Resonant capacitor change-over switch circuit for wireless charging and working method of resonant capacitor change-over switch circuit

Abstract

The invention relates to the technical field of wireless charging, and provides a resonant capacitor change-over switch circuit for wireless charging and a working method thereof, the circuit comprises a receiving end circuit, a starting circuit and a charge pump circuit which are connected in sequence; and the charge pump circuit is used for driving the starting circuit to start the receiving end circuit in a low-frequency mode after the output voltage of the receiving end circuit is subjected to bootstrap voltage-multiplying processing. According to the invention, the charge pump circuit is ingeniously utilized to increase the output voltage Vrect of the internal circuit of the receiving end to two times of the level, and the minimum voltage required when the change-over switch is started is remarkably reduced, so that the starting problem in a low-frequency mode is effectively solved.

Description

Technical Field

[0001] The present invention relates to the technical field of wireless charging, and in particular to a resonant capacitor switching switch circuit for wireless charging and a working method thereof. Background Art

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

[0003] At the wireless charging receiver, in order to adapt to a wider range of transmitter (Tx) operating frequency bands, it is usually necessary to add a switch to switch the resonant capacitor of the receiver (Rx) to match the operating frequency of the transmitter. From the perspective of system compatibility, a smaller resonant capacitor (2nF~5nF) is usually kept in a hard-wired state by default in the LC resonant circuit of the receiver, which is mainly used to adapt to high-frequency LC networks. Subsequently, a larger resonant capacitor (300nF~1000nF) is selectively connected through an electronic switch to adapt to low-frequency applications. This design is feasible in the scenario of starting the transmitter in high-frequency mode. However, when the transmitter is in low-frequency mode when the user turns on the power, the electronic switch responsible for switching the resonant capacitor at the receiver lacks sufficient starting voltage due to severe detuning of the LC resonant circuit, and the electronic switch cannot be turned on, which ultimately causes the wireless charging system to fail to work properly. Summary of the invention

[0004] The present invention aims to provide a resonant capacitor switching switch circuit for wireless charging and a working method thereof, so as to solve the problem of starting the wireless charging system in a low-frequency mode.

[0005] A resonant capacitor switching switch circuit for wireless charging provided by the present invention comprises a receiving end circuit, a starting circuit and a charge pump circuit connected in sequence; The charge pump circuit is used to bootstrap the output voltage of the receiving end circuit to double the voltage, so that the driving start-up circuit can start the receiving end circuit in a low-frequency mode.

[0006] In some embodiments, the receiving end circuit includes a receiving end internal circuit and a resonant circuit; 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 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-up circuit turned on; The resonant circuit includes a resonant capacitor C3 and a receiving coil Co1 connected in series, and the resonant circuit is connected between an upper bridge arm and a lower bridge arm of a rectifier bridge circuit.

[0007] 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 to both ends of the resonant capacitor C3; the gate of the MOS transistor Q5 is also connected to the control logic circuit.

[0008] In some embodiments, the charge pump circuit includes a bootstrap voltage doubler circuit and a voltage holding circuit; one end of the bootstrap voltage doubler circuit is connected to the output voltage of the receiving end circuit, and the other end is connected to the start-up circuit via the voltage holding circuit; The bootstrap voltage doubling circuit is used to bootstrap and double the output voltage Vrect, specifically doubling the voltage to 2*Vrect; the voltage holding circuit is used to stably maintain 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 tube Q5 of the startup circuit, and is used to drive the MOS tube Q5 of the startup circuit.

[0009] In some embodiments, the bootstrap voltage multiplier 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.

[0010] In some embodiments, 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.

[0011] In some embodiments, the anode of the diode D1 is connected to the output voltage Vrect of the receiving end circuit via the current limiting resistor R2.

[0012] In some embodiments, the resonant capacitor switching circuit for wireless charging further includes an overvoltage protection circuit for protecting the MOS tube Q5.

[0013] In some embodiments, 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.

[0014] In some embodiments, the working method of the resonant capacitor switching circuit for wireless charging includes 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.

[0015] In summary, due to the adoption of the above technical solution, the beneficial effects of the present invention are: 1. Application of charge pump: The present invention ingeniously uses the charge pump circuit to increase the output voltage Vrect of the internal circuit of the receiving end to 2 times the level, significantly reducing the minimum voltage required for switching switch startup, thereby effectively solving the startup problem in low-frequency mode.

[0016] 2. Voltage maintenance and output: Diode D2 and capacitor C2 stably maintain the output voltage of the bootstrap voltage doubler circuit on capacitor C2. Its output voltage to ground is approximately twice the output voltage Vrect. This stable voltage can drive the MOS tube Q5 in the subsequent circuit to ensure its reliable operation.

[0017] 3. Low-voltage startup function: Combined with the driving signal Vgate of the control logic circuit of the internal circuit of the receiving end, the circuit of the present invention can provide sufficient driving voltage through the external circuit at the initial startup, even at a relatively low output voltage Vrect, so that the MOS tube Q5 is turned on by default, thereby realizing the low-voltage startup function. After the 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, and at this time, the control logic circuit of the internal circuit of the receiving end will take over the control of the MOS tube Q5.

[0018] 4. Overvoltage protection: When the output voltage Vrect of the receiving end circuit is too high, the overvoltage protection circuit can prevent the overvoltage from damaging the gate of the MOS tube Q5, thereby ensuring the safety of the circuit. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 A structural diagram of a resonant capacitor switching circuit for wireless charging provided by an embodiment of the present invention. The device parameters in the figure are only an example and should not be used to limit the present invention. DETAILED DESCRIPTION

[0020] In order to make the purpose, 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 part of the embodiments of the present invention, not all of the embodiments. Generally, the components of the embodiments of the present invention described and shown in the drawings here can be arranged and designed in various different configurations.

[0021] Therefore, the following detailed description of the embodiments of the present invention provided in the accompanying drawings is not intended to limit the scope of the invention claimed for protection, but merely represents selected embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0022] In response to the startup problem of the wireless charging system in the low-frequency mode, an embodiment of the present invention proposes a resonant capacitor switching switch circuit for wireless charging. By bootstrapping the output voltage of the rectifier bridge to double the voltage, a stable driving voltage is provided for the resonant capacitor switch, thereby effectively solving the startup problem in the low-frequency mode.

[0023] like Figure 1As shown, 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; The charge pump circuit is used to bootstrap the output voltage of the receiving end circuit to double the voltage, so that the driving startup circuit can start the receiving end circuit in the low-frequency mode, thereby solving the startup problem of the wireless charging system in the low-frequency mode.

[0024] In this embodiment, the receiving end circuit includes a receiving end internal circuit and a resonant circuit; 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 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, and its control end is BST2, and the power supply end is connected to the electrical connection point between the resonant circuit and the rectifier bridge circuit, such as AC2; it should be noted that the capacitor C5, MOS tube Q6, output end Vout, capacitor C6, etc. are other components related to the internal circuit of the receiving end, which do not affect the actual implementation of the present invention and are not described in detail here; The resonant circuit includes a resonant capacitor C3 and a receiving coil Co1 connected in series, and the resonant circuit is connected between an upper bridge arm and a lower bridge arm of a rectifier bridge circuit.

[0025] 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.

[0026] In this embodiment, the charge pump circuit includes a bootstrap voltage doubler circuit and a voltage holding circuit; one end of the bootstrap voltage doubler circuit is connected to the output voltage Vrect of the receiving end circuit, and the other end is connected to the startup circuit through the voltage holding circuit, specifically connected to the gate of the MOS tube Q5 of the startup circuit; The bootstrap voltage doubling circuit is used to perform bootstrap voltage doubling on the output voltage Vrect, specifically doubling the voltage to about 2*Vrect; the voltage holding circuit is used to stably maintain 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 tube Q5 of the startup circuit, so as to drive the MOS tube Q5 of the startup circuit to ensure its reliable operation.

[0027] Specifically, the bootstrap voltage multiplier 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 anode of the diode D1 is connected to the output voltage Vrect of the receiving end circuit via the current limiting resistor R2, 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, and is connected to the anode of the diode D2; the cathode of the diode D2 is grounded via the capacitor C2, and is connected to the gate of the MOS tube Q5. In addition, the gate of the MOS tube Q5 of the startup circuit is also connected to the control logic circuit.

[0028] When the wireless charging system is started in low-frequency mode, the gate drive voltage of the MOS tube Q5 has not been established yet, so the MOS tube Q5 is in the off state, the resonant capacitor C4 is not connected to the resonant circuit, and the resonant circuit composed of the receiving coil Co1 and the resonant capacitor C3 does not match the driving frequency (low frequency). 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. Therefore, 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): S1, at startup, when the electrical connection point between the resonant circuit and the rectifier bridge circuit ( Figure 1 When AC1 or AC2 in the rectification cycle is at a low level, 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; 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 ( Figure 1 When AC1 or AC2 in the rectification cycle is at a high level (approximately equal to the output voltage Vrect), 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. At the same time, the control logic circuit of the internal circuit of the receiving end is activated after receiving the control logic signal, and the driving signal Vgate of the control logic circuit is input to the 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. In addition, when the output voltage Vrect is too high (after the startup is completed, the output voltage Vrect will rise to the system set voltage, such as 5V, 9V, etc.), the charge pump circuit is still in a working state at this time, and the charge pump circuit outputs a voltage of 2*Vrect that exceeds the gate-source withstand voltage VGS of the MOS tube Q5. For this reason, in this embodiment, an overvoltage protection circuit is also provided, and 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. The overvoltage protection circuit can prevent the gate of the MOS tube Q5 from being damaged by overvoltage, thereby ensuring the safety of the circuit.

[0029] From the above working principle, it can be known that the resonant capacitor switching circuit for wireless charging can increase the output voltage Vrect of the rectifier bridge circuit to about 2 times the voltage level, which is used to drive the MOS tube Q5 to adapt to the problem of too low output voltage Vrect caused by low-frequency startup. 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.

[0030] The above-mentioned resonant capacitor switching circuit for wireless charging mainly has the following characteristics: 1. Application of charge pump: The charge pump circuit is cleverly used to increase the output voltage Vrect of the internal circuit of the receiving end to 2 times the level, which significantly reduces the minimum voltage required for the switching switch to start, thereby effectively solving the startup problem in low-frequency mode.

[0031] 2. Voltage maintenance and output: Diode D2 and capacitor C2 stably maintain the output voltage of the bootstrap voltage doubler circuit on capacitor C2. Its output voltage to ground is approximately twice the output voltage Vrect. This stable voltage can drive the MOS tube Q5 in the subsequent circuit to ensure its reliable operation.

[0032] 3. Low-voltage startup function: Combined with the driving signal Vgate of the control logic circuit of the internal circuit of the receiving end, the circuit of the present invention can provide sufficient driving voltage through the external circuit at the initial startup, even at a relatively low output voltage Vrect, so that the MOS tube Q5 is turned on by default, thereby realizing the low-voltage startup function. After the 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, and at this time, the control logic circuit of the internal circuit of the receiving end will take over the control of the MOS tube Q5.

[0033] 4. Overvoltage protection: When the output voltage Vrect of the receiving end circuit is too high, the overvoltage protection circuit can prevent the overvoltage from damaging the gate of the MOS tube Q5, thereby ensuring the safety of the circuit.

[0034] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A resonant capacitor switching circuit for wireless charging, characterized in that: It includes a receiving end circuit, a starting circuit and a charge pump circuit connected in sequence; The charge pump circuit is used to bootstrap the output voltage of the receiving end circuit to double the voltage, so that the driving start-up circuit can start the receiving end circuit in a low-frequency mode.

2. The resonant capacitor switching circuit for wireless charging according to claim 1, characterized in that: The receiving end circuit includes a receiving end internal circuit and a resonant circuit; 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 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-up circuit turned on; The resonant circuit includes a resonant capacitor C3 and a receiving coil Co1 connected in series, and the resonant circuit is connected between an upper bridge arm and a lower bridge arm of a rectifier bridge circuit.

3. The resonant capacitor switching circuit for wireless charging according to claim 2, characterized in that: 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.

4. The resonant capacitor switching circuit for wireless charging according to claim 3, characterized in that: The charge pump circuit comprises a bootstrap voltage doubler circuit and a voltage holding circuit; one end of the bootstrap voltage doubler circuit is connected to the output voltage of the receiving end circuit, and the other end is connected to the start-up circuit via the voltage holding circuit; The bootstrap voltage doubling circuit is used to bootstrap and double the output voltage Vrect, specifically doubling the voltage to 2*Vrect; the voltage holding circuit is used to stably maintain 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 tube Q5 of the startup circuit, so as to drive the MOS tube Q5 of the startup circuit.

5. The resonant capacitor switching circuit for wireless charging according to claim 4, characterized in that: The bootstrap voltage multiplier 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.

6. The resonant capacitor switching circuit for wireless charging according to claim 5, 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.

7. The resonant capacitor switching circuit for wireless charging according to claim 6, 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.

8. The resonant capacitor switching circuit for wireless charging according to claim 6, characterized in that: An overvoltage protection circuit for protecting the MOS tube Q5 is also included.

9. The resonant capacitor switching circuit for wireless charging according to claim 8, 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.

10. A method for operating a resonant capacitor switching circuit for wireless charging, characterized in that: The resonant capacitor switching circuit for wireless charging is the resonant capacitor switching circuit for wireless charging according to any one of claims 6 to 9; 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.

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