This paper introduces an energy harvesting circuit (EHC) for powering self-powered and wireless safety monitoring technology. The under-study magnetic harvester is a ring-shaped Nano-crystalline magnetic core. The introduced circuit includes a rectifier followed by a DC-DC buck-boost converter operates in discontinuous conduction mode (DCM). The input impedance is independent of the operating conditions such as input voltage, output voltage, and load resistance. So, the presented EHC is practical to a verity of wireless sensor nodes types with various internal impedance. To match the input impedance and reach the maximum power point tracking (MPPT),an MPPT algorithm is proposed using P$\&$O, which is capable of increasing the duty cycle step size when a significant change in the maximum power point is detected. A laboratory prototype setup has been built and the validity of the proposed EHC and MPPT algorithm have been verified via experimental results.