Patent ID: 7746014
Filing Date: 2010-06-29
Classification: H02P,Y02P

Abstract:
1. A motor driving apparatus comprising: a position detecting circuit which detects a positional relationship between a rotor magnet of a brushless motor and driving coils; an energization signal generating circuit which outputs an energization switching timing signal for the driving coils on the basis of a result of the detection by the position detecting circuit; a speed deviation detecting circuit which detects whether a rotational speed of the brushless motor falls within a speed region based on a target rotational speed obtained from a speed command signal and outputs a certain rotation detecting signal as a result of the detection and speed difference information indicating a difference between the rotational speed of the brushless motor and the target rotational speed based on the speed command signal; a rotational speed controlling circuit which outputs a speed controlling signal serving as an acceleration command or a deceleration command on the basis of the speed difference information; first, second, and third positive-side driving transistors having drains which are supplied with a power supply voltage and are commonly connected; first, second, and third negative-side driving transistors having sources which are grounded via a resistor and are commonly connected and the drains which are connected to sources of the first, second, and third positive-side driving transistors, respectively; a power supply monitoring circuit which monitors the power supply voltage and outputs a driving mode switching signal which has a first value if the power supply voltage is not less than a predetermined value and has a second value if the power supply voltage is less than the predetermined value; and an output PWM control section to which the energization switching timing signal, the certain rotation detecting signal, the speed controlling signal, and the driving mode switching signal are input and which is connected to gates of the positive-side driving transistors and negative-side driving transistors to perform on/off control and switches a mode of driving from synchronous rectification PWM driving to one-way PWM driving on the basis of a change of the driving mode switching signal from the second value to the first value, wherein the power supply monitoring circuit has: