Model reference following commutation circuit and adjusting method thereof

摘要

A circuit and method for controlling commutation of an electric motor includes first and second n-bit counters. The counters alternately serve as model reference and model following counters during alternate zero-cross intervals of a detected back-emf signal which is generated during rotation of the electric motor. The model following counter counts clock cycles occurring since a detected zero cross and continues counting until an optimal commutation switching point is detected, which is ideally located halfway through a commutation interval. A masking circuit is provided to mask spurious zero cross detections during a desired masking interval. A soft switching circuit determines commutation starting and ending points which are symmetrically located with respect to a center point of a commutation interval. Overflow protection circuits protect the counters from overflow during long commutation intervals and the like, and the internal clock is modulated to prevent overflow during certain operating conditions.