US Patent 7503746 Fan of heat sink

A fan of a heat sink comprising a hub, a plurality of ribs and a set of blades is provided. A distal end of the ribs is connected to circular sidewall of the hub and the set of blades are connected to the primal end of the ribs. The set of blades comprises an outer ring, multiple first blades, a guiding ring connected to the inner side of the first blades and multiple second blades positioned at the inner side of the first blades extending upwards from the top side of the guiding ring. The primal end of the ribs is connected to the guiding ring having an inclined slope extending from the hub towards the outer ring. The first and the second blades are adopted for increasing the air flow area, and thereby increase the air volume and air pressure and the inclined slope of the guiding ring is adopted to smoothly change the flow direction of the sucked air and thereby reduce the resistance to the air flow.