METHODS AND APPARATUS TO CLAMP OVERVOLTAGES FOR ALTERNATING CURRENT SYSTEMS

• US 20120050931A1
• Filed: 08/31/2010
• Published: 03/01/2012
• Est. Priority Date: 08/31/2010
• Status: Active Grant

• Current Assignee: Texas Instruments, Inc.
• Original Assignee: Texas Instruments, Inc.
• Inventors: Terry, Stephen Christopher, Brohlin, Paul L.
• Granted Patent: US 8,830,637 B2
• Time in Patent Office: Days
• US Class Current: 361/91.5
• CPC Class Codes: H02H 3/20 responsive to excess voltage
• CPC Class Codes: H02H 7/122 for inverters, i.e. dc/ac converters
• CPC Class Codes: H02H 7/1252 responsive to overvoltage in input or output, e.g. by load dump
• CPC Class Codes: H02H 9/04 responsive to excess voltage lightning arrestors H01C7/12, H01C8/04, H01G9/18, H01T
• CPC Class Codes: H02J 50/12 of the resonant type
• CPC Class Codes: H02J 7/00308 Overvoltage protection

Abstract

Methods and apparatus to clamp overvoltages for inductive power transfer systems are described herein. An example overvoltage protection circuit is described, including a first terminal configured to receive an alternating current signal for conversion to a second signal, a capacitor, a first switch configured to selectively electrically couple the capacitor to the first terminal based on an overvoltage detection signal to reduce an overvoltage on the second signal, and an overvoltage detector. The example overvoltage detector is configured to determine a signal level of the second signal and, in response to determining that the signal level of the second signal is greater than a threshold, to output the overvoltage detection signal to cause the switch to electrically couple the capacitor between the first terminal and a second terminal.

Claims

1. An overvoltage protection circuit, comprising:

a first terminal configured to receive an alternating current signal for conversion to a second signal;

a second terminal to receive the second signal based on the alternating current signal;

a capacitor in circuit with the first terminal;

a switch in circuit with the capacitor and the first terminal configured to selectively electrically couple the capacitor to the first terminal based on an overvoltage detection signal to reduce an overvoltage on the second signal; and

an overvoltage detector in circuit with the second terminal and the switch and configured to determine a signal level of the second signal and, in response to determining that the signal level of the second signal is greater than a threshold, to output the overvoltage detection signal to cause the switch to electrically couple the capacitor between the first terminal and a second terminal.

2. An overvoltage protection circuit as defined in claim 1, wherein the overvoltage detector comprises a comparator configured to compare the second signal to the threshold and to generate the overvoltage detection signal when the second signal is greater than the threshold.

3. An overvoltage protection circuit as defined in claim 1, wherein the overvoltage detector comprises a pull down resistor and a breakdown diode that has a breakdown voltage substantially equal to the threshold, wherein the breakdown diode is configured to output the overvoltage detection signal when a voltage on the second signal exceeds the breakdown voltage.

4. An overvoltage protection circuit as defined in claim 1, further comprising a rectifier circuit in circuit with the first and second terminals, the capacitor, and the switch and configured to generate the second signal.

5. An overvoltage protection circuit as defined in claim 4, wherein the capacitor comprises first and second capacitors and wherein the switch selectively couples the first capacitor between the first terminal and a reference.

6. An overvoltage protection circuit as defined in claim 5, further comprising a second switch configured to selectively couple the second capacitor between a third terminal and the reference based on the overvoltage detection signal when a second electrical signal level on the third terminal is less than a second threshold.

7. An overvoltage protection circuit as defined in claim 1, further comprising a switch driver configured to receive the overvoltage detection signal and to selectively output a clamp signal to cause the switch to electrically couple the capacitor to the first terminal.

8. An overvoltage protection circuit as defined in claim 7, wherein the switch driver comprises a comparator configured to compare the overvoltage detection signal to the threshold and output the clamp signal based on the comparison, and a latch configured to output the clamp signal to the switch when the alternating current signal is less than a second threshold.

9. An overvoltage protection circuit as defined in claim 8, wherein the switch driver comprises a second comparator configured to compare the alternating current signal to the second threshold.

10. An overvoltage protection circuit as defined in claim 7, wherein the switch driver outputs the clamp signal when the alternating current signal is substantially at a neutral signal level.

11. An overvoltage protection circuit as defined in claim 1, further comprising a rectifier capacitor configured to smooth the rectified signal.

12. A method to clamp an overvoltage, comprising:

receiving an alternating current signal at a first power source terminal;

rectifying the alternating current signal to generate a rectified signal;

comparing the rectified signal to a threshold signal level; and

coupling a capacitor to the first power source terminal when the rectified signal is greater than the threshold signal level.

13. A method as defined in claim 12, wherein the comparing comprises applying the rectified signal to a breakdown diode having a breakdown voltage and generating a clamp signal when the rectified signal is greater than the breakdown voltage.

14. A method as defined in claim 13, wherein coupling the clamp capacitor to the first power source terminal comprises activating a switching element in response to the clamp signal.

15. A method as defined in claim 12, further comprising delaying the coupling until the electrical power signal is less than a second threshold signal level.

16. A method as defined in claim 12, wherein coupling the clamp capacitor to the first power source terminal comprises coupling the clamp capacitor between the first power source terminal and a second power source terminal.

17. A method as defined in claim 16, wherein coupling the clamp capacitor between the first power source terminal and the second power source terminal comprises coupling a first capacitor between the first power source terminal and a reference when the electrical power signal at the first power source terminal is substantially at a neutral signal level, and coupling a second capacitor between the second power source terminal and the reference when a second electrical power signal at the second power source terminal is substantially at the neutral signal level.

18. A method as defined in claim 12, further comprising decoupling the clamp capacitor from the first power source terminal when the rectified signal is less than the first threshold signal level.

19. A method as defined in claim 18, further comprising delaying the coupling until the electrical power signal is less than a second threshold signal level.

20. An inductive power transfer system having overvoltage protection, comprising:

a receiver coil having first and second terminals and configured to generate an alternating current signal over the first and second terminals based on a voltage, a current, and a frequency of a transmitter coil;

a rectifier configured to rectify the alternating current signal and to output a rectified signal;

an overvoltage protection circuit, the overvoltage protection circuit comprising;

a first clamp capacitor and a second clamp capacitor;

a first switch configured to selectively electrically couple the first clamp capacitor between the first terminal and a reference to reduce an overvoltage of the rectified signal based on a first clamp signal;

a second switch configured to selectively electrically couple the second clamp capacitor between the second terminal and the reference to reduce the overvoltage based on a second clamp signal;

an overvoltage detector configured to determine a signal level of the rectified signal and, in response to determining that the signal level of the rectified signal is greater than a first threshold, to output the overvoltage detection signal;

a first switch driver configured to receive the overvoltage detection signal and to output the first clamp signal to cause the first switch to selectively electrically couple the first terminal to the reference when a first power signal at the first terminal is less than a second threshold; and

a second switch driver configured to receive the overvoltage detection signal and to output the second clamp signal to cause the second switch to selectively electrically couple the second terminal to the reference when a second power signal at the second terminal is less than the second threshold.