Control system for sensorless brushless DC motor

摘要

Control circuitry for a brushless direct current motor is premised on constructing phase to phase back emf signals representing the differences between the back electromotive force efforts produced in each phase winding of the motor. The phase to phase back emf signals are used to produce logic level signals having logic level changes at the zero voltage crossover points of the phase to phase back emf signals. Detection of the zero voltage crossover points is dictated by selectively activated comparator circuits. A method is also disclosed as to how the values of certain circuit elements may be derived.