Communication switching power supply rectifier common heat dissipation method
The design of communication switching power supply cooling technology must first meet the technical performance requirements of the industry. In order to better adapt to the special environment of the communication equipment room, the cooling method is required to adapt to the change of the ambient temperature. At present, the common cooling methods of rectifiers are natural cooling, pure fan cooling, natural cooling and fan cooling. Natural cooling has no mechanical failure, high reliability; no air flow, less dust, is conducive to heat dissipation; no noise. Pure fan cooling has the advantages of light weight and low cost. The combination of fan and natural cooling technology has the characteristics of effectively reducing the size and weight of the device, high service life of the fan, and strong self-adapting ability of the fan.
1, natural cooling
The natural cooling method is the traditional cooling method of switching power supply in the early stage. This method mainly relies on a large metal heat sink for direct heat conduction heat dissipation. The heat exchange amount Q = KA Δt (K heat transfer coefficient, A heat exchange area, Δt temperature difference). When the output power of the rectifier increases, the temperature of the power component will rise, and the temperature difference of Δt also increases. Therefore, when the heat exchange area of the rectifier A is sufficient, there is no time lag in the heat dissipation, and the temperature difference of the power component is small, and the thermal stress is The thermal shock is small. However, the main disadvantage of this method is that the heat sink is bulky and heavy. The winding of the transformer is to reduce the temperature rise as much as possible, and to prevent the rise of temperature 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 environmental cleanliness requirements, there are still some applications for small-capacity communication power sources in small professional communication networks, such as electric power, petroleum, radio and television, military, water conservancy, national security, and public security.
2, fan cooling
With the development of fan manufacturing technology, the working stability and service life of the fan have been greatly improved, and the average time between failures is 50,000 hours.
The use of a fan to dissipate heat can reduce the bulky heat sink, 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 current main trend.
The main disadvantage of this method is that the average fault-free time of the fan is shorter than the rectifier's 100,000-hour time. If the fan fails, it will have a great impact on the power failure rate. Therefore, in order to ensure the service life of the fan, the speed of the fan changes with the temperature inside the device. The heat dissipation amount Q=KmΔt (K heat exchange coefficient, m heat exchange air quality, Δt temperature difference). m heat exchange air quality is related to the speed of the fan. When the output power of the rectifier increases, the temperature of the power component will rise, and the temperature of the power component changes to the rectifier to detect this change, and then increase the speed of the fan. In order to enhance heat dissipation, there is a great lag in time. If the load is frequently mutated, 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 component. Make it prematurely invalid.
3, the combination of fan and natural cooling
Due to changes in ambient temperature and changes in load, the heat dissipation during power operation, combined with a fan and natural cooling, can dissipate heat more quickly. In this way, while increasing the heat dissipation of the fan, the heat sink area can be reduced, so that the power component operates under a relatively stable temperature field, and the service life is not affected by the external condition change. This not only overcomes the shortcomings of the heat dissipation adjustment hysteresis of the power components of the pure fan cooling, but also avoids the low reliability of the fan and affects the overall reliability of the rectifier. Especially in the case where the ambient temperature of the equipment room is very unstable, the cooling technology combining air cooling and self cooling has better cooling performance. In this way, the material cost of the rectifier is between the pure fan cooling and the natural cooling, and the weight is low and the maintenance is convenient.
Especially when using intelligent air-cooling and self-cooling technology, the rectifier can be operated under low load conditions, the module temperature rise is small, and the module fan is running at low speed.
The module heats up under high load operating conditions. The module is heated above 55 °C. The fan speed increases linearly with temperature. The fan fault is detected in the position. After the fan fails, the fan fails to limit the output and the fault alarms. Since the number of fan runs is related to the load size, the service life of the fan is longer than that of pure air cooling, and the reliability is greatly improved.
The communication switching power supply adopts a combination of fan and natural cooling to effectively reduce the operating temperature inside the rectifier, prolong the service life of the device, and at low ambient temperature and low load. The rectifier fan reduces the speed and extends the life of the fan. The heat sink is used for heat dissipation, and the device spacing and creepage distance can be relatively long. In the case of high humidity, the safety performance is high. The smaller size and lighter weight of the rectifier make maintenance easier.
In order to ensure the reliable and stable operation of the rectifier of the communication switching power supply, it is a key technology to reduce the working temperature rise. The combination of intelligent air cooling and self cooling is adopted. It has the technical advantages of stronger adaptability to the environment, long service life, reliability and stability.
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