introduction

Brushless DC (BLDC) fan is widely used in air circulation and air cooling applications, such as PC cooling fan and car seat ventilation fan, due to its high efficiency, low cost, simple structure and long service life.

Features of single phase BLDC motor fan:

Brushless direct current (BLDC) motor is a type of motor which is rapidly popularized. It is widely used in household appliances, automobiles, consumer goods, medical treatment, industry and other industries.

BLDC has no brush and uses electronic commutation. Compared with brushless DC motor and induction motor, it has the following advantages:

Better torque characteristics, high efficiency, long service life, simple structure, low rotation noise, higher speed range

At the same time, BLDC control is relatively complex and requires high chip resources.

According to the number of BLDC rotor windings, it can be divided into single-phase, two-phase and three-phase. Single phase BLDC is the main choice of automotive seat ventilation fan. This kind of motor has the advantages of simple structure, convenient driving, low cost and long service life.

Rapid development of single-phase BLDC motor fan applications:

Single phase BLDC motor usually needs the following system architecture:

Due to the low power consumption of the control circuit, LDO with high input voltage is generally selected for power supply; the motor is driven by H-bridge; the grid drive is selected according to the MOS switching frequency related to the motor speed; the current and voltage detection are applied on the motor bus to prevent over-current and over-voltage; the hall device is used to measure the motor speed and detect the motor commutation; the communication interface and speed regulating interface are added according to the product requirements MCU needs to be able to output 2 pairs of complementary PWM, ADC input, signal frequency duty cycle measurement module, PID module, depending on the product needs to choose communication interface, usually Lin or can bus.

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Single phase BLDC control block diagram

The core control principle of single-phase BLDC motor uses two pairs of complementary PWM to control the forward and reverse rotation of the motor

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Microchip is a leading supplier of embedded control solutions dedicated to intelligence, interconnection and security. In addition to MCU / MPU microprocessors, it also has a wealth of analog / interface / storage products, which can meet the needs of customers in different applications.

In the application of single-phase BLDC motor, microchip has mcp1790 / 1 and mcp1792 / 3 Series LDO to choose from. Mcp1790 / 1vinmax30v, iout70ma, suitable for 12V system; mcp1792 / 3vinmax55v, iout100ma, suitable for 24V system; the above LDO has the advantages of high voltage, low voltage difference, low static power consumption, working temperature as high as 150 ℃, and passed aec-q100 standard, suitable for automotive applications.

Gate driver, microchip has high side / low side / half bridge / H bridge / three-phase bridge drive and special motor drive. Mic4605 half bridge drive is commonly used in single-phase BLDC motor applications. The driving current is 1a, which is suitable for single-phase BLDC motor applications under 80V voltage, and also passed the aec-q100 standard. In addition, in some low power motor applications, because the motor power is small and the speed is not high, the power device of H-bridge does not need large driving current, and can be directly driven by mcuio, which saves the cost.

In OP operational amplifier part, microchip has rich op amp products, including general op amp / zero drift op amp / instrument amplifier. In the motor application, microchip’s mcp6001 / 2 series has a strong versatility. 1MHz gbwp, 4.5mv vosmax, ib1pa, railto

Rail I / O, SC – seventy / SOT – 23 parameters make it suitable for many analog signal processing applications. On the basis of good performance, its price is also good, so it has been widely used. In motor applications, if the / The precision of voltage acquisition is not high, and the MCU integrates operational amplifier / ADC, also can consider using MCU internal analog peripherals to collect analog signals.

In the communication interface part, microchip is the leading semiconductor manufacturer in the can / Lin transceiver market, with a complete range of can / LIN bus products. Can bus part, can (FD) controller, can (FD) transceiver. Among them, ata6560 / 1 and mcp2561 / 2Can transceivers are respectively suitable for 12V / 24V system; ata6563 transceivers meet the functional safety asilb; mcp2518fdcan controller is suitable for the occasions where MCU needs to expand can port; mcp25625 is a rare device integrating can transceivers and controller SPI to can, which has high integration and saves space. In the LIN bus part, there are independent Lin transceivers, integrated LDO / reset / WDT / Lin transceivers, and multiple models can be selected. Among them, ata663454 conforms to functional safety asilb and is suitable for automotive applications with relevant requirements.

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Microchip overall solution (microchip owns most of the products in the block diagram)

Pic16f161xcip introduction

Pic16f161x series belongs to microchip 8-bit machine with medium performance and rich resources. In particular, independent of kernel peripherals (CIP) with microchip features, internal peripherals can be freely combined through software configuration to meet different applications. CIP can reduce kernel interference, improve MCU performance and reduce product power consumption.

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Some CIP modules of microchip 8bit MCU

Pic16f161x series key peripherals for motor applications

CWG

CWG is a complementary waveform generator, which can cooperate with PWM module to generate full bridge, half bridge or steering PWM waveform. When configured in full bridge or half bridge mode, complementary waveforms with dead time control of rising edge and falling edge can be output. Suitable for H-bridge drive control. In addition, CWG is also equipped with relevant cut-off source, which can be controlled by internal peripheral module such as comparator output or external pin input to realize automatic protection function.

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Block diagram of CWG full bridge mode

SMT

SMT is the signal measurement timer. It is a 24 bit counter with advanced clock and gating logic, which can be used to measure various digital signal parameters. For example, pulse width, frequency and duty cycle. In the application of single-phase BLDC, it can be used to measure the frequency of hall input signal and calculate the motor speed; it can also measure the frequency and duty cycle of external PWM signal and analyze the speed control command.

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SMT block diagram

MathAccelerator

Mathaccelerator is a mathematical accelerator, which can be used as PID controller. Used to adjust the error of motor speed.

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Mathacc block diagram

According to the above characteristics, the cooling fan with external PWM input duty cycle is developed

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Pic161x single phase BLDC motor fan scheme block diagram

control logic

Quick configuration with MCC

MCC (mplabcode configurator) is a graphical configuration tool of microchip MCU development environment mplabxide, which is integrated in ide as a plug-in. Can be intuitive configuration of peripheral resources, pin definition, a key to generate peripheral drivers. It can simplify the development process, avoid frequent access to data manual registers, and allow engineers to carry out rapid software development.

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Some key module configurations:

CWG

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MathACC

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SMT

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Software control strategy

Two feedback loops are used. The internal loop is responsible for the electronic commutation control of the motor, and the external loop is responsible for the speed control and correction. There are speed reference and fault detection.

Speed reference

The speed setting is set by external PWM. The duty cycle determines the speed of the motor, the higher the duty cycle, the faster the motor speed.

External loop

The external loop provides measurement and control of motor speed. The purpose of motor speed control is to maintain the motor speed at the required value under different conditions (such as bus voltage, load demand change, interference and temperature drift). Make necessary speed correction to maintain the required value, so as to determine the actual speed of the motor.

Internal loop

To make the rotor rotate, there must be a rotating magnetic field produced by the stator. A single winding is electrically excited to produce a rotating magnetic field. In order to provide continuous rotation and prevent permanent magnet rotor and stator from sticking, the excitation on stator winding must be arranged in a specific way, and the accurate position of rotor magnet must be known. The rotor magnet position is determined by using a Hall effect sensor.

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Control strategy chart

The final sensor and drive sequence diagram is as follows

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Fan demo

Microchip curiity (dm164137) is used as PWM generator to control the fan.

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summary

Pic161x series has CIP resources such as CWG, mathacc and SMT, which are suitable for single-phase BLDC. Using MCC, we can quickly complete the application development of single-phase BLDC motor fan according to the actual demand. If you have application requirements such as PC or server cooling fan, automobile air conditioning seat ventilation fan, you can refer to microchippan2049, an1779 and other application manuals to quickly develop related applications.

Author: Tony Zhang abit

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