The values of the elements of the Butterworth filter are more practical and less critical than many other filter types. The Butterworth filter achieves its flatness at the expense of a relatively wide transition region from pass band to stop band, with average transient characteristics. It has no ripple in the pass band or the stop band because of this, it is sometimes called a maximally flat filter. The Butterworth filter is the best compromise between attenuation and phase response. Also, both of these might be traded off against filter complexity, and therefore cost. The importance of frequency domain response versus time domain response must be determined. The one that is selected will depend on the particular system. Many transfer functions may be used to satisfy the attenuation and/or phase requirements of a particular filter. The filter tool is then employed to design the filter. Several different standard responses are discussed, and their attenuation, group delay, step response, and impulse response are presented. This application note is intended to help in Step 1. In Step 2, the topology of the filter-how it is built-is defined. In Step 1, the response of the filter is determined, meaning the attenuation and/or phase response of the filter is defined. The filter design process consists of two steps. The Analog Devices Active Filter Design Tool assists the engineer in designing all-pole active filters. However, not simulating isn't really a viable option these days because you will definitely significantly improve your chances of getting close to a pass by doing so and, pretty much, all from the comfort of your desk.AN-649: Using the Analog Devices Active Filter Design Tool $$\boxed$$īut, there's no guarantees you will pass your conducted emission test because reality is never the same as a simulation. The very first thing I would do is simulate the circuit in order to understand the current consumption and harmonics in the worst case loading scenario. The specific application I am designing a filter for is a 24V, 120Wįlyback converter in the consumer electronics market. My design (and the reference designs I am using) does not feature any Y-Caps because the line cord does not have an earth-ground connection prong.īasically, I just need some help on how to initially determine the values for these components. TI's application notes on the filter inductor put it in the context of a CLC filter, which is confusing because I thought we chose the input/smoothing capacitor value based on the input power and not the required attenuation. I will admit that I am not sure how to calculate the power consumption of a capacitor in this context. X capacitor selection for SMPS power supply I believe the X-Cap choice is based on power consumption and power factor (according to post linked below)? You then verify this choice experimentally. I believe that the common-mode choke is first selected based on its attenuation curve and what you think the the trouble frequencies will be. The CM Choke and Y-Caps are in charge of attenuating the common-mode noise, while the Y-cap and Filter inductor are in charge of attenuating the differential-mode noise. The input EMI filter has 4 main components: Common-Mode choke, X-Cap, Y-Cap, and Filter Inductor. My basic question is "How do you select the component values for your EMI input filter?" The specific application I am designing a filter for is a 24V, 120W flyback converter in the consumer electronics market. I have been reading and watching TI's material on EMI input filter design, and I have a few questions.
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