CHARGER FOR LITHIUM ION SECONDARY BATTERY, AND METHOD OF CHARGING THE SAME

Abstract

A charger for a lithium ion secondary battery includes a series circuit of a reverse-current preventive switch, a charging switch and a current-detecting resistor, connected between the battery and the ground a charging control circuit controlling the reverse-current preventive switch and the charging switch, so as to make the battery repeat charging and opening at regular intervals, and so as to detect voltage difference between the specified voltage and the open circuit voltage of the battery during the opening; and a constant-current/constant-voltage control circuit commanding constant-current charging at a first set voltage set relatively high in a range not exceeding the upper limit voltage of the battery, so far as the voltage difference does not exceed a predetermined change-over voltage difference, and commanding constant-voltage charging at a second set voltage, which is lowered from the first set voltage, when the voltage difference becomes smaller than the change-over voltage difference.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will become more readily appreciated and understood from the following detailed description of embodiments and examples of the present invention when taken in conjunction with the accompanying drawings, in which:

FIG. 1 is a drawing of an embodiment of a charger for lithium ion secondary battery of the present invention;

FIG. 2 is a line chart explaining the embodiment of the present invention;

FIG. 3 is a flow chart explaining the embodiment of the present invention;

FIG. 4 is a line chart explaining a related art; and

FIG. 5 is a line chart explaining another related art.

Claims

1. A charger for lithium ion secondary battery comprising: a series circuit of a reverse-current preventive switch, a charging switch and a current-detecting resistor, connected between a lithium ion secondary battery to be charged and the ground;a charging control circuit controlling said reverse-current preventive switch and said charging switch, so as to make said lithium ion secondary battery repeat charging and opening at regular intervals, and so as to detect voltage difference between the specified voltage and the open circuit voltage of said lithium ion secondary battery during said opening; anda constant-current/constant-voltage control circuit commanding constant-current charging at a first set voltage which is set relatively high in a range not exceeding the upper limit voltage of said lithium ion secondary battery, so far as said voltage difference does not exceed a predetermined change-over voltage difference, and commanding constant-voltage charging at a second set voltage, which is lowered from said first set voltage, when said voltage difference becomes smaller than said change-over voltage difference.

2. The charger for lithium ion secondary battery as claimed in claim 1, further comprising a pulse width modulation (PWM) control circuit supplying a pulse width modulation signal to a transistor so as to switch the transistor, thereby controlling an output signal appeared on the secondary coil of a transformer.

3. The charger for lithium ion secondary battery as claimed in claim 1, wherein said constant-current/constant-voltage control circuit supplies a control signal allowing the constant-current charging to proceed at said first set voltage, which is set relatively high in a range not exceeding the upper limit voltage of said lithium ion secondary battery, through a photo-coupler to a pulse width modulation (PWM) control circuit, so far as said voltage difference does not exceed a predetermined change-over voltage difference, and thereby controls said pulse width modulation control circuit using said control signal.

4. The charger for lithium ion secondary battery as claimed in claim 1, wherein said constant-current/constant-voltage control circuit supplies a control signal allowing the constant-voltage charging to proceed at said second set voltage, which is lowered from said first set voltage, through a photo-coupler to a pulse width modulation (PWM) control circuit, when said voltage difference becomes smaller than said change-over voltage difference, and thereby controls said pulse width modulation control circuit using said control signal.

5. A method of charging a lithium ion secondary battery for repeating charging and opening of the lithium ion secondary battery at regular intervals, the method comprising the steps of: detecting voltage difference between the specified voltage and the open circuit voltage of said lithium ion secondary battery during said opening;performing constant-current charging at a first set voltage which is set relatively high in a range not exceeding the upper limit voltage of said lithium ion secondary battery, so far as said voltage difference does not exceed a predetermined change-over voltage difference;performing constant-voltage charging at a second set voltage, which is lowered from said first set voltage, when said voltage difference becomes smaller than said change-over voltage difference; andterminating the charging when said voltage difference becomes smaller than said predetermined change-over voltage difference.

6. The method of charging a lithium ion secondary battery as claimed in claim 5, further comprising the step of supplying a pulse width modulation signal to a transistor so as to switch the transistor, to thereby control an output signal appeared on the secondary coil of a transformer based on pulse width modulation (PWM) control.