Patent Number: 6,166,521

Title: Current-to-voltage transition control of a battery charger

Abstract: A control circuit is provided to minimize the charging cycle time of a battery charging system by maximizing the length of time that high constant charging current is applied to a discharged battery. The control circuit includes a constant current (CC) error amplifier, a constant voltage (CV) error amplifier, an output amplifier, and two pole-splitting compensation networks. The control circuit works in conjunction with a power source to charge a secondary battery. The pole-splitting compensation networks allow the CC, CV, and output amplifiers to be configured for high gain, without sacrificing output stability. The control circuit provides a sharp transition between the CC mode and CV mode of operation. In the CC mode, fast bulk battery charging is provided. In the CV mode, the control circuit initially provides a "top-off" charge to the battery and subsequently safely maintains the battery at its fully charged state. By using bi-directional transconductance error amplifiers as the CC and CV error amplifiers, the control circuit can be optimized for pole-splitting compensation. The control circuit can be operated with a constant internal reference voltage or a variable internal reference voltage. When a variable internal reference voltage is applied, the charging cycle time of the control circuit is further minimized through a charge current compensation technique.

Inventors: Mercer; Mark J. (Tucson, AZ), Shacter; Stuart B. (Tucson, AZ)

Assignee: National Semiconductor Corporation

International Classification: H02J 7/00 (20060101); H02J 007/00 (); H02J 007/14 ()

Expiration Date: 12/26/2017