![]() ![]() 1 Conducted EMI filter design for Jukka-Pekka Sjöroos Helsinki University of Technology Power Electronics Laboratory Conducted EMI filter design for Introduction EMI in Common Mode(CM noise Differential Mode(DM noise Minimizing EMI in design Measuring conducted EMI EMI filter design Emi filter components Emi filter topology Calculating CM filter component values Calculating DM filter component values Determining filter corner frequencies Design steps Conclusions 2 1Ģ Introduction The threat of generating EMI from the fast switching pulses in has always been a serious concern Thus achieving the electromagnetic compatibility (EMC has become a requirement as important as meeting the power conversion specifications EMI includes three elements Source of the electromagnetic emission Coupling path A receiver of the EMI (victim Conducted emissions 150kHz-30MHz Common mode(cm measured between each power line and ground Differential mode measured between power lines Radieted emissions 30MHz-1GHz 3 EMI in Because of the fast switching in they generate large amount of electromagnetic interferences and that s usually the reason for not to comply the EMC standards EMI filter is usually needed in the input of the to achieve the required standards Conducted emissions 150kHz-30MHz CM common mode emissions : paracitic capacitances and the switching voltage waveform across the switch i CM = C par du dt DM differential emissions: The swiching action causes current pulses at the input u switching = spike di L dt Thus switching spikes exist as a differential mode noise source Radiated emissions 30MHz-1GHZ Magnetic and Elecric fields 4 2ģ EMI in Operation conditions also affects to the filter design The worst case should be always considered Highest input voltage leads to peak du/dt value CM noise will be maximum Lowest input voltage and maximum load current would lead to peak di/dt value DM noise will be maximum 5 EMI in Sources of CM noise 6 3Ĥ EMI in Sources of DM noise The switching action of the power mosfet causes current pulses at the input and voltage ripple at the output 7 EMI in Minimizing EMI in design Because of economical reasons EMC has to be considered in the early stage of the design Combating CM EMI The parasitic capacitances of heatsink and transformer are two major components to cause CM EMI in CM EMI can be minimized by minimizing stray capacitances between the circuit and ground Component selection Combating DM EMI Semiconductor devices like power mosfet are usually DM EMI sources Proper layout design can reduce DM EMI for example wires that carries a switching waveform should be as close as possible to each other Emi sensitive circuits like control circuits should not locate near circuit elements that carries the switching waveform.
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