Harvest the Power Needed for Power-Loss Braking

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Modern server applications need uninterrupted service. Accommodating this requirement can result in adverse scenarios—from inefficient airflows created by reverse-rotating fan blades that have lost power to dangerous maintenance and repair procedures conducted in the presence of high-speed fan blades. To overcome these adverse airflows and maintenance scenarios, features can be implemented to stop a fan when it loses power or begins to rotate from an unpowered state. A fan with such a power-loss brake (PLB) can reduce energy cost and improve thermal efficiency. This article discusses how the back-electromagnetic force (BEMF) from the motor of a fan that has lost power can be harnessed to implement a PLB function that improves efficiency and creates safer operational environments. Newly introduced sensorless fan drivers with the PLB capability are presented as options that provide the desired improved safety and thermal efficiency and simplify fan design and logistics.