Have fabricated a circuit that takes a low power solar cell (3 volts ((Max)) at 4.2 mA full sun , 4.2uA interior room l)0ight) and dumps charge into starage cap. When voltage is high enough and on a varaible period, and implse sign triggers the dc c conversion of the stroed enrgy into a reguated outpt to pulse charge batteries.
The driving force behiund this design was to extend the life time of a battery operated, and wirless sensor pod... "indefinately". The sensor pod consumes and average current of 42 uA... with a typical drain of 20 uA and wirless poweed time slots of 10 mA... using alakaline batteires this would last 3-4 years. a very reasonable perodand an improvent over exisitng devcies ( these are primarily a PIR motion detector, temp humidity and a wi fi tx tx ability. akey to the design was lowering the current and voltage that a PIR based motion sensor uses as this function cannot be switched of to save power!
Adding the solar power scavenger should replace the energy used through out the day, during a typical 6 hours of abmient room light. The period varies with light influx and state of cahrge on the storage capacitor. This circuit is created with the latest dc dc converters, and ultra-low power discrete components. this design can be modualrized or added to another design in about 2 sqaure inches of space for pcb, a solar panel (or other power source)and smal hole to enable ambient light sensing for feedback inot timing control....
Does anybody else have requirments like this for thier battery operated products?
Best regards,
Marc Popek