Lithium ion charging means and method using ionic relaxation control

• US 6,127,804 A
• Filed: 09/10/1999
• Issued: 10/03/2000
• Est. Priority Date: 09/10/1999
• Status: Expired due to Term

• Current Assignee: Motorola Solutions, Inc.
• Original Assignee: Motorola, Inc. (Motorola Solutions, Inc.)
• Inventors: Herrmann, John Edward, Oglesbee, John Wendell, Geren, Michael D.
• Primary Examiner(s): Tso, Edward H.
• Application Number:
  US09/393,478
• Time in Patent Office: 389 Days
• Field of Search: 320/100, 320/127, 320/128, 320/129, 320/130, 320/160, 320/157, 320/125, 320/FOR 118, 320/FOR 119, 320/FOR 120, 320/FOR 121
• US Class Current: 320/125
• CPC Class Codes: H01M 10/052 Li-accumulators
• CPC Class Codes: H02J 7/00 Circuit arrangements for charging or depolarising batteries or for supplying loads from batteries
• CPC Class Codes: H02J 7/00711 with introduction of pulses during the charging process
• CPC Class Codes: Y02E 60/10 Energy storage using batteries

Abstract

This invention combines linear charging techniques with ionic relaxation pulse charging to rapidly charge lithium ion batteries to full capacity. The preferred embodiment incorporates a blocking diode and series resistor to multiplex an ionic relaxation control circuit with a linear regulated charging circuit, thereby utilizing a single, common, shared power transistor.

Claims

1. A battery charging system, comprising:

A) a power supply having a power input, wherein the power supply is capable of delivering a constant current output;

B) A lithium based rechargeable battery cell having a termination voltage;

C) A linear regulated charging circuit coupled in series between the power supply and the lithium based rechargeable battery cell, wherein the linear regulated charging circuit provides a constant and limited value of charging current until the termination voltage of the lithium based rechargeable battery cell is reached, wherein the linear regulated charging control regulates at the value of the termination voltage;

D) A power switch having a control terminal coupled in parallel with the linear regulated charging control circuit;

E) An upper voltage reference and a lower voltage reference; and

F) An ionic relaxation charging control circuit coupled to the control terminal of the power switch wherein the ionic relaxation control circuit closes the power switch when the voltage of the lithium based rechargeable battery cell is below the lower voltage reference and opens the power switch when the voltage of the lithium based rechargeable battery cell is above the upper voltage reference.

2. A battery charger as described in claim 1 wherein the ionic relaxation charging control circuit further comprises a delay circuit for maintaining a minimum time for the power switch to be open.

3. A battery charger as described in claim 2 wherein the power switch comprises a PNP Bipolar Transistor.

4. A battery charger as described in claim 2 wherein the power switch comprises a P-type MOSFET.

5. A battery charging system, comprising:

A) a power supply having a power input, wherein the power supply is capable of delivering a constant current output;

B) A lithium based rechargeable battery cell having a termination voltage;

C) A single power switch having a control terminal coupled in series between the power supply and the lithium based rechargeable battery cell;

D) A linear regulated charging control circuit to the control terminal of the power switch, wherein the linear regulated charging control circuit provides control signal proportional to a constant and limited value of charging current until the termination voltage of the lithium based rechargeable battery cell is reached, wherein the linear regulated charging control produces a control signal corresponding to the value of the termination voltage;

E) A resistor coupled in series between the linear regulated charging control circuit and the control terminal of the power switch;

F) An upper voltage reference and a lower voltage reference; and

G) An ionic relaxation charging control circuit coupled to the control terminal of the power switch wherein the ionic relaxation control circuit closes the power switch when the voltage of the lithium based rechargeable battery cell is below the lower voltage reference and opens the power switch when the voltage of the lithium based rechargeable battery cell is above the upper voltage reference; and

H) A diode coupled in series between the control terminal of the power switch and the ionic relaxation charging control circuit, with the anode towards the control terminal of the power switch.

6. A battery charger as described in claim 5 wherein the ionic relaxation charging control circuit further comprises a delay circuit for maintaining a minimum time for the power switch to be open.

7. A battery charger as described in claim 6 wherein the power switch comprises a PNP Bipolar Transistor.

8. A battery charger as described in claim 6 wherein the power switch comprises a P-type MOSFET.

9. A method of charging a battery, the method comprising the following steps:

A) charging the cell at a rapid current until an upper predetermined cell voltage is reached;

B) reducing charging current;

C) charging the cell at a low current, in a linear fashion until either the cell is fully charged or a lower predetermined cell voltage is reached; and

D) repeating these steps until the cell is fully charged.