A high precision power supply for magnets in magnetic resonance imaging systems: the “quadratic” power cell

The implementation of a high current, wide output range (both voltage 5-100 V and current 0.5-20 A) DC-to-DC power converter with 16-bit linearity is investigated. This power converter is intended to be the power supply for the coils of a multipolar magnet for a magnetic resonance imaging system. A mixed linear and switch-mode technique, i.e. the combination of a linear final regulator and a switching preregulator, makes it possible to achieve high accuracy and good efficiency. The reasons leading to the choice of a “quadratic” cell with a state-of-the-art switching frequency are discussed. Regulation characteristics, maximum stresses on the critical components, efficiency, stationary and dynamic behavior are evaluated by means of CAD tools and compared with the well-matched performances measured in a full power prototype