With the emergence of new companies in all walks of life and the increasing competition in the market, how to reduce product costs while ensuring product quality has become a new issue for every company. The following is a brief introduction to how to design an appropriate switching power supply peripheral circuit according to the application environment of electronic products.
In the international standard IEC61000, electronic products are divided into three categories according to the application environment: Category 1 is residential, commercial and light industrial environment; Category 2 is industrial environment; Category 3 is electrical equipment for measurement, control and laboratory use. It is less used, so I won’t go into details here.
Electronic products used in category 1 have relatively low requirements for electromagnetic immunity and higher requirements for conducted radiation; while category 2 products are just the opposite, with relatively high requirements for electromagnetic immunity and conducted radiation. Relatively low. This is determined by the characteristics of the environment. The commercial power grid environment is clean, while the industrial power grid environment will be much more complicated.
For this reason, in the actual application of switching power supply, you can use this rule to make certain adjustments to the peripheral circuit. The following takes the AC-DC conduction test as an example.
It can be seen from the figure that the limit value of the conduction test (here called: CLASS B) for Type 1 products is 10dB lower than that for Type 2 products (CLASS A). If the power supply used in the product is a low-power AC-DC module with only one level of filtering inside, it is usually no problem to pass CLASS A, then it is used in a class 2 product, and you can consider not adding some filtering according to the comprehensive test situation. The device thus saves a certain cost.
The peripheral design idea of ​​EMS is basically the same as that of EMI. Take surge as an example, generally Class 1 commercial equipment or electrical appliances, anti-surge device varistor only need to choose 471KD07 (varistor voltage is 470V, the maximum withstand pulse current is 1200A, the parameters of different manufacturers will be different) is enough If it is used in an industrial environment with a very complex environment (large relays and motors work nearby), it is necessary to use a pressure-sensitive device 471KD10 (or 471KD14) that can withstand larger pulse currents. For the peripheral design circuit, please refer to the application circuit 2 in our power supply manual.
Therefore, according to different products in different applications, on-site data and experience can be used to properly use protective devices, which can not only meet the EMC requirements of the product, but also reduce costs.
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