Introduction of the three heat dissipation methods for power supply
1,Convection cooling method
Convection cooling refers to the transfer of heat through the fluid medium air to achieve the heat dissipation effect. It is our common heat dissipation method. Convection methods are generally divided into two types, forced convection and natural convection. Forced convection refers to the transfer of heat from the surface of the heating source to the flowing air, and natural convection refers to the transfer of heat from the surface of the heating source to the surrounding air at a lower temperature. The advantages of using natural convection are simple implementation, low cost, no need for an external cooling fan, and high reliability. In order for forced convection to reach the substrate temperature for normal use, it requires a larger heat sink and takes up space.
Pay attention to the design of natural convection radiator. If the horizontal radiator has poor heat dissipation effect, the area of the radiator should be appropriately increased or forced convection to dissipate heat when installed horizontally.
2,Conduction cooling method
When the power module is working, the heat on the substrate must be conducted to the far heat dissipation surface through the heat-conducting element, so that the temperature of the substrate will be equal to the sum of the temperature of the heat-dissipating surface, the temperature rise of the heat-conducting element, and the temperature rise of the two contact surfaces. In this way, the heat energy can be volatilized in an effective space to ensure that the components can work normally. The thermal resistance of a thermal element is directly proportional to the length, and inversely proportional to its cross-sectional area and thermal conductivity. If the installation space and cost are not considered, the radiator with the smallest thermal resistance should be used. Because the substrate temperature of the power supply drops a little, the mean time between failures will be significantly improved, the stability of the power supply will be improved, and the service life will be longer.
Temperature is an important factor that affects the performance of the power module, so when choosing a heat sink, you should focus on its manufacturing materials. In practical applications, the heat generated by the module is conducted from the substrate to the heat sink or heat-conducting element. However, there will be a temperature difference on the contact surface between the power substrate and the heat-conducting element, and this temperature difference must be controlled. The temperature of the substrate should be the sum of the temperature rise of the contact surface and the temperature of the heat conducting element. If it is not controlled, the temperature rise of the contact surface will be particularly significant. Therefore, the area of the contact surface should be as large as possible, and the smoothness of the contact surface should be within 5 mils, that is, within 0.005 inches.
In order to eliminate the unevenness of the surface, the contact surface should be filled with thermal conductive glue or thermal pad. After taking appropriate measures, the thermal resistance of the contact surface can be reduced to below 0.1°C/W. Only by reducing the heat dissipation and thermal resistance or power consumption can the temperature rise be reduced. The maximum output power of the power supply is related to the application environment temperature. The influencing parameters generally include: power loss, thermal resistance and maximum power supply case temperature. Power supplies with high efficiency and better heat dissipation will have a lower temperature rise, and their usable temperature will have a margin at the rated power output. Power supplies with lower efficiency or poor heat dissipation will have a higher temperature rise because they require air cooling or need to be derated for use.
3,Radiation cooling method
Radiation heat dissipation is the successive radiative transfer of heat that occurs when two interfaces with different temperatures face each other. The influence of radiation on the temperature of a single object depends on many factors, such as the temperature difference of various components, the outside of the components, the position of the components and the distance between them. In practical applications, these factors are difficult to quantify, and coupled with the influence of the surrounding environment's own radiant energy exchange, it is difficult to accurately calculate the messy effects of radiation on temperature.
In practical applications, it is impossible for a power module to use a single radiation heat dissipation method, because this method generally can only dissipate 10% or less of the total heat. It is usually used as an auxiliary means of the main heat dissipation method. It is generally not used in thermal design. Consider its effect on temperature. In the working state of the power supply, its temperature is generally higher than the temperature of the outside environment, and the radiation transfer helps the overall heat dissipation. But under special circumstances, heat sources near the power supply, such as high-power resistors, device boards, etc., the radiation of these objects will cause the temperature of the module to rise.
