THE CIRCUIT REDUCING HARMONICS

Current harmonics produced by switching of a triac 116, which controls AC current supply to a load 114 such as a motor, are attenuated by inductive filters 118,120 inserted in each conductor of the AC supply 112. The filters each comprise two parallel coils L11,L12 and L13,L14 wound on a core, with the coils L11, L12 stacked on top of each other and coils L13, L14 stacked on top of each other. L11 and L13 are wound toward the load by the right hand rule, and L12 and L14 are wound toward the AC source 112 by the right hand rule. There may be a filter in one conductor only, and the filters may comprise 1,2 or 3 coils. The filters may also comprise resistors parallel to the coils (figures 12,16,24,25). Single-coil filters in each conductor may be coupled (figures 17 and 20).