LLC resonant converter, power supply circuit and method of generating an output voltage thereof

Abstract

The application discloses an LLC resonant converter, a power supply circuit and a method for generating an output voltage. The LLC resonant converter comprises a full-bridge switching circuit, a transformer, a resonant circuit and a bridge rectifier. The full-bridge switching circuit comprises a first transistor, a second transistor, a third transistor and a fourth transistor, the first ends of the first transistor and the third transistor are connected to a direct current input voltage, and the second ends of the first transistor and the third transistor are respectively connected to the first ends of the second transistor and the fourth transistor. The two ends of a secondary winding of the transformer are respectively connected to the second ends of the fourth transistor and the second transistor. The resonant circuit is connected between a first switching node formed by the first transistor and the second transistor and a second switching node formed by the third transistor and the fourth transistor. The bridge rectifier is connected between the two ends of the secondary winding to generate a rectified output signal, and the rectified output signal is filtered to generate an output voltage. The application improves the efficiency of the LLC resonant converter.

Description

Technical Field

[0001] Embodiments of the present invention relate to an electronic circuit, and more particularly, to an LLC resonant converter and a power supply circuit including the LLC resonant converter. Background Technology

[0002] A converter is an electronic circuit that converts an input voltage into an output voltage. An LLC resonant converter is a type of converter that uses a resonant circuit to convert a DC input voltage into a DC output voltage. This resonant circuit includes a resonant capacitor, a resonant inductor, and the magnetizing inductance of a transformer. An LLC resonant converter contains a bridge switching circuit for converting the DC input voltage into a square wave. The square wave excites the resonant circuit to generate a sine wave signal, which is then scaled and adjusted by the transformer. The scaled and adjusted signal is rectified by a rectifier and then filtered by an output capacitor to produce a DC output voltage. The bridge switching circuit and the rectifier are located on different sides of the transformer. More specifically, the bridge switching circuit is located on the primary side of the transformer (also known as the "high-voltage side"), while the rectifier is located on the secondary side (also known as the "low-voltage side"). In particular, the bridge switching circuit is coupled between the positive and negative terminals (i.e., reference ground) of the DC input voltage. Summary of the Invention

[0003] This invention provides an LLC resonant converter, a power supply circuit, and a method for generating the output voltage of the LLC resonant converter.

[0004] According to an embodiment of the present invention, an LLC resonant converter is provided, comprising: a full-bridge switching circuit, a transformer, a resonant circuit, and a bridge rectifier. The full-bridge switching circuit includes a first transistor, a second transistor, a third transistor, and a fourth transistor, each transistor including a first terminal and a second terminal, wherein the first terminals of the first and third transistors are connected to a DC input voltage, the second terminal of the first transistor is connected to the first terminal of the second transistor, and the second terminal of the third transistor is connected to the first terminal of the fourth transistor. The transformer includes a primary winding and a secondary winding, each winding having a first terminal and a second terminal, wherein the first terminal of the secondary winding is connected to the second terminal of the fourth transistor, and the second terminal of the secondary winding is connected to the second terminal of the second transistor. The resonant circuit includes a resonant capacitor, a resonant inductor, and a magnetizing inductance of the primary winding of the transformer, wherein the resonant circuit is connected between a first switching node formed by the first and second transistors and a second switching node formed by the third and fourth transistors. The bridge rectifier is connected between the first and second terminals of the secondary winding to generate a rectified output signal, wherein the rectified output signal is filtered to generate a DC output voltage at an output node.

[0005] According to an embodiment of the present invention, a power supply circuit is provided, comprising: a full-bridge switching circuit, a transformer, a resonant circuit, a bridge rectifier, and an LLC resonant controller. The full-bridge switching circuit includes a first transistor, a second transistor, a third transistor, and a fourth transistor. Each transistor includes a first terminal and a second terminal. The first terminals of the first and third transistors are connected to a DC input voltage. The second terminal of the first transistor is connected to the first terminal of the second transistor, and the second terminal of the third transistor is connected to the first terminal of the fourth transistor. The transformer includes a primary winding and a secondary winding. Each winding has a first terminal and a second terminal. The first terminal of the secondary winding is connected to the second terminal of the fourth transistor, and the second terminal of the secondary winding is connected to the second terminal of the second transistor. The resonant circuit includes a resonant capacitor, a resonant inductor, and a magnetizing inductance of the primary winding of the transformer. The resonant circuit is connected between a first switching node formed by the first and second transistors and a second switching node formed by the third and fourth transistors. The bridge rectifier is connected between the first and second terminals of the secondary winding to generate a rectified output signal, wherein the rectified output signal is filtered to generate a DC output voltage at an output node. The LLC resonant controller generates multiple control signals to control the first transistor, the second transistor, the third transistor, and the fourth transistor to generate the DC output voltage on an output capacitor.

[0006] According to an embodiment of the present invention, a method for generating an output voltage at an output node of an LLC resonant converter is proposed. The method includes the following steps: alternately turning on and off a first pair of switches and a second pair of switches of a full-bridge switching circuit to excite the resonant circuit to generate a sinusoidal current flowing through the primary winding of a transformer and to the output node; generating a second sinusoidal current through the coupling of the primary and secondary windings of the transformer, the second sinusoidal current flowing through the secondary winding of the transformer and then to the output node; rectifying the first and second sinusoidal currents flowing through the primary and secondary windings of the transformer using a bridge rectifier; and filtering the rectified output signal of the bridge rectifier to generate the output voltage of the LLC resonant converter.

[0007] Compared to traditional topologies, the LLC resonant converter of this invention allows the primary-side current to flow directly to the output voltage node, thus the secondary winding only needs to handle a portion of the load current. This reduces the power density of the LLC resonant converter, thereby improving its efficiency and reducing its cost. Attached Figure Description

[0008] To better understand this invention, it will be described in detail with reference to the following drawings. Identical or similar elements are referred to by the same reference numerals.

[0009] Figure 1 A circuit diagram of an LLC resonant converter 100 according to an embodiment of the present invention is shown.

[0010] Figure 2 The present invention includes, as shown in the embodiments thereof, Figure 1 A schematic diagram of the power supply circuit 200 of the LLC resonant converter 100 shown.

[0011] Figure 3 Examples of embodiments of the present invention are shown. Figure 2 The simulation waveform of the power supply circuit shown is shown in Figure 300.

[0012] Figure 4 This shows the effect during the positive half-cycle, as follows: Figure 1 The schematic diagram of the LLC resonant converter 100 is shown.

[0013] Figure 5 This shows the effect during the negative half-cycle, as follows: Figure 1 The schematic diagram of the LLC resonant converter 100 is shown.

[0014] Figure 6 A flowchart of a method 600 for generating the output voltage of an LLC resonant converter according to an embodiment of the present invention is shown. Detailed Implementation

[0015] Specific embodiments of the present invention will now be described in detail. It should be noted that the embodiments described herein are for illustrative purposes only and are not intended to limit the invention. In the following description, numerous specific details are set forth in order to provide a thorough understanding of the invention. However, it will be apparent to those skilled in the art that these specific details are not necessary to practice the invention. In other instances, well-known circuits, materials, or methods have not been specifically described to avoid obscuring the invention. Terms used herein such as “connection” and “coupled” are defined as directly or indirectly coupled in an electrical or non-electrical manner. Terms such as “a,” “the,” and “described” include a plurality of them. The phrase “in one embodiment” as used herein does not necessarily refer to the same embodiment, but may refer to the same embodiment.

[0016] For ease of explanation, the transistor used herein is a metal-oxide-semiconductor field-effect transistor (MOSFET) having a first terminal (drain), a second terminal (source), and a control terminal (gate). Those skilled in the art will understand that other types of transistors can also be used, with corresponding modifications to the transistor coupling method. It should be understood by those skilled in the art that the foregoing terminology is not intended to limit the meaning of these terms, but is merely illustrative.

[0017] Figure 1A circuit diagram of an LLC resonant converter 100 according to an embodiment of the present invention is shown. Figure 1 In the illustrated embodiment, the LLC resonant converter 100 includes a bridge switching circuit 110, a resonant circuit 120, a transformer T1, and a bridge rectifier circuit 130.

[0018] exist Figure 1 In the illustrated embodiment, the bridge switching circuit 110 includes a full-bridge switching circuit comprising transistors Q1, Q2, Q3, and Q4. The drain of transistor Q1 is connected to the positive terminal of the DC input voltage Vin (input voltage node 102), and the source of transistor Q1 is connected to the drain of transistor Q2 (first switching node 103). Similarly, the drain of transistor Q3 is also connected to the positive terminal of the DC input voltage Vin (input voltage node 102), and the source of transistor Q3 is connected to the drain of transistor Q4 (second switching node 104).

[0019] Transformer T1 includes a primary winding W1 and a secondary winding W2. The primary winding W1 and the secondary winding W2 have polarities, and by convention, their corresponding terminals are indicated by dots as shown in the diagram. The primary winding W1 has a magnetizing inductance Lm.

[0020] The resonant circuit 120 includes a resonant capacitor Cr, a resonant inductor Lr, and the magnetizing inductance Lm of the primary winding W1 of transformer T1. The resonant capacitor Cr, the resonant inductor Lr, and the magnetizing inductance Lm of the primary winding W1 form a series circuit to create a resonant slot. Figure 1 In the illustrated embodiment, the first end of the resonant inductor Lr is connected to the first switching node 103, and the second end of the resonant inductor Lr is connected to the first end of the primary winding W1. The second end of the primary winding W1 is connected to the first end of the resonant capacitor Cr, and the second end of the resonant capacitor Cr is connected to the second switching node 104.

[0021] The bridge rectifier circuit 130 includes a full-bridge rectifier circuit composed of transistors S1, S2, S3, and S4. The drain of transistor S3 and the drain of transistor S1 are connected to the output voltage Vo (output voltage node 101). The source of transistor S4 and the source of transistor S2 are connected to the negative terminal of the input voltage Vin (reference node 108). The source of transistor S3 is connected to the drain of transistor S4 to form a switching node, which is connected to the first terminal of the secondary winding W2. The source of transistor S1 is connected to the drain of transistor S2 to form a switching node, which is connected to the second terminal of the secondary winding W2. The first terminal of the secondary winding W2 is connected to the source of transistor Q4. The second terminal of the secondary winding W2 is connected to the source of transistor Q2.

[0022] The input capacitor Cin, used for noise filtering, is connected across the DC input voltage Vin. The output capacitor Co filters the signal output from the bridge rectifier circuit 130, and the output voltage Vo is generated across the output capacitor Co. The resistor RL represents the load of the LLC resonant converter 100.

[0023] Figure 2 The present invention includes, as shown in the embodiments thereof, Figure 1 This diagram illustrates the power supply circuit 200 of the LLC resonant converter 100. The power supply circuit 200 includes an LLC resonant controller 201 and the LLC resonant converter 100. The LLC resonant controller 201 may include a commercially available LLC resonant controller or be derived from an existing resonant controller. The LLC resonant controller is available from various suppliers, such as Monolithic Power Systems, Inc. The LLC resonant controller 201 generates control signals to drive the gates of the transistors (i.e., transistors Q1, Q2, Q3, Q4, S1, S2, S3, and S4) of the LLC resonant converter 100, thereby controlling the switching of the transistors of the LLC resonant converter 100 on and off. Those skilled in the art will understand that the control signals can control the gate-source voltage of a MOSFET, thereby turning the MOSFET on or off.

[0024] LLC resonant controller 201 controls transistors Q1, Q2, Q3, and Q4 to generate square waves at switching nodes 103 and 104, respectively, to excite resonant circuit 120 to generate a sinusoidal signal. This sinusoidal signal is scaled and adjusted according to the turns ratio of the primary winding W1 and the secondary winding W2. The turns ratio of the primary winding W1 and the secondary winding W2 can be adjusted according to different scaling requirements in actual applications. LLC resonant controller 201 controls transistors S1 to S4 to rectify the scaled sinusoidal signal. Output capacitor Co filters the rectified signal to generate an output voltage Vo, which is then sent to the load RL. Normally, resonant circuit 120 acts as a voltage divider. When resonance does not occur, the impedance of resonant circuit 120 increases, thereby reducing the output voltage Vo. LLC resonant controller 201 adjusts the switching frequencies of transistors Q1, Q2, Q3, and Q4, thereby adjusting the operating frequency of resonant circuit 120 to maintain the output voltage Vo within the control range.

[0025] Now refer to Figures 3-5 This describes an operational example of the power supply circuit 200. Figure 3 Examples of embodiments of the present invention are shown. Figure 2 The simulation waveform of the power supply circuit shown is shown in Figure 300. Figure 4 and Figure 5 The figures for the positive and negative half-cycles are shown respectively. Figure 1 The schematic diagram of the LLC resonant converter 100 is shown.

[0026] Figure 3 The waveform 223 of the current iLr through the resonant inductor Lr is shown, with the vertical axis representing the current. It should be noted that the current iLr is a sine wave. Accordingly, the current flowing through the primary winding W1 and the secondary winding W2 is also a sine wave.

[0027] exist Figure 3 In the illustrated embodiment, waveform 224 shows the control signals (gate-source voltage Vgs) used to control the on and off switching of transistors Q2, Q3, S1, and S4, with the vertical axis representing voltage. Waveform 225 shows the control signals (gate-source voltage Vgs) used to control the on and off switching of transistors Q1, Q4, S2, and S3, with the vertical axis representing voltage. Figure 3 In the illustrated embodiment, the horizontal axis represents time. The time period from t0 to t1 is the positive half-cycle, and the current iLr flows in the positive direction (i.e., the current iLr flows from the first switching node 103 to the primary winding W1). The time period from t1 to t2 is the negative half-cycle, and the current iLr flows in the negative direction (i.e., the current iLr flows from the second switching node 104 to the primary winding W1).

[0028] Figure 4 This shows the positive half-cycle (i.e. Figure 3 A schematic diagram of an LLC resonant converter 100 during the time interval t0 to t1. During the positive half-cycle, transistors Q1, Q4, S2, and S3 are turned on, while transistors Q2, Q3, S1, and S4 are turned off. For ease of illustration, other components not operating during the positive half-cycle are not shown. Figure 4 As shown in the image.

[0029] When transistors Q1 and Q4 are turned on and transistors Q2 and Q3 are turned off, the current iLr flows in the positive direction through the resonant inductor Lr and then flows to the primary winding W1 (as shown by arrow 301). Figure 3 The portion of waveform 223 during the time interval t0 to t1 indicates that the current iLr is positive at this time. A current flows from the second terminal of the primary winding W1 through transistor Q4, and then through transistor Q4 to the output voltage node 101. According to the polarity indicated by the dot markings on the transformer, the positive current iLr generates an induced current flowing through the secondary winding W2. This induced current flows from the secondary winding W2 to the source of transistor S3 (as shown by arrow 302), and then from transistor S3 to the output voltage node 101 (as shown by arrow 303).

[0030] Figure 5 A schematic diagram of an LLC resonant converter 100 during the negative half-cycle is shown, i.e. Figure 3The time interval from t1 to t2. During the negative half-cycle, transistors Q2, Q3, S1, and S4 are turned on, while transistors Q1, Q4, S2, and S3 are turned off. For ease of explanation, other components not operating during the negative half-cycle are not shown. Figure 5 As shown in the image.

[0031] When transistors Q2 and Q3 are turned on and transistors Q1 and Q4 are turned off, the current iLr flows in the negative direction through the resonant inductor Lr, that is, from the primary winding W1 to the first switching node 103 (as shown by arrow 351), and then through transistors Q2 and S1 to the output voltage node 101. Figure 3 The portion of waveform 223 during the time interval t1 to t2 indicates that the current iLr is negative at this time. According to the polarity indicated by the dot on the transformer, the negative current iLr generates an induced current flowing through the secondary winding W2 through the transformer. This induced current flows from the secondary winding W2 to the source of transistor S1 (as shown by arrow 352), and then from transistor S1 to the output voltage node 101.

[0032] Compared to traditional topologies, in the LLC resonant converter 100, the primary current flows directly to the output voltage node 101. Therefore, while transistors S1 and S3 on the secondary side handle the entire load current, transistors S2 and S4, as well as the secondary winding W2, only handle a portion of the load current. This reduces the power density of the LLC resonant converter 100, thereby improving its efficiency and reducing its cost.

[0033] Figure 6 A flowchart of a method 600 for generating the output voltage of an LLC resonant converter according to an embodiment of the present invention is shown. Method 600 can be performed using various circuit components of the LLC resonant converter 100. Those skilled in the art will understand that other circuit components can also be used to perform method 600 without affecting the spirit of the invention.

[0034] In method 600, a full-bridge switching circuit receives a DC input voltage (step 601). The full-bridge switching circuit includes a first pair of switches and a second pair of switches, each pair of switches alternately turning on and off to excite a resonant circuit to generate a first sinusoidal current, which flows through the primary winding of the transformer and then to an output node (step 602). The first sinusoidal current flowing through the primary winding of the transformer generates a second sinusoidal current through the coupling of the primary and secondary windings. The second sinusoidal current flows through the secondary winding of the transformer and then to the output node (step 603). A bridge rectifier is used to rectify the first and second sinusoidal currents flowing through the primary and secondary windings of the transformer, and an output capacitor is used to filter the rectified output signal of the bridge rectifier to generate a DC output voltage (step 604).

[0035] Although the invention has been described with reference to several exemplary embodiments, it should be understood that the terminology used is descriptive and exemplary, and not restrictive. Since the invention can be embodied in many forms without departing from the spirit or essence of the invention, it should be understood that the above embodiments are not limited to any of the foregoing details, but should be interpreted broadly within the spirit and scope defined by the appended claims. Therefore, all variations and modifications falling within the scope of the claims or their equivalents should be covered by the appended claims.

Claims

1. An LLC resonant converter, comprising: A full-bridge switching circuit includes a first transistor, a second transistor, a third transistor, and a fourth transistor. Each transistor includes a first terminal and a second terminal, wherein the first terminal of the first transistor and the first terminal of the third transistor are connected to a DC input voltage, the second terminal of the first transistor is connected to the first terminal of the second transistor, and the second terminal of the third transistor is connected to the first terminal of the fourth transistor. A transformer includes a primary winding and a secondary winding, each winding having a first end and a second end, wherein the first end of the secondary winding is connected to the second end of a fourth transistor, and the second end of the secondary winding is connected to the second end of a second transistor. A resonant circuit includes a resonant capacitor, a resonant inductor, and a magnetizing inductor of the primary winding of a transformer, wherein the resonant circuit is connected between a first switching node formed by a first transistor and a second transistor and a second switching node formed by a third transistor and a fourth transistor. as well as A bridge rectifier is connected between the first and second ends of the secondary winding to generate a rectified output signal, wherein the rectified output signal is filtered to generate a DC output voltage at an output node.

2. The LLC resonant converter as described in claim 1, wherein the resonant capacitor, resonant inductor, and magnetizing inductance of the primary winding form a series circuit, and the series circuit is connected between the first switching node and the second switching node.

3. The LLC resonant converter of claim 1, wherein the bridge rectifier includes a fifth transistor and a sixth transistor coupled to the secondary winding.

4. The LLC resonant converter of claim 3, wherein the bridge rectifier further comprises a seventh transistor and an eighth transistor, each transistor comprising a first terminal and a second terminal, wherein the first terminal of the fifth transistor and the first terminal of the seventh transistor are connected to an output node, the second terminal of the fifth transistor is connected to the first terminal of the sixth transistor and the second terminal of the secondary winding, the second terminal of the seventh transistor is connected to the first terminal of the eighth transistor and the first terminal of the secondary winding, and the second terminals of the sixth transistor and the second terminals of the eighth transistor are connected to a reference node.

5. The LLC resonant converter as described in claim 4, further comprising: An output capacitor includes a first terminal and a second terminal, wherein the first terminal of the output capacitor is connected to the first terminal of the fifth transistor and the first terminal of the seventh transistor, and the second terminal of the output capacitor is connected to the second terminal of the sixth transistor and the second terminal of the eighth transistor.

6. The LLC resonant converter of claim 5, wherein the first transistor, the second transistor, the third transistor, the fourth transistor, the fifth transistor, the sixth transistor, the seventh transistor, and the eighth transistor comprise metal-oxide-semiconductor field-effect transistors (MOSFETs).

7. A power supply circuit, comprising: A full-bridge switching circuit includes a first transistor, a second transistor, a third transistor, and a fourth transistor. Each transistor includes a first terminal and a second terminal, wherein the first terminal of the first transistor and the first terminal of the third transistor are connected to a DC input voltage, the second terminal of the first transistor is connected to the first terminal of the second transistor, and the second terminal of the third transistor is connected to the first terminal of the fourth transistor. A transformer includes a primary winding and a secondary winding, each winding having a first end and a second end, wherein the first end of the secondary winding is connected to the second end of a fourth transistor, and the second end of the secondary winding is connected to the second end of a second transistor. A resonant circuit includes a resonant capacitor, a resonant inductor, and a magnetizing inductance of the primary winding of a transformer, wherein the resonant circuit is connected between a first switching node formed by a first transistor and a second transistor and a second switching node formed by a third transistor and a fourth transistor. A bridge rectifier is connected between the first and second ends of the secondary winding to generate a rectified output signal, wherein the rectified output signal is filtered to generate a DC output voltage at an output node; as well as An LLC resonant controller generates multiple control signals to control a first transistor, a second transistor, a third transistor, and a fourth transistor to generate the DC output voltage across an output capacitor.

8. The power supply circuit as described in claim 7, wherein the resonant capacitor, resonant inductor, and magnetizing inductance of the primary winding form a series circuit, and the series circuit is connected between the first switching node and the second switching node.

9. The power supply circuit of claim 7, wherein the bridge rectifier includes a fifth transistor and a sixth transistor connected to the secondary winding.

10. The power supply circuit of claim 9, wherein the bridge rectifier further comprises a seventh transistor and an eighth transistor, wherein a first terminal of the fifth transistor and a first terminal of the seventh transistor are connected to an output node, a second terminal of the fifth transistor is connected to a first terminal of the sixth transistor and a second terminal of the secondary winding, a second terminal of the seventh transistor is connected to a first terminal of the eighth transistor and a first terminal of the secondary winding, and a second terminal of the sixth transistor and a second terminal of the eighth transistor are connected to a reference node.

11. The power supply circuit of claim 10, wherein the LLC resonant controller further generates a control signal to control the fifth transistor, the sixth transistor, the seventh transistor, and the eighth transistor to generate the DC output voltage on the output capacitor.

12. The power supply circuit of claim 10, wherein the output capacitor includes a first terminal and a second terminal, the first terminal of the output capacitor is connected to the first terminal of the fifth transistor and the first terminal of the seventh transistor, and the second terminal of the output capacitor is connected to the second terminal of the sixth transistor and the second terminal of the eighth transistor.

13. The power supply circuit of claim 10, wherein the first transistor, second transistor, third transistor, fourth transistor, fifth transistor, sixth transistor, seventh transistor, and eighth transistor comprise metal-oxide-semiconductor field-effect transistors (MOSFETs).

14. A method for generating an output voltage at an output node of an LLC resonant converter, comprising: The first and second pairs of switches of the full-bridge switching circuit are alternately turned on and off to excite the resonant circuit to generate a first sinusoidal current that flows through the primary winding of the transformer and to the output node. A second sinusoidal current is generated by the coupling of the primary and secondary windings of the transformer. The second sinusoidal current flows through the secondary winding of the transformer and then to the output node. A bridge rectifier is used to rectify the first sinusoidal current and the second sinusoidal current flowing through the primary and secondary windings of the transformer. as well as The rectified output signal of the bridge rectifier is filtered to generate the output voltage of the LLC resonant converter.

15. The method of claim 14, wherein the step of filtering the rectified output signal of the bridge rectifier includes connecting an output capacitor across the two ends of the bridge rectifier.

16. The method of claim 15, wherein the step of alternately turning the first pair of switches and the second pair of switches on and off comprises: During the first time period, the first pair of switches is turned on and the second pair of switches is turned off, so that the first sinusoidal current flows to the first end of the primary winding. as well as During the second time period, the first pair of switches is turned off and the second pair of switches is turned on, so that the first sinusoidal current flows to the second end of the primary winding.

17. The method of claim 15, wherein the step of generating the second sinusoidal current comprises: During the first duration, the second sinusoidal current flows to the first end of the secondary winding; as well as During the second duration, the second sinusoidal current flows to the second end of the secondary winding.

18. The method of claim 14, further comprising providing an input voltage to the full-bridge switching circuit.

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