A new high-precision current supply for magnets

A new, high-precision, low-ripple current power supply (CPS) for magnets, based on a combination of an SCR converter and a single transistor switched mode power supply (SMPS) is described. The load power is primarily supplied by the SCR converter. The SMPS handles only a small fraction of the load power, and also, what is more significant, a very small part of the load current. In this paper, the topology and operating principle of the new power supply is discussed. A CPS, rated at 200 A at 45 V, was constructed and tested. The power supply energizes a family of quadrupole magnets at the Brazilian Synchrotron Light Source-LNLS. Making use of the current limit modulation control method, magnetic field variations at full current are 5 ppm, with only 8 A passing through the switching transistor. The design and performance of the power supply under different operating conditions are described. Variations of the proposed topology, suitable for high-current and high-voltage loads, are also discussed