US 5,402,055 AGranted

AC adapter including differential comparator for tracking battery voltage during trickle charge

AssigneeCompaq Computer Corporation

InventorHai N. Nguyen

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Abstract

A differential input comparator for controlling the output voltage of an AC adapter to track the voltage of a rechargeable battery during trickle charge. An output voltage sensing circuit typically used to regulate the AC adapter output voltage at a maximum level is modified to regulate the output voltage at a minimum DC voltage approximately equivalent to a fully discharged battery plus a nominal voltage level. The differential input comparator is coupled to a current limiter coupled in the charge path of the battery and to the sense signal to provide a separate current path used to modify the voltage level of the sense signal. The differential input comparator regulates the voltage across the current limiter to the nominal voltage level by controlling the AC adapter output voltage through the sense signal during trickle charge of the battery.

Claims10

Dependent claims

An AC adapter for charging a battery and for powering an electronic device, the electronic device having a maximum power requirement, the AC adapter comprising:

means having a sense input and an output, said means for providing electrical power up to a predetermined maximum power level and developing a voltage level at said output, wherein said voltage level of said output is regulated by a sense signal provided at said sense input and wherein said predetermined maximum power level exceeds the maximum power requirement of the electronic device;
a battery coupled between said power providing means output and ground;
means coupled to said power providing means for sensing said voltage level of said output and for providing said sense signal at a level so that said power providing means regulates said output at a predetermined minimum voltage level, wherein said predetermined minimum voltage level corresponds to the voltage level of said battery when fully discharged;
a current limiter coupled in a charge path of said battery providing a signal indicative of a voltage developed across said current limiter;
and
a differential comparator coupled to said power providing means sense input and receiving said signal indicative of a voltage developed across said current limiter for modifying said sense signal to a level so that said power providing means regulates said voltage level of said output at a level to maintain said current limiter signal at a predetermined nominal voltage level.

3 more elements

Dependencies are inferred from the claim text.