Auto resonant driver for wireless power transmitter sensing required transmit power for optimum efficiency

• US 9,305,700 B2
• Filed: 04/12/2013
• Issued: 04/05/2016
• Est. Priority Date: 10/04/2012
• Status: Active Grant

• Current Assignee: Analog Devices International Unlimited Company (Analog Devices, Inc.)
• Original Assignee: Linear Technology Corporation (Analog Devices, Inc.)
• Inventors: Lisuwandi, Eko Tan
• Primary Examiner(s): BOATENG, ALEXIS ASIEDUA
• Application Number:
  US13/862,200
• Publication Number:
  US 20140097791A1
• Time in Patent Office: 1,089 Days
• Field of Search: 320/107, 320/108, 320/117, 320/118, 320/116, 320/119, 320/112, 320/134, 320/126, 320/121, 320/120, 320/103, 320/162, 320/128, 307/66, 307/71, 307/26, 307/46, 307/80, 307/110
• US Class Current: 1/1
• CPC Class Codes: B60L 58/18 of two or more battery modules
• CPC Class Codes: H01F 38/14 Inductive couplings for wireless supply or distribution of electric power using inductive coupling H02J50/10
• CPC Class Codes: H01M 10/441 for several batteries or cells simultaneously or sequentially
• 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: H02J 7/0016 using shunting, discharge or bypass circuits
• CPC Class Codes: H02J 7/0024 Parallel/serial switching of connection of batteries to charge or load circuit
• CPC Class Codes: H02J 7/00304 Overcurrent protection
• CPC Class Codes: H02J 7/00308 Overvoltage protection
• CPC Class Codes: H04B 5/79 for data transfer in combination with power transfer
• CPC Class Codes: Y02E 60/10 Energy storage using batteries
• CPC Class Codes: Y02T 10/70 Energy storage systems for electromobility, e.g. batteries

Abstract

An auto-resonant driver for a transmitter inductor drives the inductor at an optimal frequency for maximum efficiency. The transmitter inductor is magnetically coupled, but not physically coupled, to a receiver inductor, and the current generated by the receiver inductor is used to power a load. The system may be used, for example, to remotely charge a battery (as part of the load) or provide power to motors or circuits. A feedback circuit is used to generate the resonant driving frequency. A detector in the transmit side wirelessly detects whether there is sufficient current being generated in the receiver side to achieve regulation by a voltage regulator powering the load. This point is achieved when the transmitter inductor peak voltage suddenly increases as the driving pulse width is ramped up. At that point, the pulse width is held constant for optimal efficiency.

Claims

1. A power transmission system for wirelessly supplying power to a load comprising:

a transmitter inductor;

a transmitter capacitor connected to the transmitter inductor to create a tank circuit having a resonant frequency;

a first switch coupled to a first node of the tank circuit and to a first voltage to cause the tank circuit to be intermittently charged;

a second switch coupled to the first node of the tank circuit and to a second voltage to cause the tank circuit to be intermittently discharged; and

a feedback circuit for switching the power switch, the feedback circuit comprising;

a first comparator coupled to the first voltage and to the first node and having a first comparator output terminal;

a second comparator coupled to the second voltage and to the first node and having a second comparator output terminal;

a latch having a first latch input terminal coupled to the first comparator output terminal;

the latch having a second latch input terminal coupled to the second comparator output terminal; and

a latch output terminal automatically generating switching signals for the first switch and the second switch at the resonant frequency,

wherein the first comparator, second comparator, and latch are configured such that positive and negative currents flow through the inductor as the first switch and the second switch are switched, wherein,

a. at a negative to positive inductor current transition while the second switch is on, the first node goes from above the second voltage to below the second voltage, triggering the second comparator and the latch and turning on the first switch, wherein,

b. at a positive to negative inductor current transition while the first switch is on, the first node goes from below the first voltage to above the first voltage, triggering the first comparator and the latch and turning on the second switch, and wherein,

c. steps a and b repeat.

2. The system of claim 1 further comprising a first diode across the first switch and a second diode across the second switch.

3. The system of claim 1 further comprising an oscillator coupled to the first switch and the second switch to initiate switching.

4. The system of claim 3 wherein the latch output terminal and an oscillator output terminal are coupled to inputs of an OR gate, an output terminal of the OR gate being coupled to drive the first switch and the second switch.

5. The system of claim 1 further comprising:

a first one-shot circuit that generates a first pulse of a controllable pulse width at a first one-shot circuit output terminal,

the first one-shot circuit having a start-pulse input terminal coupled to the latch output terminal for being triggered when the latch has triggered,

the first one-shot circuit having a pulse width control terminal connected to receive a pulse width control signal for setting the pulse width of the first pulse,

the first one-shot circuit output terminal being coupled to drive the first switch and the second switch with a selectable pulse width; and

a second one-shot circuit coupled between the second comparator output terminal and the first latch input terminal for triggering the latch when the transmitter inductor current waveform transitions from negative to positive while the second switch is on.

6. The system of claim 1 wherein the first switch and the second switch form a half bridge drive circuit.

8. The system of claim 1 further comprising:

a receiver inductor magnetically coupled to the transmitter inductor;

a voltage regulator receiving power from the receiver inductor to generate a regulator output voltage; and

a load coupled to an output of the voltage regulator, wherein power in the transmitter inductor is wirelessly coupled to the receiver inductor for being converted to a regulated voltage by the regulator for driving the load.

9. The system of claim 8 wherein the receiver inductor is housed along with the load in a device for recharging a battery in the device.

10. The system of claim 8 further comprising:

a peak voltage detector coupled to detect a peak voltage on the transmitter inductor, wherein a peak voltage on the transmitter inductor is affected by an ability of the voltage regulator, receiving power from the receiver inductor, to achieve regulation for driving the load; and

a controller for controlling a peak current through the transmitter inductor, the controller being controlled to modulate the peak current through the transmitter inductor so as to modulate a peak current through the receiver inductor, wherein the peak voltage on the transmitter inductor increases during a time when the voltage regulator is able to achieve regulation,

wherein the controller is configured to terminate modulating the peak current through the transmitter inductor, based on a change in the peak voltage, so that the voltage regulator is able to achieve regulation.

11. The system of claim 10 wherein the controller is controlled to modulate the peak current through the transmitter inductor by modulating the first voltage.

12. The system of claim 10 wherein the controller is controlled to modulate the peak current through the transmitter inductor by modulating a pulse width of driving pulses applied to the first switch.

13. The system of claim 10 wherein the controller sets the peak current through the transmitter inductor to a level equal to or above than that needed for the voltage regulator to achieve regulation but below a level that is 25% more than that needed for regulation.

7. A power transmission system for wirelessly supplying power to a load comprising:

a transmitter inductor;

a transmitter capacitor connected to the transmitter inductor to create a tank circuit having a resonant frequency;

a first switch coupled to a first node of the tank circuit and to a first voltage to cause the tank circuit to be intermittently charged;

a second switch coupled to the first node of the tank circuit and to a second voltage to cause the tank circuit to be intermittently discharged; and

a feedback circuit for switching the power switch, the feedback circuit comprising;

a first comparator coupled to the first voltage and to the first node and having a first comparator output terminal;

a second comparator coupled to the second voltage and to the first node and having a second comparator output terminal;

a latch having a first latch input terminal coupled to the first comparator output terminal;

the latch having a second latch input terminal coupled to the second comparator output terminal;

a latch output terminal automatically generating switching signals for the first switch and the second switch at the resonant frequency;

a third switch coupled to a second node of the tank circuit and to the first voltage; and

a fourth switch coupled to the second node of the tank circuit and to the second voltage, wherein the tank circuit is coupled between the first node and the second node, wherein the first switch, the second switch, the third switch, and the fourth switch form a full bridge drive circuit for the tank circuit,

the latch output terminal being coupled to control the full bridge drive circuit.