of the two converters for providing a feedback signal in dependence upon the phase difference therebetween, which feedback signal is fed back via signal combining means to control the phase of one of the two converters so that it bears a predetermined phase relationship to the phase of the other of the two converters as determined by the amplitude of a demand signal contribution fed into the signal combining means.

Claim 10

A resonant converter arrangement as claimed in claim 7, wherein the signal combining means comprises a first combiner in which a control signal level is combined with a signal level derived from the output of the resonant converter arrangement thereby to provide a resultant signal, and a second combiner in which the resultant signal and the feedback signal are combined to provide a control signal effective to control the phase of the said one of the two resonant converters.