13-06-2012, 03:43 PM
Conducted EMI filter design for SMPS
[attachment=24361]
Introduction
• The threat of generating EMI from the fast switching pulses in SMPS 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
EMI in SMPS
• Because of the fast switching in SMPS they generate large amount of electromagnetic
interferences and that’s usually the reason for SMPS not to comply the EMC standards
• EMI filter is usually needed in the input of the SMPS to achieve the required standards
• Conducted emissions 150kHz-30MHz
EMI in SMPS
Minimizing EMI in SMPS design
• Because of economical reasons EMC has to be considered in the early stage of the SMPS design
• Combating CM EMI
• The parasitic capacitances of heatsink and transformer are two major components to cause CM
EMI in SMPS
• 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. The goal is to prevent electromagnetic coupling between these circuits
• The use of RC-snubbers is to reduce ringing and protect the switch
• Component selection
Conclusions
A simple method for designing input filter for SMPS has been presented. This
design method is quick and it meets the conducted emission
requirements. The component selection is made according the required
Insertion loss. After little modification to the layout and wire contstruction
would made the filter also meet the radiated emission requirements.
[attachment=24361]
Introduction
• The threat of generating EMI from the fast switching pulses in SMPS 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
EMI in SMPS
• Because of the fast switching in SMPS they generate large amount of electromagnetic
interferences and that’s usually the reason for SMPS not to comply the EMC standards
• EMI filter is usually needed in the input of the SMPS to achieve the required standards
• Conducted emissions 150kHz-30MHz
EMI in SMPS
Minimizing EMI in SMPS design
• Because of economical reasons EMC has to be considered in the early stage of the SMPS design
• Combating CM EMI
• The parasitic capacitances of heatsink and transformer are two major components to cause CM
EMI in SMPS
• 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. The goal is to prevent electromagnetic coupling between these circuits
• The use of RC-snubbers is to reduce ringing and protect the switch
• Component selection
Conclusions
A simple method for designing input filter for SMPS has been presented. This
design method is quick and it meets the conducted emission
requirements. The component selection is made according the required
Insertion loss. After little modification to the layout and wire contstruction
would made the filter also meet the radiated emission requirements.