an15TOPSwitch Power Supply Design Techniques for EMI and Safety Application Note AN-15 Offline switching power supplies have high voltage and high current switching waveforms that generate Electromagnetic Interference (EMI) in the form of both conducted and radiated emissions. Consequently, all off-line power supplies must be designed to attenuate or suppress EMI emissions below commonly acceptable limits. This application note presents design techniques that reduce conducted EMI emissions in TOPSwitch power supplies below normally specified limits. Properly designed transformers, PC boards, and EMI filters not only reduce conducted EMI emissions but also suppress radiated EMI emissions and improve EMI susceptibility. These techniques can also be used in applications with DC input voltages suc……