Patent ID: 7501789

Claim:
A solar powered battery charger comprising: an input port for receiving electrical power from a solar panel; an output port for providing electrical power to a battery; and a power regulation circuit, electrically coupled to the input port and the output port, for regulating electrical power therebetween, the power regulation circuit comprises: a power transistor for operably connecting or disconnecting the input port and the output port, a collector base resistor connecting the input port to the base of the power transistor for receiving a portion of the input current for operating the power transistor; a protection diode connected in series with the power transistor for allowing said input current to flow from the input port to the output port; a resume charge switch; voltage divider resistors for dividing the output port voltage, having a first ratio for raising the divided output port voltage and a second ratio for lowering the divided output port voltage, selected by said resume charge switch: a comparator for continuously comparing said divided output port voltage with a threshold voltage; when said divided output port voltage is lower than the threshold voltage, the comparator causes the portion of the input current to flow through the collector base resistor for allowing the portion of the input current to bias the power transistor to connect the input port and the output port via the protection diode while the protection diode prevents discharging from the battery, and further causing the resume charge switch transistor to select said first ratio, and when said divided output port voltage is higher than the threshold voltage, the comparator prevents the portion of the input current to flow through the collector base resistor, causing the power transistor to disconnect the input port and output port for preventing overcharging of the battery, and further causes the resume charge switch to select said second ratio for thus creating a hysteresis window for said comparing.