Three-quarter bridge power converters for wireless power transfer applications and other applications

• US 8,779,745 B2
• Filed: 02/25/2011
• Issued: 07/15/2014
• Est. Priority Date: 03/01/2010
• Status: Active Grant

• Current Assignee: National Semiconductor Corporation (Texas Instruments, Inc.)
• Original Assignee: National Semiconductor Corporation (Texas Instruments, Inc.)
• Inventors: Brown, James Steven
• Primary Examiner(s): Berhane, Adolf
• Assistant Examiner(s): Mehari, Yemane
• Application Number:
  US13/034,975
• Publication Number:
  US 20110211380A1
• Time in Patent Office: 1,236 Days
• Field of Search: 323/282, 323/285, 363/21.06, 363/39, 363/65, 363/131, 363/132, 307/21, 307 23- 25, 307/28, 307/29, 307 43- 46
• US Class Current: 323/285
• CPC Class Codes: H02J 50/12 of the resonant type
• CPC Class Codes: H02M 3/01 Resonant DC/DC converters
• CPC Class Codes: H02M 3/33561 having more than one ouput with independent control
• CPC Class Codes: H02M 3/33569 having several active switching elements H02M3/3353 takes precedence

Abstract

A three-quarter bridge power converter includes a first switch configured to selectively couple a switch node to a higher voltage. The power converter also includes a second switch configured to selectively couple the switch node to a lower voltage. The power converter further includes a third switch configured to selectively cause a third voltage to be provided to the switch node when the first and second switches are not coupling the switch node to the higher and lower voltages. The third switch may be configured to selectively couple the switch node to an energy storage or energy source, such as a capacitor. The third switch may also be configured to selectively couple an energy storage or energy source to ground, where the energy storage or energy source is coupled to the switch node.

Claims

1. A three-quarter bridge power converter circuit configured for providing regulated power to a load, comprising:

a first switch configured to selectively couple a switch node to a higher voltage;

a second switch configured to selectively couple the switch node to a lower voltage;

a clamp voltage element configured to store a clamp voltage intermediate the higher and lower voltages;

a bi-directional clamping switch configured to selectively couple the switch node to the voltage element when the first and second switches are not coupling the switch node to the higher and lower voltages, and thereby clamp the switch node to the clamp voltage; and

a control circuit configured to generate control signals G1, G2, and G3 to cooperatively switch respectively the first and second switches and the bi-directional clamping switch, including generating G1 and G2 based on values associated with switching frequency and duty cycle, converted to respectively a reference phase value related to the switching frequency, and a variable phase value related to both the switching frequency and the duty cycle, such that

the reference phase value and the variable phase value have a predetermined resolution,

the difference between the reference phase value and the variable phase value is used to generate the G1 and G2 control signals,

the G3 control signal is asserted to clamp the switch node to the clamp voltage when neither G1 nor G2 is asserted, such that the G1, G2 and G3 control signals provide a predetermined duty factor resolution.

2. The power converter of claim 1, wherein the-voltage element comprises a capacitor.

3. The power converter of claim 1, further comprising:

a reactive element coupled between the switch node and the load.

4. The power converter of claim 3, wherein the reactive element comprises at least one coil or transformer winding.

5. The power converter of claim 4, further comprising at least one of:

a single-ended voltage sensor configured to measure a voltage across the coil or transformer winding; and

a single-ended current sensor configured to measure a current through the coil or transformer winding.

6. The power converter of claim 3 wherein the reactive element is a capacitor coupled between the switch node and an output node coupled to the load;

and

wherein the bi-directional clamping switch is coupled between the output node and ground, such that the capacitor comprises the voltage element.

7. The power converter of claim 1, wherein the control circuit is configured based on direct digital synthesis, and includes:

a phase accumulator configured to receive the switching frequency value;

an adder configured to add an output of the phase accumulator and the duty cycle value;

at least one extraction unit configured to identify a most significant bit in an output of the phase accumulator and a most significant bit in an output of the adder, respectively corresponding to the reference phase value and the variable phase value; and

combinatorial logic configured to generate the control signals G1, G2, and G3 using the most significant bits.

8. The power converter of claim 1, wherein:

the higher voltage comprises a supply voltage;

the lower voltage comprises ground; and

the clamp voltage is approximately one-half of the supply voltage.

9. A system comprising:

a load; and

a three-quarter bridge power converter configured to provide power to the load, the power converter comprising;

a first switch configured to selectively couple a switch node to a higher voltage;

a second switch configured to selectively couple the switch node to a lower voltage;

a clamp voltage element configured to store a clamp voltage intermediate the higher and lower voltages;

a bi-directional clamping switch configured to selectively couple the switch node to the voltage element when the first and second switches are not coupling the switch node to the higher and lower voltages, and thereby clamp the switch node to the clamp voltage; and

a control circuit configured to generate control signals G1, G2, and G3 to cooperatively switch respectively the first and second switches and the bi-directional clamping switch, including generating G1 and G2 based on values associated with switching frequency and duty cycle, converted to respectively a reference phase value related to the switching frequency, and a variable phase value related to both the switching frequency and the duty cycle, such that

the reference phase value and the variable phase value have a predetermined resolution,

the difference between the reference phase value and the variable phase value is used to generate the G1 and G2 control signals,

the G3 control signal is asserted to clamp the switch node to the clamp voltage when neither G1 nor G2 is asserted, such that the G1, G2 and G3 control signals provide a predetermined duty factor resolution.

10. The system of claim 9, wherein the voltage element comprises a capacitor.

11. The system of claim 9, further comprising:

a reactive element coupled between the switch node and the load.

12. The system of claim 11, wherein the reactive element comprises at least one coil or transformer winding.

13. The system of claim 12, wherein the power converter further comprises at least one of:

a single-ended voltage sensor configured to measure a voltage across the coil or transformer winding; and

a single-ended current sensor configured to measure a current through the coil or transformer winding.

14. The system of claim 11:

wherein the reactive element is a capacitor coupled between the switch node and an output node coupled to the load; and

wherein the bi-directional clamping switch is coupled between the output node and ground, such that the capacitor comprises the voltage element.

15. The system of claim 9, wherein the control circuit is configured based on direct digital synthesis, and includes:

a phase accumulator configured to receive the switching frequency value;

an adder configured to add an output of the phase accumulator and the duty cycle value;

at least one extraction unit configured to identify a most significant bit in an output of the phase accumulator and a most significant bit in an output of the adder, respectively corresponding to the reference phase value and the variable phase value; and

combinatorial logic configured to generate the control signals G1, G2, and G3 using the most significant bits.

16. The system of claim 9, wherein:

the three-quarter bridge power converter comprises a portion of a wireless power transmitter including a matrix comprising multiple transmit coils or transformer windings; and

the load comprises a wireless power receiver.

17. The system of claim 16, wherein

the higher voltage comprises a supply voltage;

the lower voltage comprises ground; and

the clamp voltage is approximately one-half of the supply voltage.

18. A method of half-bridge power conversion, comprising:

repeatedly coupling a switch node to a higher voltage and a lower voltage using first and second switches, respectively; and

selectively coupling the switch node to a clamp voltage intermediate the higher and lower voltages using a bi-directional clamping switch when the first and second switches are not coupling the switch node to the higher and lower voltages, and thereby clamping the switch node to the clamp voltage, by

generating control signals G1, G2, and G3 to cooperatively switch respectively the first and second switches and the bi-directional clamping switch, including generating G1 and G2 based on values associated with switching frequency and duty cycle converted to respectively a reference phase value related to the switching frequency, and a variable phase value related to both the switching frequency and the duty cycle, such that

the reference phase value and the variable phase value have a predetermined resolution,

the difference between the reference phase value and the variable phase value is used to generate the G1 and G2 control signals, and

asserting the G3 control signal to clamp the switch node to the clamp voltage when neither G1 nor G2 is asserted, such that the G1, G2 and G3 control signals provide a predetermined duty factor resolution.

19. The method of claim 18, further comprising a capacitor coupled between the switch node and an output node coupled to the load, and wherein:

selectively coupling the switch node to a clamp voltage is accomplished by selectively coupling the output node to ground, such that a voltage on the capacitor comprises the clamp voltage.

20. The method of claim 18, adapted for use in a wireless power transmitter that includes a matrix comprising multiple transmit coils or transformer windings, such that wireless power is supplied to a load comprising a wireless power receiver.