Power Supply Fan Cooling Introduction
natural cooling
The natural cooling method is the traditional cooling method in the early stage of switching power supply. This method mainly relies on large metal radiators for direct heat conduction heat dissipation. Heat transfer Q=KA△t (K heat transfer coefficient, A heat transfer area, △t temperature difference). When the output power of the rectifier increases, the temperature of its power components will rise, and the △t temperature difference will also increase. Therefore, when the heat exchange area of rectifier A is sufficient, there is no time lag in heat dissipation, and the temperature difference of power components is small, and its thermal stress and Small thermal shock. But the main disadvantage of this method is the large volume and weight of the heat sink. The winding of the transformer is to reduce the temperature rise as much as possible to prevent the temperature rise from affecting its working performance, so the material selection margin is large, and the volume and weight of the transformer are also large. The material cost of the rectifier is high, and maintenance and replacement are inconvenient. Due to its low requirements on the cleanliness of the environment, at present, small-capacity communication power supplies are still used in some small-scale professional communication networks, such as electric power, petroleum, radio and television, military, water conservancy, national security, public security, etc.
fan cooling
With the development of fan manufacturing technology, the working stability and service life of fans have been greatly improved, and the average time between failures is 50,000 hours. The use of fans for heat dissipation can reduce the bulky heat sink, greatly improving the volume and weight of the rectifier, and greatly reducing the cost of raw materials. With the intensification of market competition and the decline of market prices, this technology has become the current main trend.
The main disadvantage of this method is that the mean time between failures of the fan is shorter than the 100,000 hours of the rectifier, and if the fan fails, it will have a great impact on the failure rate of the power supply. Therefore, in order to ensure the service life of the fan, the speed of the fan changes with the temperature inside the device. Its heat dissipation Q=Km△t (K heat transfer coefficient, m heat transfer air quality, △t temperature difference). mHeat exchange air quality is related to the speed of the fan. When the output power of the rectifier increases, the temperature of its power components will rise, and the change of the temperature of the power components can be detected by the rectifier, and then the speed of the fan can be increased. In order to strengthen heat dissipation, there is a big lag in time. If the load changes frequently, or the mains input fluctuates greatly, it will cause rapid thermal changes in the power components. The thermal stress and thermal shock caused by the sudden semiconductor temperature difference will cause stress cracks in different material parts of the components. cause it to fail prematurely.
