Lithium-ion and lithium polymer battery recharging

• US 6,242,893 B1
• Filed: 06/24/1999
• Issued: 06/05/2001
• Est. Priority Date: 06/24/1999
• Status: Expired due to Fees

• Current Assignee: Bren-Tronics, Inc.
• Original Assignee: Bren-Tronics, Inc.
• Inventors: Freedman, Robert P.
• Primary Examiner(s): Wong, Peter S.
• Assistant Examiner(s): TIBBITS, PIA FLORENCE
• Application Number:
  US09/339,452
• Time in Patent Office: 712 Days
• Field of Search: 320/135, 320/132, 320/134, 320/136, 320/143
• US Class Current: 320/135
• CPC Class Codes: H02J 7/0029 with safety or protection devices or circuits

Abstract

A safety circuit for lithium-ion and lithium polymer cells which provides for greater accuracy in control of the limiting voltages and currents during discharging and recharging and which includes recognition circuitry to determine presence of a particular battery type. MOSFETS, normally used to provide charge limiting voltages, in recharging cells or batteries but which are relatively imprecise, are removed from the circuit to the extent that they are not used in the measurement of current for control purposes. The function of current limit determinations is instead provided by highly accurate resistive elements.

Claims

1. A battery charger having a safety device for controlling charging and discharging of one or more electrochemical cells, the safety device comprising:

a battery circuit having a high side and a low side, configured and adapted for placement of at least one electrochemical cell between the high side and the low side for charging and/or discharging of the cell;

an integrated circuit positioned in the battery circuit for controlling voltage and current, the integrated circuit having a high side current sensor and a low side current sensor, wherein the integrated circuit is set to interrupt charging at a first predetermined current that is proportional to a first predetermined voltage, and to interrupt discharging at a second predetermined current that is proportional to a second predetermined voltage;

a first resistor in the low side of the battery circuit; and

first means for measuring a first resistor current through the first resistor, the current measuring means connected to the low side current sensor;

wherein

during the charging or discharging of one or more electrochemical cells, a first resistor voltage exists across the first resistor, resulting in the first resistor current, proportional to the first resistor voltage, and wherein the first resistor current is detected by the low side current sensor, such that if the first voltage and resulting first current exceed predetermined values, the integrated circuit interrupts the charging or discharging of the one or more cells.

2. The battery charger of claim 1, wherein the first means for measuring the first resistor current comprises a first voltage divider across the first resistor, the first voltage divider comprising a second resistor and a third resistor and a first voltage divider junction connecting the second resistor to the third resistor, wherein the first voltage divider junction is connected to the low side current sensor of the integrated circuit, such that the a first voltage divider current proportional to the first resistor current flows through the first voltage divider junction, and is detected by the low side current sensor.

3. The battery charger of claim 1, wherein the first resistor is a precision resistor.

4. The battery charger of claim 1, further comprising two MOSFETs in the high side of the battery circuit and a second voltage divider across one of the MOSFETs, the second voltage divider comprising a fourth resistor and a fifth resistor and a second voltage divider junction connecting the fourth and fifth resistors, the second voltage divider junction connected to the high side current sensor of the integrated circuit to allow charging of one or more electrochemical cells.

5. The battery charger of claim 1, wherein the safety device is adapted for controlling charging and discharging at least one of lithium-ion and lithium polymer cells.

6. The battery charger of claim 5, wherein the safety device further comprises an initial charge controller, providing recognition acknowledgement of a proper battery for charging before allowing the battery circuit to be activated for charging, thereby preventing charging of cells having similar physical characteristics to lithium-ion and lithium polymer cells, but different electrochemical properties.

7. The battery charger of claim 6, wherein the safety device further comprises circuit control cell recognition means to prevent charging of a cell unless the recognition means recognizes the cell, the cell recognition means comprising an optoisolator comprising an LED, the optoisolator connected in series with a charge lead of the integrated circuit as a normally-closed switch, wherein the optoisolator switch is held closed until current is drawn by an LED in the optoisolator, thereby preventing the integrated circuit from enabling one of the MOSFETs to turn ON, disabling charging, and wherein recognition of a cell to be charged by the circuit closes the switch, allowing charging to proceed.

8. The battery charger of claim 7, wherein the charger is adapted to monitor a line that is low when a lithium-ion or lithium polymer battery is not present, and the cell recognition means is adapted to provide a mating contact to a terminal on a case for the cell connected to a port on at least one cell to be charged, such that when a lithium-ion or lithium polymer cell case is placed in the charger a current is drawn through a resistor and the LED in the optoisolator, the current through the resistor causing the line to go high, causing the line to go high, and energizing the optoisolator to turn on a charge MOSFET, enabling charging.

9. A method for controlling charging or discharging at least one electrochemical cell, the method comprising:

providing a charger in accordance with claim 1;

determining a maximum charging current value, a maximum charging voltage value, a maximum discharge current value, and a minimum discharge voltage value for the cell;

setting the integrated circuit to interrupt charging and discharging at the determined voltages;

placing at least one cell between the high side and the low side of the batter circuit; and

charging or discharging the cell.

10. The method of claim 9, further comprising setting the maximum charging voltage at from about 4.2 to about 4.4 volts, and setting the minimum discharge voltage to from about 2 to about 2.25 volts.