The invention relates to a method and a controlling apparatus for controlling the magnitude and direction of a current (I) through a winding (L). The method and controlling apparatus are based on a drive circuit (TR.sub.1, D.sub.1, TR.sub.2, D.sub.2, TR.sub.3, D.sub.3, TR.sub.4, D.sub.4) which is controllable...http://www.google.ca/patents/US4908562?utm_source=gb-gplus-sharePatent US4908562 - Method and apparatus for controlling the magnitude and direction of a current through a winding
