Switching power supply is a common power supply device widely used in electronic equipment. However, due to its special working principle and EMI characteristics, it may cause EMI to other equipment and systems. Therefore, Electromagnetic Compatibility (EMC) must be fully considered in switching power supply design and testing to ensure that the switching power supply can work properly without interfering with other devices.
First of all, in order to realize EMC, we must understand the working principle of switching power supply and electromagnetic interference mechanism. Switching power supply basically consists of input (mains), switching circuit, transformer, output circuit and filtering circuit. During operation, when the switches of the switching power supply are periodically switched, high-frequency current and voltage variations are generated, and these variations produce electromagnetic fields that may interfere with other equipment and systems.
In order to reduce the electromagnetic interference of the switching power supply, the following design and testing measures can be taken:
Filter circuit design: The filter circuit is a key component in suppressing the high-frequency interference signal at the output of the switching power supply to a low level. By selecting appropriate filter capacitors, filter inductors and filter networks, high-frequency noise at the output of the switching power supply can be effectively reduced.
Grounding design: Good grounding design is very important for reducing electromagnetic interference. It should be ensured that the grounding points of the switching power supply and related equipment and systems are stable and low-noise, and that all grounding points are accurately connected. At the same time, grounding wires should avoid overlapping with other conductors (e.g. power and signal wires) to minimize mutual interference.
Shielding design: In the design of switching power supply, metal shielding box or shielding material can be used to reduce electromagnetic radiation. The shielding box can limit the electromagnetic radiation inside the switching power supply to the inside of the box, thus reducing the interference to other equipment and systems.
Line layout design: In switching power supply design, line layout is crucial. Cross-layout of high-frequency lines with low-frequency lines should be avoided, and the length and area of the lines should be compressed to reduce the radiation and mutual interference caused by high-frequency signal transmission.
As for testing, the following test methods can be used to evaluate the EMC performance of switching power supplies:
Radiation test: Radiation test is used to evaluate the performance of switching power supply in sending electromagnetic radiation. Commonly used test methods include radio frequency (RF) radiation tests and electromagnetic field scanning tests. These tests should be conducted in specific frequency ranges to ensure that the switching power supply does not generate excessive electromagnetic radiation in these frequency ranges.
Conducted Tests: Conducted tests are used to evaluate the performance of a switching power supply in terms of conducted electromagnetic interference. Commonly used test methods include conducted coupling and conducted conduction tests. These tests evaluate the conducted interference characteristics of a switching power supply by applying interference signals of specific frequencies to its inputs and outputs.
Sensitivity Test: The sensitivity test is used to evaluate the resistance of a switching power supply to external electromagnetic interference. By applying specific frequency electromagnetic interference signals to the input of a switching power supply, the stability and reliability of its output under these disturbances can be evaluated.
EMI Filtering Test: The EMI Filtering Test is used to evaluate the performance of switching power supply filters. This can be done by injecting specific frequency interference signals into the input or output to assess the filter's ability to suppress these interference signals.
In summary, the EMC design and testing of switching power supplies is the key to ensuring that switching power supplies work properly without interfering with other equipment. In the design process, factors such as filter circuit, grounding design, shielding design and line layout need to be considered. And in the testing process, radiation test, conduction test, susceptibility test and EMI filtering test are needed to evaluate the EMC performance of the switching power supply. Through these design and testing steps, the EMC performance of the switching power supply can be effectively improved.
