At least two components are required in a Power Over Ethernet (PoE) system. The PSE, or Power Sourcing Equipment, is typically a switch, router, hub, or midspan injector. It is responsible for detecting a valid 25k signature resistance and applying power to the data or spare pairs of an Ethernet cable. On the other end of the cable is the PD, or powered device, which is responsible for presenting the 25k signature resistance and receiving power from either set of pairs. Both the PSE and PD need separate controller ICs (in this case, the LTC4266 high power PSE controller and LTC4265 PD controller) and transformers for isolation. The PD also requires a bridge rectifier to receive power from the cables.