To realize the control of the motor speed, there must be a speed signal. The speed signal is obtained by a similar method of obtaining the position signal. The simplest speed sensor is a combination of a frequency-measuring tachogenerator and an electronic circuit.
The commutation circuit of the brushless DC motor consists of two parts, the driving part and the control part. The two parts are not easy to separate. Especially for low-power circuits, the two parts are often integrated into a single application-specific integrated circuit.
In higher power motors, the drive circuit and the control circuit can each be integrated. The drive circuit outputs electric power, drives the armature winding of the motor, and is controlled by the control circuit. At present, the drive circuit has changed from a linear amplification state to a pulse width modulation switching state, and the corresponding circuit composition has also changed from a transistor discrete circuit to a modular integrated circuit. Modular integrated circuits of brushless motors are composed of power bipolar transistors, power field effect transistors and isolated gate field effect bipolar transistors. Although the isolation gate field effect bipolar transistor is more expensive, it is more suitable to choose it from the point of view of reliability, safety and performance.
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