Importance

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Abstract

A motor assembly includes a brushless dc motor and a driving unit. The driving unit includes three first power transistors, each being activable to connect a respective one of three windings of a coil unit of the dc motor and a power supplying circuit. A comparing unit compares a reference voltage signal equal to a desired motor speed from a speed setting unit with an analog voltage signal corresponding to the rotating speed of the rotor from a frequency-to-voltage converter and generates an analog error voltage signal. Each of three second power transistor corresponds to one of the first power transistors and is activable to connect the power supplying circuit and a respective one of the windings of the coil unit. The driving circuit receives and processes from a sensor circuit three speed pulses representing the rotating speed of the rotor so as to activate intermittently two of the first power transistors and deactivate one of the first power transistors at any time and so as to activate one of the second power transistors corresponding to the deactivated one of the first power transistors upon receiving a modulated pulse signal which is generated by a pulse width modulating circuit having the error voltage signal as a modulating signal.

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First Claim