Battery charging circuit with undervoltage current control

摘要

This invention includes a charging circuit employing an off-the-shelf battery protection circuit. The invention offers an improvement to the battery protection circuit by providing means to accommodate trickle charging during undervoltage conditions. A pass transistor is provided with a trickle resistor coupled in parallel. The pass transistor is driven by a drooping voltage circuit that causes the pass transistor to open in undervoltage conditions, thus forcing charging current through the trickle resistor. Indicating means are also included to tell the user whether the circuit is in trickle mode or normal charging mode.