Energy harvester

A circuit, comprising:

• a charge pump for coupling between first and second power sources;
• and
• a buffering capacitor for coupling between the first power source and an input of the charge pump, the buffering capacitor storing energy from the first power source in an energy harvest mode and transferring the stored energy to the second power source in an energy transfer mode,
• wherein in an energy harvest mode, the charge pump decouples from the first and second power sources, and the first power source charges the buffering capacitor with a first voltage while the charge pump is decoupled from the first and second power sources,
• wherein in an energy transfer mode, the charge pump couples to the buffering capacitor and the second power source to transfer the first voltage from the buffering capacitor to the second power source during discharge of the first voltage from the buffering capacitor, and
• wherein the energy transfer mode comprises a startup phase to initialize a conversion ratio of the charge pump and an operation phase when the conversion ratio is constantly adjusted based on remaining charges of the buffering capacitor.