The article presents the study of a novel self-powered SECE (synchronized electric charge extraction) circuit for scavenging piezoelectric energy under low-frequency shock excitation. Specifically, the device consists of a piezoelectric cantilever beam whose tip magnet is impulsively excited by a rotating magnet. It is attached to a load-independent SECE circuit with the advantage of power enhancement at low-level output voltage. The proposed circuit includes an envelope detector for voltage detection, a voltage divider for minimizing the switching delay and a diode for recovering the charge on the detection capacitance. The result shows that the predicted harvested power agrees well with the experimental observations. In addition, the power ripples are significantly reduced due to the larger electric-induced damping drawn from the SECE technique. Finally, the load-independent property makes the observed SECE power remain constant within the output voltage operated at around 2-5 volt, and therefore outperforms the standard DC power.