Noise Separators The common mode and differential mode noises from the measured output are separated using a noise separator. Euipment Under Test (EUT) The EUT used in this setup is a 2-transistor SMPS circuit that consists of two transistors, diodes whichh act as noise sources from which conducted EMI is generated. Jayasree et al Figure 3: Schematic of LISN. The basic schematic of LISN is shown in Figure3.Ĥ 322 P.V.Y. Filter Design The basic setup shown in Figure2 consists of Line Impedance Stabilization Network (LISN), Equipment under Test (EUT) which is a 2-transistor SMPS circuit, mains power supply and a noise separator circuit Figure 2: Conducted emissions measurement setup Line Impedance Stabilization Network (LISN) The conducted EMI measurement procedure requires a 50 W/ 50 mh Line Impedance Stabilization Network (LISN) to be inserted between the equipment under test (EUT) and the ac utility line to provide specified measuring impedance for noise voltage measurement. If the emissions are found to exceed the limits specified by EMC standards, then EMI filter would be designed in order to reduce the noise produced by the equipment under test. Conducted emissions are regulated by CISPR over the frequency range from 150 KHz-30MHz. Table 1: CISPR 22 Conducted Emissions Limits for Class A Devices Frequency (MHz) µv QP (AV) db(µv) QP (AV) (1995) 79 (66) (1000) 73 (60)ģ EMI Filter Design for Reducing Common-Mode 321 Table 2: CISPR 22 Conducted Emission Limits for Class B Devices Frequency (MHz) µv QP (AV) db(µv) QP (AV) ( ) (56-46) (limit varies linearly) (199.5) 56 (46) (316) 60 (50) The frequency limits for conducted emissions are shown in Table 1 and Table 2. Among the most frequently cited EMC standards are EN55022 or its equivalent CISPR 22 standard for IT equipment, EN55011 for industrial equipment. EMI Filters EMI filtering circuits are employed so that the end product complies with the applicable EMC standards. The capacitors C P are connected in shunt to the power lines to reduce CM noise and in order to reduce DM noise capacitors should be connected across the power line. Common mode noise is given as, V cm = V P + 2 V N and differential noise is given as, V P V V dm = N 2 (1) (2) where, V P is phase voltage and V N is neutral voltage. Figure 1: Common-mode and differential-mode noise. The CM and DM noises exist as shown in Figure1. Differential mode (DM) current flows through one ac conductor and returns along another and can be suppressed by the filter which contains an inductor in series and X-capacitors connected in parallel between the two current carrying conductors. Jayasree et al EMI filter that are placed in series with each power line and by Y-capacitors that are connected from both power line conductors to ground. Common-mode (CM) noise and Differential-mode (DM) noise CM noise current flows in the same direction on both power conductors and returns via the ground conductor and can be suppressed by the use of inductors within anĢ 320 P.V.Y. The conducted interference can further be classified into two types, namely common-mode and differential-mode. EMI is in two forms- conducted and radiated, of which the term conducted emissions refers to the coupling of electromagnetic energy produced by equipment to its power cord. Keywords: Electromagnetic interference (EMI), Common-mode noise, Differential-mode noise, EMI filters, Choke, Insertion loss Introduction The use of sophisticated electronic equipment has led to rapid increase in Electromagnetic Interference (EMI). The comparison between inductor and choke filter for reducing common-mode noise is shown in this paper and a basic π filter has been designed for reducing differential-mode noise.the use of Microwave Office made the design easier and the availability of extensive tools in this software made the design more efficient and practical for use. This paper focuses on designing an EMI filter to reduce both common-mode and differential-mode noise using AWR microwave office and MATLAB. The mitigation of conducted interference is a major challenge today and the best solution is the use of EMI filters. of ECE, GITAM University, Visakhapatnam, A.P., India Abstract The demand for high-speed electronics at high frequencies is leading to increasing amounts of Electromagnetic Interference (EMI) which is in two forms - conducted and radiated. ISSN Volume 5, Number 3 (2012), pp International Research Publication House EMI Filter Design for Reducing Common-Mode and Differential-Mode Noise in Conducted Interference P.V.Y. 1 International Journal of Electronics and Communication Engineering.
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