I. Overview
The three elements of electromagnetic interference are the source of the interference, the interference transmission path, the interference receiver, EMC around these issues for research. The most basic interference suppression techniques are shielding, filtering, grounding. They are mainly used to cut off the transmission path of interference.
Today we talk about EMC filtering, EMC rectification in the commonly used filtering methods have a variety of ways, the following we will be based on these types of filtering methods, analysis of the matters needing attention in the process of use.
II. Magnetic filtering
Magnetic filtering is through the introduction of magnetic components in the circuit, inhibit the propagation of high-frequency noise and reflection, thereby reducing electromagnetic interference. Common magnetic components include magnetic rings, bar magnets, coils, etc.
(1) Frequency range: The frequency characteristics of magnetic filters limit the range of interference frequencies that they can effectively suppress. Therefore, when selecting a magnetic filter, it is necessary to determine the desired frequency range of suppression and select an appropriate filter.
(2) Filter type: Different types of magnetic filters perform differently for different types of interference sources. For example, magnetic loop filters are usually suitable for high-frequency noise sources, while coil filters are more suitable for low-frequency noise sources. Therefore, when selecting a magnetic filter, the characteristics of the interference source and the characteristics of the filter need to be considered.
(3) Installation location: Magnetic filters need to be installed between the interference source and the affected equipment in order to effectively filter out the interference. However, it is necessary to avoid placing the magnetic filter in a high temperature or high vibration environment to ensure its reliability and stability.
(4) Ground connection: The ground connection has an important effect on the effectiveness of magnetic filters. Correctly connecting the earth wire can enhance the performance of the filter, improve the suppression effect and reduce electromagnetic interference.
III. Capacitive filter
Capacitive filter: By introducing capacitive elements into the circuit, the high-frequency current is guided to the ground to reduce the radiation and propagation of electromagnetic interference.
(1) Types of capacitors: There are different types of capacitors, such as tantalum electrolytic capacitors, aluminium electrolytic capacitors and ceramic capacitors. Different types of capacitors have different performance for different frequency ranges, so you need to choose the right capacitor according to the specific situation.
(2) Frequency range: The frequency characteristics of capacitive filters limit the frequency range of interference that they can effectively suppress. Therefore, when selecting capacitive filters, it is necessary to determine the required suppression frequency range and select the appropriate filter.
(3) Selection of capacitance value: The capacitance value of the capacitor directly affects its filtering effect, the larger the capacitance value, the better the filtering effect. But do not select too large a capacitance, so as not to have a negative impact on the normal operation of the circuit.
(4) Temperature characteristics: the capacitor’s capacity will change with the change of temperature. In a high temperature environment, the capacitor’s capacity will shrink, thus affecting its filtering effect. Therefore, when selecting capacitors, it is necessary to consider their temperature characteristics and select capacitors with good temperature stability.
IV. Impedance filter
Impedance filter: By introducing impedance components into the circuit, the circuit has a high impedance to the signal of a specific frequency, thus reducing or eliminating interference and noise. Common impedance components include inductors, transformers, etc.
(1) Frequency range: The frequency characteristics of impedance filters limit the range of interference frequencies they can effectively suppress. Therefore, when selecting an impedance filter, it is necessary to determine the desired frequency range of suppression and select the appropriate filter.
(2) Impedance type: Different types of impedance have different performances for different types of interference sources. For example, inductors are suitable for high-frequency noise sources, while transformers are more suitable for low-frequency noise sources. Therefore, when selecting impedance filters, it is necessary to make a choice of appropriate numbers according to the characteristics of the interference source and the characteristics of the filter.
(3) Impedance matching: The effect of impedance filters is affected by impedance matching. If the impedance is not matched, then the effect of the filter will be greatly reduced. Therefore, when designing and installing impedance filters, it is necessary to ensure that the impedance is matched and that suitable connections are used.
(4) Installation location: Impedance filters need to be installed between the interference source and the affected equipment in order to effectively filter out the interference. However, it is necessary to avoid placing the impedance filter in a high temperature or high vibration environment to ensure its reliability and stability.
(5) Ground Connection: Adequate ground connection is the key to ensure the performance of impedance filters. Correctly connecting the earth wire can enhance the performance of the impedance filter, improve the suppression effect and reduce electromagnetic interference.
V. Band Pass Filtering
Band-pass filtering allows signals in a specific frequency range to pass through while suppressing signals in other frequency ranges.
(1) Centre frequency: The centre frequency of the band-pass filter is the frequency of the signal to be passed, so it is necessary to choose a suitable centre frequency.
(2) Bandwidth: The bandwidth of a bandpass filter defines the frequency range of the signal to be passed, so it is necessary to select a suitable bandwidth.
(3) Passband and Stopband: The passband of a bandpass filter defines the frequency range of the signal that passes through, while the stopband defines the frequency range of the signal that is suppressed. When selecting a filter, it is necessary to choose the appropriate passband and stopband ranges according to the application requirements.
(4) Filter type: There are various types of bandpass filters, such as second-order filters, Butterworth filters, Chebyshev filters, etc. Different types of filters have different characteristics. Different types of filters have different performance, so it is necessary to choose the appropriate type of filter according to the specific application scenario.
(5) Frequency response: The frequency response of a bandpass filter has an important impact on its performance. In order to ensure the transmission quality of the signal, it is necessary to ensure that the frequency response is as flat as possible and there is no undesirable resonance phenomenon in the design.
(6) Stability: Band-pass filters need to maintain stable performance, so it is necessary to select high-quality components and appropriate circuit layout to ensure the stability of the zero crossing frequency and amplitude.
(7) Temperature variation: The performance of band-pass filters will drift due to changes in ambient temperature.
VI. Summary
Filtering is one of the common means we use to solve EMC problems. To solve EMC problems well, we need to understand the problem comprehensively, make plans, implement programmes, verify the effect, continuously improve and strengthen management. Only in this way can we effectively solve EMC problems and improve the EMC performance of the system.
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Post time: Aug-09-2023