A high power density non-intrusive magnetic field wireless sensors networks is an effective solution [6]-[10]. Magnetic field energy is widely distributed in the IGBT converter valve, and the magnetic field energy harvester (MEH) has the advantages of high stability and flexibility [6], [7]. IGBT converter valves contain sufficient kHz magnetic field due to the periodic switching of IBGT devices. High frequency MEH has the advantage of high power density. An improved I-shaped core is proposed with equivalent permeability studied and engineering practical design guidance for magnetic flux convergence. Furthermore, a wide input range dual-output power management circuit is proposed for wide magnetic intensity variations. A dual energy flow strategy is adopted with combined boost energy conversion path and buck-boost energy conversion path for better utilization of harvested energy. PCB planar coils and PCB based power management system are packaged inside the I-core to eliminate the electromagnetic interference on the low power circuit. The power density of the proposed MEH reaches to 1.89mW/cm under magnetic flux density amplitude of 500μT at 1500Hz. The maximum efficiency of the boost path in the charging process reaches to 94.1% and the average efficiency for buck-boost path in the discharging process from 4.0V to 0.3V is 68.0%.