DC Brushless Motor Hall Sensor

Unlike brushed DC motors, brushless DC motors use electronic commutation. To turn a brushless motor, the stator must be energized in a certain order, so we need to know the position of the rotor to energize the corresponding stator coils in that order. The position of the stator is sensed by Hall sensors embedded in the stator. Usually 3 Hall sensors are arranged around the rotation path of the rotor. Whenever the magnetic pole of the rotor passes through the Hall element, the Hall element will output a corresponding high level or low level according to the current polarity of the rotor. In this way, only the timing based on the levels generated by the three Hall elements is required. The current position of the rotor can be judged and the stator windings can be energized accordingly.

Hall Effect: When an energized conductor is placed in a magnetic field, charges in the conductor accumulate on one side of the conductor due to the force of the magnetic field. This effect is even more pronounced when thin, flat, current-carrying conductors are placed in a magnetic field, thereby bringing one side together. The charge conductor will cancel the effect of the magnetic field. The accumulation of charge on one side of the conductor results in a voltage on both sides of the conductor. This phenomenon is called the Hall effect. EH Hall discovered this phenomenon in 1879. Hence the name.

The Hall element is placed in a fixed position of the motor. Placing the Hall element on the motor's stator is more complicated because the Hall element's measurements may not accurately reflect the placement if it is placed out of tangent to the rotor's magnetic field. In view of the above reasons, the current position of the rotor, in order to simplify the installation of Hall elements, redundant magnets are usually installed on the rotor of the motor. This magnet is specially used to sense the hall element, so it can sense the rotor magnet. In order to achieve the same effect, the Hall element is usually placed on the printed circuit board according to the circumference, and is equipped with an adjustment cover, so that the user can easily adjust the position of the Hall element according to the direction of the magnetic field, so that it can work in the best state .

The voltage range of the Hall element is 4V to 24V, and the current range is 5mA to 15mA. Therefore, when considering a controller, the current and voltage requirements of the Hall element should be considered. In addition, the output collector of the Hall element is an open circuit, and a pull-up resistor is required for use. For each commutation, one set of windings is powered in the forward direction; the second set is powered in the opposite direction. The third group was not powered. The magnetic field of the permanent magnets of the rotor interacts with the magnetic field generated by the stator steel plates to generate torque. Theoretically, when the angle between the two magnetic fields is 90°, a larger torque will be generated. When the two magnetic fields coincide, the torque becomes zero. For the rotor to rotate continuously, the stator's magnetic field needs to change sequentially, just as the rotor's magnetic field always follows the rotor's magnetic field. stator.