Motor driving apparatus, brushless motor, and method for driving the same

A brushless motor comprising:

• a rotor magnet;
• first, second, and third driving coils which are provided to oppose the rotor magnet and have one ends commonly connected;
• a position detecting circuit which detects a positional relationship between the rotor magnet and the first, second, and third 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 rotor magnet 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 rotor magnet 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 respectively connected to sources of the first, second, and third positive-side driving transistors and the other ends of the first, second, and third driving coils;
• 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 performs on/off control of the positive-side driving transistors and negative-side driving transistors 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:
• a regulator circuit which is supplied with the power supply voltage and outputs a first constant voltage;
• a first voltage dividing circuit which divides the first constant voltage and outputs a second constant voltage;
• a second voltage dividing circuit which divides the power supply voltage and outputs a voltage;
• and
• a comparator which is supplied with the second constant voltage and the voltage output from the second voltage dividing circuit and outputs a result of comparison as the driving mode switching signal.

A method for driving a brushless motor using a motor driving apparatus having a position detecting circuit, an energization signal generating circuit, a speed deviation detecting circuit, a rotational speed controlling circuit, three positive-side driving transistors, three negative-side driving transistors, a power supply monitoring circuit, and an output PWM control section,

• wherein the position detecting circuit detects a positional relationship between a rotor magnet of the brushless motor and driving coils,
• the energization signal generating circuit outputs an energization switching timing signal for the driving coils on the basis of a result of the detection by the position detecting circuit,
• the speed deviation detecting circuit 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,
• the rotational speed controlling circuit outputs a speed controlling signal serving as an acceleration command or a deceleration command on the basis of the speed difference information,
• the positive-side driving transistors and the negative-side driving transistors switch application of a power supply voltage to the driving coils,
• the power supply monitoring circuit 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
• the output PWM control section performs on/off control of the positive-side driving transistors and negative-side driving transistors on the basis of the energization switching timing signal, the certain rotation detecting signal, the speed controlling signal, and the driving mode switching signal 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 divides a first constant voltage which is generated using the power supply voltage and generates a second constant voltage, compares the second constant voltage with a voltage which is obtained by dividing the power supply voltage, and outputs a result of the comparison as the driving mode switching signal.