Several common heat dissipation methods for communication switching power supply rectifiers

　　The design of the cooling technology for communication switch power supply must first meet the various technical performance requirements of the industry. In order to better adapt to the special environment of the communication room, its cooling method is required to be highly adaptable to changes in ambient temperature. At present, there are three commonly used cooling methods for rectifiers: natural cooling, pure fan cooling, and a combination of natural cooling and fan cooling. Natural cooling has the characteristics of no mechanical failure and high reliability; no air flow, less dust, and conducive to heat dissipation; no noise. Pure fan cooling has the characteristics of light equipment weight and low cost. The technology combining fans and natural cooling has the characteristics of effectively reducing the size and weight of the equipment, long fan service life, and strong fan fault adaptive ability.

　　1. Natural cooling

　　The natural cooling method is the traditional cooling method of the early switching power supply. This method mainly relies on a large metal heat sink 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 transfer area of ​​the rectifier A is sufficient, its heat dissipation has no time lag, the temperature difference of the power components is small, and its thermal stress and thermal shock are small. However, the main disadvantage of this method is that the heat sink is large in size and weight. 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 margin of its material selection 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. Because it does not require high environmental cleanliness, it is currently used in some small professional communication networks for small-capacity communication power supplies, such as electricity, petroleum, radio and television, military, water conservancy, national security, public security, etc.

　　2. Fan cooling

　　With the development of fan manufacturing technology, the working stability and service life of fans have been greatly improved, and the average failure-free time is 50,000 hours.

　　The use of fans for heat dissipation can eliminate the bulky radiator, greatly improving the size and weight of the rectifier and greatly reducing the cost of raw materials. With the intensification of market competition and the decline in market prices, this technology has become the main trend at present.

　　The main disadvantage of this method is that the fan's MTBF is shorter than the rectifier's 100,000 hours. If the fan fails, the failure rate of the power supply will be greatly affected. Therefore, in order to ensure the service life of the fan, the fan speed changes with the temperature change in the equipment. Its heat dissipation Q = Km△t (K heat transfer coefficient, m heat exchange air mass, △t temperature difference). m heat exchange air mass is related to the fan speed. When the rectifier output power increases, the temperature of its power components will rise. There is a large time lag from the change in the power component temperature to the rectifier being able to detect this change, and then to increasing the fan speed to enhance heat dissipation. If the load often changes suddenly, or the mains input fluctuates greatly, it will cause the power component to change rapidly between hot and cold. The thermal stress and thermal shock generated by this sudden semiconductor temperature difference will cause stress cracks in different material parts of the component. Make it fail prematurely.

　　3. Combination of fans and natural cooling

　　Due to changes in ambient temperature and load, the power supply consumes heat when it is working. The combination of fan and natural cooling can dissipate the heat faster. This method can reduce the radiator area while increasing the fan heat dissipation, so that the power components work under relatively stable temperature field conditions, and the service life will not be affected by changes in external conditions. This not only overcomes the shortcomings of pure fan cooling for the lagging heat dissipation regulation of power components, but also avoids the impact of low fan service life on the overall reliability of the rectifier. Especially when the ambient temperature of the computer room is very unstable, the cooling technology that combines air cooling and self-cooling has better cooling performance. The material cost of the rectifier in this way is between pure fan cooling and natural cooling, with low weight and easy maintenance.

　　Especially when using intelligent air cooling and self-cooling technology, the rectifier can operate under low load conditions, the module temperature rise is small, and the module fan is in a low-speed operation state.

　　Under high load working conditions, the module heats up. The module temperature rises to more than 55°C. The fan speed increases linearly with the temperature change. Fan failure is detected in place. After the fan fails, the fan failure current limiting output is output and the fault alarm is triggered. Since the number of fan operation is related to the load size, the fan service life is longer than that of pure air cooling, and its reliability is greatly improved.

　　The communication switching power supply adopts a cooling method that combines fans and natural cooling. It can effectively reduce the internal working temperature of the rectifier and extend the service life of the device when the ambient temperature is high. It can also reduce the speed of the rectifier fan when the ambient temperature is low and the load is low, thereby extending the service life of the fan. The heat sink is used for heat dissipation, and the device spacing and creepage distance can be relatively far. In the case of high humidity, the safety performance is high. The rectifier is small in size and light in weight, making maintenance work easy.

　　To ensure the reliable and stable operation of the rectifier of the communication switching power supply, reducing its operating temperature rise is a key technology. It adopts a combination of intelligent air cooling and self-cooling technology. It has technical advantages such as stronger environmental adaptability, long service life, reliability and stability.