Today, there is a growing number of electronic devices that require both data connectivity and a power source to function effectively. As more innovative products hit the market, this trend is expected to increase rapidly.The IEEE 802.3af standard outlines a method for delivering power and data over LAN cables using the existing Ethernet infrastructure. A key element of this standard is that the power delivery must be isolated on the user or powered device (PD) side. This isolation requires the use of an isolated power topology within the power device.
The most cost-effective power topology to provide this isolation with acceptable efficiency is the continuous-mode flyback. To implement the flyback effectively in PDs, designers must understand the basic operation of this topology and the equations needed to properly design the flyback transformer.