Charger for lithium ion secondary battery, and method of charging the same

• US 8,098,053 B2
• Filed: 03/22/2007
• Issued: 01/17/2012
• Est. Priority Date: 03/23/2006
• Status: Active Grant

• Current Assignee: Murata Manufacturing Co Limited
• Original Assignee: Sony Corporation (Sony Group Corp.)
• Inventors: Sato, Masanao
• Primary Examiner(s): Tso, Edward
• Assistant Examiner(s): PIGGUSH, AARON C
• Application Number:
  US11/689,854
• Publication Number:
  US 20070222416A1
• Time in Patent Office: 1,762 Days
• Field of Search: 320/128, 320/134, 320/156, 320/161, 320/163
• US Class Current: 320/163
• CPC Class Codes: H02J 2207/20 Charging or discharging characterised by the power electronics converter
• CPC Class Codes: H02J 7/007182 in response to battery voltage
• CPC Class Codes: H02J 7/02 for charging batteries from ac mains by converters
• CPC Class Codes: H02J 7/04 Regulation of charging current or voltage

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.

Claims

1. A charger for a lithium ion secondary battery comprising:

a series circuit of a transistor reverse-current preventive switch, a transistor charging switch and a current-detecting resistor, the reverse-current prevention switch being continuously directly connected to a negative electrode of a lithium ion secondary battery to be charged, and the current detecting resistor being connected between the charging switch and a ground;

a rectifying circuit connected on a first side to a transformer and directly connected on a second side to a positive terminal of the lithium ion secondary battery;

a charging control circuit configured to control said reverse-current preventive switch and said charging switch, to make said lithium ion secondary battery repeat charging and opening at regular intervals, to detect a voltage difference between a specified voltage which is an upper limit voltage of the lithium ion secondary battery and an open circuit voltage of said lithium ion secondary battery during said opening at a position directly between the reverse-current preventive switch and the charging switch, and to generate a change-over signal when the detected voltage difference becomes smaller than a predetermined change-over voltage difference; and

a constant-current/constant-voltage control circuit configured to cause constant-current charging at a first set voltage which is set in a range not exceeding the upper limit voltage of said lithium ion secondary battery, when said voltage difference does not exceed the predetermined change-over voltage difference, and configured to cause constant-voltage charging at a second set voltage, which is lowered from said first set voltage based on the change-over signal received from the charging control circuit.

2. The charger for lithium ion secondary battery as claimed in claim 1, further comprising:

a pulse width modulation (PWM) control circuit configured to supply a pulse width modulation signal to a transistor to switch the transistor, thereby controlling an output signal appeared on a 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, when 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 based on the change-over signal received from the charging control circuit, and thereby controls said pulse width modulation control circuit using said control signal.

5. The charger for lithium ion secondary battery as claimed in claim 1, wherein said constant-current/constant-voltage control circuit terminates constant-voltage charging at the second set voltage when the voltage difference becomes smaller than a predetermined completion voltage difference which is based on the upper limit voltage of the lithium ion secondary battery.

6. The charger for lithium ion secondary battery as claimed in claim 1, wherein the charging control circuit detects the voltage difference between the specified voltage and the open circuit voltage of said lithium ion secondary battery during the constant-current charging and the constant-voltage charging.

7. The charger for lithium ion secondary battery as claimed in claim 1,

wherein the constant-current/constant-voltage control circuit is further configured to obtain a charging voltage at a position directly between the rectifying circuit and the positive electrode of the lithium ion secondary battery, and to cause constant-voltage charging at the second set voltage based on the obtained charging voltage.

8. The charger for lithium ion secondary battery as claimed in claim 1, wherein the reverse-current preventive switch is an N-type MOSFET transistor and the charging switch is an N-type MOSFET transistor.

9. The charger for lithium ion secondary battery as claimed in claim 1, wherein the reverse-current preventive switch and the charging switch are both on during the charging, and the reverse-current preventive switch is on and the charging switch is off during the opening.

10. A method, implemented on a charger, of charging a lithium ion secondary battery for repeating charging and opening of the lithium ion secondary battery at regular intervals, the method comprising:

detecting, at the charger including a series circuit of a transistor reverse-current preventive switch, a transistor charging switch and a current-detecting resistor, the reverse-current prevention switch being continuously directly connected to a negative electrode of the lithium ion secondary battery, and the current detecting resistor being connected between the charging switch and a ground, a voltage difference between a specified voltage which is an upper limit voltage of the lithium ion secondary battery and an open circuit voltage of said lithium ion secondary battery during said opening at a position directly between the reverse-current preventive switch and the charging switch connected between the negative electrode of the lithium ion secondary battery and the ground;

generating, at the charger, a change-over signal when the detected voltage difference becomes smaller than a predetermined change-over voltage difference;

performing, at the charger, constant-current charging at a first set voltage which is set in a range not exceeding an upper limit voltage of said lithium ion secondary battery, when said voltage difference does not exceed a predetermined change-over voltage difference;

performing, at the charger, constant-voltage charging at a second set voltage, which is lowered from said first set voltage, based on the received change-over signal; and

terminating, at the charger, the charging when said voltage difference becomes smaller than a predetermined completion voltage difference,

wherein the charger further includes a rectifying circuit connected on a first side to a transformer and directly connected on a second side to a positive terminal of the lithium ion secondary battery.

11. The method of charging a lithium ion secondary battery as claimed in claim 10, further comprising:

supplying a pulse width modulation signal to a transistor to switch the transistor, to thereby control an output signal appeared on a secondary coil of a transformer based on pulse width modulation (PWM) control.