Method and charge-up circuit capable of adjusting charge-up current

A charge-up circuit, comprising:

• a charge-up transistor that supplies a charge-up current to a secondary battery in accordance with a control signal;
• a detection resistor connected in series with the charge-up transistor to detect the charge-up current;
• a current-to-voltage conversion circuit that generates and outputs a monitor voltage in accordance with the charge-up current based on each voltage at both end terminals of the detection resistor;
• a reference voltage generator that generates a predetermined reference voltage and includes a voltage adjusting mechanism to generate the reference voltage from the constant voltage so that the charge-up current becomes a desired current;
• and
• a charge-up current control circuit that controls the charge-up transistor so that the monitor voltage becomes the reference voltage,
• wherein the current-to-voltage conversion circuit comprises
• a differential amplifier including inputs thereof coupled to respective terminals of the detection resistor, said differential amplifier outputting an amplified voltage, and
• wherein the differential amplifier includes input transistors that are configured to have respectively different current drive capacities, and
• the difference in the current drive capacities of the input transistors of the differential amplifier permitting an input offset voltage of the differential amplifier to be increased and varied with a different degree from a predetermined input offset voltage value caused by production tolerance or variations in fabrication,
• said difference in the current drive capacities of the input transistors of the differential amplifier causing said input offset voltage of the differential amplifier to be larger than the predetermined input offset voltage value caused by production tolerance or variations in fabrication.