Series resonant inductive charging circuit

• US 6,972,543 B1
• Filed: 08/21/2003
• Issued: 12/06/2005
• Est. Priority Date: 08/21/2003
• Status: Active Grant

• Current Assignee: Stryker Corporation
• Original Assignee: Stryker Corporation
• Inventors: Wells, Brannon P.
• Primary Examiner(s): Tso, Edward H.
• Application Number:
  US10/646,386
• Time in Patent Office: 838 Days
• Field of Search: 320/108, 320/137, 320/140, 320/142, 363/8, 363/170, 363/173
• US Class Current: 320/108
• CPC Class Codes: H01M 10/42 Methods or arrangements for servicing or maintenance of secondary cells or secondary half-cells H01M10/60 takes precedence
• CPC Class Codes: H02J 50/12 of the resonant type
• CPC Class Codes: H02J 7/00 Circuit arrangements for charging or depolarising batteries or for supplying loads from batteries
• CPC Class Codes: Y02E 60/10 Energy storage using batteries

Abstract

An apparatus to charge a power supply inductively, with increased efficiency due to resonance, comprises an LC series resonance circuit formed by a capacitor and a primary inductive coil coupled in series with the capacitor, and a secondary inductive coil positioned such that power is inductively transferred from the primary coil to the secondary coil. The LC circuit has a natural resonant frequency, wherein the primary coil of the resonance circuit is coupled to receive power from a source oscillating at the natural resonant frequency. The secondary coil is further coupled to the power supply so that power induced in the secondary coil causes the power supply to be charged.

Claims

1. An apparatus to charge a power supply, the apparatus comprising:

a resonance circuit including a capacitor and a primary inductor coupled to the capacitor, the primary inductor further coupled to receive power from a an oscillating source, wherein the resonance circuit has a natural resonant frequency approximately equal to a frequency of the source; and

a secondary inductor to receive power transmitted from the primary inductor by induction, the secondary inductor coupled to the power supply so that power induced in the secondary inductor causes the power supply to be charged.

2. An apparatus as recited in claim 1, wherein the capacitor and primary inductor are coupled in series.

3. An apparatus as recited in claim 1, further comprising a charging circuit coupled between the power supply and the secondary coil, the charging circuit to control the transfer of power to the power supply.

4. An apparatus as recited in claim 1, wherein the power supply is a rechargeable battery.

5. An apparatus as recited in claim 4, wherein the apparatus is contained within a housing configured to receive a portable cordless device that contains the rechargeable battery.

6. An apparatus to charge a power supply, the apparatus comprising:

a source to generate an oscillating output at a frequency;

a resonance circuit including a primary coil and a capacitor coupled in series with the primary coil, wherein the resonance circuit has a natural resonant frequency substantially equal to the frequency of the source, the primary coil further coupled to the source; and

a secondary coil to receive power, through induction, from the primary coil, the secondary coil further coupled to the chargeable power supply to cause the chargeable power supply to be charged from the power induced in the secondary coil.

7. An apparatus as recited in claim 6, further comprising a charging circuit coupled between the power supply and the secondary coil, the charging circuit to control the transfer of power to the power supply.

8. An apparatus as recited in claim 6, wherein the power supply is a rechargeable battery.

9. An apparatus as recited in claim 8, wherein the apparatus is contained within a housing configured to receive a portable cordless device that contains the rechargeable battery.

10. A charging apparatus for charging a rechargeable battery, the charging apparatus comprising:

a source generating an output oscillating at a frequency;

an LC series resonance circuit coupled to receive the output of the source, the LC series resonance circuit including a primary coil and a capacitor coupled to the primary coil, wherein a first terminal of the capacitor is coupled to a first terminal of the primary coil and a second terminal of the capacitor is coupled to a reference point, a second terminal of the primary coil is coupled to the output of the source, the LC series resonance circuit having a natural resonant frequency substantially equal to the frequency of the output of the source;

a secondary coil to receive power, through induction, from the primary coil, the secondary coil further coupled to the charging circuit to cause the rechargeable battery to be charged from the power induced in the secondary coil; and

a battery charging circuit coupled between the secondary coil and the rechargeable battery to control charging of the rechargeable battery.

11. A charging apparatus as recited in claim 10, wherein the apparatus is contained within a housing configured to receive a portable cordless device that contains the rechargeable battery.

12. A charging apparatus as recited in claim 11, wherein the natural resonant frequency, f_r, of the LC series resonance circuit is characterized as f_r=1/(2π

√

(LC)), where L is an inductance value of the primary coil and C is a capacitance value of the capacitor.