National Semiconductor Corporation

Khosrow Vijeh

Vladislav Potanin

Elena Potanina

Richard Dye

A circuit for charging a battery by selecting among two available power sources while providing overcharging and temperature protection to the battery and managing a charging current is described. A power pass and sense circuit is arranged to provide charge voltage from either power source based on control voltages from a current/voltage control circuit, which receives control signals from a logic control and timer circuit, a sensed voltage from a current setting circuit and reference and temperature voltages from a voltage reference and thermo-sense circuit. Differential amplifiers controlling power pass transistors are turned on and off depending on a power source availability and selection. A power supply circuit provides global supply voltages to all subcircuits preventing reverse current to power sources and stable supply independent of a power source availability. A pair of transistors arranged to operate as body-switcher protect power pass and sense transistors against reverse bias current.

Dual-source CMOS battery charger

Control circuitry is used to control the backlighting of electronic displays. A light sensor (such as a phototransistor) is used to continuously measure ambient light conditions that are associated with an electronic display. A linear, continuous light-level signal is produced in response to the continuous measuring by the light sensor. The light-level signal is applied to a first input pin of an operational amplifier. The operational amplifier produces an output signal that is linear with respect to the light-level signal. The output signal is coupled to a second input pin, which provides feedback for the amplifier. The output signal is further coupled to an LED driver for driving backlighting LEDs.

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Sunnyvale, CA, United States of America

Khosrow Vijeh