PoExxP Flyback Transformers Coilcraft PoExxP Flyback Transformers are designed to operate in the continuous mode at 250kHz with a 36VDC to 72VDC input voltage range. These ferrite core transformers offer 1500Vrms 1-minute isolation from primary and bias to secondary and 500Vrms 1-minute isolation between all other windings. Coilcraft PoExxP transformers are designed for 3W (PoE30P), 7W (PoE70P), and 13W (PoE13P) Power over Ethernet (PoE) applications.