Solar power supply and battery charging circuit

Claim 1

A solar power supply and battery charging circuit including in combination: a photovoltaic solar energy source of direct current; a secondary battery coupled with said photovoltaic solar energy source for being charged thereby; control circuit means coupled with said battery to sense the state of charge thereof, said control circuit means comprising a voltage comparator and a voltage reference circuit means, said voltage comparator coupled to said voltage reference circuit means and said secondary battery for producing signals on an output indicative of a predetermined relationship between the voltages supplied thereto; a short-circuit shunt open/closed switch means coupled across said entire photovoltaic solar energy source to place a full dead short circuit across said photovoltaic energy source when said switch means is closed and a fully open circuit across said photovoltaic energy source when said switch means is open; pulse width generator means coupled to the output of said voltage comparator and operated in response to the signals on the output of said comparator to produce output pulses of varying width proportional to the state of charge sensed by said control circuit means, said pulse width generator means further coupled with said shunt switch means for continuously periodically fully closing and fully opening said shunt switch means in response to the variable width output pulses produced by said pulse width generator means, causing the proportion of total time said switch means is open to decrease to a minimum amount as said battery becomes fully charged; and means for preventing said secondary battery from discharging through said shunt switch means.