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Performance of Richtek brushless DC motor control solution applied to the 40W air purifier



The rotor-stator fit is the critical factor in achieving quiet motor operation without vibrations. To ensure a rotor-stator combination that delivers optimized performance, the motor control algorithm must be very precise in order to perform accurate speed, magnetic field and current control signal generation as well as to collect feedback information. Building on long-term power management experience, Richtek has developed high-performance brushless DC motor driver solutions with unique algorithm. We have been successful in winning the trust from global Tier 1 home appliance suppliers.

Richtek’s BLDC motor driver solution has been applied to the 40W air purifier manufactured by a world-renowned Japanese home appliance supplier. With Richtek’s motor driver module, the product acoustic noise level is successfully reduced to 25dBA (from 35dBA), which is a significant improvement compared with its previous motor driver solution. The diagram below shows the results of a comparison test.

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As seen in the diagram, the blue data is measured with Richtek RT7075, the integrated control module IC; whereas the orange data indicates up to 35dBA peak noise level, which is measured with another driver IC from a Japanese IC manufacturer. Although there are many factors contributing to an air purifier’s acoustic noise level in this test the only change was replacing the IC to a Richtek design. The real case measurement results have proven the high performance of Richtek’s BLDC solutions vs. our global competitor.

Let’s have a look at the comparison of rotational vibrations on the shafts with both solutions. The amplitude of vibration reaches only 1470µm with Richtek RT7075, which is much lower than 2060µm with previous solution. The spectrum analysis of the vibrations also reveals that the difference mainly appears to be at lower frequency as shown in the diagram below.

Richtek solution

Other supplier’s solution

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From a mathematical point of view, the rotating magnetic field generated by the stator causes the rotor to revolve at the same frequency on the circumference. The stator winding current should be a perfect sine-wave to perform a smooth motor rotation. In order to achieve this, the accurate control algorithm is crucial along with a high-precision and high-performance hardware motor driver module.

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The diagram above shows the actual phase current waveform, which is measured from a fan in 150rpm driven by Richtek’s BLDC motor driver module. The current waveform is close to a required sine-wave. This also proves that Richtek’s solution has better performance than two other manufacturers’ driver ICs. This is highlighted in side by side tests, as shown in the table below.

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