Thermal design of power supply
The thermal problem of the power module will seriously harm the reliability of the module, and the failure rate of the product will increase exponentially. What should I do if the power module heats up? From the perspective of module thermal design, this article introduces you to various low-temperature rise, high-reliability power supply design and application solutions.
High temperature has a great influence on the reliability of power modules with high power density. High temperature will cause the life of electrolytic capacitors to decrease, the insulation characteristics of transformer enameled wires, transistor damage, material thermal aging, low melting point weld cracking, solder joints falling off, and mechanical stress between devices increase. Statistics show that for every 2°C increase in the temperature of electronic components, the reliability decreases by 10%.
How to design the thermal solutions?
Reduce losses from the circuit structure and components: such as adopting better control methods and technologies, high-frequency soft-switching technology, phase-shifting control technology, synchronous rectification technology, etc., in addition to selecting low-power components to reduce the number of heating components, Increase the width of the thick printed line to improve the efficiency of the power supply;
The packaging of components has a great influence on the temperature rise of the components. For example, due to the difference in technology, DFN packaged MOS tube is easier to dissipate heat than DPAK (TO252) packaged MOS tube. Under the same loss conditions, the temperature rise of the former will be relatively small. Generally, the larger the resistance of the package, the higher the rated power, and under the same loss conditions, the surface temperature rise will be smaller.
Sometimes, the circuit parameters and performance seem to be normal, but in fact there are big problems hidden. As shown in Figure 3, there is no problem with the basic performance of a certain circuit, but at room temperature, the surface temperature of the driving resistor of the MOS tube reached 95.2°C when measured with an infrared thermal imager. Under long-term work or high temperature environment, the problems of resistance burnout and module damage are very easy to occur. By adjusting the circuit parameters, the ohmic heat loss of the resistor is reduced, and the resistor package is changed from 0603 to 0805, which greatly reduces the surface temperature.
PCB design optimized thermal design
The area of the copper skin of the PCB, the thickness of the copper skin, the material of the board, and the number of PCB layers all affect the heat dissipation of the module. Commonly used board FR4 (epoxy resin) is a good thermal conductivity material, and the heat of the components on the PCB can be dissipated through the PCB. In special applications, there are also plates with lower thermal resistance such as aluminum substrates or ceramic substrates.
The layout and routing of PCB should also consider the heat dissipation of the module:
The components with large heat generation should avoid stacking layout, and try to keep the heat evenly distributed on the board;
Heat sensitive components should be kept away from heat sources in particular;
Use multi-layer PCB when necessary;
The back of the power element is coated with a copper plane to dissipate heat, and use "hot holes" to transfer heat from one side of the PCB to the other.
Use more effective heat dissipation technology: use conduction, radiation, and convection technology to transfer heat, including the use of radiators, air cooling (natural convection and forced air cooling), liquid cooling (water, oil), thermoelectric cooling, heat pipes, etc. .
In thermal design, you must also pay attention to:
For power modules with wide-voltage input, the heating points and heat distribution of high-voltage input and low-voltage input are completely different, and a comprehensive evaluation is required. The heating point and heat distribution during short-circuit protection should also be evaluated;
In potting power modules, potting glue is a material with good thermal conductivity. The surface temperature rise of the internal components of the module will be further reduced.
In addition to the above-mentioned power supply thermal design techniques, high-performance isolated DC-DC power modules can also be directly selected, which can quickly provide a highly reliable power supply isolation solution for the system. Based on the accumulation of nearly 20 years of power supply design experience, ZHIYUAN Electronics has independently developed and designed independent power supply ICs to create the P series of optimized constant voltage DC-DC power supplies for all working conditions to meet the needs of all working conditions and provide users with stable and high-quality power supply solutions plan. Compared with traditional solutions, ZHIYUAN Electronics’ autonomous power supply IC integrates protection functions such as short-circuit protection and over-temperature protection. It has higher integration and reliability, ensuring high-efficiency and stable power supply under all working conditions, and can provide users with I/O and communication. Applications such as isolation provide standard and reliable power supply solutions.
