Design and selection of power modules should consider what the performance parameters 1, stable and reliable Stability is the fundamental reliability, if the work of the power module is stable and reliable can not be guaranteed, the other performance will not mention. From the design point of view, it is important to consider the electrical and thermal stresses of each device in the module when the module is in the harshest of environments and to ensure that there is some margin for the electrical stress and thermal stress in the module, and should be stable when the system is subject to some interference. From the application point of view, although some of the performance can not be tested, but according to the specification limit test conditions test power supply stability and reliability, such as the maximum and minimum voltage, maximum and minimum temperature, maximum load, etc .; also recommended in accordance with the specification book shown in Figure 1 , Test module surge immunity, electrostatic immunity, burst immunity, etc .; also test the module continued short circuit, repeated switching machines. Of course, these tests themselves are destructive, will cause some damage to the module, after the test should not be used on the product. 2, capacitive load and over-current protection The greater the capacity of the power capacitive load, often means that the current limit set higher. In the boot and output short circuit usually leads to higher electrical stress, and even the transformer saturation. On the other hand, when the power supply is within the load range from the rated load to the current limit point, the power supply can not achieve over-current protection, which will seriously affect the reliability and life of the power supply. 3, load regulation and minimum load requirements On a single output power supply, generally no minimum load requirements. However, when the load is reduced to less than 10% of rated load, intermittent operation mode will be entered to reduce the power no-load or light-load power consumption. Although this will not affect its normal operation, ripple may increase and auditory noise may occur. Therefore, the power when selecting the power module also need to be considered. If the maximum load is less than 1W, but choose 10W or more power is obviously not suitable. In addition, it is common to require at least 10% of rated load on each side for dual and more outputs. Take the dual output as an example. If the main road is full and the auxiliary road with the rated load less than 10%, the output voltage of the auxiliary road will be much higher than the rated value. If the main road is under 10% of rated load, , Will result in auxiliary output voltage lower than the rated output value is more. In addition, it is worth noting that if the main path suddenly changes from heavy to light load or vice versa, it will result in undershoot or undershoot of the auxiliary voltage. Obviously this means that the "big move" on the main road will likely result in anomalous work on the secondary road. The module itself can add more fake load, of course, it will increase its loss. When choosing a power supply module design system, especially for multiple output modules, consider the lightest load issues. 4, other basic performance Other need to compare the performance such as: ripple noise, voltage accuracy, voltage regulation, boot overshoot, rise time, power-down hold time, no-load power consumption, efficiency and so on. However, the test should be used standardized test methods. Such as testing the ripple noise should limit the bandwidth of 20M, by test or parallel line test method. 5, concluded To sum up, comparing only one or two aspects of the performance, it is unwise to conclude that a single power supply has better performance, and designers often may sacrifice another for some other performance. For the user, the module should be selected according to the actual situation. Usually, under the premise of being stable and reliable, the application can be fulfilled, and the best performance is not required. Module design is usually to meet the general requirements, in some cases, can not meet the specific application, should contact the module design manufacturers to provide the appropriate solution. For designers, attention should be paid to the mutual influence of each performance to optimize the overall performance.