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Brushless DC motor uses semiconductor switching devices to realize electronic commutation, that is, electronic switching devices are used to replace the traditional contact commutator and brush. It has the advantages of high reliability, non reversing spark, low mechanical noise, etc. It is widely used in high-end recording stands, video recorders, electronic instruments and automatic office equipment.
Brushless DC motor is composed of permanent magnet rotor, multipole winding stator, position sensor, etc. According to the change of the rotor position, the position sensor will carry out the commutation of the current of the stator winding along a certain order (that is, detect the position of the rotor pole relative to the stator winding, and generate the position sensing signal at the determined position, which will be processed by the signal conversion circuit to control the power switch circuit, and switch the winding current according to a certain logic relationship). The working voltage of the stator winding is provided by the electronic switch circuit controlled by the output of the position sensor.
There are three types of position sensors: magnetic sensor, photoelectric sensor and electromagnetic sensor.
For brushless DC motor with magnetic sensitive position sensor, its magnetic sensor components (such as Hall element, magnetic diode, magnetic sensitive pole tube, magnetic resistor or special integrated circuit) are installed on the stator components to detect the magnetic field changes generated when the permanent magnet and rotor rotate.
Brushless DC motor with photoelectric position sensor is equipped with photoelectric sensor on the stator assembly according to a certain position, the rotor is equipped with a light shield, and the light source is a light emitting diode or a small bulb. When the rotor rotates, due to the function of the light shield, the photosensitive components on the stator will generate pulse signals intermittently at a certain frequency.
Brushless DC motor with electromagnetic position sensor is equipped with electromagnetic sensor components (such as coupling transformer, proximity switch, LC resonant circuit, etc.) on the stator assembly. When the position of permanent magnet rotor changes, the electromagnetic effect will cause the electromagnetic sensor to generate high-frequency modulated signal (its amplitude varies with the rotor position).


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