Compact backup power supply using intermittent charging for an optical network unit in FTTH systems

An ONU (optical network unit) backup power supply has been developed that uses intermittent charging circuitry and high-energy-density Ni-MH (nickel metal-hydride) batteries. The intermittent charging is controlled based on the open-circuit voltage, which has a strong relationship with the battery charge near the fully charged condition. This charging method uses simple circuitry, its operation was confirmed by charge testing. A power supply using this circuit and Ni-MH batteries is about 45% smaller than one using conventional charging circuitry and Ni-Cd (nickel-cadmium) batteries.