Patent Publication Number: US-10312736-B2

Title: Wireless power transmitter

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of U.S. patent application Ser. No. 14/872,483, filed Oct. 1, 2015, entitled “WIRELESS POWER TRANSMITTER”, incorporated herein by reference. 
    
    
     TECHNICAL FIELD 
     Embodiments of the present invention are related to wireless power transmission. 
     DISCUSSION OF RELATED ART 
     Wireless power charges are quickly becoming a widespread and popular method of charging portable devices such as laptop computers, mobile phones, tablets, e-Readers, media players and other devices. A device that includes a wireless receiver can be placed in proximity to a wireless transmitter and become charged without the need of charging cables or other devices. Wireless transmitters can be located in a multitude of locations, including public locations as well as in the home or office environment. 
     One standard, the Alliance for Wireless Power (A4WP), provides for ubiquitous power availability in multiple environments for loosely-coupled wireless power transmitter systems. In such systems, wireless power transmitters are widely distributed and consumers may charge compatible portable devices by placing them in proximity to the transmitters, for example by placing them on a charging matt. Such systems may support the simultaneous charging of multiple devices that are placed on the charging matt. 
     Multiple challenges exist in supplying power transmitter technologies in loosely-coupled wireless power transmission systems. These challenges include, for example, efficiently and safely supplying power to particular receiving devices. Therefore, there is a need to develop better wireless charging technologies for charging portable devices. 
     SUMMARY 
     In accordance with aspects of the present invention a wireless power transmission system is disclosed. In some embodiments, a transmission unit includes a first inductor with a center tap, a first end tap, and a second end tap; a pre-regulator coupled to provide current to the center tap; a switching circuit coupled to the first end tap and the second end tap, the switching circuit alternately coupling the first end tap and the second end tap to ground at a frequency; and a resonant circuit magnetically coupled to the first inductor, the resonant circuit wirelessly transmitting power. 
     In some embodiments, a resonant transmission unit includes a first inductor with a center tap, a first end tap and a second end tap; a first transistor coupled between the first end tap and a ground; a second transistor coupled between the second end tap and the ground; a pre-regulator coupled to provide current to the center tap; and a resonant circuit magnetically coupled to the first inductor, wherein gates of the first transistor and the second transistor are driven to transmit power with the resonant circuit. 
     A method of wireless transmission according to some embodiments includes providing current to a center tap of a first inductor; alternately coupling a first end of the first inductor and a second end of the first inductor to ground at a frequency; and magnetically coupling a resonant circuit with the first inductor. 
     These and other embodiments are further discussed below with respect to the following figures. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIGS. 1A and 1B  illustrates an example of a wireless power transmission system. 
         FIG. 2  illustrates a block diagram of a wireless power transmitter according to some embodiments of the present invention. 
         FIG. 3  illustrates a detailed diagram of a wireless power transmitter corresponding with the block diagram illustrated in  FIG. 2 . 
         FIG. 4  illustrates another block diagram of a wireless power transmitter corresponding with the block diagram illustrated in  FIG. 2 . 
         FIG. 5  (consisting of  FIGS. 5A, 5B, 5C, 5D, 5E, 5F and 5G ) illustrates a detailed diagram of a wireless power transmitter corresponding with the block diagram illustrated in  FIG. 2 . 
     
    
    
     DETAILED DESCRIPTION 
     In the following description, specific details are set forth describing some embodiments of the present invention. It will be apparent, however, to one skilled in the art that some embodiments may be practiced without some or all of these specific details. The specific embodiments disclosed herein are meant to be illustrative but not limiting. One skilled in the art may realize other elements that, although not specifically described here, are within the scope and the spirit of this disclosure. 
     This description and the accompanying drawings that illustrate inventive aspects and embodiments should not be taken as limiting—the claims define the protected invention. Various changes may be made without departing from the scope of this description and the claims. In some instances, well-known structures and techniques have not been shown or described in detail in order not to obscure the invention. 
     Elements and their associated aspects that are described in detail with reference to one embodiment may, whenever practical, be included in other embodiments in which they are not specifically shown or described. For example, if an element is described in detail with reference to one embodiment and is not described with reference to a second embodiment, the element may nevertheless be claimed as included in the second embodiment. 
     Electronic components that are described as single components may include multiple components. For example, a capacitor may be formed of multiple capacitors. Similarly, inductors and resistors may be formed of multiple inductors and resistors, respectively. 
       FIG. 1A  illustrates a wireless charging system  100  in which embodiments of the present invention may be used. System  100  includes a power transmitter unit (PTU)  102 . PTU  102  can, in some cases, transmit power to one or more power receive units (PRU)  104 - 1  through  104 -N. System  100  may, for example, conform to the Alliance for Wireless Power (A4WP) standards. A4WP systems utilize loosely-coupled wireless power systems operating at 6.78 MHz for transmission of power from PTU  102  to PRU  104 . Furthermore, in the A4WP standard, system communications between PTU  102  and PRU  104  are accomplished, for example, using Bluetooth communications at 2.4 GHz. The A4WP standard is discussed, for example, in Ryan Tseng, Bill von Novak, Sumukh Shevde and Kamil Grajski, “Introduction to the Alliance for Wireless Power Loosely-Coupled Wireless Power Transfer System Specification Version 1.0,” IEEE Wireless Power Transfer Conference 2013, Technologies, Systems and Applications, May 15-16, 2013 Perugia, Italy. Loosely-coupled wireless power transfer is further described in Kamil Grajski, Ryan Tseng and Chuck Wheatley, “Loosely-Coupled Wireless Power Transfer: Physics, Circuits, Standards,” Microwave Workshop Series on Innovative Wireless Power Transmission: Technologies, Systems and Applications (IMWS), 2012, IEEE MTT-S International, DOI: 10.1109/IMWS.2012.6215828. 
     Embodiments of the present invention may operate within the A4WP standard. However, embodiments are not restricted to do so and may operate in conformance with other requirements. For example, embodiments of the present invention may operate within different frequency ranges and may support other communication methods to transmit data and instructions between PTU  102  and PRU  104 . 
       FIG. 1B  illustrates in more detail PTU  102  transmitting power to a PRU  104 . As shown in  FIG. 1B , PTU  104  includes a power source  106 , an amplifier  108 , and matching circuits  110 . PTU  104  drives a transmit resonator  112 . Power source  106  can be any source of power at the operating frequency of PTU  104 , for example the 6.78 MHz in conformance with the A4WP standard. Power source  106  may use wall power (e.g. 110V at 60 Hz), may be battery powered, or may input other DC or AC sources of power. Amplifier  108  can adjust the voltage supplied to matching circuits  110  in order drive transmit resonator  112 . Matching circuit  110  matches the impedance of transmit resonator  112 . Transmit resonator  112  includes a coil, which may be embedded in a mat or table on which PRU  104  is placed. 
     As shown in  FIG. 1B , PRU  104  receives power at receive resonator  116 . Receive resonator  116  may be much smaller than transmit resonator  112  so that multiple ones of receive resonator  116  can be placed in proximity to transmit resonator  112  in order to receive power. Power received in receive resonator  116  is input to regulator  118 , which provides DC power to DC-DC converter  120 . DC-DC converter  120  provides power to a load  122 , which corresponds to the user device to be charged. 
     In some embodiments, a separate communications channel is provided between PRU  104  and PTU  102 . Signaling  126  of PRU  104  is in communications with signaling  124  in PTU  102 . In some embodiments, communications can be performed by modulating the power link between receiver resonator  116  and transmit resonator  112 . Communications between signaling  126  and signaling  124  can be, for example, by Bluetooth or other wireless link. 
       FIG. 2  illustrates a PTU  200  according to some embodiments of the present invention. As shown in  FIG. 2 , a pre-regulator  202  receives a voltage Vin and provides current through an inductor  204  to a center tap of inductor  216 , which forms a transformer with inductor  206 . A first end of inductor  216  is coupled through transistor  210  to ground while the opposite end of inductor  216  is coupled through transistor  208  to ground. A first capacitor  214  is coupled between the source and drain of transistor  210  while a second capacitor  212  is coupled between the source and drain of transistor  208 . In some embodiments, transistors  208  and  210  can be power FETs. Although transistors  208  and  210  can be any FETs, in some embodiments transistors  208  and  210  can be GaN FETs. 
     Inductor  216  is magnetically coupled to inductor  206 , forming a transformer. Power from inductor  216  drives PTU resonator circuit  222 . PTU resonator circuit  222  includes a capacitor  218  coupled between inductor  216  and resonator coil  220 . PTU resonator circuit  222  completes the resonant transmission of wireless power from PTU  200 . Coil  220  in resonator circuit  222  can be sized to cover an area to accommodate a number of PRUs  104 . 
     Transistors  208  and  210  are driven to alternately couple each side of inductor  216  to ground, though in some cases this may be through a current sense resistor (not shown). Transistors  208  and  210  can be driven at or near the resonant frequency of resonant circuit  222 , for example 6.78 MHz as provided for in the A4WP standard. Current supplied by pre-regulator  202  is then alternately switched across inductor  216 , inducing power in resonant  222  at the switching frequency. 
     In some embodiments, pre-regulator  202  can actively control power transmitted by coil  220  by controlling the output current through inductor  204 . In some embodiments, pre-regulator  202  may control the power transmitted by PTU resonator circuit  222  in accordance with power requirements received by one or more PRUs  104 . In some embodiments, pre-regulator  202  may control the power transmitted by PTU resonator circuit  222  in response to detected conditions, for example currents, detected in various locations in PTU  200 . 
       FIG. 3  further illustrates PTU  200 . As shown in  FIG. 3 , a current detector  302  can detect the current in resonator circuit  222 . In some embodiments, current detector  302  can include a rectifier circuit in order to produce a current signal for pre-regulator  202 . Pre-regulator  202  can then compare the current signal with a threshold signal and increase the current through inductor  204  accordingly. 
     Another current sensor  306 , which detects current through transistors  208  and  210 , can also be used to adjust the current through inductor  204 . In some embodiments, a voltage from current sensor  306  can be compared to a threshold voltage that is set in response to a voltage from current sense  302  in a dual current feedback loop system. In some embodiments, the first current signal from current sensor  302  and the second current signal from current sensor  304  are averaged so that the feedback loops are operated in average current mode control. In some embodiments, the current or voltage at other locations in PTU  200  can be monitored in pre-regulator  202  and adjustments made in response to those currents. 
     As is further illustrated in  FIG. 3 , an over-voltage control monitor  304  can detect the current through inductor  204  or voltage at inductor  204 . A current signal from monitor  304  can also be input to pre-regulator  202 . Various other current or voltage sensors can be provided in PTU  202  to monitor and control the operation of PTU  202 . 
     As is further shown in  FIG. 3 , a switch control circuit  308  drives the gates of transistors  210  and  212 . As discussed above, switch control circuit  308  drives the gates of transistors  208  and  210  at or near the resonant frequency of the resonant circuit  222 . As such, switch control  308  can include a voltage controlled oscillator circuit or a similar circuit. In some embodiments, switch control  308  can operate a fixed frequency, such as the 6.78 MHz of the A4WP standard for example. Switching at the resonant frequency can result in zero switching losses in the PTU  200 . Current sensor  306  can measure the current that is flowing through transistors  210  and  208  and provide a switching current signal to switch control  308 , which may be used to adjust the switching frequency of transistors  208  and  210 . The switching current signal from current sensor  306  can further be used in pre-regulator  202  in a comparison with the second current signal from current sensor  304 . The comparison, as discussed above, can be used to adjust the threshold voltage. 
       FIG. 4  illustrates an example of PTU  200  that uses average current mode control for controlling the power output of PTU resonator coil  220 . As shown in  FIG. 4 , pre-regulator  202  includes two control loops, an inner current loop for controlling the inductor current and an outer current loop for regulating the current through resonant circuit  222 . As shown in  FIG. 4 , pre-regulator  202  includes a buck regulator with driven transistors  414  and  420  coupled to inductor  416  and capacitor  418 . The inner current loop receives a signal from current sensor  306 , which monitors the current through inductor  416  and capacitor  418 , into current-sense amplifier  402 . Current sense amplifier  402  provides a signal to current-error amplifier  408 . Current-error amplifier provides a signal to a pulse wave modulator comparator  410 , which also receives a signal from a ramp generator (not shown). The precision current amplifier  402  amplifies the voltage difference across resistor Rs of current sense  306 , which is sensed by the inverting input of the current error amplifier  408 . Current error amplifier  408  outputs the difference between the output of the current amplifier  402  and the output of a voltage error amplifier  406 . The output signal from current error amplifier  408  may be coupled to a current frequency compensator. At the start of every clock cycle, driver  412  enables transistor  414  and initiates a pulse-wave modulation on-cycle. Comparator  410  compares the output voltage from the current error amplifier  408  with the ramp voltage and, when the ramp voltage exceeds the voltage output of current error amplifier  408 , signals drive  412  to turn transistor  414  off and turn transistor  420  on, ending the on cycle. 
     The outer current loop includes a differential amplifier  404 , which receives input signals from current sense  302 . The output signal from differential amplifier  404  is coupled to the input of voltage error amplifier  406 , which provides the second input to current error amplifier  408 . voltage error amplifier  406  compares the output signal from differential amplifier  404  with a threshold and, in turn, provides a threshold to current error amplifier  408  for comparison with the output signal from current amplifier  402 . 
     Consequently, the output voltage supplied to inductor  204  is adjusted by the currents sensed in the resonant circuit  222 , the current flowing through inductor  204 , and the current flowing through transistors  210  and  208 . As shown in  FIG. 4 , in some embodiments multiple components of the system can be implemented on a control chip  400 . In some embodiments, control chip  400  can be a high efficiency PWM controller such as that provided by Maxim Integrated LED Driver MAX16818, for example. 
     Other sensors may also be utilized. For example,  FIG. 4  illustrates a sensor  426  monitoring the current between inductor  416  and inductor  204 . Further, monitoring  304 , which is not shown in  FIG. 4 , may also be used. 
     As is further illustrated in  FIG. 4 , switch control  308  can include an oscillator  422  and gate drivers  424 . Oscillator  422  provides an alternating voltage at or near the resonant frequency of resonance circuit  222  while gate drivers  424  drive the gates of transistors  208  and  210  accordingly. 
       FIG. 5  illustrates a complete circuit diagram that implements PTU  202  as described in above with  FIG. 2  through  FIG. 4 .  FIG. 5  illustrates in detail the configuration PTU  200 . Component values and chip designations provided on  FIG. 5  are examples only and are not intended to be limiting in any way. 
     The embodiment of PTU  200  illustrated in  FIG. 5  includes a control block  502 . Control block  502  includes driver chip  400 , transistors  414  and  420 , inductor  416 , and capacitor  418 . Control block  502  drives resonance block  504 , which includes FETs  208  and  210 , inductors  216 , and resonant circuit  222 . As shown in  FIG. 5 , sensor  302  includes an inductor pickup and rectifier that receives a current signal from resonance circuit  222 . As is further shown, over voltage monitor  304  monitors the voltage at the center tap of inductor  216 . Current sense  306  monitors the current through inductor  416 . A sensor  426 , as shown in  FIG. 4 , also monitors the current between inductor  416  and inductor  204 . 
     Pre-regulator  202  includes, in addition to control block  502 , a regulator/filter  508  that filters and regulates the input voltage, regulator  510  that provides regulated power to PTU  200 . Additionally, a microprocessor can be connected to a connector  506  which serves as the connector to a processor. A Processor receives signals from sensor  426 , monitor  304 , sensor  306 , and other sensors and provides control signals to control block  502  through connector block  506 . 
     As is further shown in  FIG. 5 , oscillator  422  of switch control  308  can be a fixed oscillator, although an oscillator with a controllable frequency may also be used. 
     The above detailed description is provided to illustrate specific embodiments of the present invention and is not intended to be limiting. Numerous variations and modifications within the scope of the present invention are possible. The present invention is set forth in the following claims.