Why you should be turning on brushless DC motors

Brushless DC (BLDC) motors are becoming increasingly popular in automation applications due to their ability to provide precise control over speed and energy consumption. Unlike traditional brushed DC motors, BLDC motors use electronic commutation to control the flow of current to the stator coils. This allows for more efficient and flexible control of the motor's rotation.


One of the key challenges of using BLDC motors is the need for advanced commutation circuitry. In the past, this added cost to the overall system, but today's focus on energy efficiency has made the benefits of electronic commutation more valuable. BLDC motors are commonly available in single-phase and three-phase configurations.


A single-phase BLDC motor uses a single stator winding along four arms of the stator to form four magnetic poles. The external rotor contains permanent magnets arranged to form two pole pairs. Current is applied to the stator through transistors in an H-bridge, and when the rotor has turned through 180°, the direction of current in the stator winding is reversed, causing the rotor to continue turning through 180° and complete a full revolution.


A three-phase BLDC motor, on the other hand, has three separate stator windings, commonly referenced as u, v, and w. The current delivered to each winding is controlled using three half-bridges. The control circuit comprises six power transistors. The rotor begins to turn when current flows through one of the three stator windings to produce an electromagnetic pole. The magnetic field generated attracts the closest rotor magnet of opposing polarity. The controller turns on successive adjacent phases in sequence, causing the rotor to revolve.


When designing a BLDC motor drive, it's important to choose the right power switches for the motor-control bridge circuit. For example, if a MOSFET is used, a device with low RDS(on) should be chosen for optimum efficiency. Other critical parameters include the gate capacitance (Cg) and gate charge (Qg), which will influence the choice of gate drivers or power modules. Other factors such as package size and price must also be considered, as well as the package's thermal performance and operating power, which will affect thermal management and cooling.


In summary, BLDC motors offer precise control over speed and energy consumption and are becoming increasingly popular in automation applications. However, designing a BLDC motor drive can be challenging, and it's important to choose the right components to ensure optimal efficiency and performance. With the help of Avnet FAEs, the process can be simplified, allowing engineers to focus on the unique demands of their applications.

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