A resonant capacitor switching switch circuit for wireless charging and its working method

Abstract

The present invention relates to the field of wireless charging technology, and provides a resonant capacitor switching circuit for wireless charging and its working method. The circuit includes a receiving end circuit, a starting circuit, and a charge pump circuit connected in sequence; the charge pump circuit is used to boost the output voltage of the receiving end circuit through bootstrap voltage doubling processing, so as to drive the starting circuit to start the receiving end circuit in the low-frequency mode. The present invention ingeniously uses the charge pump circuit to boost the output voltage Vrect of the internal circuit of the receiving end to twice the level, significantly reducing the minimum voltage required for the switching switch to start, thereby effectively solving the starting problem in the low-frequency mode.

Description

Technical Field

[0001] The present invention relates to the technical field of wireless charging, and more particularly, to a resonant capacitor switching circuit for wireless charging and its working method. Background Art

[0002] The Wireless Power Consortium (WPC) and its related standards (such as Qi and Qi2) are strictly restricted by regulations in different countries and regions regarding the use of charging frequency bands. Common frequency bands include 100 kHz - 148.5 kHz, 315 kHz - 405 kHz, 1700 kHz - 1800 kHz, 2000 kHz - 2170 kHz, 6765 kHz - 6795 kHz, and 13553 kHz - 13567 kHz. In the international market, the 360 kHz frequency band of Qi and Qi2 standards is widely used, especially in devices supporting the MagSafe function.

[0003] At the wireless charging receiver end, in order to adapt to a wider range of transmitter (Tx) operating frequency bands, a switch is usually added to switch the resonant capacitor at the receiver (Rx) to match the operating frequency of the transmitter. From the perspective of system compatibility, a relatively small resonant capacitor (2 nF - 5 nF) is usually kept in a hard-wired state in the LC resonant circuit at the receiver end by default, which is mainly used to adapt to the high-frequency LC network. Subsequently, a larger resonant capacitor (300 nF - 1000 nF) is selectively connected through an electronic switch to adapt to low-frequency applications. This design is feasible in scenarios where the transmitter is started in the high-frequency mode. However, when the transmitter is in the low-frequency mode when the user turns on the device, the electronic switch responsible for resonant capacitor switching at the receiver end will lack sufficient startup voltage due to severe detuning of the LC resonant circuit, resulting in the inability to turn on the electronic switch and ultimately causing the wireless charging system to malfunction. Summary of the Invention

[0004] The present invention aims to provide a resonant capacitor switching circuit for wireless charging and its working method to solve the startup problem of the wireless charging system in the low-frequency mode.

[0005] A resonant capacitor switching circuit for wireless charging provided by the present invention includes a receiver circuit, a startup circuit, and a charge pump circuit connected in sequence;

[0006] The charge pump circuit is used to drive the startup circuit to start the receiver circuit in the low-frequency mode after bootstrapping and voltage doubling the output voltage of the receiver circuit.

[0007] In some embodiments, the receiver circuit includes an internal receiver circuit and a resonant circuit;

[0008] The internal circuit of the receiving end includes a rectifier bridge circuit and a control logic circuit; the rectifier bridge circuit is a rectifier bridge circuit formed by the parasitic diodes of MOS transistor Q1, MOS transistor Q2, MOS transistor Q3, and MOS transistor Q4; the control logic circuit is used to maintain the conduction of the startup circuit;

[0009] The resonant circuit includes a series-connected resonant capacitor C3 and a receiving coil Co1, and the resonant circuit is connected between the upper bridge arm and the lower bridge arm of the rectifier bridge circuit.

[0010] In some embodiments, the startup circuit includes a resonant capacitor C4 and a MOS transistor Q5; the resonant capacitor C4 is connected in series with the drain and source of the MOS transistor Q5 and then connected in parallel across both ends of the resonant capacitor C3; the gate of the MOS transistor Q5 is also connected to the control logic circuit.

[0011] In some embodiments, the charge pump circuit includes a bootstrap voltage multiplier circuit and a voltage holding circuit; one end of the bootstrap voltage multiplier circuit is connected to the output voltage of the receiving end circuit, and the other end is connected to the startup circuit through the voltage holding circuit;

[0012] The bootstrap voltage multiplier circuit is used to perform a bootstrap voltage multiplication process on the output voltage Vrect, specifically doubling it to 2*Vrect; the voltage holding circuit is used to stably hold the output voltage of the bootstrap voltage multiplier circuit as 2*Vrect; the voltage of 2*Vrect is input to the gate of the MOS transistor Q5 of the startup circuit to drive the MOS transistor Q5 of the startup circuit.

[0013] In some embodiments, the bootstrap voltage multiplier circuit includes a diode D1 and a capacitor C1;

[0014] The positive electrode of the diode D1 is connected to the output voltage Vrect of the receiving end circuit, and the negative electrode of the diode D1 is connected to the electrical connection point between the resonant circuit and the rectifier bridge circuit through the capacitor C1 on one hand, and is connected to the voltage holding circuit on the other hand.

[0015] In some embodiments, the voltage holding circuit includes a diode D2 and a capacitor C2;

[0016] The positive electrode of the diode D2 is connected to the bootstrap voltage multiplier circuit, and the negative electrode of the diode D2 is grounded through the capacitor C2 on one hand and connected to the gate of the MOS transistor Q5 on the other hand.

[0017] In some embodiments, the positive electrode of the diode D1 is connected to the output voltage Vrect of the receiving end circuit through a current limiting resistor R2.

[0018] In some embodiments, the resonant capacitor switching switch circuit for wireless charging further includes an overvoltage protection circuit for protecting the MOS transistor Q5.

[0019] In some embodiments, the overvoltage protection circuit includes a series-connected resistor R1 and a Zener diode D3. One end of the overvoltage protection circuit is connected to the source electrode of MOS transistor Q5, and the other end is connected to the electrical connection point between diode D2 and capacitor C2. The electrical connection point between resistor R1 and Zener diode D3 is connected to the gate electrode of MOS transistor Q5.

[0020] In some embodiments, the working method of the above-mentioned resonant capacitor switching circuit for wireless charging includes the following steps:

[0021] S1. At startup, when the electrical connection point between the resonant circuit and the rectifier bridge circuit is at a low level in the rectification period, the output voltage Vrect charges capacitor C1 through diode D1 until the voltage of capacitor C1 reaches the output voltage Vrect.

[0022] S2. Diode D2 conducts, and capacitor C2 is also charged to the output voltage Vrect.

[0023] S3. The output voltage Vrect continues to be connected to the gate electrode of MOS transistor Q5. At this time, the output voltage Vrect is relatively low and is not sufficient to turn on MOS transistor Q5.

[0024] S4. When the electrical connection point between the resonant circuit and the rectifier bridge circuit is at a high level in the rectification period, the voltage of the lower plate of capacitor C1 rises to the output voltage Vrect. Since the voltages of the two plates of capacitor C1 cannot change suddenly, the voltage of the upper plate of capacitor C1 will become 2*Vrect. At this time, diode D1 will be reverse-biased and cut off, and diode D2 will conduct. Part of the charge accumulated on capacitor C1 is transferred to capacitor C2. This cycle repeats, and the voltage of capacitor C2 will eventually reach 2*Vrect.

[0025] S5. When the voltage of capacitor C2 finally reaches 2*Vrect, and 2*Vrect is higher than the conduction threshold voltage of MOS transistor Q5, MOS transistor Q5 conducts, the resonant capacitor C4 is connected to the resonant circuit, the output voltage Vrect rises until the internal circuit of the receiving end can be started, the control logic circuit of the internal circuit of the receiving end is activated, and the driving signal Vgate of the control logic circuit is input to turn on MOS transistor Q5 to maintain the conduction of MOS transistor Q5 by actively outputting a high level. Thus, the internal circuit of the receiving end completes the startup in the low-frequency mode.

[0026] In summary, due to the adoption of the above technical solutions, the beneficial effects of the present invention are as follows:

[0027] 1. Application of the charge pump: The present invention cleverly uses the charge pump circuit to boost the output voltage Vrect of the internal circuit of the receiving end to twice the level, significantly reducing the minimum voltage required for the switching switch to start, thereby effectively solving the startup problem in the low-frequency mode.

[0028] 2. Voltage Holding and Output: Diode D2 and capacitor C2 stably hold the output voltage of the bootstrap voltage multiplier circuit on capacitor C2. The output voltage to ground is approximately twice the output voltage Vrect. This stable voltage can drive MOS transistor Q5 in the subsequent stage circuit to ensure its reliable operation.

[0029] 3. Low-Voltage Startup Function: In combination with the drive signal Vgate of the control logic circuit inside the receiving end, at the initial stage of startup, even when the output voltage Vrect is relatively low, the circuit of the present invention can provide sufficient drive voltage through an external circuit to make MOS transistor Q5 conduct by default, realizing the low-voltage startup function. After startup is completed, the output voltage Vrect will rise to a level sufficient to activate the control logic circuit inside the receiving end. At this time, the control logic circuit inside the receiving end will take over the control of MOS transistor Q5.

[0030] 4. Overvoltage Protection: When the output voltage Vrect of the receiving end circuit is too high, the overvoltage protection circuit can prevent overvoltage from damaging the gate of MOS transistor Q5, thereby ensuring the safety of the circuit. Description of the Drawings

[0031] Figure 1 It is a structural diagram of a resonant capacitor switching circuit for wireless charging provided by an embodiment of the present invention. Among them, the parameters of each device in the figure are only examples and should not be used to limit the present invention. Detailed Embodiment

[0032] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are some, but not all, of the embodiments of the present invention. Usually, the components of the embodiments of the present invention described and illustrated herein can be arranged and designed in various different configurations.

[0033] Therefore, the following detailed description of the embodiments of the present invention provided in the drawings is not intended to limit the scope of the claimed present invention, but merely represents selected embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the scope of protection of the present invention.

[0034] Aiming at the startup problem of the wireless charging system in the low-frequency mode, an embodiment of the present invention proposes a resonant capacitor switching circuit for wireless charging, which effectively solves the startup problem in the low-frequency mode by performing bootstrap voltage multiplication on the output voltage of the rectifier bridge to provide a stable drive voltage for the resonant capacitor switch.

[0035] AsFigure 1 As shown in Figure 1 , a resonant capacitor switching switch circuit for wireless charging includes a receiving end circuit, a starting circuit, and a charge pump circuit connected in sequence.

[0036] The charge pump circuit is used to drive the starting circuit to start the receiving end circuit in the low-frequency mode after bootstrapping and voltage doubling the output voltage of the receiving end circuit, thus solving the starting problem of the wireless charging system in the low-frequency mode.

[0037] In this embodiment, the receiving end circuit includes an internal receiving end circuit and a resonant circuit.

[0038] The internal receiving end circuit includes a rectifier bridge circuit and a control logic circuit; the rectifier bridge circuit is a rectifier bridge circuit composed of parasitic diodes of MOS transistor Q1, MOS transistor Q2, MOS transistor Q3, and MOS transistor Q4; the control logic circuit is used to maintain the conduction of the starting circuit, its control terminal is BST2, and the power supply terminal is connected to the electrical connection point of the resonant circuit and the rectifier bridge circuit, such as AC2; it should be noted that capacitor C5, MOS transistor Q6, output terminal Vout, capacitor C6, etc. are other devices related to the internal receiving end circuit and do not affect the actual implementation of the present invention, so they will not be elaborated here.

[0039] The resonant circuit includes a series-connected resonant capacitor C3 and a receiving coil Co1, and the resonant circuit is connected between the upper bridge arm and the lower bridge arm of the rectifier bridge circuit.

[0040] The starting circuit includes a resonant capacitor C4 and a MOS transistor Q5; the resonant capacitor C4 is connected in series with the drain and source of the MOS transistor Q5 and then connected in parallel across the resonant capacitor C3.

[0041] In this embodiment, the charge pump circuit includes a bootstrap voltage doubling circuit and a voltage holding circuit; one end of the bootstrap voltage doubling circuit is connected to the output voltage Vrect of the receiving end circuit, and the other end is connected to the starting circuit through the voltage holding circuit, specifically connected to the gate of the MOS transistor Q5 of the starting circuit.

[0042] The bootstrap voltage doubling circuit is used to perform bootstrap voltage doubling on the output voltage Vrect, specifically doubling it to approximately 2*Vrect; the voltage holding circuit is used to stably hold the output voltage of the bootstrap voltage doubling circuit at 2*Vrect; the voltage of 2*Vrect is input to the gate of the MOS transistor Q5 of the starting circuit to drive the MOS transistor Q5 of the starting circuit to ensure its reliable operation.

[0043] Specifically, the bootstrap voltage doubling circuit includes a diode D1 and a capacitor C1; the voltage holding circuit includes a diode D2 and a capacitor C2. In some embodiments, the positive electrode of the diode D1 is connected to the output voltage Vrect of the receiving end circuit via a current limiting resistor R2. The negative electrode of the diode D1 is connected to the electrical connection point between the resonant circuit and the rectifier bridge circuit via the capacitor C1 on one hand, and connected to the positive electrode of the diode D2 on the other hand; the negative electrode of the diode D2 is grounded via the capacitor C2 on one hand, and connected to the gate of the MOS transistor Q5 on the other hand. In addition, the gate of the MOS transistor Q5 of the startup circuit is also connected to the control logic circuit.

[0044] When the wireless charging system starts in the low-frequency mode, the gate drive voltage of the MOS transistor Q5 has not had time to be established yet. Therefore, the MOS transistor Q5 is in the off state, the resonant capacitor C4 is not connected to the resonant circuit, and the resonant circuit formed by the receiving coil Co1 and the resonant capacitor C3 does not match the drive frequency (low frequency), and the resonant circuit is in a detuned state, resulting in the output voltage Vrect of the rectifier bridge circuit being insufficient to start the internal circuit of the receiving end. Thus, the working principle of the resonant capacitor switching circuit for wireless charging is as follows (it should be noted that the following voltage data is a rough estimate based on ignoring the forward conduction voltage drop of the diode, and all voltage descriptions are relative to the ground GND):

[0045] S1. At startup, when the electrical connection point between the resonant circuit and the rectifier bridge circuit ( Figure 1 AC1 or AC2 in it) is at a low level during the rectification period, the output voltage Vrect is limited by the resistor R2, and then charges the capacitor C1 through the diode D1 until the voltage of the capacitor C1 reaches the output voltage Vrect.

[0046] S2. The diode D2 conducts, and the capacitor C2 is also charged to the output voltage Vrect.

[0047] S3. The output voltage Vrect continues to be connected to the gate of the MOS transistor Q5. At this time, the output voltage Vrect is relatively low and is not sufficient to turn on the MOS transistor Q5.

[0048] S4. When the electrical connection point between the resonant circuit and the rectifier bridge circuit ( Figure 1 AC1 or AC2 in it) is at a high level during the rectification period (approximately equal to the output voltage Vrect), the voltage of the lower plate of the capacitor C1 rises to the output voltage Vrect. Since the voltages of the two plates of the capacitor C1 cannot change suddenly, the voltage of the upper plate of the capacitor C1 will become 2*Vrect. At this time, the diode D1 will be reverse-biased and cut off, and the diode D2 will conduct. Part of the charge accumulated on the capacitor C1 will be transferred to the capacitor C2; this cycle repeats, and the voltage of the capacitor C2 will eventually reach 2*Vrect.

[0049] S5. When the voltage of capacitor C2 finally reaches 2*Vrect, and 2*Vrect is higher than the turn-on threshold voltage of MOS transistor Q5, MOS transistor Q5 turns on, the resonant capacitor C4 is connected to the resonant circuit, the output voltage Vrect rises to the point where the internal circuit of the receiving end can start. At the same time, the control logic circuit of the internal circuit of the receiving end is activated after receiving the control logic signal. The drive signal Vgate of the control logic circuit is input to MOS transistor Q5 to turn it on, so as to maintain the conduction of MOS transistor Q5 by actively outputting a high level. Thus, the internal circuit of the receiving end completes the start-up in the low-frequency mode. In addition, when the output voltage Vrect is too high (after start-up, the output voltage Vrect will rise to the system-set voltage, such as 5V, 9V, etc.), at this time, the charge pump circuit is still in working state, and the voltage of 2*Vrect output by the charge pump circuit will exceed the gate-source breakdown voltage VGS of MOS transistor Q5. Therefore, in this embodiment, an overvoltage protection circuit is also provided. The overvoltage protection circuit includes a series-connected resistor R1 and a Zener diode D3. One end of the overvoltage protection circuit is connected to the source electrode of MOS transistor Q5, and the other end is connected to the electrical connection point between diode D2 and capacitor C2; the electrical connection point between resistor R1 and Zener diode D3 is connected to the gate electrode of MOS transistor Q5. This overvoltage protection circuit can prevent the gate electrode of MOS transistor Q5 from being damaged by overvoltage, thus ensuring the safety of the circuit.

[0050] From the above working principle, it can be seen that the resonant capacitor switching switch circuit for wireless charging can boost the output voltage Vrect of the rectifier bridge circuit to about twice the voltage level to drive MOS transistor Q5, so as to adapt to the problem of too low output voltage Vrect caused by low-frequency start-up. Resistor R2 plays a current-limiting role in this circuit, which is used to control the charging current of capacitor C1 to ensure the stable operation of the circuit.

[0051] The above-mentioned resonant capacitor switching switch circuit for wireless charging mainly has the following characteristics:

[0052] 1. Application of charge pump: The charge pump circuit is cleverly used to boost the output voltage Vrect of the internal circuit of the receiving end to twice the level, significantly reducing the minimum voltage required for the switching switch to start, thus effectively solving the start-up problem in the low-frequency mode.

[0053] 2. Voltage holding and output: Diode D2 and capacitor C2 stably hold the output voltage of the bootstrap voltage multiplier circuit on capacitor C2. The output voltage to ground is about twice the output voltage Vrect. This stable voltage can drive MOS transistor Q5 in the subsequent circuit to ensure its reliable operation.

[0054] 3. Low-voltage startup function: In combination with the driving signal Vgate of the control logic circuit of the internal circuit of the receiving end, at the initial stage of startup, even at a relatively low output voltage Vrect, the circuit of the present invention can provide sufficient driving voltage through an external circuit to make the MOS transistor Q5 conduct by default, thereby realizing the low-voltage startup function. After startup is completed, the output voltage Vrect will rise to a level sufficient to activate the control logic circuit of the internal circuit of the receiving end. At this time, the control logic circuit of the internal circuit of the receiving end will take over the control of the MOS transistor Q5.

[0055] 4. Overvoltage protection: When the output voltage Vrect of the receiving end circuit is too high, the overvoltage protection circuit can prevent the gate of the MOS transistor Q5 from being damaged by overvoltage, thereby ensuring the safety of the circuit.

[0056] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. For those skilled in the art, the present invention can have various changes and modifications. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A method for operating a resonant capacitor switching circuit for wireless charging, characterized in that: The resonant capacitor switching circuit for wireless charging comprises a receiving end circuit, a starting circuit and a charge pump circuit connected in sequence; the charge pump circuit is used to drive the starting circuit to start the receiving end circuit in a low-frequency mode after the output voltage of the receiving end circuit is processed by bootstrap voltage doubling; The receiving end circuit includes an internal receiving end circuit and a resonant circuit; the internal receiving end circuit includes a rectifier bridge circuit and a control logic circuit; the rectifier bridge circuit is a rectifier bridge circuit composed of parasitic diodes of MOS tubes Q1, MOS tubes Q2, MOS tubes Q3 and MOS tubes Q4; the control logic circuit is used to maintain the start circuit on; the resonant circuit includes a resonant capacitor C3 and a receiving coil Co1 connected in series, and the resonant circuit is connected between the upper bridge arm and the lower bridge arm of the rectifier bridge circuit; The startup circuit includes a resonant capacitor C4 and a MOS transistor Q5; the resonant capacitor C4 is connected in series with the drain and source of the MOS transistor Q5 and then connected in parallel to both ends of the resonant capacitor C3; the gate of the MOS transistor Q5 is also connected to the control logic circuit; The charge pump circuit includes a bootstrap voltage doubling circuit and a voltage holding circuit; one end of the bootstrap voltage doubling circuit is connected to the output voltage of the receiving end circuit, and the other end is connected to the startup circuit via the voltage holding circuit; the bootstrap voltage doubling circuit is used to bootstrap the output voltage Vrect to double the voltage, specifically to 2*Vrect; the voltage holding circuit is used to stably maintain the output voltage of the bootstrap voltage doubling circuit to 2*Vrect; the voltage of 2*Vrect is input to the gate of the MOS tube Q5 of the startup circuit, so as to drive the MOS tube Q5 of the startup circuit; The bootstrap voltage doubler circuit includes a diode D1 and a capacitor C1; the anode of the diode D1 is connected to the output voltage Vrect of the receiving end circuit, and the cathode of the diode D1 is connected to the electrical connection point between the resonant circuit and the rectifier bridge circuit via the capacitor C1 on one hand, and is connected to the voltage holding circuit on the other hand; The working method comprises the following steps: S1, at startup, when the electrical connection point between the resonant circuit and the rectifier bridge circuit is at a low level in the rectification cycle, the output voltage Vrect charges the capacitor C1 through the diode D1 until the voltage of the capacitor C1 reaches the output voltage Vrect; S2, diode D2 is turned on, and capacitor C2 is also charged to the output voltage Vrect; S3, the output voltage Vrect continues to be connected to the gate of the MOS transistor Q5. At this time, the output voltage Vrect is low and is not enough to turn on the MOS transistor Q5. S4, when the electrical connection point between the resonant circuit and the rectifier bridge circuit is at a high level in the rectification cycle, the voltage of the lower plate of capacitor C1 rises to the output voltage Vrect. Since the voltages of the two plates of capacitor C1 cannot change suddenly, the voltage of the upper plate of capacitor C1 will become 2*Vrect. At this time, diode D1 will be reversely cut off, diode D2 will be turned on, and part of the charge accumulated on capacitor C1 will be transferred to capacitor C2. This cycle repeats, and the voltage of capacitor C2 will eventually reach 2*Vrect. S5, when the voltage of capacitor C2 finally reaches 2*Vrect, and 2*Vrect is higher than the conduction threshold voltage of MOS tube Q5, MOS tube Q5 is turned on, resonant capacitor C4 is connected to the resonant circuit, and the output voltage Vrect rises to the point where the internal circuit of the receiving end can be started, and the control logic circuit of the internal circuit of the receiving end is activated. The driving signal Vgate of the control logic circuit is input to MOS tube Q5 to turn on, so as to maintain the conduction of MOS tube Q5 by actively outputting a high level. At this point, the internal circuit of the receiving end completes the startup in the low-frequency mode.

2. The working method of the resonant capacitor switching circuit for wireless charging according to claim 1, characterized in that: The voltage holding circuit includes a diode D2 and a capacitor C2; The positive electrode of the diode D2 is connected to the bootstrap voltage doubler circuit, and the negative electrode of the diode D2 is grounded via the capacitor C2 on one hand, and connected to the gate of the MOS tube Q5 on the other hand.

3. The working method of the resonant capacitor switching circuit for wireless charging according to claim 2, characterized in that: The anode of the diode D1 is connected to the output voltage Vrect of the receiving end circuit via the current limiting resistor R2.

4. The working method of the resonant capacitor switching circuit for wireless charging according to claim 2, characterized in that: An overvoltage protection circuit for protecting the MOS tube Q5 is also included.

5. The working method of the resonant capacitor switching circuit for wireless charging according to claim 4, characterized in that: The overvoltage protection circuit includes a resistor R1 and a Zener diode D3 connected in series. One end of the overvoltage protection circuit is connected to the source of the MOS tube Q5, and the other end is connected to the electrical connection point between the diode D2 and the capacitor C2; the electrical connection point between the resistor R1 and the Zener diode D3 is connected to the gate of the MOS tube Q5.

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