The present disclosure relates to front-end circuits for wireless power receivers, integrated circuits including such front-end circuits, near field communication devices, and mobile communication devices including such front-end circuits. It further relates to methods of receiving power wirelessly.
Typical wireless power receivers include an antenna which may be in the form of a coil. In the presence of an applied varying magnetic field, the induced magnetic field in the loop generates an AC current and an AC voltage. By rectifying and smoothing the AC voltage, the receiver may harvest power from the magnetic field. The power may be stored for instance in a capacitor, and typically after a DC to DC conversion or being supplied to a voltage regulator, may be used in the device or apparatus with which the receiver is associated or into which it is integrated. Example devices may be mobile devices such as smart phones tablets and the like. Other applications may include NFC (Near Field Communication) devices, in which the received power may be used to operate a microcontroller unit or other functionality, and the antenna is used at other times to transmit a signal incorporating information or data, by modifying the magnetic field.
In the event of a rapid change to the strength of the applied magnetic field, and in particular in the event that the applied magnetic field is a very strong, the voltage and current generated in the antenna may be more than is required or desired.
According to a first aspect of the present disclosure, there is provided a front-end circuit for a wireless power receiver, the circuit comprising: input terminals for connection to an antenna; a rectifier configured to rectify an AC signal having a peak input voltage received at the input terminals and to provide an output having an output voltage; an over-voltage detector configured to at least one of detect the output voltage exceeding a threshold voltage an overvoltage and detect the peak input voltage exceeding the threshold voltage; and an over-voltage controller configured to provide an electrical short-circuit across the input terminals in response to the respective output voltage or peak input voltage exceeding the threshold voltage. Providing a short-circuit across the input terminals may reduce one or other of the power dissipated, and efficiency losses, associated with other methods of providing overvoltage protection or overvoltage clamping.
In one or more embodiments, the rectifier comprises two rectifying elements configured as a half-bridge rectifier. In other embodiments, the rectifier comprises four rectifying elements configured as a full-bridge rectifier. A full bridge rectifier may generally be more efficient compared with a half-bridge rectifier.
In one or more embodiments, the front-end circuit further comprises a synchronous rectification controller, and at least two of the rectifying elements are switches adapted to be controlled by the synchronous rectification controller to provide synchronous rectification. Use of switches, such as transistors, to provide synchronous rectification may typically result in lower loss than use of diodes to provide passive rectification. In one or more embodiments the over-voltage controller is configured to, in response the output voltage exceeding the threshold voltage, control two of the switches to be in a closed state to provide the electrical short-circuit. In one or more other embodiments the over-voltage controller is configured to, in response the output voltage exceeding the threshold voltage, control one of the switches to be in a closed state to provide the electrical short-circuit. In such embodiments the short circuit might occur during only one of each pair of half-cycles which generally constitute an AC cycle. In such embodiments, the reduction of power transferred is smaller than the reduction or cessation of power transfer which is associated with shorting the inputs terminals.
In one or more embodiments, the over-voltage detector is further adapted to a detect the output voltage exceeding a second threshold voltage, and the controller is further configured to, subsequent to providing the electrical short-circuit, break the short-circuit in response to the output voltage not exceeding the second threshold voltage. Breaking the short-circuit—which may generally be achieved by opening one or more of the switches used to form the short-circuit and thus may also be referred to as opening the short-circuit, or disabling the voltage clamping—may enable effective transfer of power to recommence, thereby preventing an under-voltage situation. An apparatus or device which is associated with the front-end circuit might thereby be enabled to continue operation, without having to shut-down in response to an overvoltage situation resulting in an under-voltage situation.
In one more embodiments, the front-end circuit further comprises the antenna wherein the antenna is a loop antenna configured to generate the AC signal from a varying magnetic field. The front-end circuit may further comprise a decoupling capacitor connected between the output and a ground, for smoothing the output voltage. Such a decoupling capacitor may alternatively be known as a smoothing capacitor.
According to another aspect, there is provided an integrated circuit, for a wireless power transfer receiver and comprising a front-end circuit as described above, and at least one of a regulated voltage output, an unregulated voltage output, and a communication interface, wherein the front-end circuit is configured to provide power to at least one of the other functional blocks of the integrated circuit.
According to a further aspect, there is provided a near field communication (NFC) device comprising a front-end circuit as described above. The NFC device may be adapted to, in a transmit mode, modify an impedance at the input terminals to change a magnetic field at the antenna.
According to a yet further aspect, there is provided a mobile device. The mobile device comprises at least one of an integrated circuit and a near field communication device as described above. The mobile device may further comprise a memory block, wherein the front-end circuit is configured to provide power to at least the memory block.
According to another aspect, there is provided controller configured to control a front end circuit as described above, and comprising: at least one of an output voltage input for receiving a signal representative of the output voltage, and a peak input voltage input for receiving a signal representative of the peak input voltage; an over-voltage detector unit configured to use the respective signal representative of the output voltage and the signal representative of the peak input voltage, to at least one of detect the output voltage exceeding a threshold voltage an overvoltage and detect the peak input voltage exceeding the threshold voltage; and an over-voltage controller configured to provide the electrical short-circuit across the input terminals in response to the respective output voltage or peak input voltage exceeding the threshold voltage.
According to a different aspect, there is provided a method of providing over-voltage protection to a resonant wireless power transfer receiver, the method comprising: rectifying an AC signal received at input terminals to provide an output having an output voltage; one of detecting the output voltage exceeding a threshold voltage and detecting the voltage across the input terminals exceeding a threshold voltage; and providing an electrical short-circuit across the input terminals in response to the respective output voltage or the voltage across the input terminals exceeding the threshold voltage.
The method may include rectifying an AC signal received at input terminals to provide an output having an output voltage comprises actively controlling at least two switches in a rectifier circuit to provide synchronous rectification, and providing an electrical short-circuit across the input terminals comprises controlling two of the switches to be in a closed state.
These and other aspects of the invention will be apparent from, and elucidated with reference to, the embodiments described hereinafter.
Embodiments will be described, by way of example only, with reference to the drawings, in which
It should be noted that the Figures are diagrammatic and not drawn to scale. Relative dimensions and proportions of parts of these Figures have been shown exaggerated or reduced in size, for the sake of clarity and convenience in the drawings. The same reference signs are generally used to refer to corresponding or similar features in modified and different embodiments
As long as the power consumed from the rectifier output is equivalent to the power being received from the wireless power receiver antenna/coil, the output-voltage is stable and can be controlled within the allowed operating voltage range of the receiver and further connected circuits. However. a sudden change of the load connected to the rectifier output will lead to an increase of the rectifier output voltage. Depending on the time required and/or the general ability to reduce the wireless power transmitter's energy, the rectifier voltage might exceed allowed and safe levels and could damage the rectifier itself and/or connected circuits. Therefore, the rectifier output voltage should be kept below a maximum threshold. This threshold might be dependent on any of technology, system or regulatory constraints.
One option or approach is to add a switchable load 310 or a controllable load 320 to the rectifier output. Such a load is generally referred to as a bleeder load. A switchable load may comprise a resistive element 330 switchedly connectable between the output voltage and ground by a switch 335, as shown. A controllable load 320 may be implemented as a variable current sink 325 as shown. Both (as shown), or just one or the other may be included. The load is enabled to drain power from the rectifier output and level the rectifier output voltage. Due to the antenna/system impedance, the maximum current that can be drawn from the wireless power receiver antenna is limited, so the maximum current depends on the basic system implementation.
In this approach, the power dissipated equals the maximum current that can be delivered from the receiver antenna multiplied by the output voltage. Furthermore, the typically connected decoupling capacitors are discharged resulting in an additional power loss:
Pdrain=Vrect*Idrain
where Idrain is the discharge current. Furthermore, in the case that the wireless power source is not a controlled wireless power transmitter but a different source that emits power in the same frequency range the receiver typically works in, the only guaranteed power limit would be the receiver antenna coil impedance and the antenna's natural maximum current delivery capability (I coilmax). In this case, the maxim power dissipated would equal
Pdrain=Rload*Icoilmax2
for a resistive load path with Resistance Rload, or
Pdrain=Icoilmax*Vrect,
for a controlled current sink. The power dissipation can be significant, as the rectifier output voltage has to be kept in a range such that the wireless power receiver is still operation, and thus may be undesirable.
Another approach, which may be used in conjunction with or independently from the additional load approach, is to connect through a switch 340 to additional connected circuits so that the rectifier can be disconnected from the decoupling/low-pass capacitors in an over-voltage event. An advantage of this approach is that the capacitors are not actively discharged by the controlled discharge path. However, the switch connecting the rectifier output and any additional circuit introduces at least some additional losses during regular operation.
Due to the losses involved, both of these approaches reduce the performance of the device.
According to one of more embodiments in the present disclosure a front-end circuit comprises: input terminals for connection to an antenna; a rectifier configured to rectify an AC signal having a peak input voltage received at the input terminals and to provide an output having an output voltage; an over-voltage detector configured to at least one of detect the output voltage exceeding a threshold voltage an overvoltage and detect the peak input voltage exceeding the threshold voltage; and an over-voltage controller configured to provide an electrical short-circuit across the input terminals in response to the respective output voltage or peak input voltage exceeding the threshold voltage. The front-end circuit may be for a resonant or inductive power converter.
Pdrain=Rdson*Icoilmax2.
Operation of a front-end circuit in accordance with one or more embodiments will now be described with reference to
Once the output voltage 720 falls below a second threshold voltage VOVP OFF 740, the controller reopens the switches to break the short-circuit across the input terminals. Of course, the skilled person will appreciate that in embodiments such as that shown in
In consequence, the rectifier recommences charging the decoupling capacitor C3, and the output voltage starts to rise, as shown at the start of interval 704. The skilled person will appreciate that were the strong magnetic field to remain, the output voltage would rise again to the first threshold value 730, resulting in a repetition of the short-circuiting process. As shown in
In one or more other embodiments, an alternative method they may be used to disable clamping again, that is to say, to break the short-circuit, without measuring the rectifier output voltage and comparing it with the second threshold voltage 740 as described above. In such embodiments, in particular those in which the switches short-circuit the antenna to ground, the current going through the transistors while they short the antenna to ground is monitored. Provided that the transmitter is notified that clamping is enabled—that is to say, the receiver antenna is short-circuited—and reduces its power output, the receiver may wait for a decrease of peak current to disable the shorts again. In particular, to the extent that shorting the antenna does not detune it, the antenna will continue to deliver power AC, and generating AC current through the shorting transistors. Of course, in this case a significant voltage will not be built up.
At 930 the method detects whether the output voltage exceeds a threshold voltage VOPN ON. T
In the event that the output voltage exceeds the threshold voltage, the method continues by, at 940, setting the OVP flag to high, and providing an electrical short-circuit across the input terminals in response to the output voltage exceeding the threshold voltage, shown at 960. The method then returns to 930, to recheck whether the output voltage exceeds the threshold.
In the event that the output voltage does not the threshold voltage, in this embodiment the method then continues by, at 970, detecting whether the output voltage exceeds a second threshold voltage VOPN OFF. If it is detected that the output voltage does not exceed the second threshold voltage, the short-circuit is broken, thereby disabling the voltage clamping, and un-grounding the AC pins, at 980. The method then reverts to step 910.
From reading the present disclosure, other variations and modifications will be apparent to the skilled person. Such variations and modifications may involve equivalent and other features which are already known in the art of wireless power receivers, and which may be used instead of, or in addition to, features already described herein. In particular, the skilled person that the switches need not be implemented by a single transistors as shown, but for instance could be implemented as a pair of transistors in parallel, or other switchable electronic component which has, in forward conduction i.e. closed state, a lower loss than that attributable to a diode
Although the appended claims are directed to particular combinations of features, it should be understood that the scope of the disclosure of the present invention also includes any novel feature or any novel combination of features disclosed herein either explicitly or implicitly or any generalisation thereof, whether or not it relates to the same invention as presently claimed in any claim and whether or not it mitigates any or all of the same technical problems as does the present invention.
Features which are described in the context of separate embodiments may also be provided in combination in a single embodiment. Conversely, various features which are, for brevity, described in the context of a single embodiment, may also be provided separately or in any suitable sub-combination. The applicant hereby gives notice that new claims may be formulated to such features and/or combinations of such features during the prosecution of the present application or of any further application derived therefrom.
For the sake of completeness it is also stated that the term “comprising” does not exclude other elements or steps, the term “a” or “an” does not exclude a plurality, and reference signs in the claims shall not be construed as limiting the scope of the claims.
100, 200, 300, 400 front-end circuit
110 rectifier
210 rectifier
280 controller
310 switchable load
320 controllable load
325 variable current sink
330 resistive element
335 switch
340 switch
405 antenna
580 controller
620 output voltage
630 threshold voltage VOVP ON
601, 602, 603, 604, 605 interval
680 controller
681 controller
800 mobile device
805 antenna
815 front-end circuit
816, 817 inputs
825 overvoltage detector
840 communication interface
830 regulated voltage output
835 unregulated voltage output
860 integrated circuit
880 controller
AC1 and AC2 input terminals
C1 shunt capacitor
C2 series capacitor
C3 decoupling capacitor
D1-D4 diodes
S6 switch
S7 switch
T1-T4 switches
Number | Date | Country | Kind |
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14189224.0 | Oct 2014 | EP | regional |