An Efficient Power Over Ethernet (PoE) Interface With Current-Balancing and Hot-Swapping Control

This paper presents an energy efficient Power over Ethernet interface for applications that require higher power delivery than that of IEEE 802.3af and 802.3at standards allow. The proposed architecture increases the power delivered to the powered-device by utilizing all four pairs of the CAT5 cable. Maximum power is guaranteed by a current-balancing control block which equalizes the currents in the CAT5 cable. The current-balancing control is implemented in an efficient way of regulating the pass p-type metal-oxide-semiconductor transistor in the diode bridge stage. The proposed interface also includes a hot-swapping control block that protects the devices in the power conduction path by limiting both the maximum load current and the maximum voltage ramping rate. The voltage and current-limiting functions are controlled by two separated regulation loops. To reduce the power loss, a single pass n-type metal-oxide-semiconductor transistor is inserted in the ground current path and is shared by both regulation loops. The experimental result of the assembled prototype showed balanced currents among all four pairs in the CAT5 cable. In cases of hot-plugging, the proposed prototype exhibited both well-controlled inrush current and limited voltage-ramping rate under various load capacitance conditions.