Reducing electromagnetic interferences in flyback AC-DC converters based on the frequency modulation technique

One of the most preferable types of switched-mode power supplies (SMPS) is the flyback converter, due to its wide range of application areas. Properties such as low cost, provision of multiple output voltage terminals, and higher efficiencies make it important, and hence its usage in technologies including cell phone chargers, personal computers, set-top boxes, and televisions is increasing. Special attention should be paid to the design of this type of converter due to its working principles and electromagnetic interference (EMI) performance. Rapid switching of high current and high voltage during the operation of SMPS causes an EMI problem. The level of the EMI noise should be reduced in order to not interfere with the operation of other equipment. One of the methods for mitigating EMI emissions is the frequency modulation (PM) technique. In this paper, the FM technique, which has been increasingly used as an EMI-reduction method in SMPS, is investigated. The modulation technique that was applied to the switching frequency of the flyback converter is analyzed and its effect on the EMI performance is discussed. The FM technique was tested on an AC-DC flyback converter prototype that was built with an L6566B integrated circuit. Conducted emission noises from the SMPS were measured using an EMI receiver. Experimental results showed that EMI levels were reduced after the application of the FM method