An LLC power supply circuit

Abstract

The application relates to the technical field of switching power supply, and discloses an LLC power supply circuit which comprises an input rectification filter circuit, a PFC circuit, an LLC conversion circuit, an output voltage control circuit and a variable ratio switching circuit; the input rectification filter circuit, the PFC circuit and the LLC conversion circuit are sequentially connected. The input end of the output voltage control circuit is connected with the output end of the LLC conversion circuit, the output end is connected with the feedback control end of the LLC conversion circuit, and the output voltage specification of the LLC conversion circuit is changed. The secondary winding of a resonant transformer in the LLC conversion circuit is provided with a plurality of pairs of switching taps, the variable ratio switching circuit is used for switching the switching taps connected with the resonant transformer according to the voltage output by the LLC conversion circuit, and the equivalent resistance of the load side equivalent to the primary side of the resonant transformer remains unchanged. The LLC power supply circuit can support a plurality of voltage specification loads without sacrificing the power supply efficiency of any voltage output specification.

Description

Technical Field

[0001] This invention relates to the field of switching power supply technology, and more specifically to an LLC power supply circuit. Background Technology

[0002] With the widespread application of switching power supplies, various power supply topologies have emerged. LLC topology is widely used due to its high efficiency. Since LLC-based power supplies primarily achieve soft switching through the resonant characteristics between the transformer's magnetizing inductance, resonant inductance, and resonant capacitor, thereby reducing switching losses and achieving high efficiency, the resonant parameters or frequency of the LLC resonant network need to be designed according to the required output voltage to maintain the most suitable zero-voltage switching (ZVS) conditions for soft switching and to maintain the optimal gain curve. This results in an excessively narrow output voltage range for LLC power supplies, essentially limiting their high efficiency to single-output specifications. Consequently, power supply manufacturers need to stock multiple specifications of LLC power supplies to accommodate different voltage requirements, increasing their inventory pressure. While some LLC power supplies can achieve two output voltage specifications, both are achieved through the switching frequency or input power of the LLC topology. This means that one output voltage specification may fail to maintain high efficiency due to a mismatch between the resonant parameters or frequency of the LLC resonant network. Therefore, it is necessary to design an LLC power supply solution that can maintain high efficiency across multiple output voltage specifications. Summary of the Invention

[0003] In order to overcome the shortcomings of the prior art, the present invention aims to provide an LLC power supply circuit that can adaptively adjust the turns ratio of the resonant transformer according to the output voltage of the LLC converter circuit, so that the equivalent resistance from the load side to the primary side of the resonant transformer does not change, and the LLC power supply circuit can maintain the optimal operating point and maintain high efficiency.

[0004] To solve the above problems, the technical solution adopted by the present invention is as follows: An LLC power supply circuit, comprising: an input rectifier and filter circuit, the input terminal of which is connected to AC mains power; a PFC circuit, the input terminal of which is connected to the output terminal of the input rectifier and filter circuit; an LLC converter circuit, the input terminal of which is connected to the output terminal of the PFC circuit, and the output terminal of which is connected to a load, wherein the secondary winding of the resonant transformer in the LLC converter circuit is provided with several pairs of switching taps, and two of the switching taps in each pair are symmetrically arranged on both sides of the center tap of the secondary winding of the resonant transformer; an output voltage control circuit, the input terminal of which is connected to the output terminal of the LLC converter circuit, and the output terminal of which is connected to the feedback control terminal of the LLC converter circuit, for changing the feedback voltage fed back to the feedback control terminal of the LLC converter circuit under the control of an external control signal, so as to change the output voltage of the LLC converter circuit; and a turns ratio switching circuit, for switching the switching taps connected to the resonant transformer according to the voltage output by the LLC converter circuit, so as to adjust the turns ratio of the resonant transformer and keep the equivalent resistance from the load side to the primary side of the resonant transformer unchanged.

[0005] The aforementioned LLC power supply circuit includes a transformer ratio switching circuit comprising several switching relays and a switching control circuit. A pair of common contacts of the switching relays are respectively connected to the input terminals of the output rectifier and filter circuit in the LLC converter circuit. A pair of normally closed contacts of the first switching relay are respectively connected to both ends of the secondary winding of the resonant transformer. A pair of normally open contacts of several switching relays are respectively connected to two of the several pairs of switching taps. The switching control circuit is used to drive the corresponding switching relay to operate according to the output voltage of the LLC converter circuit.

[0006] In the aforementioned LLC power supply circuit, the transformation ratio switching circuit includes a switching relay, and the switching control circuit includes a first MOSFET. The source of the first MOSFET is connected to a switching reference voltage, the gate of the first MOSFET is connected to the positive terminal of the output of the LLC converter circuit, the drain of the first MOSFET is connected to the first terminal of the coil of the switching relay, and the second terminal of the coil of the switching relay is connected to signal ground. The value of the switching reference voltage is between the first and second output voltages preset by the LLC converter circuit.

[0007] The aforementioned LLC power supply circuit includes a turns ratio switching circuit comprising at least three switching relays. The switching control circuit comprises multiple second MOSFETs, multiple third MOSFETs, a controller, and a regulating signal receiving circuit. The source of each second MOSFET is connected to signal ground, the gate of each second MOSFET is connected to the controller, the drain of each second MOSFET is connected to the gate of the corresponding third MOSFET, and the drain of each second MOSFET is also connected to a switching reference voltage via a current-limiting resistor. The source of each third MOSFET is connected to the switching reference voltage, and the drain of each third MOSFET is connected to the first terminal of the coil of the corresponding switching relay. The second terminals of the coils of each switching relay are all grounded. The regulating signal receiving circuit is connected to the controller and is used to receive external voltage regulation signals. The controller is used to send a switching control signal to the gate of the corresponding second MOSFET based on the voltage value corresponding to the voltage regulation signal received by the regulating signal receiving circuit.

[0008] The aforementioned LLC power supply circuit includes an output voltage control circuit comprising an input controller, a feedback adjustment circuit, and an optocoupler. The input terminal of the feedback adjustment circuit is connected to the positive terminal of the output terminal of the LLC power supply circuit. The control terminal of the feedback adjustment circuit is connected to the input controller. The output terminal of the feedback adjustment circuit is connected to the input terminal of the optocoupler. The output terminal of the optocoupler is connected to the feedback control terminal of the LLC power supply circuit. The feedback adjustment circuit is used to adjust the current output to the optocoupler under the control of the input controller, thereby changing the feedback voltage output from the optocoupler to the feedback control terminal of the LLC power supply circuit.

[0009] In the aforementioned LLC power supply circuit, the input controller is an coded switch. The feedback regulation circuit includes a three-terminal voltage regulator chip and several resistors. The anode of the three-terminal voltage regulator chip is connected to signal ground, and the reference terminal of the three-terminal voltage regulator chip is connected to signal ground through resistor R20. The series structure formed by the input controller and resistor R21 is connected in parallel across resistor R20. One end of resistor R20 connected to the reference terminal of the three-terminal voltage regulator chip is connected to the positive terminal of the output terminal of the LLC power supply circuit through resistor R19. The positive terminal of the input terminal of the optocoupler is connected to the positive terminal of the output terminal of the LLC power supply circuit. The cathode of the three-terminal voltage regulator chip is connected to the negative terminal of the input terminal of the optocoupler through resistor R18. A resistor R17 is connected in series between the positive and negative terminals of the input terminal of the optocoupler.

[0010] The aforementioned LLC power supply circuit includes an output voltage control circuit comprising a controller, a regulating signal receiving circuit, a feedback regulating circuit, and an optocoupler. The input terminal of the feedback regulating circuit is connected to the positive terminal of the LLC power supply circuit's output terminal. The control terminal of the feedback regulating circuit is connected to the controller. The output terminal of the feedback regulating circuit is connected to the input terminal of the optocoupler. The output terminal of the optocoupler is connected to the feedback control terminal of the LLC power supply circuit. The regulating signal receiving circuit is connected to the controller. The regulating signal receiving circuit receives external voltage regulating signals. The controller outputs a corresponding voltage regulation control signal to the feedback regulating circuit based on the voltage regulating signal received by the regulating signal receiving circuit, thereby regulating the current output from the feedback regulating circuit to the optocoupler and changing the feedback voltage output from the optocoupler to the feedback control terminal of the LLC power supply circuit.

[0011] The LLC power supply circuit described above includes a feedback regulation circuit comprising a three-terminal voltage regulator chip, a capacitor, and several resistors. The anode of the three-terminal voltage regulator chip is connected to signal ground, and the reference terminal of the three-terminal voltage regulator chip is connected to signal ground through resistor R20. A series structure formed by resistor R21 and capacitor C12 is connected in parallel across resistor R20. The connection node between resistor R21 and capacitor C12 is connected to the controller through resistor R21A. One end of resistor R20 connected to the reference terminal of the three-terminal voltage regulator chip is connected to the positive terminal of the output terminal of the LLC power supply circuit through resistor R19. The positive terminal of the input terminal of the optocoupler is connected to the positive terminal of the output terminal of the LLC power supply circuit. The cathode of the three-terminal voltage regulator chip is connected to the negative terminal of the input terminal of the optocoupler through resistor R18. A resistor R17 is connected in series between the positive and negative terminals of the input terminal of the optocoupler.

[0012] The aforementioned LLC power supply circuit includes at least one of a wireless communication circuit, a voltage regulation signal processing circuit, or an input control device.

[0013] The aforementioned LLC power supply circuit includes a wireless communication circuit, such as an NFC communication circuit, a Bluetooth communication circuit, or a Wi-Fi communication circuit.

[0014] Compared to existing technologies, the advantages of this invention are as follows: This LLC power supply circuit can adaptively change the turns ratio of the resonant transformer according to the output of the LLC converter circuit, thereby keeping the equivalent resistance on the load side to the primary side of the resonant transformer constant. This avoids adjusting the switching frequency of the LLC topology to maintain output power, allowing the switching frequency to remain near the resonant frequency, thus maintaining the high efficiency of the LLC power supply circuit. This LLC power supply circuit can adapt to multiple different voltage output specifications with a single power supply and maintain high efficiency across various load ranges. It can switch the output voltage according to market and scenario requirements, providing better compatibility with different load specifications. It eliminates the need to stock multiple power supply models for various loads, reducing inventory pressure for power supply manufacturers. The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments. Attached Figure Description

[0015] Figure 1 This is a schematic block diagram of an LLC power supply circuit according to an embodiment of the present invention.

[0016] Figure 2 This is a schematic diagram of the PFC circuit according to an embodiment of the present invention.

[0017] Figure 3 This is a schematic diagram of the LLC converter circuit of an embodiment of the present invention and the transformation ratio switching circuit of the first embodiment.

[0018] Figure 4 This is a schematic diagram of the output voltage control circuit according to the first embodiment of the present invention.

[0019] Figure 5 This is a schematic diagram of the output voltage control circuit and the transformation ratio switching circuit according to the second embodiment of the present invention. Detailed Implementation

[0020] The embodiments of the present invention are described in detail below, with reference to... Figure 1This invention provides an LLC power supply circuit, including an input rectifier and filter circuit, a PFC circuit, an LLC converter circuit, an output voltage control circuit, and a turns ratio switching circuit. The input rectifier and filter circuit is connected to AC mains power at its input terminal and to the PFC circuit at its output terminal, converting the AC mains power into stable DC power. The PFC circuit is connected to the input terminal of the LLC converter circuit, boosting the stable DC power output from the input rectifier and filter circuit to reduce the current stress on the subsequent LLC converter circuit and improve the overall power factor of the power supply. The output terminal of the LLC converter circuit is connected to a load to perform DC-DC conversion on the power output from the PFC circuit, thereby obtaining the required stable DC voltage. The secondary winding of the resonant transformer in the LLC converter circuit has several pairs of switching taps, with two taps in each pair symmetrically positioned on either side of the center tap of the secondary winding of the resonant transformer. The input terminal of the output voltage control circuit is connected to the output terminal of the LLC converter circuit, and the output terminal is connected to the feedback control terminal of the LLC converter circuit. It is used to change the feedback voltage fed back to the feedback control terminal of the LLC converter circuit under the control of an external control signal, thereby changing the output voltage of the LLC converter circuit. The turns ratio switching circuit is used to switch the switching taps connected to the resonant transformer according to the voltage output of the LLC converter circuit, thereby adjusting the turns ratio of the resonant transformer and keeping the equivalent resistance from the load side to the primary side of the resonant transformer constant.

[0021] In practice, the ZVS condition of traditional LLC-based power supplies is affected by variations in the circuit's quality factor (Q value). The Q value of an LLC converter circuit is typically defined as: ,in, The resonant inductance of the resonant cavity in the LLC converter circuit. The resonant capacitance of the resonant cavity in the LLC converter circuit. The equivalent resistance reflected to the primary side of the resonant transformer under load conditions. Where n is the turns ratio of the resonant transformer, Vo is the output voltage of the LLC converter circuit, and Io is the output current of the LLC converter circuit. When the output voltage of the LLC converter circuit changes, if the output power remains constant, the output current of the LLC converter circuit will also change, leading to an increase in the equivalent resistance. The value of the output voltage also changes drastically, causing a corresponding drastic change in the Q value of the LLC converter circuit. This affects the ZVS condition of the LLC converter circuit, preventing it from maintaining the optimal gain curve and high efficiency. It may even fail to regulate voltage due to the loss of the ZVS condition. However, the LLC power supply circuit in this embodiment adaptively adjusts the number of turns in the secondary winding of the resonant transformer connected to the circuit according to changes in the output voltage, thereby adjusting the transformer's turns ratio to offset the impact of output voltage changes on the equivalent resistance. The effects of the output voltage increase are as follows: when the output voltage increases, the number of turns of the secondary winding coil connected to the circuit is increased, thereby reducing the turns ratio of the resonant transformer to offset the effect of the increased output voltage on the equivalent resistance, so as to maintain the Q value unchanged; when it is necessary to reduce the output voltage, the number of turns of the secondary winding coil connected to the circuit is reduced, thereby increasing the turns ratio of the resonant transformer to offset the effect of the decreased output voltage on the equivalent resistance, so as to maintain the Q value unchanged.

[0022] Understandably, referring to Figure 3 An LLC converter circuit typically consists of an inverter circuit composed of an LLC chip U2 and its peripheral circuitry, a resonant cavity composed of a resonant inductor T2 and a resonant capacitor CX1, a resonant transformer T3, and an output rectifier and filter circuit composed of diodes D5 and D6 and an electrolytic capacitor EC3. The secondary winding of the resonant transformer T3 can be a single winding or multiple windings connected in series. The center tap of the secondary winding serves as the negative terminal of the LLC converter circuit's output and is directly connected to the load. The two ends of the secondary winding, the switching taps, and the input terminal of the output rectifier and filter circuit are all connected to the turns ratio switching circuit. Understandably, in practice, it is necessary to calculate the number of turns in the secondary winding to maintain a constant equivalent resistance based on the required output voltage specifications, the equivalent resistance calculation formula mentioned above, and the number of turns in the primary winding of the resonant transformer. This calculation is then used to design the distance between the two switching taps and the center tap.

[0023] It is understandable that the switching ratio circuit can use controllable switching devices such as relays or silicon controlled rectifiers (SCRs) to switch the switching taps. (Refer to...) Figure 3In this embodiment, the turns ratio switching circuit includes several switching relays and a switching control circuit. A pair of common contacts of the switching relays are connected to the input terminals of the output rectifier and filter circuit in the LLC converter circuit, i.e., connected to the cathodes of diodes D5 and D6, respectively. A pair of normally closed contacts of the first switching relay are connected to both ends of the secondary winding of the resonant transformer. A pair of normally open contacts of several switching relays are connected to two switching taps among several pairs of switching taps. The switching control circuit drives the corresponding switching relay to operate according to the output voltage of the LLC converter circuit, thereby changing the switching tap connected to the input terminal of the output rectifier and filter circuit, thus changing the number of turns of the secondary winding of the resonant transformer T3 actually connected to the circuit, to counteract the effect of output voltage changes on the equivalent resistance on the load side.

[0024] Reference Figure 3In some embodiments, when the required output voltage specification is small, the switching control circuit can be a voltage comparison control circuit. This circuit acquires the output voltage of the LLC converter circuit and compares it with a preset switching reference voltage. Based on the comparison result, it drives the switching relay to operate, thereby achieving adaptive switching of the resonant transformer turns ratio. In some embodiments, the switching control circuit includes a first MOSFET Q4. The source of the first MOSFET Q4 is connected to the switching reference voltage VD3, the gate is connected to the positive terminal of the output of the LLC converter circuit, and the drain is connected to the first terminal of the coil of the switching relay KY1. The second terminal of the coil of the switching relay KY1 is connected to signal ground, and a pair of normally open contacts of the switching relay KY1 are connected to switching taps NSA1 and NSB1, respectively. The value of the switching reference voltage VD3 is between the preset first and second output voltages of the LLC converter circuit. The first MOSFET Q4 is a PMOS transistor. Assuming the first output voltage > switching reference voltage VD3 > second output voltage, when the LLC converter circuit outputs the first output voltage, the first MOSFET Q4 is cut off because its gate voltage is greater than its drain voltage. The switching reference voltage VD3 cannot supply power to the coil of the switching relay KY1. The switching relay KY1 operates in its initial state. The two ends of the secondary winding of the resonant transformer T3 are connected to the circuit through the normally closed contact of the switching relay KY1. The entire secondary winding of the resonant transformer is connected to the circuit. At this time, the parameters of the resonant cavity are designed according to the first output voltage, causing the LLC converter circuit to operate at... Optimal operating point: When the LLC converter circuit drops from the first output voltage to the second output voltage, the first MOSFET Q4 turns on because its gate voltage is less than its drain voltage. At this time, the switching reference voltage VD3 is input to the coil of the switching relay KY1 through the first MOSFET Q4, causing the switching relay KY1 to operate. The normally closed contact opens and the normally open contact closes, thereby connecting the switching taps NSA1 and NSB1 to the circuit. Since NSA1 and NSB1 are closer to the center tap of the secondary winding, the number of turns of the secondary winding in the actual circuit is reduced, which increases the turns ratio of the resonant transformer T3. This counteracts the effect of the output voltage drop on the Q value, keeping the Q value constant and allowing the LLC converter circuit to maintain its optimal operating point and high efficiency.

[0025] Reference Figure 5In some embodiments, when the LLC power supply circuit needs to output more than two voltage specifications, in order to reduce the design cost of the switching control circuit, the switching control circuit may also include multiple second MOSFETs QG0 to QGN, multiple third MOSFETs QK0 to QKN, a controller, and a regulation signal receiving circuit. The source of the second MOSFET is connected to signal ground, the gate of the second MOSFET is connected to an IO pin of the controller, and the drain is connected to the gate of the corresponding third MOSFET. The drains of the multiple second MOSFETs are also connected to the switching reference voltage VD3 through corresponding current-limiting resistors RK0 to RKN. The source of the third MOSFET is connected to the switching reference voltage VD3, and the drain of the third MOSFET is connected to the first terminal of the coil of the corresponding switching relays KY0 to KYN. The second terminal of the coil of the switching relays is grounded. The regulation signal receiving circuit is connected to the controller. The regulation signal receiving circuit is used to receive external voltage regulation signals. The controller is used to send a switching control signal to the gate of the corresponding second MOSFET according to the voltage value corresponding to the voltage regulation signal received by the regulation signal receiving circuit. Multiple switching relays KY1 to KYN correspond one-to-one with multiple preset voltage output specifications, from the second output voltage to the (N+1)th output voltage, with the first output voltage decreasing sequentially to the (N+1)th output voltage. Multiple pairs of switching taps NSA1-NSB1 to NSAN-NSBN on the secondary winding of the resonant transformer T3 are sequentially closer to the center tap, and are connected to the normally open contacts of their corresponding switching relays KY1 to KYN. In the initial state, the controller sends a low-level signal to the gates of all second MOSFETs, turning off the NMOS transistors and consequently the PMOS transistors, causing all switching relays to operate in the initial state. The normally closed contact of the first switching relay KY0 is opened, connecting both ends of the secondary winding of the resonant transformer T3 to the circuit, ensuring the secondary winding is fully connected. Since the parameters of the resonant cavity are set based on the first output voltage, the LLC converter circuit operates at its optimal operating point.When it is necessary to reduce the output voltage of the LLC converter circuit, the controller adjusts the frequency of the LLC converter circuit according to the voltage adjustment signal received by the adjustment signal receiving circuit, so that the output of the LLC converter circuit switches to the selected N+1th output voltage. A high-level switching control signal is sent to the gate of the second MOSFET QG0 and the gate of the second MOSFET QGN connected to the coil of the N+1th switching relay KYN corresponding to the N+1th output voltage, causing the corresponding second MOSFET to conduct. This, in turn, causes the corresponding third MOSFET to conduct. The switching reference voltage VD3 can be transmitted through the third MOSFET to the coils of the first switching relay KY0 and the N+1th switching relay KYN, causing the first switching relay KY0 and the N+1th switching relay KYN to operate. This disconnects the two ends of the secondary winding of the resonant transformer T3 from the circuit and connects the secondary winding to the circuit through the switching taps NSAN and NSBN corresponding to the required N+1th output voltage. The number of turns of the secondary winding connected to the circuit is just enough to maintain the Q value of the LLC converter circuit at the preset N+1th output voltage, thus maintaining high efficiency. It is understandable that the switching of relays KY1 to KYN should be interlocked, meaning that only one of relays KY1 and KYN can be activated at the same time. This interlock can be implemented through the control program in the controller.

[0026] Reference Figure 3 and Figure 4 In some embodiments, when the required output voltage specifications are few, the output voltage can be adjusted using an input controller with multiple positions, such as a DIP switch or rotary switch. The output voltage control circuit may include an input controller, a feedback regulation circuit, and an optocoupler. The input terminal of the feedback regulation circuit is connected to the positive terminal of the output terminal of the LLC power supply circuit, the control terminal is connected to the input controller, and the output terminal is connected to the input terminal of the optocoupler. The output terminal of the optocoupler is connected to the feedback control terminal of the LLC power supply circuit. The feedback regulation circuit is used to adjust the current output to the optocoupler under the control of the input controller, thereby changing the feedback voltage output from the optocoupler to the feedback control terminal of the LLC power supply circuit.

[0027] It is understood that the feedback regulation circuit can be a controllable voltage regulation circuit. In this embodiment, when only two voltage specifications need to be output, refer to... Figure 3 and Figure 4The input control device is an encoder switch TS1. The feedback regulation circuit includes a three-terminal voltage regulator chip U4 and several resistors. The anode of the three-terminal voltage regulator chip U4 is connected to signal ground, and the reference terminal is connected to signal ground through resistor R20. The series structure formed by the encoder switch TS1 and resistor R21 is connected in parallel across resistor R20. One end of resistor R20 connected to the reference terminal of the three-terminal voltage regulator chip U4 is connected to the positive terminal of the output of the LLC power supply circuit through resistor R19. The positive terminal of the input of optocoupler U3 is connected to the positive terminal of the output of the LLC power supply circuit. The cathode of the three-terminal voltage regulator chip U4 is connected to the negative terminal of the input of optocoupler U3 through resistor R18. A resistor R17 is connected in series between the positive and negative terminals of the input of optocoupler U3. The emitter of the output of optocoupler U3 is connected to the power supply ground and is connected to the feedback control pin 4 of LLC chip U2 through resistor R12. The collector is connected to the feedback control pin 4 of LLC chip U2 through resistor R13. In this embodiment, the voltage of the feedback control pin 4 of the selected LLC chip U2 decreases, and the switching frequency of the LLC converter circuit increases accordingly, thereby reducing the output voltage of the LLC converter circuit. Initially, the encoding switch TS1 is off, and the LLC chip U2 controls the LLC converter circuit to output a default first output voltage based on the output voltage of the optocoupler U3. When a lower second output voltage needs to be switched, the encoding switch TS1 is closed, causing resistors R21 and R20 to be connected in parallel. This reduces the resistance of the pull-down resistor of the three-terminal voltage regulator chip U4, thereby increasing the voltage at the reference terminal of the three-terminal voltage regulator chip U4. This increases the cathode current of the three-terminal voltage regulator chip U4, leading to an increase in the luminous intensity of the optocoupler U3 and a decrease in the on-resistance at the output terminal. Consequently, the collector current at the output terminal increases, pulling down the voltage of the feedback control pin 4 of the LLC chip U2, causing the output voltage of the LLC converter circuit to drop to the second output voltage.

[0028] Reference Figure 5 In some embodiments, when there are multiple output voltage specifications, it is advisable to use a controller and a regulating signal receiving circuit to control the switching of the output voltage specifications of the LLC converter circuit. The control terminal of the feedback regulating circuit is connected to the controller, which outputs a corresponding voltage regulation control signal based on the voltage regulation signal received by the regulating signal receiving circuit. Under the control of the voltage regulation control signal, the current output by the feedback regulating circuit to the optocoupler is adjusted, thereby changing the feedback voltage output by the optocoupler to the feedback control terminal of the LLC power supply circuit, and realizing the switching of the output voltage specifications of the LLC converter circuit.

[0029] Reference Figure 5In this embodiment, the controller and regulating signal receiving circuit of the output voltage control circuit can be shared with the transformation ratio switching circuit. The controller regulates the voltage at the reference terminal of the three-terminal regulator chip U4 through a PWM signal. The PWM pin of the controller is connected to the reference terminal of the three-terminal regulator chip U4 through a conversion circuit composed of resistor R21, capacitor C12, and resistor R21A. A series structure composed of resistor R21 and capacitor C12 is connected in parallel across resistor R20. The connection node between resistor R21 and capacitor C12 is connected to the controller through resistor R21A. The controller outputs a PWM signal with a corresponding duty cycle according to the signal received by the regulating signal receiving circuit, thereby regulating the voltage at the reference terminal of the three-terminal regulator chip U4, thereby regulating the current output from the three-terminal regulator chip U4 to the optocoupler U3, changing the voltage at the feedback control pin 4 of the LLC chip U2, and thus causing the LLC converter circuit to output the corresponding output voltage specification.

[0030] Understandably, the controller can be a controllable programmable device such as a microcontroller. The regulating signal receiving circuit can acquire the voltage regulation signal via wired or wireless means. This circuit can include at least one of an input control device, a wireless communication circuit, and a voltage regulation signal processing circuit. The input control device can be an input terminal such as a touchscreen or a button circuit; the voltage regulation signal processing circuit can be a signal amplification circuit or a signal decoding circuit; and the wireless communication circuit can be an NFC communication circuit, a Bluetooth communication circuit, or a Wi-Fi communication circuit. (See reference...) Figure 5 In this embodiment, the regulating signal receiving circuit includes an NFC communication circuit. Before leaving the factory, the voltage regulation signal can be sent to the controller wirelessly via an NFC communication device according to the power supply specifications. This modifies the voltage output specification configuration stored in the controller's storage medium, so that during operation, the controller outputs a PWM signal with the corresponding duty cycle to the reference terminal of the three-terminal voltage regulator chip U4, controls the LLC converter circuit to output the required output voltage, and sends a high-level signal to the gate of the second MOS transistor connected to the corresponding switching relay, driving the corresponding switching relay to operate. This matches the number of coil turns of the secondary winding of the resonant transformer actually connected to the circuit with the required output voltage, so that the power supply can still operate at the optimal operating point and ensure the efficiency of the power supply.

[0031] A rectifier-filter circuit typically consists of a rectifier bridge and a filter, while a PFC circuit typically consists of a PFC chip and its peripheral circuitry. (See reference...) Figure 2In this embodiment, the PFC circuit includes resistors R1-9, capacitors C1-2, transformer T1, capacitor EC1, power transistor Q1, PFC chip U1, and diode D1. Specifically, pin 1 of PFC chip U1 is the PFC input voltage detection pin, used to identify the current input voltage; pin 2 is the PFC feedback compensation pin, and pin 4 is the PFC output voltage detection pin. When the voltage at this pin exceeds or falls below a preset voltage, the PFC circuit output is adjusted to achieve the designed PFC voltage; pin 5 is the PFC current detection pin, used to limit the maximum PFC output current by detecting the current flowing through the source of power transistor Q1; pin 6 is the PFC PWM output pin, connected to an external power transistor Q1 for switching control, adjusting the PFC circuit output; pin 7 is the PFC demagnetization detection pin, used to determine the state of transformer T1; and pins 3 and 8 of PFC chip U1 are the chip's ground and power supply pins, respectively. Through the above system, the PFC circuit can stably output 420V high-voltage DC, thereby reducing the current loss in the DC-DC conversion process of the subsequent LLC converter circuit and further improving the efficiency of the entire power supply.

[0032] It should be noted that in the description of this invention, any descriptions of orientation, such as up, down, front, back, left, right, etc., indicating orientation or positional relationships, are based on the orientation or positional relationships shown in the accompanying drawings. They are only for the purpose of facilitating the description of this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed or operated in a specific orientation, and should not be construed as a limitation of this invention.

[0033] In the description of this invention, "several" means one or more, "more than" means two or more, "greater than," "less than," "exceeding," etc. are understood to exclude the stated number, while "above," "below," "within," etc. are understood to include the stated number. If "first" or "second" is mentioned, it is only for the purpose of distinguishing technical features and should not be construed as indicating or implying relative importance, or implicitly indicating the number of indicated technical features, or implicitly indicating the order of the indicated technical features.

[0034] In the description of this invention, unless otherwise explicitly defined, terms such as "set up," "install," and "connect" should be interpreted broadly, and those skilled in the art can reasonably determine the specific meaning of the above terms in this invention in conjunction with the specific content of the technical solution.

[0035] The above embodiments are merely preferred embodiments of the present invention and should not be construed as limiting the scope of protection of the present invention. Any non-substantial changes and substitutions made by those skilled in the art based on the present invention shall fall within the scope of protection claimed by the present invention.

Claims

1. An LLC power supply circuit, characterized in that, include: The input rectifier and filter circuit has its input terminal connected to AC mains power. The input terminal of the PFC circuit is connected to the output terminal of the input rectifier and filter circuit. The LLC converter circuit has its input terminal connected to the output terminal of the PFC circuit, and its output terminal used to connect to the load. The secondary winding of the resonant transformer in the LLC converter circuit is provided with several pairs of switching taps. Two of the switching taps in each pair are symmetrically arranged on both sides of the center tap of the secondary winding of the resonant transformer. An output voltage control circuit has its input terminal connected to the output terminal of the LLC converter circuit and its output terminal connected to the feedback control terminal of the LLC converter circuit. It is used to change the feedback voltage fed back to the feedback control terminal of the LLC converter circuit under the control of an external control signal, so as to change the output voltage of the LLC converter circuit. A turns ratio switching circuit is used to switch the switching taps connected to the resonant transformer according to the voltage output by the LLC converter circuit, so as to adjust the turns ratio of the resonant transformer and keep the equivalent resistance of the load side to the primary side of the resonant transformer unchanged.

2. The LLC power supply circuit according to claim 1, characterized in that, The transformation ratio switching circuit includes several switching relays and a switching control circuit. A pair of common contacts of the switching relays are respectively connected to the input terminals of the output rectifier and filter circuit in the LLC converter circuit. A pair of normally closed contacts of the first switching relay are respectively connected to the two ends of the secondary winding of the resonant transformer. A pair of normally open contacts of several switching relays are respectively connected to two of the several pairs of switching taps. The switching control circuit is used to drive the corresponding switching relay to operate according to the output voltage of the LLC converter circuit.

3. The LLC power supply circuit according to claim 2, characterized in that, The transformation ratio switching circuit includes a switching relay, and the switching control circuit includes a first MOSFET. The source of the first MOSFET is connected to a switching reference voltage, the gate of the first MOSFET is connected to the positive terminal of the output of the LLC converter circuit, the drain of the first MOSFET is connected to the first terminal of the coil of the switching relay, and the second terminal of the coil of the switching relay is connected to signal ground. The value of the switching reference voltage is between the first output voltage and the second output voltage preset by the LLC converter circuit.

4. The LLC power supply circuit according to claim 2, characterized in that, The transformation ratio switching circuit includes at least three switching relays. The switching control circuit includes multiple second MOSFETs, multiple third MOSFETs, a controller, and an adjustment signal receiving circuit. The source of the second MOSFET is connected to signal ground, the gate of the second MOSFET is connected to the controller, the drain of the second MOSFET is connected to the gate of the corresponding third MOSFET, and the drain of the second MOSFET is also connected to a switching reference voltage through a current-limiting resistor. The source of the third MOSFET is connected to the switching reference voltage, and the drain of the third MOSFET is connected to the first terminal of the coil of the corresponding switching relay. The second terminals of the coils of the switching relays are all grounded. The adjustment signal receiving circuit is connected to the controller and is used to receive external voltage adjustment signals. The controller is used to send a switching control signal to the gate of the corresponding second MOSFET according to the voltage value corresponding to the voltage adjustment signal received by the adjustment signal receiving circuit.

5. The LLC power supply circuit according to claim 1, characterized in that, The output voltage control circuit includes an input controller, a feedback adjustment circuit, and an optocoupler. The input terminal of the feedback adjustment circuit is connected to the positive terminal of the output terminal of the LLC power supply circuit. The control terminal of the feedback adjustment circuit is connected to the input controller. The output terminal of the feedback adjustment circuit is connected to the input terminal of the optocoupler. The output terminal of the optocoupler is connected to the feedback control terminal of the LLC power supply circuit. The feedback adjustment circuit is used to adjust the current output to the optocoupler under the control of the input controller, so as to change the feedback voltage output by the optocoupler to the feedback control terminal of the LLC power supply circuit.

6. The LLC power supply circuit according to claim 5, characterized in that, The input controller is an coded switch. The feedback adjustment circuit includes a three-terminal voltage regulator chip and several resistors. The anode of the three-terminal voltage regulator chip is connected to signal ground, and the reference terminal of the three-terminal voltage regulator chip is connected to signal ground through resistor R20. The series structure formed by the input controller and resistor R21 is connected in parallel across resistor R20. One end of resistor R20 connected to the reference terminal of the three-terminal voltage regulator chip is connected to the positive terminal of the output terminal of the LLC power supply circuit through resistor R19. The positive terminal of the input terminal of the optocoupler is connected to the positive terminal of the output terminal of the LLC power supply circuit. The cathode of the three-terminal voltage regulator chip is connected to the negative terminal of the input terminal of the optocoupler through resistor R18. A resistor R17 is connected in series between the positive and negative terminals of the input terminal of the optocoupler.

7. The LLC power supply circuit according to claim 1, characterized in that, The output voltage control circuit includes a controller, a regulating signal receiving circuit, a feedback regulating circuit, and an optocoupler. The input terminal of the feedback regulating circuit is connected to the positive terminal of the output terminal of the LLC power supply circuit. The control terminal of the feedback regulating circuit is connected to the controller. The output terminal of the feedback regulating circuit is connected to the input terminal of the optocoupler. The output terminal of the optocoupler is connected to the feedback control terminal of the LLC power supply circuit. The regulating signal receiving circuit is connected to the controller. The regulating signal receiving circuit is used to receive external voltage regulating signals. The controller is used to output a corresponding voltage regulation control signal to the feedback regulating circuit according to the voltage regulating signal received by the regulating signal receiving circuit, so as to regulate the current output by the feedback regulating circuit to the optocoupler and change the feedback voltage output by the optocoupler to the feedback control terminal of the LLC power supply circuit.

8. The LLC power supply circuit according to claim 7, characterized in that, The feedback regulation circuit includes a three-terminal voltage regulator chip, a capacitor, and several resistors. The anode of the three-terminal voltage regulator chip is connected to signal ground, and the reference terminal of the three-terminal voltage regulator chip is connected to signal ground through resistor R20. A series structure formed by resistor R21 and capacitor C12 is connected in parallel across resistor R20. The connection node between resistor R21 and capacitor C12 is connected to the controller through resistor R21A. One end of resistor R20 connected to the reference terminal of the three-terminal voltage regulator chip is connected to the positive terminal of the output terminal of the LLC power supply circuit through resistor R19. The positive terminal of the input terminal of the optocoupler is connected to the positive terminal of the output terminal of the LLC power supply circuit. The cathode of the three-terminal voltage regulator chip is connected to the negative terminal of the input terminal of the optocoupler through resistor R18. A resistor R17 is connected in series between the positive and negative terminals of the input terminal of the optocoupler.

9. The LLC power supply circuit according to any one of claims 4, 7, and 8, characterized in that, The regulating signal receiving circuit includes at least one of a wireless communication circuit, a voltage regulation signal processing circuit, or an input control device.

10. The LLC power supply circuit according to claim 9, characterized in that, The wireless communication circuit includes an NFC communication circuit, a Bluetooth communication circuit, or a Wi-Fi communication circuit.

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