Charge and discharge control circuit with function detecting charge and discharge current and chargeable power supply unit

Abstract

A charge and discharge control circuit and a chargeable power supply unit incorporating the charge and discharge control circuit are provided with a current detecting element capable of detecting low currents with high accuracy and detecting high currents wuthout excessive power dissipation. The charge and discharge control circuit detects a charge and discharge state of a secondary cell and controls the charging and discharging of the secondary cell in accordance with the detected state. A switch circuit and the current detecting element are connected in series with the secondary cell. The current detecting element has an adjustable resistance value which is varied in accordance with the value of a current flowing therethrough, and comprises a first resistor and a second resistor connected in series, and a switch element connected in parallel to the second resistor. When current is low, the switch is operated so that current flows through the first and second resistors so that increased detection accuracy is possible. When is high, the switch is operated so that current flows only through the first resistor so that detection accuracy remains high but power dissipation is not increased.

Dependencies are inferred from the claim text.