Method and apparatus for protecting a wireless charging receiver

Abstract

Various embodiments of the present disclosure are directed to methods and apparatus for protecting a wireless charging receiver. The wireless charging receiver includes a controller configured to: determine that a first overvoltage threshold is met, and based on this, enable a first switch to couple an output of a rectifier to electrical ground through a first resistor; determine that a second overvoltage threshold is met, and based on this, enable a receive resonant circuit switch to short the receive resonant circuit; determine that a hysteresis threshold is met, and based on this, disable the receive resonant circuit switch to open the receive resonant circuit; and determine that a hysteresis cycle threshold is met and the receive resonant circuit switch is disabled, and based on this, enable a second switch to couple a second resistor to electrical ground; and communicate with a wireless charging transmitter to reduce the power level on the wireless charging receiver side.

Description

Technical Field

[0001] The present invention generally relates to methods and apparatus for protecting wireless charging receivers. Background Art

[0002] Powering electronic devices has been a challenge for system designers. Early electronic devices were tethered to a power source via a power cord. Batteries provide freedom of mobility, but the batteries still need to be replaced or recharged. Recharging the battery requires plugging the battery or electronic device into a power source using a power cord.

[0003] Wireless charging systems eliminate power cords by transferring power in free space, where the power can be used to charge rechargeable batteries or directly power electronic devices. Wireless charging systems eliminate the difficulties associated with plugging power cords into electronic devices, such as fumbling with the orientation of the plug, ensuring the correct power cord is used, wear and tear on the physical connectors and connections, etc. Therefore, wireless charging systems are attractive to end users. Summary of the invention

[0004] According to an embodiment, a wireless charging receiver is provided. The wireless charging receiver includes: a voltage rectifier operably coupled to a receiving resonant circuit, the voltage rectifier being configured to output a direct current (DC) voltage according to received energy received by the receiving resonant circuit from a wireless charging transmitter; a first resistor operably coupled to the output of the voltage rectifier; a second resistor operably coupled to the output of the voltage rectifier; a receiving resonant circuit switch operably coupled to the receiving resonant circuit; a first switch operably coupled between the first resistor and electrical ground; a second switch operably coupled between the second resistor and electrical ground; and a controller operably coupled to the receiving resonant circuit switch, the first switch, and the second switch, the controller being programmed to: determine that a first overvoltage threshold is met and based on this, enable the first switch to couple the first resistor to electrical ground; determine that a second overvoltage threshold is met and based on this, enable the receiving resonant circuit switch to short the receiving resonant circuit; determine that a hysteresis threshold is met and based on this, disable the receiving resonant circuit switch to open the receiving resonant circuit; and determine that a hysteresis cycle threshold is met and based on this, enable the second switch to couple the second resistor to electrical ground.

[0005] According to an embodiment, a method implemented by a wireless charging receiver is provided. The method includes: detecting that a first overvoltage threshold is met, and based on this, enabling a first switch to couple a first resistor to electrical ground, the first resistor being coupled to an output of a rectifier of the wireless charging receiver; detecting that a second overvoltage threshold is met, and based on this, enabling a receiving resonant circuit switch to short-circuit a receiving resonant circuit of the wireless charging receiver; detecting that a hysteresis threshold is met, and based on this, disabling the receiving resonant circuit switch to open the receiving resonant circuit; and detecting that a hysteresis cycle threshold is met and the receiving resonant circuit switch is disabled, and based on this, enabling a second switch to couple a second resistor to electrical ground.

[0006] According to an embodiment, a wireless charging receiver is provided. The wireless charging receiver includes: a voltage rectifier operably coupled to a receiving resonant circuit, the voltage rectifier being configured to output a direct current (DC) voltage according to received energy received by the receiving resonant circuit from a wireless charging transmitter; a first resistor operably coupled to the output of the voltage rectifier; a second resistor operably coupled to the output of the voltage rectifier; a receiving resonant circuit switch operably coupled to the receiving resonant circuit; a first switch operably coupled between the first resistor and electrical ground; a second switch operably coupled between the second resistor and electrical ground; a non-transitory memory storage device including instructions; and a communication device communicating with the memory storage device. One or more processors, wherein the one or more processors execute instructions to: determine that a first overvoltage threshold is met, and based on this, enable a first switch to couple a first resistor to electrical ground, the first resistor being coupled to an output of a rectifier of a wireless charging receiver; determine that a second overvoltage threshold is met, and based on this, enable a receive resonant circuit switch to short-circuit a receive resonant circuit of the wireless charging receiver; determine that a hysteresis threshold is met, and based on this, disable the receive resonant circuit switch to open the receive resonant circuit; and determine that a hysteresis cycle threshold is met and the receive resonant circuit switch is disabled, and based on this, enable a second switch to couple a second resistor to electrical ground.

[0007] An advantage of an embodiment is that the overvoltage condition is mitigated, preventing potential damage to the wireless charging receiver, while enabling communication between the wireless charging receiver and the wireless charging transmitter so that the overvoltage condition can be remedied without interrupting power transfer. BRIEF DESCRIPTION OF THE DRAWINGS

[0008] For a more complete understanding of the present invention and its advantages, reference is now made to the following description taken in conjunction with the accompanying drawings, in which:

[0009] Figure 1 A conventional wireless charging system is illustrated;

[0010] Figure 2Aillustrates a conventional wireless charging system highlighting a well-aligned wireless charging device;

[0011] Figure 2B illustrates a conventional wireless charging system highlighting a situation where a wireless charging device is poorly aligned;

[0012] Figure 3 A prior art wireless charging receiver is shown;

[0013] Figure 4 A graph of VRECT over time is shown, highlighting Figure 3 The behavior of prior art wireless charging receivers under OVP conditions that result in poor charging performance identified by the inventors of the present application;

[0014] Figure 5A A first example wireless charging receiver according to embodiments presented herein is illustrated;

[0015] Figure 5B illustrates a second example wireless charging receiver according to embodiments presented herein;

[0016] Fig. 6A FIG. 1 illustrates a graph of VRECT over time according to an embodiment proposed herein, which highlights Figure 5A The behavior of wireless charging receiver under OVP condition;

[0017] Figure 6B FIG. 1 illustrates a graph of VRECT over time according to an embodiment proposed herein, which highlights Figure 5A The wireless charging receiver behaves in an OVP condition, but the wireless charging transmitter does not respond within the time limit; and

[0018] Figure 7 A flow diagram illustrating example operations occurring in a wireless charging receiver according to embodiments presented herein.

[0019] Corresponding numerals and symbols in the different figures generally refer to corresponding parts unless otherwise indicated.The figures are drawn to clearly illustrate the relevant aspects of the embodiments and are not necessarily drawn to scale. DETAILED DESCRIPTION

[0020] In the following description, one or more specific details are illustrated to provide an understanding of the examples of the embodiments. The embodiments can be obtained without one or more of the specific details or with other methods, components, materials, etc. In other cases, known structures, materials, or operations are not illustrated or described in detail so that some aspects of the embodiments are not obscured.

[0021] References to "an embodiment" or "an embodiment" in the framework of this description are intended to indicate that a particular configuration, structure, or characteristic described with respect to that embodiment is included in at least one embodiment. Thus, phrases such as "in an embodiment" or "in an embodiment" that may be present in one or more places in this description do not necessarily refer to the same embodiment. Moreover, particular configurations, structures, or characteristics may be combined in any suitable manner in one or more embodiments.

[0022] The references used herein are provided for convenience only and therefore do not limit the scope of protection or the scope of the embodiments.

[0023] In wireless charging, electromagnetic coupling is used to achieve wireless energy transfer. When the wireless charging transmitter outputs power through the transmitting coil into the wireless field received or coupled by the receiving coil of the wireless charging receiver, energy is transferred from the wireless charging transmitter to the wireless charging receiver by using electric fields, magnetic fields, electromagnetic fields, etc. The transmission and reception process results in wireless power transfer from the wireless charging transmitter to the wireless charging receiver.

[0024] Figure 1 A conventional wireless charging system 100 is illustrated. The wireless charging system 100 includes a wireless charging transmitter 105 and a wireless charging receiver 110. The wireless charging transmitter 105 coupled to a power source 115 provides energy to the wireless charging receiver 110, which in turn provides power to a device 120. The power provided to the device 120 can be used to charge a rechargeable battery in the device 120 or to directly power the device 120. The process of providing energy is called power transfer.

[0025] The wireless charging transmitter 105 includes a transmitting resonant circuit 125. The resonant circuit is characterized by the inductance (L) and capacitance (C) of the resonant circuit (shown in the highlighted areas 127 and 132), and the power transferred between the wireless charging transmitter 105 and the wireless charging receiver 110 is a function of the inductance and capacitance of the resonant circuit of the wireless charging transmitter 105 and the wireless charging receiver 110. The purpose of the capacitance (C) is to improve the efficiency of power transfer, and the inductance L is used to transfer power (the transmitting coil converts the current into magnetic flux, and the receiving coil converts the magnetic flux into electromotive force). The transmitting resonant circuit 125 uses the transmitting coil to transmit an excited wireless field (shown as line 135). The excited wireless field (line 135) is received by the receiving resonant circuit 130 of the wireless charging receiver 110. In addition to transmitting and receiving the excited wireless field, changes in the parameters of the receiving resonant circuit 130 can be used to communicate from the wireless charging receiver 110 to the wireless charging transmitter 105. For example, in the communication between the wireless charging receiver 110 and the wireless charging transmitter 105, the information being transmitted can be used to modulate the amplitude of the wireless field, thereby enabling the transmission or reception of information. For example, in the communication between the wireless charging transmitter 105 and the wireless charging receiver 110, the information being transmitted can be used to modulate the frequency of the wireless field, thereby enabling the transmission or reception of information. As an example, the wireless charging transmitter 105 and the wireless charging receiver 110 communicate to initiate a wireless charging session, set a charging mode, control the amount of energy transmitted by the wireless charging transmitter 105, control the amount of energy received by the wireless charging receiver 110, terminate the wireless charging session, and so on. The communication performed is mainly in the uplink direction, for example, from the wireless charging receiver 110 to the wireless charging transmitter 105. The details of the communication can be found in the Qi standard defined by the Wireless Power Consortium (WPC).

[0026] The wireless charging transmitter 105 and the wireless charging receiver 110 are at a distance 140. Generally, given a fixed energy transmission level, and for a transmit coil design, the amount of energy received by the wireless charging receiver 110 depends on the spacing between the coils of the wireless charging transmitter 105 and the wireless charging receiver 110. As an example, for a coil design that remains constant, when the distance 140 is small, the energy received by the wireless charging receiver 110 is generally large, and when the distance 140 is large, the energy received by the wireless charging receiver 110 is generally small. The increased distance 140 can be compensated by increasing the transmit energy level of the wireless charging transmitter 105.

[0027] In addition to the distance between the wireless charging transmitter and the wireless charging receiver, another physical factor that plays a role in determining the energy received by the receiving coil of the wireless charging receiver is the misalignment of the transmitting coil and the receiving coil. The misalignment of the two coils can be defined as the spatial difference along one axis (or two axes) of the center of the two coils. As an example, if the wireless charging transmitter and the wireless charging receiver are located on a table, where the positions of the wireless charging transmitter and the wireless charging receiver are restricted to different positions on the top of the table, the misalignment of the transmitting coil and the receiving coil can be expressed in only one of the two axes (e.g., up / down or left / right), where the distance between the wireless charging transmitter and the wireless charging receiver is another axis. As another example, if the wireless charging transmitter and the wireless charging receiver can be freely positioned in three dimensions, the misalignment of the transmitting coil and the receiving coil can be expressed in two of the three axes (e.g., up / down and left / right, up / down and in / out, or left / right and in / out), where the distance between the wireless charging transmitter and the wireless charging receiver is the third axis.

[0028] The distance and misalignment may be combined to characterize the alignment of the wireless charging device. As an example, for a particular coil design, if the distance between the wireless charging devices is small and the misalignment is also small, the wireless charging device may be referred to as being well aligned. As another example, for a particular coil design, if the distance between the wireless charging devices is large and the misalignment is also large, the wireless charging device may be referred to as being poorly aligned.

[0029] Figure 2A A conventional wireless charging system 200 is illustrated, which highlights a well-aligned wireless charging device. The wireless charging system 200 includes: a wireless charging transmitter 205, which has a transmit resonant circuit with a transmit coil 207; and a wireless charging receiver 210, which has a receive resonant circuit with a receive coil 212. The wireless charging transmitter 205 and the wireless charging receiver 210 are placed on a table top, so there are only two free axes. The transmit coil 207 and the receive coil 212 are separated by a distance 225. The misalignment of the transmit coil 207 and the receive coil 212 (shown as alignment 230) is very small. Because the transmit coil 207 and the receive coil 212 have a small misalignment (because the alignment 230 is very good) and the separation is also small, the wireless charging device can be considered to be well aligned.

[0030] Figure 2B A conventional wireless charging system 200 is illustrated, which highlights a situation where the wireless charging device is poorly aligned. Figure 2BIn the illustrated case, the transmit coil 207 and the receive coil 212 are separated by a distance 225, and the misalignment (shown as alignment 260) of the transmit coil 207 and the receive coil 212 is large. Because the transmit coil 207 and the receive coil 212 have a large misalignment (because the alignment 260 is poor) and the separation is also large, the wireless charging device can be considered to be poorly aligned.

[0031] Once a wireless charging session begins, the alignment of the wireless charging transmitter and the wireless charging receiver may change, thereby changing the coil coupling (coil coupling is a function of the alignment of the wireless charging transmitter and the wireless charging receiver). Improving the alignment of the wireless charging transmitter and the wireless charging receiver will tend to increase the coil coupling and increase the energy received at the wireless charging receiver. As an example, a user may notice that the wireless charging receiver (e.g., a smartphone with a built-in wireless charging receiver) is poorly placed on the wireless charging transmitter and move the wireless charging receiver so that the wireless charging receiver is closer to the wireless charging transmitter (or better aligned with the wireless charging transmitter, or both are closer and better aligned). The user moving the wireless charging receiver (relative to the wireless charging transmitter) will change the coil coupling and, therefore, will change the energy received at the wireless charging receiver.

[0032] Once the alignment changes, the coil coupling also changes, and the energy received at the wireless charging receiver also changes. As an example, if the alignment changes from poor alignment to good alignment, the coil coupling increases, and the received energy may change from small to large. The increased received energy increases the power available to recharge a rechargeable battery or power an electronic device.

[0033] Typically, the wireless charging transmitter only adjusts its operating point, such as frequency, duty cycle, inverter voltage, etc., based on requests from the wireless charging receiver. Because the energy received at the wireless charging receiver is based on the operating point of the wireless charging transmitter and the load varies, coil coupling (e.g., alignment) may affect the received energy.

[0034] However, the increased received energy may exceed the power limit of a wireless charging receiver (such as wireless charging receiver 110), thereby causing damage to the wireless charging receiver. Therefore, a method and apparatus for protecting a wireless charging receiver is needed.

[0035] Figure 3A prior art wireless charging receiver 300 is illustrated. The wireless charging receiver 300 includes an integrated circuit 305 that controls the operation of the wireless charging receiver 300, including communicating with a wireless charging transmitter, establishing a wireless charging session, controlling the power provided to an electronic device coupled to the wireless charging receiver 300, and the like. The integrated circuit 305 includes a microcontroller 310 that executes a program to control the operation of the wireless charging receiver 300, a frequency shift keying (FSK) demodulation circuit 312 that demodulates FSK communications from the wireless charging transmitter, a receiver (RX) rectifier / transmit (TX) driver circuit 314 that rectifies an alternating current (AC) signal wirelessly received by the wireless charging receiver 300 (from the wireless charging transmitter) or drives a signal transmitted by the wireless charging receiver 300 when operating as a wireless charging transmitter, a sensing and amplitude shift keying (ASK) demodulation circuit 316 that senses and demodulates an ASK modulated signal (when operating as a wireless charging transmitter), an RX low dropout (LDO) circuit 318 that regulates voltage, and a memory (including a read only memory (ROM) 320 for storing code executed by the microcontroller 310, a random access memory (RAM) 322 for storing data, and a non-volatile (NV) memory 324 for storing configuration information).

[0036] The wireless charging receiver 300 further comprises a receiving resonant circuit 335 comprising an actual coil and a capacitor. The coil and the capacitor define the resonant circuit of the wireless charging receiver 300, which is coupled with the coil of the resonant circuit of the wireless charging transmitter.

[0037] The outputs from the wireless charging receiver 300 include an output voltage (VRECT) of the RX rectifier / TX driver circuit 314 and an output voltage (VOUT) for recharging a rechargeable battery or directly powering an electronic device coupled to the wireless charging receiver 300. If VRECT exceeds a specified threshold, an overvoltage (OVP) condition may occur, which may result in interruption of power delivery to the electronic device or damage to the electronic device of the wireless charging receiver 300.

[0038] The change in the received energy at the wireless charging receiver 300 causes the output voltage (VRECT) of the RX rectifier / TX driver circuit to change. Therefore, if the change in the alignment of the wireless charging receiver 300 significantly improves the coil coupling, the received energy and VRECT at the wireless charging receiver 300 also increase significantly.

[0039] The wireless charging receiver 300 monitors VRECT to detect the occurrence of a first OVP and responds. After detecting the occurrence of the first OVP, for example by comparing VRECT to a first OVP threshold, the wireless charging receiver 300 enables an external resistor (REXT1) 340 by enabling (or turning on or closing) a switch 345 (e.g., establishing a current path to ground). The term "external" refers to the outside of the integrated circuit 305, not the outside of the wireless charging receiver 300. The current flowing through REXT1 340 reduces VRECT by dissipating a portion of the power output by the RX rectifier / TX driver circuit 314 of the wireless charging receiver 300.

[0040] However, unless the wireless charging receiver 300 is able to communicate with the wireless charging transmitter about the OVP condition, the wireless charging transmitter will not change its operating point. Because the operating point remains unchanged, the wireless charging transmitter will continue to provide more energy than the wireless charging receiver 300 requires, and (due to the improved coupling) VRECT will continue to increase even if REXT1 340 dissipates some power.

[0041] The wireless charging receiver 300 monitors VRECT to detect and respond to the occurrence of the second OVP. After detecting the occurrence of the second OVP, for example by comparing VRECT to the second OVP threshold, the wireless charging receiver 300 shorts the receiving resonant circuit 335 to ground, for example by enabling (or turning on or closing) the switch 350. Shorting the receiving resonant circuit 335 to ground discharges VRECT. VRECT may decrease until the wireless charging receiver 300 detects that VRECT reaches a low voltage threshold (e.g., UVLO). The wireless charging receiver 300 may then reset and initiate a new wireless charging session.

[0042] Figure 4 A graph 400 of VRECT over time is shown, which highlights Figure 3 4. The behavior of a prior art wireless charging receiver under an OVP condition that results in poor charging performance identified by the inventors of the present application. Trace 405 represents VRECT over time. During a first time interval 407, VRECT remains stable, indicating that the wireless charging session is proceeding as expected. However, during a second time interval 409, VRECT increases dramatically. The dramatic increase in VRECT may indicate that the wireless charging receiver 300 is receiving more energy than during interval 407, which may be due to, for example, a change in the alignment of the wireless charging receiver 300 and the wireless charging transmitter that improves coil coupling.

[0043] At about time 410, the wireless charging receiver 300 determines that a first OVP has occurred (e.g., by comparing VRECT to a first OVP threshold (SOVP) 412). The wireless charging receiver 300 turns on the external resistor REXT1 340 by enabling the switch 345 to establish a current path to ground. REXT1 340 dissipates power (shown as region 415). In general, whenever VRECT is greater than the first OVP threshold (SOVP) 412, the external resistor REXT1 is turned on.

[0044] Although REXT1 340 is dissipating power, VRECT continues to increase (because the wireless charging receiver 300 continues to receive more energy than required). At about time 420, the wireless charging receiver 300 determines that a second OVP has occurred (e.g., by comparing VRECT to a second OVP threshold (HOVP) 422). The wireless charging receiver 300 shorts the receive resonant circuit 335 to ground by enabling the switch 350. After the receive resonant circuit 335 is shorted to ground, VRECT drops rapidly. At about time 425, VRECT drops below a low voltage threshold (UVLO) 427, and the wireless charging receiver 300 resets and initiates a new wireless charging session with the wireless charging transmitter, or the wireless charging transmitter simply stops supplying power due to a communication timeout because the wireless charging receiver 300 did not communicate with the wireless charging transmitter in the time interval between time 420 and time 425.

[0045] After the receiving resonant circuit 335 is shorted, little power is available to recharge the rechargeable battery or power the electronic device coupled to the wireless charging receiver 300. In addition, when the wireless charging receiver 300 is reset, power delivery to the electronic device coupled to the wireless charging receiver 300 is interrupted because the wireless charging transmitter stops supplying power due to unexpected communication during power transfer after resetting the wireless charging receiver 300 or due to lack of communication (i.e., communication timeout) during an extended duration. Therefore, the duration that the receiving resonant circuit 335 is shorted needs to be reduced (from about time 420 to about time 425), and the resetting of the wireless charging receiver 300 needs to be avoided so that power transfer is not interrupted.

[0046] According to an example embodiment, a receive resonant circuit switch with hysteresis operation is provided. Rather than simply shorting the receive resonant circuit to ground with a switch, the receive resonant circuit switch with hysteresis operation shorts the receive resonant circuit to ground or its own terminals until VRECT drops below a hysteresis threshold (HOVP HYST). Once the hysteresis threshold (HOVP HYST) is met, the receive resonant circuit switch is disabled to open the short circuit, allowing the wireless charging receiver to resume normal operation. As the wireless charging receiver resumes normal operation, VRECT will increase (because the wireless charging receiver continues to receive more energy than required) until the second OVP threshold (HOVP) is met again, at which point the receive resonant circuit switch with hysteresis operation is enabled to short the receive resonant circuit to ground or its own terminals. Enabling and disabling the receive resonant circuit switch as VRECT rises and falls between the second OVP threshold (HOVP) and the hysteresis threshold is referred to as a hysteresis cycle, where a single hysteresis cycle includes a single enable-disable cycle of the receive resonant circuit switch with hysteresis operation. In theory, hysteresis operation can continue indefinitely, but due to interference caused by the receiving resonant circuit being shorted to ground, the communication from the wireless charging receiver to the wireless charging transmitter cannot be correctly decoded on the wireless charging transmitter side, so the number of hysteresis cycles should be limited. When the wireless charging receiver operates in hysteresis operation, charging of the rechargeable battery coupled to the wireless charging receiver continues.

[0047] In an embodiment, a receive resonant circuit switch with hysteresis operation has a hysteresis window built into the design. Thus, the hysteresis operation is inherent in the design. Thus, when a hysteresis condition is met, the receive resonant circuit switch may be automatically disabled. In an embodiment, hysteresis operation is emulated with the receive resonant circuit switch by the wireless charging receiver comparing VRECT to a hysteresis condition (e.g., a voltage threshold) and enabling or disabling the receive resonant circuit switch based on the relationship between VRECT and the hysteresis condition and a second OVP threshold (HOVP).

[0048] In an embodiment, the number of hysteresis cycles is configurable. Although charging of a rechargeable battery coupled to a wireless charging receiver continues during the hysteresis cycle, charging may not be efficient because VRECT varies between the hysteresis threshold and the second OVP threshold (HOVP), and thus the power available for charging the rechargeable battery varies. In addition, during hysteresis operation, communication from the wireless charging receiver to the wireless charging transmitter is unstable or unreliable. Therefore, it may not be beneficial to allow the wireless charging receiver to operate in hysteresis operation indefinitely. In an embodiment, the number of hysteresis cycles may be a count threshold, i.e., a specific number of hysteresis cycles that have occurred. In an embodiment, the number of hysteresis cycles may be a time threshold, i.e., a duration approximately corresponding to the number of hysteresis cycles configured. As an example, the number of hysteresis cycles is as small as one, which means that as long as the receive resonant circuit switch is enabled to short the receive resonant circuit to ground or its own terminal, and VRECT drops below the hysteresis threshold, the wireless charging receiver will attempt to resume normal operation by taking the next step of protection (e.g., REXT2 enable), which allows communication with the wireless charging transmitter. As an example, the number of hysteresis cycles is large enough to allow transient changes in coil coupling to settle before the wireless charging receiver enables REXT2 and attempts to resume normal operation. The number of hysteresis cycles should be large enough to allow several seconds of hysteresis cycling before the wireless charging receiver attempts to resume normal operation. For example, the number of hysteresis cycles is about 1 to 20, depending on the load provided to the device. As an example, low load means more hysteresis cycles, while high load means fewer hysteresis cycles.

[0049] According to an example embodiment, after a configured number of hysteresis cycles occur, the second external resistor REXT2 is turned on to establish a second current path between VRECT and ground (where the external resistor REXT1 provides a first current path between VRECT and ground). In an embodiment, the power dissipated by the second external resistor REXT2 sufficiently reduces VRECT by potentially preventing VRECT from meeting a second OVP threshold (HOVP), thereby preventing the wireless charging receiver from having to short the receive resonant circuit to ground or its own terminals, and allowing the wireless charging receiver to communicate with the wireless charging transmitter to request the wireless charging transmitter to change the operating point to reduce the energy sent to the wireless charging receiver. The reduced energy sent by the wireless charging transmitter reduces the energy received by the wireless charging receiver, thereby potentially preventing the overvoltage condition from continuing.

[0050] In an embodiment, the value of the second external resistor REXT2 is small enough to dissipate enough power to sufficiently reduce VRECT to give the wireless charging receiver enough time to communicate with the wireless charging transmitter to request the wireless charging transmitter to change its operating point. In an embodiment, the second external resistor REXT2 is smaller in value than the external resistor REXT1.

[0051] Figure 5A A first example wireless charging receiver 500 according to embodiments presented herein is illustrated. The wireless charging receiver 500 includes an integrated circuit 502 including circuitry for controlling the operation of the wireless charging receiver 500, wherein the circuitry is labeled with reference numerals. The reference numerals used in FIG. 5 are the same as those used in FIG. Figure 3 Where similar reference numerals are used, the associated circuits operate similarly.

[0052] The wireless charging receiver 500 includes an external resistor REXT1 505 that is controllably coupled to ground through a switch 510 when VRECT meets a first OVP threshold (SOVP). The external resistor REXT1 505 is external to the integrated circuit 502, but not external to the wireless charging receiver 500. The external resistor REXT1 505 should be large to dissipate and maintain a large current for an extended period of time to increase the amount of time before VRECT meets a second OVP threshold (HOVP). The wireless charging receiver 500 also includes a receive resonant circuit switch 515 with hysteresis operation that shorts the resonant circuit 335 to ground when enabled. For example, when VRECT meets the second OVP threshold (HOVP), the receive resonant circuit switch 515 with hysteresis operation is enabled, and when VRECT meets the hysteresis threshold, for example, the receive resonant circuit switch is disabled. When the receive resonant circuit switch with hysteresis operation 515 is enabled, VRECT decreases, and when the receive resonant circuit switch with hysteresis operation 515 is disabled, VRECT increases. If the receive resonant circuit switch with hysteresis operation 515 has a hysteresis window built into the design, the receive resonant circuit switch with hysteresis operation 515 can be automatically enabled or disabled based on VRECT. If the receive resonant circuit switch with hysteresis operation 515 does not have a hysteresis window built into the design, the microcontroller 310 can simulate hysteresis operation by comparing VRECT to a second OVP threshold (HOVP) to determine when to enable the receive resonant circuit switch with hysteresis operation 515, and comparing VRECT to the hysteresis threshold to determine when to disable the receive resonant circuit switch with hysteresis operation 515. The enable-disable cycle of the receive resonant circuit switch with hysteresis operation 515 is called a hysteresis cycle.

[0053] The wireless charging receiver 500 also includes a second external resistor REXT2 520, which is controllably coupled to ground through a switch 525 when the wireless charging receiver 500 undergoes a configured number of hysteresis cycles. The second external resistor REXT2 520 is external to the integrated circuit 502, but not external to the wireless charging receiver 500. When the second external resistor REXT2 520 is coupled to ground, a current path is established, and the second external resistor REXT2 520 dissipates power and reduces VRECT. The reduction in VRECT is sufficient to prevent subsequent hysteresis cycles and allows the wireless charging receiver 500 to communicate with the wireless charging transmitter to request the wireless charging transmitter to change its operating point to, for example, reduce the energy received by the wireless charging receiver. VRECT may continue to rise even when both the external resistor REXT1 505 and the second external resistor REXT2 are dissipating power. However, the rise in VRECT is typically gradual and smooth, and therefore does not prevent communication between the wireless charging receiver 500 and the wireless charging transmitter from occurring. If for any reason VRECT rises and meets the second OVP threshold (HOVP), the receive resonant circuit switch 515 with hysteresis operation will be permanently enabled even when REXT2 and REXT1 are dissipating power until VRECT drops below UVLO. In this case, the hysteresis function of the receive resonant circuit switch 515 with hysteresis operation is disabled.

[0054] In an embodiment, switches 510 , 515 , and 525 may be implemented using field effect transistors (FETs), such as junction FETs (JFETs), N-channel JFETs, P-channel JFETs, metal oxide semiconductor FETs (MOSFETs), enhancement mode MOSFETs, depletion mode MOSFETs, and the like.

[0055] Figure 5B A second wireless charging receiver 550 is illustrated in accordance with embodiments presented herein. The wireless charging receiver 550 is similar to the wireless charging receiver 500, with similar reference numerals referring to similar circuits. The wireless charging receiver 550 includes a receive resonant circuit switch 555 with hysteresis operation that is coupled across the terminals of the receive resonant circuit 335. Thus, when enabled, the receive resonant circuit switch 555 with hysteresis operation shorts the terminals of the receive resonant circuit 335, rather than shorting the terminals of the receive resonant circuit 335. Figure 5A In the case of the receive resonant circuit switch 515 with hysteresis operation, the receive resonant circuit 335 is short-circuited to electrical ground. However, short-circuiting the terminals of the receive resonant circuit 335 also causes VRECT to drop, just like short-circuiting the receive resonant circuit 335 to electrical ground.

[0056] Fig. 6A A graph 600 is shown of VRECT over time, highlighting the Figure 5A The behavior of the wireless charging receiver 500 under OVP conditions. Fig. 6A (as well as Figure 6B ) focuses on Figure 5A Wireless charging receiver 500, but Fig. 6A and 6B The behavior shown also applies to Figure 5B Therefore, focusing on the wireless charging receiver 500 should not be construed as limiting the scope of the present invention.

[0057] Trace 605 represents VRECT over time. During a first time interval 607, VRECT increases at a relatively steady rate. At approximately time 610, the wireless charging receiver 500 determines that a first OVP has occurred (e.g., by comparing VRECT to a first OVP threshold (SOVP) 612). The wireless charging receiver 500 turns on the external resistor REXT1 505 by enabling switch 510 to establish a current path to ground. REXT1 505 dissipates power (shown as region 615).

[0058] During the second time interval 620, VRECT continues to increase at a relatively steady rate (after an initial rate decrease corresponding to the turning on of the external resistor REXT1 505). At approximately time 625, the wireless charging receiver 500 determines that a second OVP has occurred (e.g., by comparing VRECT to a second OVP threshold (HOVP) 627). The wireless charging receiver 500 enables the receive resonant circuit switch 515 with hysteresis operation to short the receive resonant circuit 335 to ground or across its terminals. The enabling of the receive resonant circuit switch 515 with hysteresis operation causes VRECT to drop. At approximately time 630, the wireless charging receiver 500 determines that the hysteresis threshold 632 is met, and disables the receive resonant circuit switch 515 with hysteresis operation to decouple the receive resonant circuit 335 from ground or from its own terminals.

[0059] After the wireless charging receiver 500 completes the specified number of hysteresis cycles (shown as interval 635), the wireless charging receiver 500 turns on the second external resistor REXT2 520 by enabling the switch 525 to establish a current path to ground. REXT2 520 dissipates power (shown as region 640). The power dissipated by REXT2 520 at least temporarily reduces VRECT and stops the hysteresis cycle (shown as interval 645), which allows the wireless charging receiver 500 to communicate with the wireless charging transmitter. For example, the wireless charging receiver 500 may request the wireless charging transmitter to change its operating point to reduce the energy received by the wireless charging receiver 500. The wireless charging receiver 500 may transmit an indication of its current received energy, and the wireless charging transmitter may adjust the transmission energy level or operating point, for example, based on the indication. After the wireless charging transmitter changes its operating point, the energy received by the wireless charging receiver 500 decreases, resulting in a decrease in VRECT (shown as interval 650). In an embodiment, the wireless charging receiver 500 may also request the wireless charging transmitter to stop power transfer altogether in the time interval 645 .

[0060] In an embodiment, the second external resistor REXT2 520 is turned on for a limited amount of time to protect the second external resistor REXT2 520 and the associated switch 525 from damage. During the time that the second external resistor REXT2 520 is turned on, the wireless charging receiver 520 communicates with the wireless charging transmitter to change the operating point of the wireless charging transmitter. In an embodiment, the amount of time that the second external resistor REXT2 520 is turned on is configurable. For example, the amount of time can be based on the load of the device coupled to the wireless charging receiver 500.

[0061] In an embodiment, power transfer continues even during hysteresis operation (i.e., interval 635 of FIG. 6 ), thereby allowing wireless charging to continue. In an embodiment, power transfer also continues after the second external resistor REXT2 520 is turned on and begins to dissipate power. In an embodiment, the wireless charging session does not need to be interrupted and VRECT does not need to drop below a low voltage threshold (e.g., 100V) before a new wireless charging session is initiated. Figure 4 UVLO 427). Because the wireless charging session does not need to be interrupted and a new wireless charging session does not need to be initiated, wireless charging efficiency can be improved and wireless charging time can be reduced. In this case, the device may not notify the user that wireless charging has been interrupted.

[0062] In an embodiment, if VRECT drops to a sufficient level, the wireless charging receiver 500 turns off the second external resistor REXT2 520 so that the second external resistor REXT2 520 no longer dissipates power. The second external resistor REXT2 520 is turned on only for a limited time required for communicating with the wireless charging transmitter and for the wireless charging transmitter to adjust the operating point to avoid damaging the wireless charging receiver 500. During the time that the second external resistor REXT2 520 is turned on, the wireless charging transmitter responds to the communication and changes its operating point.

[0063] If the wireless charging transmitter does not respond and adjust the operating point, the second external resistor REXT2 520 is turned off. VRECT meets the second OVP threshold (HOVP) and the receiving resonant circuit 335 is permanently shorted until VRECT drops below the low voltage threshold (UVLO) and the wireless charging receiver 500 resets.

[0064] Figure 6B A graph 650 is shown of VRECT over time, highlighting the Figure 5A The wireless charging receiver 500 behaves in an OVP condition, but the wireless charging transmitter does not respond within the time limit corresponding to when the second external resistor REXT2520 is turned on. Figure 6B As shown, VRECT (trace 665) until the end of interval 645 is Fig. 6A The VRECT shown (trace 605) is the same, and some portions are omitted to simplify the drawing. However, at the end of interval 645, the wireless charging transmitter has not responded to the communication (e.g., a request to reduce its power transmission) from the wireless charging receiver 500. Therefore, at about time 670, the wireless charging receiver 500 turns off the second external resistor REXT2 520, and VRECT resumes increasing.

[0065] At about time 675, the wireless charging receiver 500 determines that a second OVP has occurred (e.g., by comparing VRECT to a second OVP threshold (HOVP) 627). The wireless charging receiver 500 shorts the receive resonant circuit 335 (to ground or across its own terminals, such as by enabling the receive resonant circuit switch 515 with hysteresis operation). Figure 5B ), the receive resonant circuit switch 515 has a hysteresis operation that is disabled to short-circuit the receive resonant circuit 335. When the receive resonant circuit 335 is short-circuited to ground ( Figure 5A ) or short-circuit across its own terminals ( Figure 5B), VRECT drops rapidly. At about time 677, VRECT drops below the first OVP threshold (SOVP), and the wireless charging receiver 500 disables the external resistor REXT1 505. At about time 680, VRECT drops below the low voltage threshold (UVLO) 685, and the wireless charging receiver 500 resets and initiates a new wireless charging session with the wireless charging transmitter, or the wireless charging transmitter simply stops supplying power due to a communication timeout because the wireless charging receiver 500 did not communicate with the wireless charging transmitter in the time interval between time 625 and time 680.

[0066] In an embodiment, if VRECT drops to a sufficient level, the wireless charging receiver 500 turns off the external resistor REXT1 505 so that power is no longer dissipated by the external resistor REXT1 505. Turning off the external resistor REXT1 505 may temporarily increase VRECT.

[0067] Figure 7 A flow diagram of example operations 700 occurring in a wireless charging receiver according to embodiments presented herein is illustrated. Operations 700 may indicate operations occurring in a wireless charging receiver as the wireless charging receiver responds to an OVP condition. The wireless charging receiver responds to the OVP condition and takes steps to recover from the OVP condition. Operations 700 may be performed in a microcontroller, processor, or microprocessor of the wireless charging receiver.

[0068] Operation 700 begins with the wireless charging receiver performing a power transfer with the wireless charging transmitter (block 705). The power transfer may be part of a wireless charging session established between the wireless charging receiver and the wireless charging transmitter. The wireless charging receiver performs a check to detect (or determine) whether a first voltage condition is met (block 707). The wireless charging receiver may detect (or determine) whether the first voltage condition is met, for example, by comparing VRECT to a first OVP threshold (SOVP). If VRECT meets the first OVP threshold (SOVP), the wireless charging receiver enables or turns on the external resistor REXT1 (block 709). For example, the wireless charging receiver may enable or turn on the external resistor REXT1 by enabling a switch that couples the external resistor REXT1 to ground. Enabling (or turning on) the external resistor REXT1 establishes a current path between VRECT and ground. If the first voltage condition is not met, the wireless charging receiver disables or turns off the external resistor REXT1 (block 737) and continues the power transfer (block 705).

[0069] The wireless charging receiver performs a check to detect (or determine) whether the second voltage condition is met (block 711). The wireless charging receiver may detect (or determine) whether the second voltage condition is met, for example, by comparing VRECT to a second OVP threshold (HOVP). If VRECT meets the second OVP threshold (HOVP), the wireless charging receiver shorts the receive resonant circuit (block 713). The wireless charging receiver may short the receive resonant circuit to ground or short the terminals of the receive resonant circuit to discharge VRECT. For example, the wireless charging receiver enables a receive resonant circuit switch with hysteresis operation to short the receive resonant circuit. If the second voltage condition is not met, the wireless charging receiver continues to monitor the second overvoltage condition and the first overvoltage condition by returning to block 707.

[0070] The wireless charging receiver performs a check to detect (or determine) whether the hysteresis condition is met (block 715). For example, the check for the hysteresis condition is a check to detect (or determine) whether VRECT has dropped by a sufficient amount and the receive resonant circuit can be turned back on (i.e., stop shorting the receive resonant circuit to ground or stop shorting the terminals of the receive resonant circuit). If the hysteresis condition is not met, the wireless charging receiver keeps shorting the receive resonant circuit (block 713). If the hysteresis condition is met (e.g., VRECT<hysteresis threshold), the wireless charging receiver resumes receive resonant circuit operation (block 717). The wireless charging receiver can resume receive resonant circuit operation by disabling a receive resonant circuit switch with hysteresis operation (e.g., to decouple the receive resonant circuit from ground or decouple the terminals of the receive resonant circuit).

[0071] The wireless charging receiver performs a check to detect (or determine) whether the hysteresis cycle condition is met (block 719). The hysteresis cycle condition is related to the number of hysteresis cycles that the wireless charging receiver has experienced, and can be a check of the configured number of hysteresis cycles or a duration related to the configured number of hysteresis cycles. If the hysteresis cycle condition is met, the wireless charging receiver enables or turns on the second external resistor REXT2 (block 721). For example, the wireless charging receiver can enable or turn on the second external resistor REXT2 by enabling a switch that couples the second external resistor REXT2 to ground. Enabling (or turning on) the second external resistor REXT2 establishes a second current path between VRECT and ground. If the hysteresis cycle condition is not met, the wireless charging receiver returns to block 707 to perform a check to detect whether the first voltage and the second voltage are met and continue the hysteresis cycle operation. If VRECT unexpectedly drops below SOVP, the first voltage condition is checked to enable exiting the OVP protection scheme and returning to normal operation. Blocks 737 and 705 constitute exiting the OVP protection scheme.

[0072] With the second external resistor REXT2 enabled, the wireless charging receiver communicates with the wireless charging transmitter (block 723). For example, the wireless charging receiver may request the wireless charging receiver transmitter to reduce the transmit power. Alternatively, the wireless charging receiver transmits its current receive power level or VRECT to indicate to the wireless charging transmitter that the wireless charging receiver is experiencing an overvoltage condition.

[0073] The wireless charging receiver performs a check to detect (or determine) whether the first voltage condition is met (block 725). The wireless charging receiver may detect (or determine) whether the first voltage condition is met, for example, by comparing VRECT to a first OVP threshold (SOVP). For example, if VRECT satisfies the first OVP threshold (SOVP), which means that VRECT>SOVP, the wireless charging receiver performs a check to detect (or determine) whether a timer or counter has expired or whether the second voltage condition is met (block 727). For example, the timer or counter may be associated with a time interval in which the second external resistor REXT2 is enabled. In other words, the wireless charging receiver performs a check to determine whether it can communicate with the wireless charging transmitter within a time interval in which the second external resistor REXT2 is enabled and the VRECT level drops below the first OVP threshold (SOVP). If the timer or counter has not expired, the wireless charging receiver returns to block 723 to continue communicating with the wireless charging transmitter (or continue attempting to communicate).

[0074] If the timer or counter has expired or the second voltage condition is met (VRECT>HOVP), the wireless charging transmitter shorts the receive resonant circuit (block 729). The wireless charging receiver may short the receive resonant circuit to ground or short the terminals of the receive resonant circuit to discharge VRECT. For example, the wireless charging receiver enables a receive resonant circuit switch without hysteresis operation (e.g., the switch will be enabled for a long time until UVLO is met) to short the receive resonant circuit. The wireless charging receiver also disables or turns off the second external resistor REXT2 and REXT1 (block 731). For example, the wireless charging receiver may disable or turn off the second external resistor REXT2 by disabling a switch that couples the second external resistor REXT2 to ground. Disabling (or turning off) the second external resistor REXT2 disconnects the second current path between VRECT and ground. The wireless charging receiver waits for a communication timeout to occur or VRECT to drop below the UVLO threshold (block 733). In either case (eg, communication times out or VRECT falls below a UVLO threshold), the wireless charging session may be terminated and a new wireless charging session established.

[0075] If the wireless charging receiver detects (or determines) that the first voltage condition is not met (block 725), the power transmitted by the wireless charging transmitter has dropped to a sufficiently low level (or the power received by the wireless charging receiver has dropped to a sufficiently low level) such that VRECT is out of the overvoltage condition, and the wireless charging receiver disables both the external resistor REXT1 and the second external resistor REXT2 (block 735) and returns to power transfer in block 705.

[0076] Although the present invention has been described with reference to illustrative embodiments, the description is not intended to be interpreted in a limiting sense. Various modifications and combinations of the illustrative embodiments and other embodiments of the present invention will be apparent to those skilled in the art upon reference to the description. Therefore, the appended claims are intended to cover any such modifications or embodiments.

Claims

1. A wireless charging receiver, comprising: a voltage rectifier operatively coupled to the receiving resonant circuit, the voltage rectifier being configured to output a direct current (DC) voltage according to received energy received by the receiving resonant circuit from the wireless charging transmitter; a first resistor operatively coupled to an output of the voltage rectifier; a second resistor operably coupled to the output of the voltage rectifier; a receive resonant circuit switch operably coupled to the receive resonant circuit; a first switch operably coupled between the first resistor and electrical ground; a second switch operably coupled between the second resistor and the electrical ground; as well as a controller operably coupled to the receive resonant circuit switch, the first switch, and the second switch, the controller being programmed to: determining that a first overvoltage threshold is satisfied, and based on the first overvoltage threshold being satisfied, enabling the first switch to couple the first resistor to the electrical ground, wherein the first overvoltage threshold is satisfied when the DC voltage is greater than the first overvoltage threshold; determining that a second overvoltage threshold is satisfied, and enabling the receive resonant circuit switch to short the receive resonant circuit based on the second overvoltage threshold being satisfied, wherein the second overvoltage threshold is satisfied when the DC voltage is greater than the second overvoltage threshold, wherein the first overvoltage threshold is lower than the second overvoltage threshold; determining that a hysteresis threshold is satisfied, and disabling the receive resonant circuit switch to open the receive resonant circuit based on the hysteresis threshold being satisfied, wherein the hysteresis threshold is between the first overvoltage threshold and the second overvoltage threshold, wherein the hysteresis threshold is satisfied when the DC voltage decreases below the hysteresis threshold; as well as determining that a hysteresis cycle threshold is satisfied, and based on the hysteresis cycle threshold being satisfied, enabling the second switch to couple the second resistor to the electrical ground, wherein the hysteresis cycle threshold is one of a cycle count threshold or an elapsed time threshold, wherein the hysteresis cycle threshold is satisfied when the number of hysteresis cycles reaches the cycle count threshold or when the duration of a hysteresis cycle reaches the elapsed time threshold; The controller is further programmed to: communicate with the wireless power transmitter to change an operating point of the wireless power transmitter after the second switch is enabled; wherein the operating point is changed to reduce the reception energy received by the reception resonant circuit. 2 . The wireless charging receiver of claim 1 , wherein the first resistor is larger than the second resistor. 3 . The wireless charging receiver according to claim 1 , wherein the reception resonant circuit is short-circuited between terminals of the reception resonant circuit. 4 . The wireless charging receiver of claim 1 , wherein the receive resonant circuit is short-circuited to electrical ground. 5 . The wireless charging receiver of claim 1 , wherein the wireless charging receiver is coupled to an electronic device having a rechargeable battery, and wherein the wireless charging receiver charges the rechargeable battery or powers the electronic device.

6. The wireless charging receiver of claim 5, wherein after any one or more of the first overvoltage threshold, the second overvoltage threshold, the hysteresis threshold is met, or the hysteresis cycle threshold is met, the wireless charging receiver continues to charge the rechargeable battery or power the electronic device.

7. A method implemented by the wireless charging receiver of claim 1, the method comprising: detecting that a first overvoltage threshold is met, and based on the first overvoltage threshold being met, enabling a first switch to couple a first resistor to electrical ground, the first resistor being coupled to an output of a rectifier of the wireless charging receiver, wherein the first overvoltage threshold is met when a DC voltage is greater than the first overvoltage threshold; detecting that a second overvoltage threshold is met, and enabling a receive resonant circuit switch to short-circuit a receive resonant circuit of the wireless charging receiver based on the second overvoltage threshold being met, wherein the second overvoltage threshold is met when the DC voltage is greater than the second overvoltage threshold, wherein the first overvoltage threshold is lower than the second overvoltage threshold; detecting that a hysteresis threshold is satisfied, and disabling the receive resonant circuit switch to open the receive resonant circuit based on the hysteresis threshold being satisfied, wherein the hysteresis threshold is between the first overvoltage threshold and the second overvoltage threshold, wherein the hysteresis threshold is satisfied when the DC voltage decreases below the hysteresis threshold; and detecting that a hysteresis cycle threshold is met and the receive resonant circuit switch is disabled, and enabling a second switch to couple a second resistor to the electrical ground based on the hysteresis cycle threshold being met and the receive resonant circuit switch being disabled, wherein the hysteresis cycle threshold is one of a cycle count threshold or an elapsed time threshold, wherein the hysteresis cycle threshold is met when the number of hysteresis cycles reaches the cycle count threshold or when the duration of the hysteresis cycles reaches the elapsed time threshold; communicating with the wireless power transmitter to change an operating point of the wireless power transmitter after the second switch is enabled; wherein the operating point is changed to reduce the reception energy received by the reception resonant circuit. The method of claim 7 , wherein the first resistor is larger than the second resistor.

9. The method of claim 7, the receive resonant circuit being shorted to electrical ground.

10. The method of claim 7, the reception resonant circuit being short-circuited between terminals of the reception resonant circuit.

11. The method of claim 7, wherein after any one or more of the first overvoltage threshold, the second overvoltage threshold, the hysteresis threshold, or the hysteresis cycle threshold is met, the wireless charging receiver continues to charge a rechargeable battery of the electronic device or to power the electronic device.

12. A wireless charging receiver, comprising: a voltage rectifier operatively coupled to the receiving resonant circuit, the voltage rectifier being configured to output a direct current (DC) voltage according to received energy received by the receiving resonant circuit from the wireless charging transmitter; a first resistor operatively coupled to an output of the voltage rectifier; a second resistor operably coupled to the output of the voltage rectifier; a receive resonant circuit switch operably coupled to the receive resonant circuit; a first switch operably coupled between the first resistor and electrical ground; a second switch operably coupled between the second resistor and the electrical ground; a non-transitory memory storage device including instructions; and one or more processors in communication with the memory storage device, wherein the one or more processors execute the instructions to: determining that a first overvoltage threshold is met, and based on the first overvoltage threshold being met, enabling the first switch to couple the first resistor to the electrical ground, the first resistor being coupled to an output of a rectifier of the wireless charging receiver, wherein the first overvoltage threshold is met when the DC voltage is greater than the first overvoltage threshold; determining that a second overvoltage threshold is satisfied, and enabling a receive resonant circuit switch to short the receive resonant circuit of the wireless charging receiver based on the second overvoltage threshold being satisfied, wherein the second overvoltage threshold is satisfied when the DC voltage is greater than the second overvoltage threshold, wherein the first overvoltage threshold is lower than the second overvoltage threshold; determining that a hysteresis threshold is satisfied, and disabling the receive resonant circuit switch to open the receive resonant circuit based on the hysteresis threshold being satisfied, wherein the hysteresis threshold is between the first overvoltage threshold and the second overvoltage threshold, wherein the hysteresis threshold is satisfied when the DC voltage decreases below the hysteresis threshold; as well as determining that a hysteresis cycle threshold is satisfied and the receive resonant circuit switch is disabled, and based on the hysteresis cycle threshold being satisfied and the receive resonant circuit switch being disabled, enabling the second switch to couple the second resistor to the electrical ground; wherein the hysteresis cycle threshold is one of a cycle count threshold or an elapsed time threshold, and the hysteresis cycle threshold is satisfied when the number of hysteresis cycles reaches the cycle count threshold or when the duration of the hysteresis cycles reaches the elapsed time threshold; wherein the one or more processors further execute the instructions to communicate with the wireless power transmitter to change an operating point of the wireless power transmitter after the second switch is enabled; wherein the operating point is changed to reduce the reception energy received by the reception resonant circuit.

13. The wireless charging receiver of claim 12, wherein the wireless charging receiver is coupled to an electronic device having a rechargeable battery, and wherein the wireless charging receiver charges the rechargeable battery or powers the electronic device.

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