Control Method of LLC Resonant Converter and LLC Resonant Converter to Which the Control Method Is Applied

Abstract

The present disclosure relates to a control method for an LLC resonant converter, comprising: (S10) starting to start the LLC resonant converter; (S20) driving the LLC resonant converter to operate in a first modulation mode so that the LLC resonant converter provides an output voltage greater than or equal to a middle value voltage; (S30) confirming whether the output current is greater than 0; (S40) when the confirmation result of step (S30) is no, re-executing step (S20), and when the confirmation result of step (S30) is yes, confirming whether the output voltage is greater than a preset reference voltage; (S50) when the confirmation result of step (S40) is yes, driving the LLC resonant converter to operate in the first modulation mode and re-executing step (S30); and (S60) when the confirmation result of step (S40) is no, driving the LLC resonant converter to operate in a second modulation mode so that the LLC resonant converter provides an output voltage less than the middle value voltage and re-executing step (S30). The present disclosure also relates to an LLC resonant converter.

Description

Technical Field

[0001] The present disclosure relates to a control method, and particularly to a control method for an LLC resonant converter and an LLC resonant converter applicable thereto. Background Art

[0002] LLC resonant converters featuring zero voltage switching (ZVS) and zero current switching (ZCS) have been widely used in various electrical products. When an LLC resonant converter is applied to a constant voltage output occasion, the switching loss of the power switch can be significantly reduced by using the LLC resonant converter, thereby improving the efficiency of the power supply device.

[0003] Please refer to Figure 1 , which is a schematic diagram showing the relationship between the output voltage and the output current when an LLC resonant converter is applied to a constant current output occasion. As Figure 1 shown, when an LLC resonant converter is applied to a constant current output occasion, such as being used in a constant current output type LED power supply device to drive an LED load, since the LED load is replaceable and different LED loads have different voltage requirement specifications, the output voltage range of the LED power supply device generally reaches 2 to 4 times wider. However, under the condition that the output voltage range is 2 to 4 times wider, if the control method of the LLC resonant converter applied to the constant current output occasion still adopts the same control method as that of the LLC resonant converter applied to the constant voltage output occasion, the LLC resonant converter applied to the constant current output occasion will not be able to work at a high-efficiency resonant frequency operating point in response to the different voltage requirements of the LED load. For example, if the resonant frequency operating point of the LLC resonant converter is designed for a low output voltage, when the output voltage increases, a large resonant current will be generated by the LLC resonant converter, resulting in poor efficiency of the LED power supply device.

[0004] Therefore, how to develop a control method for an LLC resonant converter and an LLC resonant converter applicable thereto to improve the above-mentioned existing technology is an urgent need at present. Summary of the Invention

[0005] The present disclosure relates to a control method for an LLC resonant converter and an LLC resonant converter applicable thereto, so as to solve the problem of poor efficiency of the LLC resonant converter when the traditional LLC resonant converter is applied to a constant current output occasion.

[0006] To achieve the above object, the present disclosure provides a control method applicable to an LLC resonant converter. The LLC resonant converter converts an input voltage to provide an output voltage and a fixed output current to a DC load, where the output voltage is between a predetermined voltage and N times the predetermined voltage. The LLC resonant converter includes a voltage detector for detecting the output voltage and a current detector for detecting the output current. The control method includes: (S10) starting to start the LLC resonant converter; (S20) driving the LLC resonant converter to operate in a first modulation mode so that the LLC resonant converter provides an output voltage greater than or equal to a middle value voltage, where the middle value voltage is half of the sum of the predetermined voltage and N times the predetermined voltage; (S30) confirming whether the output current is greater than 0 through the detection result of the current detector; (S40) when the confirmation result of step (S30) is no, re-executing step (S20), and when the confirmation result of step (S30) is yes, confirming whether the output voltage is greater than a preset reference voltage through the detection result of the voltage detector; (S50) when the confirmation result of step (S40) is yes, driving the LLC resonant converter to operate in the first modulation mode and re-executing step (S30); and (S60) when the confirmation result of step (S40) is no, driving the LLC resonant converter to operate in a second modulation mode so that the resonant converter provides an output voltage less than the middle value voltage and re-executing step (S30).

[0007] To achieve the above object, the present disclosure further provides an LLC resonant converter for converting an input voltage to provide an output voltage and a fixed output current to a DC load. The LLC resonant converter includes: a primary side circuit; an isolation transformer including a primary side winding and a secondary side winding, the primary side winding being electrically connected to the primary side circuit; a secondary side circuit including a bridge rectifier circuit, a unidirectional controllable power switch, a voltage detector, and a current detector, the bridge rectifier circuit being electrically connected to the secondary side winding and including a plurality of diodes, the unidirectional controllable power switch being electrically connected in parallel with one of the plurality of diodes, the voltage detector being used to detect the output voltage, and the current detector being used to detect the output current; and a controller for controlling the operation of the LLC resonant converter; wherein after the LLC resonant converter is started, the controller drives the LLC resonant converter to operate in a first modulation mode to control the unidirectional controllable power switch to conduct, so that the secondary side circuit provides an output voltage greater than or equal to a middle value voltage, where the middle value voltage is half of the sum of a predetermined voltage and N times the predetermined voltage; wherein after the LLC resonant converter is started and the LLC resonant converter operates in the first modulation mode, the controller further confirms whether the output current is greater than 0 through the detection result of the current detector, and when it is confirmed that the output current is not greater than 0, the controller drives the LLC resonant converter to operate in the first modulation mode, and when it is confirmed that the output current is greater than 0, the controller further confirms whether the output voltage is greater than a preset reference voltage through the detection result of the voltage detector, and when it is confirmed that the output voltage is greater than the preset reference voltage, the controller drives the LLC resonant converter to operate in the first modulation mode, and when it is confirmed that the output voltage is less than or equal to the preset reference voltage, the controller drives the LLC resonant converter to operate in a second modulation mode to control the unidirectional controllable power switch to turn off, so that the secondary side circuit provides an output voltage less than the middle value voltage.

[0008] To achieve the above object, the present disclosure further provides an LLC resonant converter for converting an input voltage to provide an output voltage and a fixed output current to a DC load. The LLC resonant converter includes: a primary side circuit including a switching circuit and a resonant circuit, wherein the switching circuit receives the input voltage, is electrically connected to the resonant circuit, and includes four switches to form a full-bridge circuit; an isolation transformer including a primary side winding and a secondary side winding, the primary side winding being electrically connected to the primary side circuit; a secondary side circuit including a bridge rectifier circuit, a voltage detector, and a current detector, the bridge rectifier circuit being electrically connected to the secondary side winding, the voltage detector being used to detect the output voltage, and the current detector being used to detect the output current; and a controller for controlling the operation of the LLC resonant converter. When the LLC resonant converter is started, the controller drives the LLC resonant converter to operate in a first modulation mode to control the four switches of the switching circuit to switch in the form of a full-bridge circuit, so that the LLC resonant converter provides an output voltage greater than or equal to a middle value voltage, where the middle value voltage is half of the sum of a predetermined voltage and N times the predetermined voltage. After the LLC resonant converter is started and operates in the first modulation mode, the controller further confirms whether the output current is greater than 0 through the detection result of the current detector. When it is confirmed that the output current is not greater than 0, the controller drives the LLC resonant converter to operate in the first modulation mode. When it is confirmed that the output current is greater than 0, the controller further confirms whether the output voltage is greater than a preset reference voltage through the detection result of the voltage detector. When it is confirmed that the output voltage is greater than the preset reference voltage, the controller drives the LLC resonant converter to operate in the first modulation mode. When it is confirmed that the output voltage is less than or equal to the preset reference voltage, the controller drives the LLC resonant converter to operate in a second modulation mode to control the four switches of the switching circuit to switch in the form of a half-bridge circuit, so that the LLC resonant converter provides an output voltage less than the middle value voltage. Description of the Drawings

[0009] Figure 1 Schematic diagram of the relationship between the output voltage and the output current when the LLC resonant converter is applied to the occasion of constant current output;

[0010] Figure 2 Schematic diagram of the circuit architecture of the LLC resonant converter according to the first preferred embodiment of the present disclosure;

[0011] Figure 3 Flow chart of the steps of the control method according to the preferred embodiment of the present disclosure;

[0012] Figures 4A to 4E Respectively show the switching condition of the working mode of the resonant converter and the schematic diagram of the relationship between the corresponding output voltage and output current;

[0013] Figure 5Schematic diagram of the circuit architecture of the LLC resonant converter according to the second preferred embodiment of the present disclosure.

[0014] Description of reference numerals:

[0015] 1, 1a: LLC resonant converter

[0016] Vin: Input voltage

[0017] Vo: Output voltage

[0018] Io: Output current

[0019] 2: DC load

[0020] 120: Primary side circuit

[0021] 130: Isolation transformer

[0022] 140: Secondary side circuit

[0023] 150: Controller

[0024] 122: Switching circuit

[0025] 124: Resonant circuit

[0026] S1, S2, S3, S4: Switches

[0027] Cr: Resonant capacitor

[0028] Lr: Resonant inductor

[0029] Lm: Magnetizing inductor

[0030] Np: Primary side winding

[0031] Ns: Secondary side winding

[0032] 142: Bridge rectifier circuit

[0033] Smp: Unidirectional controllable power switch

[0034] Co: Output capacitor

[0035] 144: Voltage detector

[0036] 146: Current detector

[0037] D1 - D4: Diodes

[0038] R1, R2, R3: Resistors

[0039] S10 - S60: Steps of the control method of the LLC resonant converter Detailed implementation manners

[0040] Some exemplary embodiments embodying the features and advantages of the present disclosure will be described in detail in the following description. It should be understood that the present disclosure can have various variations in different embodiments, all of which do not depart from the scope of the present disclosure, and the descriptions and illustrations therein are for illustrative purposes in nature and not intended to limit the present disclosure.

[0041] Please refer to Figure 2 , which is a schematic circuit diagram of the LLC resonant converter according to the first preferred embodiment of the present disclosure. As Figure 2 shown, the LLC resonant converter 1 of this embodiment can be selectively electrically connected to the DC load 2, and convert the input voltage Vin received as a DC voltage to provide an output voltage Vo and an output current Io to the DC load 2 to drive the DC load 2, where the output current Io is a fixed value, and the above-mentioned selectivity means that the DC load 2 can choose to be electrically connected to the output terminal of the LLC resonant converter 1 when it is not electrically connected to the output terminal of the LLC resonant converter 1, or the DC load 2 can choose to remove the DC load 2 when it is electrically connected to the output terminal of the LLC resonant converter 1. In addition, the LLC resonant converter 1 can be applied to an LED power conversion device, so the DC load 2 correspondingly includes at least one LED lamp string or a plurality of serially connected LED lamp strings. However, the application scenario of the LLC resonant converter 1 and the composition of the DC load 2 are not limited to the above description, and the following takes the DC load 2 including at least one LED lamp string as an example for illustrative purposes. Moreover, in some embodiments, in order to match the type and quantity of the DC load 2 connected in series at the output terminal, the LLC resonant converter 1 can provide a wide range of output voltages Vo to the DC load 2 to meet the voltage specification requirements of different DC loads 2, where the output voltage Vo is between a predetermined voltage and N times the predetermined voltage, and N is a positive number greater than 1 but less than 4.

[0042] In this embodiment, the LLC resonant converter 1 includes a primary side circuit 120, an isolation transformer 130, a secondary side circuit 140, and a controller 150. The primary side circuit 120 is electrically connected to the primary winding Np of the isolation transformer 130 and receives the input voltage Vin to provide a primary side current flowing through the primary side winding Np according to the input voltage Vin. The primary side circuit 120 includes a switching circuit 122 and a resonant circuit 124. The switching circuit 122 is electrically connected to the resonant circuit 124 to convert the input voltage Vin into a high-frequency AC voltage and output it to the resonant circuit 124. In some embodiments, the switching circuit 122 can adopt a half-bridge architecture to implement a half-bridge resonant converter in the primary side circuit 120, but the present disclosure is not limited thereto. Additionally, the switching circuit 122 includes a switch S1 and a switch S2 connected in series, where the switches S1 and S2 are selectively turned on or off.

[0043] The resonant circuit 124 is electrically connected between the switching circuit 122 and the primary side winding Np. The resonant circuit 124 is configured to receive a high-frequency alternating voltage from the switching circuit 122 and generate resonance to provide a primary side current flowing through the primary side winding Np. In some embodiments, the resonant circuit 124 may include, but is not limited to, a resonant capacitor Cr, a resonant inductor Lr, and an exciting inductor Lm. The resonant capacitor Cr, the resonant inductor Lr, and the primary side winding Np of the isolation transformer 130 are connected in series with each other. The exciting inductor Lm and the primary side winding Np of the isolation transformer 130 are connected in parallel with each other. In some embodiments, the resonant inductor Lr and the exciting inductor Lm may respectively magnetically integrate the leakage inductance and the magnetizing inductance of the isolation transformer 130.

[0044] The primary side winding Np of the isolation transformer 130 can receive the primary side current from the resonant circuit 124. The secondary side winding Ns of the isolation transformer 130 can then induce the primary side current flowing through the primary side winding Np to output a secondary side current, enabling the isolation transformer 130 to achieve energy transfer between the primary side and the secondary side.

[0045] In this embodiment, the secondary side circuit 140 includes a bridge rectifier circuit 142, a unidirectional controllable power switch Smp, an output capacitor Co, a charge pump capacitor Ccp, a voltage detector 144, and a current detector 146. The bridge rectifier circuit 142 is electrically connected to the secondary side winding Ns and includes a plurality of diodes D1 - D4 to rectify the secondary side current through the plurality of diodes D1 - D4. The charge pump capacitor Ccp is electrically connected between the secondary side winding Ns and the bridge rectifier circuit 142. The unidirectional controllable power switch Smp is electrically connected in parallel with one of the plurality of diodes D1 - D4 in the bridge rectifier circuit 142, for example, in parallel with the diode D4, to selectively conduct or turn off. The output capacitor Co is electrically connected to the bridge rectifier circuit 142 to provide an output voltage Vo according to the secondary side current. The voltage detector 144 is electrically connected to the output terminal of the LLC resonant converter 1 to detect the output voltage Vo on the output terminal of the LLC resonant converter 1 and transmit the detection result to the controller 150, where the voltage detector 144 may include, but is not limited to, a voltage division circuit formed by two resistors R1 and R2 connected in series. The current detector 146 is electrically connected to the output terminal of the LLC resonant converter 1 to detect the output current Io on the output terminal of the LLC resonant converter 1 and transmit the detection result to the controller 150, where the current detector 146 may include, but is not limited to, a resistor R3. Of course, in other embodiments, the current detector 146 may also include a current transformer.

[0046] In some embodiments, the unidirectional controllable power switch Smp may be an npn-type bipolar transistor. The emitter terminal of the bipolar transistor is electrically coupled to the anode terminal of the diode D4, and the collector terminal is electrically coupled to the cathode terminal of the diode D4. In other words, in this embodiment, the unidirectional controllable power switch Smp is reversely connected in parallel with the diode D4 in the bridge rectifier circuit 142, but the present disclosure is not limited thereto. Of course, the unidirectional controllable power switch Smp is not limited to an npn-type bipolar transistor. For example, the unidirectional controllable power switch Smp may also include a pnp-type bipolar junction transistor (BJT), an insulated gate bipolar transistor (IGBT), a silicon controlled rectifier (SCR), and so on.

[0047] In this embodiment, when the unidirectional controllable power switch Smp is turned on, the secondary side circuit 140 operates in a voltage multiplier rectification mode to provide an output voltage Vo greater than or equal to the intermediate voltage, where the intermediate voltage is half of the sum of a predetermined voltage and N times the predetermined voltage. When the unidirectional controllable power switch Smp is turned off, the secondary side circuit 140 operates in a full bridge rectification mode to provide an output voltage Vo less than the intermediate voltage.

[0048] The controller 150 is used to control the operation of the LLC resonant converter 1. After the LLC resonant converter 1 is started, the controller 150 drives the LLC resonant converter 1 to operate in a first modulation mode, that is, the controller 150 controls the unidirectional controllable power switch Smp to be turned on, so that the secondary side circuit 140 provides an output voltage Vo greater than or equal to the intermediate voltage. At this time, the output voltage Vo provided by the secondary side circuit 140 is at least twice the predetermined voltage or more. Since after the LLC resonant converter 1 is started, the LLC resonant converter 1 operates in the first modulation mode to provide an output voltage Vo through the secondary side circuit 140 that is at least twice the predetermined voltage or more, when the DC load 2 is connected to the output terminal of the LLC resonant converter 1, whether the DC load 2 is high-voltage driven or low-voltage driven, the LLC resonant converter 1 can immediately drive the DC load 2 to emit light.

[0049] In addition, after the LLC resonant converter 1 starts and operates in the first modulation mode, the controller 150 further confirms whether the output current Io is greater than 0 based on the detection result of the current detector 146 to determine whether the output terminal of the LLC resonant converter 1 is electrically connected to the DC load 2. When the controller 150 confirms that the output current Io is not greater than 0, it means that the output terminal of the LLC resonant converter 1 is not yet electrically connected to any DC load 2. At this time, the controller 150 drives the LLC resonant converter 1 to operate in the first modulation mode, so that the secondary side circuit 140 continuously provides an output voltage Vo greater than or equal to the intermediate voltage, waiting for the DC load 2 to be connected at any time and immediately driving the DC load 2 to light up.

[0050] Conversely, when the controller 150 confirms that the output current Io is greater than 0, it means that the output terminal of the LLC resonant converter 1 is already electrically connected to the DC load 2. At this time, it is necessary to further confirm whether the DC load 2 is high-voltage driven or low-voltage driven, so that the LLC resonant converter 1 can correspondingly adjust the output voltage Vo and operate at a high-efficiency resonant frequency operating point. Therefore, in this embodiment, the controller 150 further confirms whether the output voltage Vo is greater than the preset reference voltage based on the detection result of the voltage detector 144. When the detection result of the voltage detector 144 is that the output voltage Vo is greater than the preset reference voltage, it means that the DC load 2 needs high-voltage drive. Therefore, the controller 150 drives the LLC resonant converter 1 to operate in the first modulation mode and makes the secondary side circuit 140 continuously provide an output voltage Vo greater than or equal to the intermediate voltage. Conversely, when the detection result of the voltage detector 144 is that the output voltage Vo is less than or equal to the preset reference voltage, it means that the DC load 2 needs low-voltage drive. Therefore, the controller 150 drives the LLC resonant converter 1 to operate in the second modulation mode, that is, the controller 150 controls the unidirectional controllable power switch Smp to turn off, so that the secondary side circuit 140 provides an output voltage Vo less than the intermediate voltage.

[0051] As can be seen from the above, the LLC resonant converter 1 of the present disclosure can detect the output voltage Vo based on the detection result of the voltage detector 144 and compare the detection result with the preset reference voltage, thereby judging whether the DC load 2 electrically connected to the output terminal of the LLC resonant converter 1 is high-voltage driven or low-voltage driven, and adjusting the working mode of the LLC resonant converter 1 according to the comparison result (that is, switching between the first modulation mode and the second modulation mode), so that the LLC resonant converter 1 can operate at a high-efficiency resonant frequency operating point. Therefore, the LLC resonant converter 1 can still achieve the advantage of high efficiency in applications with a wide output voltage range.

[0052] Of course, in some embodiments, the controller 150 of the present disclosure can also control the over-voltage protection (OVP) mechanism according to the detection result of the voltage detector 144, and can control the over-current protection (OCP) mechanism according to the current detector 146. The control mechanisms of over-voltage protection and over-current protection are common in the circuit field, and thus the control mechanisms of over-voltage protection and over-current protection will not be described herein. In addition, the controller 150 can also control the operation of the primary side circuit 120. Moreover, the controller 150 can be, but is not limited to, a microprocessor.

[0053] Please refer to Figure 3 , which is a flowchart of the steps of the control method of the preferred embodiment of the present disclosure.

[0054] As Figure 3 shown, the control method of this embodiment is applicable to an LLC resonant converter, such as Figure 2 shown in the controller 150 of the LLC resonant converter 1, and the control method includes the following steps.

[0055] In step S10, start to start the LLC resonant converter 1.

[0056] In step S20, drive the LLC resonant converter 1 to operate in a first modulation mode, so that the LLC resonant converter 1 provides an output voltage Vo greater than or equal to the intermediate voltage, where the intermediate voltage is half of the sum of the predetermined voltage and N times the predetermined voltage.

[0057] In step S30, confirm whether the output current Io is greater than 0 through the detection result of the current detector 146. When the confirmation result of step S30 is that the output current Io is not greater than 0, then re-execute step S20. On the contrary, when the confirmation result of step S30 is that the output current Io is greater than 0, then execute step S40.

[0058] In step S40, confirm whether the output voltage Vo is greater than the preset reference voltage through the detection result of the voltage detector 144. When the confirmation result of step S40 is that the output voltage Vo is greater than the preset reference voltage, then execute step S50. On the contrary, when the confirmation result of step S40 is that the output voltage Vo is not greater than the preset reference voltage, then execute step S60.

[0059] In step S50, drive the resonant converter 1 to operate in the first modulation mode and re-execute step S30.

[0060] In step S60, drive the resonant converter 1 to operate in a second modulation mode, so that the LLC resonant converter provides an output voltage less than the intermediate voltage, and re-execute step S30.

[0061] In the above embodiments, step S20 and step S50 further respectively include controlling the unidirectional controllable power switch Smp in the secondary-side circuit 140 to conduct, so that the secondary-side circuit 140 provides an output voltage Vo greater than or equal to the intermediate value voltage. Step S60 further includes controlling the unidirectional controllable power switch Smp in the secondary-side circuit 140 to disconnect, so that the secondary-side circuit 140 provides an output voltage Vo less than the intermediate value voltage.

[0062] According to the above content, the following will use Figures 4A to 4E to illustrate the switching condition of the operating mode of the resonant converter 1 and the corresponding conditions of the output voltage Vo and the output current Io. Please refer to Figures 4A to 4E and cooperate with Figure 2 and Figure 3 where Figures 4A to 4E are respectively schematic diagrams of the switching condition of the operating mode of the resonant converter and the relationship between the corresponding output voltage Vo and the output current Io. As Figures 4A to 4E shows, if the output terminal of the resonant converter 1 is electrically connected to the high-voltage-driven DC load 2, then as Figure 4A shows, when the resonant converter 1 starts up at time t1, it will first operate in the first modulation mode. Then, at time t2, the controller 150 confirms through the detection result of the current detector 146 that the output current Io is greater than 0, and through the detection result of the voltage detector 144 that the output voltage Vo is greater than the preset reference voltage. The controller 150 then drives the resonant converter 1 to continue operating in the first modulation mode. Among them, in Figure 4A , in the interval from time t1 to time t2, the controller 150 performs the control mechanism of overvoltage protection. Therefore, at this time, the output voltage Vo will be maintained at the protection voltage level, and Figures 4B to 4E shows the same control mechanism of overvoltage protection, which will not be elaborated here.

[0063] If the output terminal of the resonant converter 1 is electrically connected to the low-voltage-driven DC load 2, then as Figure 4B shows, when the resonant converter 1 starts up at time t1, it will first operate in the first modulation mode. Then, at time t2, the controller 150 confirms through the detection result of the current detector 146 that the output current Io is greater than 0, and through the detection result of the voltage detector 144 that the output voltage Vo is not greater than the preset reference voltage. The controller 150 then drives the resonant converter 1 to operate in the second modulation mode.

[0064] If the output terminal of the resonant converter 1 is not electrically connected to any DC load 2, then as Figure 4CAs shown, when the resonant converter 1 starts up at time t1, it first operates in the first modulation mode. Then, at time t2, the controller 150 confirms through the detection result of the current detector 146 that the output current Io is not greater than 0. Therefore, the controller 150 drives the resonant converter 1 to continue operating in the first modulation mode, waiting for the DC load 2 to be connected.

[0065] If, after the resonant converter 1 starts up, the high-voltage-driven DC load 2 is removed from the output terminal of the resonant converter 1 at Figure 4A the time t3 shown, then as Figure 4D shown, at time t3, the controller 150 confirms through the detection result of the current detector 146 that the output current Io is not greater than 0. The controller 150 drives the resonant converter 1 to operate in the first modulation mode. At this time, the controller 150 performs an overvoltage protection control mechanism to maintain the output voltage Vo at the protection voltage level.

[0066] If, after the resonant converter 1 starts up, the low-voltage-driven DC load 2 is removed from the output terminal of the resonant converter 1 at Figure 4B the time t3 shown, then as Figure 4E shown, at time t3, the controller 150 confirms through the detection result of the current detector 146 that the output current Io is not greater than 0. The controller 150 drives the resonant converter 1 to switch from the second modulation mode to the first modulation mode. At this time, the controller 150 performs an overvoltage protection control mechanism to maintain the output voltage Vo at the protection voltage level.

[0067] Please refer to Figure 5 , which is a schematic diagram of the circuit architecture of the LLC resonant converter according to the second preferred embodiment of the present disclosure. The output current Io output by the LLC resonant converter 1a in this embodiment is a fixed value, and the output voltage Vo output by the LLC resonant converter 1a is between a predetermined voltage and N times the predetermined voltage. Moreover, the circuit architecture of the LLC resonant converter 1a is similar to Figure 2 the LLC resonant converter 1 shown. Therefore, only the same symbols are used to represent the circuit structure and operation mode that are similar and will not be described in detail here. The secondary side circuit 140 of the LLC resonant converter 1a in this embodiment only includes a bridge rectifier circuit 142, an output capacitor Co, a voltage detector 144, and a current detector 146, and does not include Figure 2 the unidirectional controllable power switch Smp shown. Therefore, regardless of whether the controller 150 drives the resonant converter 1a to operate in the first modulation mode or the second modulation mode, the secondary side circuit 140 operates in a full-bridge rectification mode.

[0068] In addition, the switching circuit 122 of the primary side circuit 120 of the LLC resonant converter 1a in this embodiment is changed to adopt a full-bridge architecture. Therefore, in addition to including the switches S1 and S2 that form the bridge arms, it also includes the switches S3 and S4 that form the other bridge arm and are connected in series. In addition, when the controller 150 drives the resonant converter 1a to operate in the first modulation mode, the controller 150 controls the switches S1, S2, S3, and S4 of the switching circuit 122 to switch in the form of a full-bridge circuit, so that the primary side circuit 120 forms a full-bridge resonant circuit, thereby enabling the input voltage Vin to provide the primary side current flowing through the primary side winding Np, so that the resonant converter 1 provides an output voltage Vo greater than or equal to the intermediate voltage, where the intermediate voltage is half of the sum of a predetermined voltage and N times the predetermined voltage. When the controller 150 drives the resonant converter 1 to operate in the second modulation mode, the controller 150 controls the switches S1, S2, S3, and S4 of the switching circuit 122 to switch in the form of a half-bridge circuit. For example, the control switch S3 is controlled to be constantly off, the switch S4 is constantly on, and the switches S1 and S2 are selectively turned on or off, so that the primary side circuit 120 forms a half-bridge resonant circuit, thereby enabling half of the input voltage Vin to provide the primary side current flowing through the primary side winding Np, so that the resonant converter 1 provides an output voltage Vo less than the intermediate voltage.

[0069] Of course, the foregoing Figure 3 shown control method is still applicable to Figure 5 the LLC resonant converter 1a shown, and Figure 5 the secondary side circuit 140 of the LLC resonant converter 1a shown does not include Figure 2 the unidirectional controllable power switch Smp shown, and the switching circuit 122 of the primary side circuit 120 of the resonant converter 1a is changed to adopt a full-bridge architecture. Therefore, in some embodiments, Figure 3 the steps S20 and S50 shown further include controlling the switches S1, S2, S3, and S4 of the switching circuit 122 to switch in the form of a full-bridge circuit, so that the resonant converter 1a provides an output voltage Vo greater than or equal to the intermediate voltage. Step S60 further includes controlling the switches S1, S2, S3, and S4 of the switching circuit 122 to switch in the form of a half-bridge circuit, so that the resonant converter 1a provides an output voltage Vo less than the intermediate voltage.

[0070] In summary, the present disclosure provides an LLC resonant converter. The LLC resonant converter can detect the output voltage based on the detection result of a voltage detector, and compare the detection result with a preset reference voltage, thereby determining whether the DC load electrically connected to the output end of the LLC resonant converter is high-voltage driven or low-voltage driven, and adjusting the operating mode of the LLC resonant converter according to the comparison result, so that the LLC resonant converter can operate at a high-efficiency resonant frequency operating point. Therefore, the LLC resonant converter still has the advantage of high efficiency in applications with a wide output voltage range.

Claims

1. A control method, applicable to an LLC resonant converter, which converts an input voltage to provide an output voltage and a fixed output current to a DC load, wherein the output voltage is between a predetermined voltage and N times the predetermined voltage, and the LLC resonant converter includes a voltage detector for detecting the output voltage and a current detector for detecting the output current, and N is an integer. The control method includes: (S10) Start the LLC resonant converter; (S20) Drive the LLC resonant converter to operate in a first modulation mode, so that the LLC resonant converter provides an output voltage greater than or equal to a middle value voltage, where the middle value voltage is half of the sum of the predetermined voltage and N times the predetermined voltage; (S30) Confirm whether the output current is greater than 0 through the detection result of the current detector; (S40) When the confirmation result of step (S30) is no, re - execute step (S20). When the confirmation result of step (S30) is yes, confirm whether the output voltage is greater than a preset reference voltage through the detection result of the voltage detector; (S50) When the confirmation result of step (S40) is yes, drive the LLC resonant converter to operate in the first modulation mode and execute step (S30); and (S60) When the confirmation result of step (S40) is no, drive the LLC resonant converter to operate in a second modulation mode, so that the resonant converter provides an output voltage less than the middle value voltage, and execute step (S30).

2. The control method according to claim 1, wherein N is a positive number greater than 1.5 and less than 4.

3. The control method according to claim 1, wherein the LLC resonant converter includes: A primary - side circuit; An isolation transformer, including a primary - side winding and a secondary - side winding, the primary - side winding is electrically connected to the primary - side circuit; and A secondary - side circuit, including a bridge rectifier circuit, a unidirectional controllable power switch, the voltage detector and the current detector. The bridge rectifier circuit includes a plurality of diodes electrically connected, and the unidirectional controllable power switch is electrically connected in parallel with one of the plurality of diodes.

4. The control method according to claim 3, wherein in step (S20) and step (S50), it further includes respectively: controlling the unidirectional controllable power switch to conduct, so that the secondary - side circuit provides an output voltage greater than or equal to the middle value voltage.

5. The control method according to claim 3, wherein in step (S60), it further includes respectively: controlling the unidirectional controllable power switch to disconnect, so that the secondary - side circuit provides an output voltage less than the middle value voltage.

6. The control method according to claim 1, wherein the LLC resonant converter includes: A primary - side circuit, including a switching circuit and a resonant circuit, wherein the switching circuit receives the input voltage, is electrically connected to the resonant circuit, and includes four switches to form a full - bridge circuit; An isolation transformer, including a primary - side winding and a secondary - side winding, the primary - side winding is electrically connected to the resonant circuit; and A secondary side circuit, including a bridge rectifier circuit, the voltage detector, and the current detector.

7. The control method according to claim 6, wherein in the step (S20) and the step (S50), it further includes respectively: controlling the four switches of the switching circuit to switch in the form of a full-bridge circuit, so that the primary side circuit forms a full-bridge resonant circuit, and enabling the LLC resonant converter to provide the output voltage greater than or equal to the intermediate value voltage.

8. The control method according to claim 6, wherein in the step (S60), it further includes: controlling the four switches of the switching circuit to switch in the form of a half-bridge circuit, so that the primary side circuit forms a half-bridge resonant circuit, and enabling the LLC resonant converter to provide the output voltage less than the intermediate value voltage.

9. An LLC resonant converter for converting an input voltage to provide an output voltage and a fixed output current to a DC load, the LLC resonant converter comprising: A primary side circuit; An isolation transformer, including a primary side winding and a secondary side winding, the primary side winding being electrically connected to the primary side circuit; A secondary side circuit, including a bridge rectifier circuit, a unidirectional controllable power switch, a voltage detector, and a current detector, the bridge rectifier circuit being electrically connected to the secondary side winding and including a plurality of diodes, the unidirectional controllable power switch being electrically connected in parallel with one of the plurality of diodes, the voltage detector being used to detect the output voltage, and the current detector being used to detect the output current ； and A controller for controlling the operation of the LLC resonant converter; wherein after the LLC resonant converter is started, the controller drives the LLC resonant converter to operate in a first modulation mode to control the unidirectional controllable power switch to conduct, so that the secondary side circuit provides the output voltage greater than or equal to an intermediate value voltage, wherein the intermediate value voltage is half of the sum of a predetermined voltage and N times the predetermined voltage; wherein after the LLC resonant converter is started and the LLC resonant converter operates in the first modulation mode, the controller further confirms whether the output current is greater than 0 through the detection result of the current detector, and when it is confirmed that the output current is not greater than 0, the controller drives the LLC resonant converter to operate in the first modulation mode, and when it is confirmed that the output current is greater than 0, the controller further confirms whether the output voltage is greater than a preset reference voltage through the detection result of the voltage detector, and when it is confirmed that the output voltage is greater than the preset reference voltage, the controller drives the LLC resonant converter to operate in the first modulation mode, and when it is confirmed that the output voltage is less than or equal to the preset reference voltage, the controller drives the LLC resonant converter to operate in a second modulation mode to control the unidirectional controllable power switch to disconnect, so that the secondary side circuit provides the output voltage less than the intermediate value voltage.

10. An LLC resonant converter for converting an input voltage to provide an output voltage and a fixed output current to a DC load, the LLC resonant converter comprising: A primary side circuit, comprising a switching circuit and a resonant circuit, wherein the switching circuit receives the input voltage, is electrically connected to the resonant circuit, and comprises four switches to form a full-bridge circuit; An isolation transformer, comprising a primary side winding and a secondary side winding, wherein the primary side winding is electrically connected to the primary side circuit; A secondary side circuit, comprising a bridge rectifier circuit, a voltage detector and a current detector, wherein the bridge rectifier circuit is electrically connected to the secondary side winding, the voltage detector is used for detecting the output voltage, and the current detector is used for detecting the output current ； and A controller, used for controlling the operation of the LLC resonant converter; Wherein after the LLC resonant converter is started, the controller drives the LLC resonant converter to operate in a first modulation mode, to control the four switches of the switching circuit to switch in the form of a full-bridge circuit, so that the LLC resonant converter provides an output voltage greater than or equal to an intermediate voltage, wherein the intermediate voltage is half of the sum of a predetermined voltage and N times the predetermined voltage; Wherein after the LLC resonant converter is started and the LLC resonant converter operates in the first modulation mode, the controller further confirms whether the output current is greater than 0 through the detection result of the current detector, and when it is confirmed that the output current is not greater than 0, the controller drives the LLC resonant converter to operate in the first modulation mode, and when it is confirmed that the output current is greater than 0, the controller further confirms whether the output voltage is greater than a preset reference voltage through the detection result of the voltage detector, and when it is confirmed that the output voltage is greater than the preset reference voltage, the controller drives the LLC resonant converter to operate in the first modulation mode, and when it is confirmed that the output voltage is less than or equal to the preset reference voltage, the controller drives the LLC resonant converter to operate in a second modulation mode, to control the four switches of the switching circuit to switch in the form of a half-bridge circuit, so that the LLC resonant converter provides an output voltage less than the intermediate voltage.

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