Brushless motor is a kind of motor that uses electronic phase converter to control the speed of the motor, which has the advantages of high efficiency, low noise and long life. The core component of the brushless motor is the inverter, which is responsible for converting DC power to AC power, thus driving the motor to rotate. Brushless motor has the advantages of high efficiency, low noise, small size, light weight, long life, etc., and is widely used in industrial control, household appliances and other fields.

The commutator of the brushless motor is a key part of controlling the motor speed and torque, which needs to switch the positive and negative poles of the power supply in time according to the position and direction of the rotor, so as to generate a suitable magnetic field to drive the rotor to rotate. The main switching element of the inverter is the MOSFET field effect transistor - the MOSFET field effect transistor has the characteristics of low junction capacitance and low internal resistance, which is of great help to improve the performance of the brushless motor.

Wide application of brushless motor

The application effect can be illustrated from the following aspects:

Increase efficiency:

The on-resistance of MOSFET is low, which means that in the on-state, the current through MOSFET is large, and the magnetic field generated is strong, thereby improving the output power and efficiency of the brushless motor. At the same time, the MOSFET switching speed is faster, which means that in the switching state, the current through the MOSFET is small and the loss is low, thus reducing the input power and loss of the brushless motor.

Reduce noise:

The switching speed of MOSFET is faster, which means that in the switching state, the current through MOSFET changes faster, and the electromagnetic interference generated is smaller, thus reducing the noise of the brushless motor. At the same time, the MOSFET‘s drive power consumption is low, which means that in the drive state, the gate current through the MOSFET is small and the heat generated is less, thus reducing the temperature rise and noise of the brushless motor.

Increase life expectancy:

The on-resistance of MOSFET is low, which means that in the on-state, the power loss through MOSFET is small, thus extending the life of MOSFET. At the same time, the drive power consumption of the MOSFET is low, which means that in the drive state, the temperature increase through the MOSFET is small, thus extending the life of the MOSFET.

In addition, when using MOSFET, you also need to pay attention to the following aspects:

1

Select the right MOSFET model. Different brushless motors require different drive voltages and currents, so it is necessary to select the appropriate MOSFET model according to the parameters of the brushless motor to meet its on-resistance, voltage resistance, current resistance and other requirements. In general, the voltage resistance of MOSFET should be more than 2 times the maximum working voltage of the brushless motor, the on-resistance should be less than 1/10 of the phase resistance of the brushless motor, and the current resistance should be more than 5 times the maximum working current of the brushless motor.

2

Ensure heat dissipation of MOSFET. Because the MOSFET will produce a certain power consumption during the switching process, its temperature will rise, if the temperature is too high, it will affect its performance or even damage. Therefore, it is necessary to provide sufficient heat dissipation measures for the MOSFET, such as the use of heat sinks, fans, etc., while taking care to avoid abnormal conditions such as short circuit or overload.

3

Prevents reverse breakdown of MOSFET. When the MOSFET is turned off, due to the inductive circuit of the brushless motor, a certain reverse voltage will be generated, and if the reverse voltage exceeds the breakdown voltage of the MOSFET, it will cause damage. Therefore, it is necessary to parallel a reverse diode between the drain and source of the MOSFET or use a MOSFET with a built-in reverse diode to provide a discharge path and protect the MOSFET from reverse breakdown.

4

Control the switching time of the MOSFET. In order to improve the efficiency of the brushless motor and reduce noise, it is necessary to control the switching time of the MOSFET, so that it is synchronized with the commutated signal of the brushless motor, and minimize its dead time. Dead time refers to the time difference between two adjacent MOSFETs when switching, if the dead time is too long, it will cause the brushless motor to lose torque or produce sparks; If the dead interval is too short, two adjacent MOSFETs will be on at the same time, resulting in a short circuit. Therefore, it is necessary to select the appropriate switching time according to the speed and commutation frequency of the brushless motor, and use the appropriate driver chip or driver circuit to control the MOSFET.

5

Ensure the parameter consistency of the three half-bridges. The drive circuit of a brushless motor is usually composed of three half Bridges, each half bridge is composed of two MOSFETs, which respectively control the forward and reverse current of the stator windings. In order to ensure the normal operation of the brushless motor, it is necessary to ensure the parameter consistency of the three half-bridges, that is, the MOSFET of each half-bridge has the same on-resistance, gate capacitance, switching time and other parameters. Parameter inconsistency will affect the commutation precision of the brushless motor, cause the phase deviation between the stator magnetic field and the rotor magnetic field, and reduce the output power and efficiency of the brushless motor. Parameter inconsistency will increase the harmonic loss of the brushless motor, generate additional heat, and accelerate the aging and damage of MOSFETs;

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To sum up

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