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Design method of EMI filter for power supply

Design method of EMI filter for power supply

EMI filters are required to protect electrical equipment from electromagnetic interference (EMI). Filter design and selection depends on EMI regulations, electrical codes, and other design requirements. In most cases, standard off-the-shelf filters will suffice for the application, but in many cases, a custom EMI filter solution becomes necessary to meet application-specific parameters.

Why You May Need a Custom Design EMI Filter Solution

The effects of electromagnetic interference vary widely. In some cases, EMI is just an annoyance causing interruptions. However, in critical applications such as medical and military, such problems can be fatal.

There are two main modes of propagation of EMI – conduction and radiation. Conducted EMI propagates through cables such as power lines, wires, and signal lines. Radiated disturbances travel through the air from sources such as electrical appliances, motors, power supplies, cell phones and radio transmission equipment.

EMI occurs when high-frequency noise signals generated by electrical or electronic switches interrupt the operation of electronic equipment. For sound-producing devices such as speakers, this can produce static or crackling. Other electronic products may experience interruptions, malfunctions or errors.

Although electromagnetic radiation can interfere with the operation of electronic circuits, it can also cause equipment to fail to comply with EMI regulations. If a device suffers from radio frequency interference or fails EMI testing, a filter is required to mitigate the interference and bring the device into compliance.

Electromagnetic Compatibility (EMC) engineers attempt to reduce interruptions and failures caused by conducted and radiated disturbances and emissions.

In many cases, preventing interference is a must-see task. For example, if a product is sold in the European Union, it must comply with the EMC Directive 89/336/EEC, which requires equipment to be reduced in emissions and protected from external interference. In the US, there are commercial (FCC Parts 15 and 18) and military standards requiring similar EMI compliance.

In many cases, although US, EU, and international EMC regulations do not apply, equipment may still require EMI filters to protect them from noisy environments. How to choose an EMI filter depends on several design considerations such as current, voltage, frequency, space, interconnection and most importantly required insertion loss.

For most applications, standard products can meet the design requirements, but if the standard products cannot meet the required design considerations, a custom design is required

Generally speaking, the low frequency of noise is manifested as conducted interference (disturbance), and the noise filter mainly relies on the inductive reactance of the choke coil to provide noise suppression. At the high end of the noise frequency, the conducted noise power is absorbed by the equivalent resistance of the choke coil and bypassed by the distributed capacitance. At this time, the radiation disturbance becomes the main form of interference.

Radiation disturbance induces noise currents on nearby components and leads, which can cause circuit self-excitation in severe cases, which becomes more prominent in the case of small and high-density circuit component assembly. Most anti-EMI devices are inserted into circuits as low-pass filters to suppress or absorb noise interference. The filter cut-off frequency fcn can be designed or selected according to the noise frequency to be suppressed.

We know that the noise filter is inserted into the circuit as a noise mismatcher, and its function is to severely mismatch the noise above the signal frequency. Using the concept of noise mismatch, the role of the filter can be understood as follows: through the noise filter, the noise may reduce the noise output level due to voltage division (attenuation), or absorb noise power due to multiple reflections, or destroy parasitic due to channel phase changes. oscillation conditions, thereby improving the noise margin of the circuit.

We should also pay attention to the following issues when designing and using anti-EMI devices:

1. First of all, we must understand the electromagnetic environment and choose a reasonable frequency range;

2. Judging whether there is DC or strong AC in the circuit where the noise filter is located, to prevent the core of the device from being saturated and failing;

3. Fully understand the magnitude and nature of the impedance before and after insertion into the circuit to achieve noise mismatch. The impedance of the choke coil is generally 30-500Ω, which is more suitable for use under low source impedance and load impedance;

4. Also pay attention to the inductive crosstalk between distributed capacitance and adjacent components and wires;

5. In addition, pay attention to controlling the temperature rise of the device, generally not exceeding 60°C.

The above is the design method of the power EMI filter that DOREXS shared with you today, I hope it will be helpful to you!


DOREXS EMI industry leader

If you need effective EMI protection, DOREXS offers durable and reliable EMI filters for every application. Our filters are suitable for professional applications in the military and medical fields, as well as for residential and industrial use. For applications requiring a custom solution, our professional team can design an EMI filter to meet your specific requirements.

With 15 years of experience in solving electromagnetic interference, DOREXS is a trusted manufacturer of high-quality EMI filters for medical, military, and commercial applications. All of our EMI filters are designed to meet industry standards and comply with EMC regulations. Explore our selection of EMI filters or submit a custom quote request to get the perfect EMI filter for your needs. For more information on DOREXS custom and standard EMI filters, please contact us.

Email: eric@dorexs.com
Tel: 19915694506
Whatsapp: +86 19915694506
Website: scdorexs.com


Post time: Feb-07-2023