Novel voltage converter circuits are provided which step-up very low DC input voltages to higher voltages capable of supporting low-power loads. According to embodiments, a voltage step-up power converter circuit may be formed of an oscillator sub-circuit which receives a DC voltage and outputs an AC voltage; a voltage doubler sub-circuit which receives the AC voltage and outputs an augmented AC voltage; and a voltage step-up converter sub-circuit which receives the augmented AC voltage, as a control voltage, and the initial DC voltage and outputs a voltage which is more than the initial DC voltage. These circuits allow electrical energy to be harvested from very low voltage sources and to convert it as efficiently as possible to run a load.