Patent ID: 8193779

Claim:
A battery charger comprising: a first input configured to accept DC power from an AC adapter; a second input configured to accept DC power from a Universal Serial Bus power interface; a first output configured to provide power to a system load; a second output configured for connection to a battery; a bi-directional pass element coupled between the first output and the second output, wherein the bi-directional pass element conducts a charging current in a first direction to the second output during charging of the battery, wherein the bi-directional pass element conducts a discharging current in a second direction from the second output during discharging of the battery, the bi-directional pass element becoming at least a partially enhanced switch to provide a low-impedance path from second output to the first output during discharging of the battery, and wherein the bi-directional pass element varies the charging current based at least in part on the system load; and circuitry that is configured to automatically use the power from the Universal Serial Bus power interface when the AC Adapter is not active; a charging controller configured to regulate the charging current of the bi-directional pass element based on the current flow from the Universal Serial Bus power interface when the Universal Serial Bus power interface is providing power to the system load, wherein the charging controller varies the charging current of the bi-directional pass element so that the combination of the power provided to the system load and the charging current provided to the battery does not exceed a maximum allowed current from the Universal Serial Bus power interface.