Switch mode power converters; present and future

More than 600 switch mode power converters are installed in LEP (Large Electron Positron colliding beam accelerator) to power the main ring magnet system. The horizontal and vertical magnets are fed by 520 bipolar, four-quadrant units of 675-W output rating. The short chains of quadrupole and sextupole magnets with copper windings are powered by 105 modular resonant-type power converters of a DC output rating of 3.75 kW. Their transformer-coupled output stage makes it possible to choose three different output ratings, i.e. 300 A/125 V, 200 A/188 V, and 150 A/250 V. Eight high-current 2000-A, 10-V converters feed the superconducting quadrupoles for the low- beta insertions in the physics interaction regions. Details are given on the initial CERN design work leading to the choice of circuit topology, in order to meet the strict accelerator requirements, particularly on efficiency, size, and reliability.<>