The same input and output voltage, the same power, the same package, different manufacturers of power modules, which performance is better? For a good performance power module, there are many projects to be tested, and these performances are closely related. This article selects the performance of several aspects to compare and explain.
1, stable and reliable
Stable reliability is fundamental. If the power module is stable and reliable during operation, it cannot be guaranteed. Other performances are not mentioned.
From a design point of view, it is necessary to consider that when the module is in the harshest environment, the electrical stress and thermal stress of each device in the module are within the allowable range and ensure a certain margin, and should be stable when the system is subjected to certain interference.
From the application point of view, although some performance can not be tested, but the power supply stability reliability can be tested according to the specification limit test conditions, such as the highest minimum voltage, the highest minimum temperature, the maximum load, etc.; the circuit can also be recommended according to the specification as shown in Figure 1. Test module surge immunity, static immunity, pulse group immunity, etc.; also test module continuous short circuit, repeat switch machine, etc.
Of course, these tests are inherently destructive and can cause certain damage to the module and should not be used on the product after testing.
2. Capacitive load and overcurrent protection
The greater the capacitive capacity of the power supply, the higher the current limit setting. High power stresses are caused during startup and output shorts, even saturating the transformer. On the other hand, in the range of the rated load from the rated load to the current limit point, the power supply cannot achieve overcurrent protection, which will seriously affect the reliability and life of the power supply.
3, load adjustment rate and minimum load requirements
For a single output power supply, there is generally no minimum load requirement. However, when the load is reduced to less than 10% of the rated load, in order to reduce the power supply no-load or light-load power consumption, it will enter the intermittent operation mode. Although it does not affect its normal operation, its ripple may increase and auditory noise may occur. Therefore, the power should also be considered when selecting a power module. If the maximum load is less than 1W, it is obviously not suitable to select a power supply of 10W or more.
In addition, for dual and more output power supplies, each path is typically required to have at least 10% of rated load. Taking the dual output as an example, if the main road is fully loaded and the auxiliary road has a rated load of 10% or less, the auxiliary circuit output voltage will be higher than the rated value; if the main road has a rated load of 10% or less, and the auxiliary road is fully loaded Will cause the auxiliary circuit output voltage to be much lower than the rated output value.
In addition, it is worth noting that if the main road suddenly changes from heavy load to very light load or vice versa, it will cause the auxiliary circuit voltage to undershoot or overshoot. Obviously this means that the "big move" of the main road will probably cause the auxiliary road to work abnormally.
The module itself can add a larger dummy load, which of course increases its losses. When selecting a power module design system, especially for multiple output modules, the lightest load problem should be considered.
4, other basic performance
Other performances that need to be compared are: ripple noise, voltage accuracy, voltage regulation, turn-on overshoot, rise time, power-down hold time, no-load power consumption, efficiency, etc. However, when testing, the standard test method should be adopted. For example, when testing ripple noise, the bandwidth should be limited to 20M, and the method of measuring or parallel line testing should be used.
5, summary
In summary, comparing only one or two aspects of performance, it is unwise to conclude that a particular power supply is better. Designers may often sacrifice another performance for some other performance.
For the application, the module should be selected according to the actual situation, usually under the premise of stable and reliable, the application can be satisfied, and it is not necessary to pursue the best performance. The design of the module is usually to meet the general requirements. If, in some cases, the specific application cannot be met, the module design manufacturer should be contacted to provide a corresponding solution.
For the designer, attention should be paid to the interaction of various performances to optimize overall performance.
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