New-Tech Europe Magazine | April 2017

Driving a single-phase BLDC motor

Mike Gomez & Mark Pallones, Microchip Technology

How to use a low-cost microcontroller as a driver for a single-winding, single- phase brushless DC motor In a low-power motor application, where cost is more important than complexity and torque requirements are reduced, a single-phase brushless DC (BLDC) motor is a good alternative to a three-phase motor. This type of motor is low cost because of its simple construction, which is easier to fabricate. Also, it only requires a single-position sensor and a few driver switches to control and energise the motor winding. Therefore, the trade- off between motor and control electronics can work out favourably.

This application uses the following peripherals: complementary waveform generator (CWG); signal measurement timer (SMT); analogue-to-digital converter (ADC); digital-to-analogue converter (DAC); capture compare PWM (CCP); fixed voltage reference (FVR): timer; comparator; and temperature indicator. These peripherals are internally connected by firmware, which reduces the number of external pins required. The full-bridge circuit, which energises the motor winding, is controlled by the CWG output. A Hall sensor is used to determine the rotor position. Current that passes through the motor winding is translated into a voltage through

To maintain the cost effectiveness, a low-cost motor driver is needed. The driver circuit described here can exploit two feedback loops. The first, the inner loop, is responsible for commutation control, while the second, the outer loop, handles speed control. The speed of the motor is referenced to an external analogue voltage and fault detection can be sensed during over-current and over-temperature conditions. Fig. 1 shows the single-phase driver based on Microchip’s PIC16F1613 8bit microcontroller, chosen because of its low pin count and on- chip peripherals that can control the driver switches, measure the motor speed, predict the rotor position and implement fault detection.

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