Patent ID: 7791319

Claim:
A battery charging circuit, comprising: a semiconductor switch having an output connected to a rechargeable battery and configurable to isolate the rechargeable battery from a portable device; a battery charge controller configured to receive power from an external universal serial bus (USB) port, and supply output power to the portable device having at least one function unrelated to the battery charge controller and to the rechargeable battery through the switch; the battery charge controller being further configured to limit the output power such that the portable device and the rechargeable battery may not draw more than a pre-determined maximum current available from the USB port; and a voltage sensing circuit configured to measure a voltage drop across the battery charge controller, and respond to the voltage drop across the battery charge controller by modulating the switch to control an amount of current supplied to the rechargeable battery such that the portable device receives a predetermined amount of power needed to operate and the rechargeable battery receives a remainder of the power available from the battery charge controller.