Brushless DC motor

A brushless DC motor comprising:

• a rotor having N pairs (N being an integer number) of magnetic poles having a magnetic field, the poles being provided by permanent magnets;
• a plurality of three-phase coils interacting with a magnetic flux of the magnetic field of said rotor;
• a plurality of first driving transistors having input and output terminals, forming current paths from a direct current power source to said three-phase coils;
• a plurality of second driving transistors having input and output terminals, the second driving transistors forming current return paths from said three-phase coil to said direct current power source;
• a plurality of first diodes in parallel across the input terminals and the output terminals of said first driving transistors;
• a plurality of second diodes in parallel across the input terminals and the output terminals of said second driving transistors;
• a position detecting means for generating a control signal by detecting a terminal voltage on an input-output terminal of said three-phase coils;
• a switching-driving means for outputting a switching signal to said first driving transistors and said second driving transistors on the basis of the control signal of said position detecting means, and for switching a current flow to said coils in the order of first terminal, second terminal, and third terminal respectively;
• and
• said position detecting means comprising:
• a first filter having integration characteristics of a first order for smoothing the terminal voltage detected on said first terminal,
• a second filter having integration characteristics of a first order for smoothing the terminal voltage detected on said second terminal,
• a third filter having integration characteristics of a first order for smoothing the terminal voltage detected on said third terminal,
• a first mixing means for mixing an output signal of said first filter and an output signal of said second filter,
• a second mixing means for mixing an output signal of said second filter and an output signal of said third filter,
• a third mixing means for mixing an output signal of said third filter and an output signal of said first filter,
• a fourth mixing means for mixing an output signal of said first filter and an output signal of said second filter and an output signal of said third filter,
• a first comparing means for generating a first digital signal by comparing an output signal of said first mixing means and an output signal of said fourth mixing means,
• a second comparing means for generating a second digital signal by comparing an output signal of said second mixing means and an output signal of said fourth mixing means,
• a third comparing means for generating a third digital signal by comparing an output signal of said third mixing means and an output signal of said fourth mixing means, and
• said digital signals of said first comparing means and said second comparing means and said third comparing means are output as control signals of said position detecting means to switch and control the current flowing states of said first driving transistors and second driving transistors.

A brushless DC motor comprising:

• a rotor having N pairs (N being an integer number) of magnetic poles having a magnetic field, the poles provided by permanent magnets;
• a plurality of three-phase coils interacting with a magnetic flux of the magnetic field of said rotor;
• a plurality of first driving transistors having input and output terminals, the first driving transistors forming current paths from a direct current power source to said three-phase coils;
• a plurality of second driving transistors having input and output terminals, the second driving transistors forming current return paths from said three-phase coils to said direct current power source;
• a plurality of first diodes in parallel across input terminals and output terminals of said first driving transistors;
• a plurality of second diodes in parallel across input terminals and output terminals of said second driving transistors;
• a position detecting means for generating a control signal by detecting terminal voltages on input-output terminals to said three-phase coils;
• a switching-driving means for issuing a switching signal of to said first driving transistors and said second driving transistors on the basis of the control signal of said position detecting means, and for switching and flowing a current to said coils sequentially in the order of a first terminal, a second terminal, and a third terminal;
• a current detecting means for detecting supply current to said coils;
• and
• said position detecting means comprising:
• a first filter having integration characteristics of a first order for smoothing a terminal voltage detected on said first terminal,
• a second filter having integration characteristics of a first order for smoothing a terminal voltage detected on said second terminal,
• a third filter having integration characteristics of a first order for smoothing a terminal voltage detected on said third terminal,
• first mixing means for mixing an output signal of said second filter and an output signal of said third filter,
• second mixing means for mixing an output signal of said third filter and an output signal of said first filter,
• third mixing means for mixing an output signal of said first filter and an output signal of said second filter,
• first comparing means for generating a first digital signal by comparing the output signal of said first filter and an output signal of said first mixing means,
• second comparing means for generating a second digital signal by comparing the output signal of said second filter and an output signal of said second mixing means,
• third comparing means for generating a third digital signal by comparing the output signal of said third filter and an output signal of said third mixing means,
• a variable mixing ratio means for varying a mixing ratio in said first mixing means and said second mixing means and said third mixing means corresponding to the output signal of said current detecting means in a manner such that when the supply current to said coil is larger than a predetermined value in comparison to the case when the output current is smaller than the predetermined value, more output signal of said third filter is included in the output signal of said first mixing means, and more output signal of said first filter means is included in the output signal of said second mixing means, and more output signal of said second filter means is included in the output signal of said third mixing means,
• said digital signals of said first mixing means and said second mixing means and said third mixing means are issued as control signals of said position detecting means to switch and control the current flowing states of said first driving transistors and second driving transistors.