Sensorless BLDC For Electronic Devices

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The sensorless brushless DC (BLDC) motor is becoming more and more popular in consumer, industrial and white goods markets with end applications such as pumps, blowers, power and garden tools, hair dryers, portable mixers and airborne drones. As the name suggests, it does away with the wear-prone brushes used in traditional motors, replacing them with an electronic controller that improves the reliability of the unit. Moreover, a BLDC motor can be made smaller and lighter than a brush type with the same power output, making it suitable for applications where space is tight.

BLDC electric motor are synchronous motors that are powered by a DC electric source via an integrated inverter/switching power supply, which produces an AC electric signal to drive the motor. These motors are classified as synchronous devices because the magnetic fields of the stator and rotor rotate at the same frequency. The stator comprises steel lamination’s, slotted axially to accommodate an even number of winding’s along the inner periphery. The rotor is constructed from permanent magnets with from two-to-eight N-S pole pairs. The BLDC motor’s electronic commutator sequentially energises the stator coils generating a rotating electric field that drags the rotor around with it. Efficient operation is achieved by ensuring that the coils are energised at precisely the right time. Sensors work well, but they add cost, increase complexity (due the additional wiring) and reduce reliability (due in part to the sensor connectors that are prone to contamination from dirt and humidity).

Allegro BLDC

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According to the press release, A4963 from Allegro is a three-phase, sensorless BLDC motor controller for use with external complementary P-channel and N-channel power MOSFETs. The release states, “A4963 can be used as a stand-alone controller communicating directly with an electronic control unit (ECU) or it can be used in a close coupled system with a local microcontroller (MCU). The motor is driven using block commutation (trapezoidal drive) where phase commutation is determined, without the need for independent position sensors, by monitoring the motor back- EMF. The sensorless start-up scheme allows the A4963 to operate over a wide range of motor and load combinations.”

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Adding further the release states, “Dedicated circuits allow the A4963 to operate over a wide range of motor speeds, from less than 100 rpm to in excess of 30,000 rpm, depending on the supply voltage and motor capability. Operating mode and control parameters can be altered through an SPI compatible serial interface. The A4963 is provided in a small, thermally enhanced 20-pin TSSOP with exposed thermal pad.”

Features and benefits of A4963 device as highlighted below.

  • Three phase sensorless BLDC motor control FET driver
  • Logic level P-N gate drive (P high-side, N low-side)
  • 2V to 50V supply range
  • Simple block commutation for maximum torque
  • Sensorless (bemf sensing) start-up and commutation
  • Programmable operating modes:
    • Integrated Speed Control
    • PWM Duty Cycle Control
    • Current mode control
  • Cross-conduction prevention
  • Wide speed range capability
  • Peak current limiting
  • Single low frequency PWM control input
  • Single Open Drain Fault output
  • SPI compatible interface providing:
    • Configuration and control
    • Programmable dead time
    • Programmable phase advance
    • Detailed diagnostic reporting
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