Patent Number: 5,387,858
Date of Patent: Feb. 7, 1995
ENERGY-CONSERVING MULTIPLE POWER SOURCE AND METHOD FOR BATTERY-OPERATED PRODUCTS
An energy conserving photovoltaic or solar rechargeable power source for commercial or industrial battery operated products is provided, enabling a high degree of reliability of continued operation through a method involving the use of a backup battery or other backup d.c. voltage source which is automatically and instantaneously selected when the rechargeable cell falls below a predetermined lower threshold voltage. As the rechargeable cell receives charge from the solar cell, the circuit automatically switches back to it as the primary power source when an upper threshold voltage is reached. Moreover, the initial connecting of the rechargeable cell to power the product is ensured upon the turn on of the product, even if not fully charged (though above the lower threshold voltage), conserving the backup source. More general applications are also disclosed.