A self-driving circuit for resonant circuit LLC and LLC

Abstract

The present application provides a self-driving circuit and LLC applied to a resonant circuit LLC; the negative input terminals of a first comparator and a second comparator in the self-driving circuit are respectively connected to the drain of a rectifier tube of the LLC, and the positive input terminals of the first comparator and the second comparator are connected to the source of the rectifier tube; the output terminal of the first comparator is respectively connected to the first input terminal of a first XOR gate and the first input terminal of a second XOR gate; the output terminal of the second comparator is connected to the second input terminal of the first XOR gate and the second input terminal of the second XOR gate; the first input terminal of a first AND gate is connected to the output terminal of the first comparator, the second input terminal of the first AND gate is connected to the output terminal of the first XOR gate, the first input terminal of the second AND gate is connected to the output terminal of the second comparator, and the second input terminal of the second AND gate is connected to the output terminal of the second XOR gate; the output terminals of the first AND gate and the second AND gate are connected to the gate of the rectifier tube.

Description

Technical Field

[0001] The present application relates to the field of circuit technology, and in particular to a self-driving circuit applied to a resonant circuit LLC and the LLC. Background Art

[0002] Currently, in the development of power electronics, low-voltage, high-current output applications have become a very important development direction. A properly designed resonant circuit LLC converter can basically ensure that the primary MOSFET always operates in the ZVS turn-on state under the full range of loads, thereby improving system efficiency. In such cases, the losses of the rectifier on the secondary side of the transformer account for the majority of the overall losses. To reduce the losses of the rectifier, synchronous rectifier technology is currently widely used in low output voltage applications. If the synchronous rectification drive scheme is complex or if a non-adjustable drive integrated circuit (IC) chip is used, the effectiveness of the synchronous rectification will be affected. Existing synchronous rectification schemes suitable for LLCs typically use a voltage bias circuit as the drive signal source. The internal structure and logic of this voltage bias circuit are complex, and it involves many components, resulting in high costs. Summary of the Invention

[0003] The purpose of the embodiments of the present application is to provide a self-driving circuit and LLC for use in a resonant circuit LLC. The specific technical solution is as follows:

[0004] In a first aspect, a self-driving circuit for a resonant circuit LLC is provided, the self-driving circuit comprising: a first comparator, a second comparator, a first XOR gate, a second XOR gate, a first AND gate, and a second AND gate; the negative input terminals of the first comparator and the second comparator are respectively connected to the drain of the rectifier tube of the LLC, and the ground terminal and the positive input terminal of the first comparator and the second comparator are connected to the source stage of the rectifier tube; the output terminal of the first comparator is respectively connected to the first input terminal of the first XOR gate and the first input terminal of the second XOR gate; the output terminal of the second comparator is respectively connected to the second input terminal of the first XOR gate and the second input terminal of the second XOR gate; the first input terminal of the first AND gate is connected to the output terminal of the first comparator, the second input terminal of the first AND gate is connected to the output terminal of the first XOR gate, the first input terminal of the second AND gate is connected to the output terminal of the second comparator, and the second input terminal of the second AND gate is connected to the output terminal of the second XOR gate; the output terminals of the first AND gate and the second AND gate are connected to the gate of the rectifier tube.

[0005] In a second aspect, a resonant circuit LLC is provided, which includes: a transformer, the self-driving circuit described in the first aspect, and a rectifier tube; wherein the rectifier tube includes a first rectifier tube and a second rectifier tube; the first end of the secondary side of the transformer is respectively connected to the drain of the first rectifier tube and the negative input terminal of the first comparator; the second end of the secondary side of the transformer is respectively connected to the drain of the second rectifier tube and the negative input terminal of the second comparator.

[0006] In a third aspect, a method for controlling a rectifier switch in an LLC based on the self-driving circuit described in the first aspect is provided, comprising: detecting a first voltage at the negative input terminal of the first comparator and a second voltage at the negative input terminal of the second comparator; when both the first voltage and the second voltage are less than 0, controlling the rectifier to be turned off; when the first voltage is less than 0 and the second voltage is not less than 0, controlling the rectifier corresponding to the first comparator to be turned on; when the first voltage is not less than 0 and the second voltage is less than 0, controlling the rectifier corresponding to the second comparator to be turned on.

[0007] The self-driving circuit in the embodiment of the present application includes a comparator, an XOR gate, and an AND gate. This means the self-driving circuit in the embodiment of the present application has fewer components and simple circuit connections, which can reduce costs while ensuring efficiency. Furthermore, based on this self-driving circuit, the rectifier can self-switch based on voltage changes in the secondary circuit, eliminating the need for a separate pulse width modulation (PWM) wave for control. This reduces the difficulty of overall circuit control and solves the problem of prior art LLC synchronous rectification schemes using a voltage bias circuit as the drive signal source, which has a complex internal structure and logic, resulting in a large number of components. BRIEF DESCRIPTION OF THE DRAWINGS

[0008] Figure 1 is a circuit diagram of a self-driving circuit according to an embodiment of the present application;

[0009] Figure 2 This is one of the circuit diagrams of the LLC according to an embodiment of the present application;

[0010] Figure 3 This is the second circuit diagram of the LLC of the embodiment of the present application;

[0011] Figure 4 This is a flow chart of a method for rectifying and controlling a circuit based on a self-driving circuit according to an embodiment of the present application;

[0012] Figure 5 is a synchronous rectification waveform based on a self-driving circuit according to an embodiment of the present application;

[0013] Figure 6This is a flow chart of a method for controlling a rectifier tube switch based on a self-driving circuit according to an embodiment of the present application. DETAILED DESCRIPTION

[0014] The technical solutions in the embodiments of the present application will be described below in conjunction with the drawings in the embodiments of the present application.

[0015] The embodiment of the present application provides a self-driving circuit applied to a resonant circuit LLC, such as Figure 1 As shown, the self-driving circuit includes: a first comparator S1, a second comparator S2, a first XOR gate S3, a second XOR gate S4, a first AND gate S5 and a second AND gate S6;

[0016] The negative input terminals of the first comparator S1 and the second comparator S2 are respectively connected to the drain of the LLC rectifier tube, and the ground terminal and the positive input terminal of the first comparator S1 and the second comparator S2 are connected to the source of the rectifier tube;

[0017] The output end of the first comparator S1 is connected to the first input end of the first XOR gate S3 and the first input end of the second XOR gate S4; the output end of the second comparator S2 is connected to the second input end of the first XOR gate S3 and the second input end of the second XOR gate S4;

[0018] A first input terminal of the first AND gate S5 is connected to the output terminal of the first comparator SA, a second input terminal of the first AND gate S5 is connected to the output terminal of the first XOR gate S3, a first input terminal of the second AND gate S6 is connected to the output terminal of the second comparator S2, and a second input terminal of the second AND gate S6 is connected to the output terminal of the second XOR gate S4;

[0019] The output ends of the first AND gate S5 and the second AND gate S6 are connected to the gate of the rectifier tube.

[0020] based on Figure 1 The detected drain voltage of the transformer's secondary-side synchronous rectifier is logically compared with its source voltage, or GND, on the secondary side. If the logical comparison result is positive, indicating that the synchronous rectifier's body diode is conducting, this is recorded as a logical "1." Otherwise, it is recorded as a logical "0." The logical result of S1 is compared with the result of another comparator, S2, and then input into an XOR gate comparator. The XOR gate comparator outputs "1" only when the input signals are different, "1" and "0." To confirm that the input "1" is the desired one, the XOR output and the comparator output are input into an AND gate logic. A logical "1" is output only when both are "1." This ensures that the two rectifiers can be correctly turned on and off even if they are not turned on at the same time.

[0021] As can be seen, the self-driving circuit in the embodiment of the present application includes a comparator, an XOR gate, and an AND gate. That is, the self-driving circuit in the embodiment of the present application has fewer components and simple circuit connections, which can reduce costs while ensuring efficiency. In addition, based on this self-driving circuit, the rectifier tube can self-switch according to the voltage level changes in the secondary circuit, without the need to provide a separate pulse width modulation (PWM) wave for control, making the overall circuit control easier. This solves the problem that the LLC synchronous rectification scheme in the prior art uses a voltage bias circuit as the drive signal source, and the internal structure and logic of the voltage bias circuit are complex, resulting in a large number of components.

[0022] It should be noted that the VCC supply voltage of the synchronous rectifier circuit in the embodiment of the present application is the driving voltage value of the rectifier. When the output is a logic "1", its level value is the rectifier driving voltage value, which can normally control the switching of the rectifier. The rectifier tube and resonant switch tube in the embodiment of the present application can be MOSFET tubes.

[0023] The embodiment of the present application also provides a resonant circuit LLC, such as Figure 2 As shown, the LLC includes: a resonant network circuit, a transformer, Figure 1 The self-driving circuit and the rectifier tube in the embodiment of the present invention are as follows; wherein the rectifier tube includes a first rectifier tube Q1 and a second rectifier tube Q2;

[0024] The resonant network circuit is connected to the primary side of the transformer, and the first end of the secondary side of the transformer is connected to the drain of the first rectifier tube Q1 and the negative input terminal of the first comparator respectively; the second end of the secondary side of the transformer is connected to the drain of the second rectifier tube Q2 and the negative input terminal of the second comparator respectively.

[0025] like Figure 3 As shown, the LLC in the embodiment of the present application also includes a first resonant switch tube Q3, a second resonant switch tube Q4, a first capacitor C1, a second capacitor C2 and a third capacitor C3; wherein, the source of the first resonant switch tube Q3 and the drain of the second resonant switch tube Q4 are respectively connected to the first end of the primary side of the transformer; the drain of the first resonant switch tube Q3 is connected to one end of the second capacitor C2, and the other end of the second capacitor C2 is respectively connected to the third capacitor C3 and the second end of the primary side of the transformer; the other end of the third capacitor C3 is connected to the source of the second resonant switch tube Q4; one end of the first capacitor C1 is connected to the drain of the first resonant switch tube, and the other end of the first capacitor is connected to the source of the second resonant switch tube Q4.

[0026] In addition, the LLC further includes a first inductor L1 and a fourth capacitor C4; wherein the first inductor L1 is connected in series between the first end of the primary side of the transformer and the source of the first resonant switch tube Q3.

[0027] One end of the fourth capacitor is connected to the secondary side of the transformer, and the other end of the fourth capacitor is connected to the source terminals of the first rectifier tube Q1 and the second rectifier tube Q2.

[0028] Furthermore, the LLC also includes a microcontroller unit MCU; wherein the MCU includes a driving circuit and a control circuit; wherein one end of the driving circuit is respectively connected to the gates of the first resonant switching tube and the second resonant switching tube; wherein one end of the control circuit is connected to the other end of the driving circuit, and the control circuit is used to control the driving circuit to send a driving signal to the first resonant switching tube and the second resonant switching tube to control the switching of the first resonant switching tube and the second resonant switching tube.

[0029] In addition, the MCU also includes: a sampling circuit and a protection circuit; the protection circuit is connected to the control circuit, and one end of the sampling circuit is connected to the control circuit; the other end of the sampling circuit is connected to the primary and secondary sides of the transformer respectively, for sampling the current of the primary side and the voltage of the secondary side of the transformer.

[0030] That is to say, the primary side of the LLC transformer in the embodiment of the present application adopts a half-bridge LLC solution, which is controlled by the MCU main chip. The MCU circuit includes a sampling circuit, a control circuit, a drive circuit and a protection circuit. The half-bridge LLC performs closed-loop control by sampling the output voltage and the resonant current of the primary side of the resonant transformer. After deducting the fixed dead time, it is driven with a fixed 50% duty cycle. The output voltage preset value is achieved by adjusting the drive frequency and the output voltage stability is ensured by the output capacitor. The output voltage and resonant current are monitored in real time. If the monitored value is too high or too low in a short period of time, the drive signal will be adjusted or the drive signal will be turned off through the MCU for corresponding protection. Furthermore, a synchronous rectification solution is used at the secondary DC output, which is controlled by a self-driving circuit built by a separation device. Among them, the frequency and duty cycle of the self-driving circuit controlling Q1 and Q2 depend on the control frequency and duty cycle of the primary-side resonant network of the transformer. The frequency and duty cycle of the resonant network are sensed to the secondary-side output end through the transformer, and the voltage between the source and drain of Q1 and Q2 changes accordingly. The self-driving circuit drives and controls the switching of Q1 and Q2 by detecting the voltage between the source and drain of Q1 and Q2 to achieve the purpose of rectification.

[0031] In the embodiment of the present application, a method based on Figure 1 The method of controlling the rectifier switch in LLC by the self-driving circuit is as follows: Figure 4 As shown, the steps of the method include:

[0032] Step 402, detecting a first voltage at a negative input terminal of a first comparator and a second voltage at a negative input terminal of a second comparator;

[0033] Step 404: When both the first voltage and the second voltage are less than 0, the rectifier tube is controlled to be turned off;

[0034] Step 406 , when the first voltage is less than 0 and the second voltage is not less than 0, controlling the rectifier tube corresponding to the first comparator to be turned on;

[0035] Step 408 : When the first voltage is not less than 0 and the second voltage is less than 0, control the rectifier tube corresponding to the second comparator to be turned on.

[0036] It can be seen that in the embodiment of the present application, only when the first voltage at the negative input terminal of the first comparator and the second voltage at the negative input terminal of the second comparator are both low voltages (less than 0), the corresponding rectifier tubes can be controlled to be turned on, and when only one of them is a low voltage, the corresponding rectifier tube can be controlled to be turned off.

[0037] Combine Figure 1 It can be seen that VCC is connected to the supply voltage of the comparator, D3 and D4 are connected to the drain of the rectifier tube such as MOSFET, GND is connected to the source of MOSFET, and G3 and G4 are connected to the gate of MOSFET. Figure 5 As shown in the figure, when the voltage value at D3 is less than 0V, G3 sends a high level to control the rectifier to turn on. When the voltage value at D3 is higher than 0V, G3 sends a low level to control the rectifier to turn off. Similarly, D4 and G4 have the same operating state. At t1~t2, D3 and D4 are both in a low level state. At this time, G3 and G4 are both in a low level state, turning off the rectifiers on both sides at the same time. Based on this, as Figure 6 As shown, the method steps of the rectification control process include:

[0038] Step 602, detecting the voltages of D3 and D4;

[0039] Step 604, determine whether D3 is less than 0, if it is less than 0, execute step 608, if it is greater than or equal to 0, execute step 602;

[0040] Step 606, determine whether D4 is less than 0, if it is less than 0, execute step 608, if it is greater than or equal to 0, execute step 602;

[0041] Step 608, determine whether D3 and D4 are both less than 0; if the determination result is no, execute step 610; if the determination result is yes, execute step 602;

[0042] Step 610 , determine whether D3 is less than 0, or determine whether D4 is less than 0; if the determination is yes, execute step 612 , if the determination is no, execute step 602 .

[0043] It can be seen that in the embodiment of the present application, based on the self-driving circuit, the rectifier tube performs self-switching according to the level change of the secondary circuit, without providing a separate PWM wave for control, which reduces the difficulty of overall circuit control.

[0044] It should be noted that, in this document, relational terms such as first and second, etc., are used only to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply the existence of any such actual relationship or order between these entities or operations. Moreover, the terms "comprises," "comprising," or any other variants thereof are intended to cover non-exclusive inclusion, so that a process, method, article, or device comprising a series of elements includes not only those elements, but also other elements not explicitly listed, or elements inherent to such process, method, article, or device. In the absence of further limitations, an element defined by the phrase "comprising a ..." does not exclude the presence of other identical elements in the process, method, article, or device comprising the element.

[0045] Each embodiment in this specification is described in a related manner. Similar parts between the various embodiments can be referred to in conjunction with each other. Each embodiment focuses on the differences between the other embodiments. In particular, the system embodiment is generally similar to the method embodiment, so the description is relatively simple. For related parts, refer to the description of the method embodiment.

[0046] The above description is only a preferred embodiment of the present application and is not intended to limit the scope of protection of the present application. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application are included in the scope of protection of the present application.

Claims

1. A self-driving circuit applied to a resonant circuit LLC, characterized in that: The self-driving circuit includes: a first comparator, a second comparator, a first XOR gate, a second XOR gate, a first AND gate and a second AND gate; The negative input terminals of the first comparator and the second comparator are respectively connected to the drain of the rectifier tube of the LLC, and the ground terminals and positive input terminals of the first comparator and the second comparator are connected to the source of the rectifier tube; The output terminal of the first comparator is connected to the first input terminal of the first XOR gate and the first input terminal of the second XOR gate respectively; the output terminal of the second comparator is connected to the second input terminal of the first XOR gate and the second input terminal of the second XOR gate respectively; A first input terminal of the first AND gate is connected to the output terminal of the first comparator, a second input terminal of the first AND gate is connected to the output terminal of the first XOR gate, a first input terminal of the second AND gate is connected to the output terminal of the second comparator, and a second input terminal of the second AND gate is connected to the output terminal of the second XOR gate; The output ends of the first AND gate and the second AND gate are connected to the gate of the rectifier tube; The LLC includes: a resonant network circuit, a transformer, the self-driving circuit, and a rectifier tube; wherein the rectifier tube includes a first rectifier tube and a second rectifier tube; The resonant network circuit is connected to the primary side of the transformer; the first end of the secondary side of the transformer is connected to the drain of the first rectifier and the negative input end of the first comparator respectively; the second end of the secondary side of the transformer is connected to the drain of the second rectifier and the negative input end of the second comparator respectively; A method for controlling a rectifier switch in an LLC based on a self-driving circuit includes: detecting a first voltage at a negative input terminal of the first comparator and a second voltage at a negative input terminal of the second comparator; When the first voltage and the second voltage are both less than 0, controlling the rectifier tube to be turned off; When the first voltage is less than 0 and the second voltage is not less than 0, controlling the rectifier tube corresponding to the first comparator to be turned on; When the first voltage is not less than 0 and the second voltage is less than 0, the rectifier tube corresponding to the second comparator is controlled to be turned on.

2. The LLC self-driving circuit according to claim 1, characterized in that: The resonant network circuit includes a first resonant switch tube, a second resonant switch tube, a first capacitor, a second capacitor and a third capacitor; The source of the first resonant switching tube and the drain of the second resonant switching tube are respectively connected to the first end of the primary side of the transformer; The drain of the first resonant switch is connected to one end of the second capacitor, and the other end of the second capacitor is connected to the third capacitor and the second end of the primary side of the transformer respectively; the other end of the third capacitor is connected to the source of the second resonant switch; One end of the first capacitor is connected to the drain of the first resonant switching tube, and the other end of the first capacitor is connected to the source of the second resonant switching tube.

3. The LLC self-driving circuit according to claim 2, characterized in that: The resonant network circuit further includes: a first inductor; The first inductor is connected in series between the first end of the primary side of the transformer and the source of the first resonant switch tube.

4. The LLC self-driving circuit according to claim 2, characterized in that: The LLC further includes a microcontroller unit (MCU); wherein the MCU includes a drive circuit and a control circuit; One end of the driving circuit is connected to the gate of the first resonant switching tube and the second resonant switching tube respectively; One end of the control circuit is connected to the other end of the drive circuit, and the control circuit is used to control the drive circuit to send a drive signal to the first resonant switch tube and the second resonant switch tube to control the switching of the first resonant switch tube and the second resonant switch tube.

5. The LLC self-driving circuit according to claim 4, characterized in that: The MCU also includes: a sampling circuit and a protection circuit; the protection circuit is connected to the control circuit, and one end of the sampling circuit is connected to the control circuit; the other end of the sampling circuit is respectively connected to the primary and secondary sides of the transformer, for sampling the current of the primary side and the voltage of the secondary side of the transformer.

6. The LLC self-driving circuit according to claim 1, characterized in that: The LLC further includes a fourth capacitor; one end of the fourth capacitor is connected to the secondary side of the transformer, and the other end of the fourth capacitor is connected to the source electrodes of the first rectifier tube and the second rectifier tube.

7. The LLC self-driving circuit according to claim 1, characterized in that: The voltage value of the power supply voltage of the first comparator and the second comparator is equal to the driving voltage value of the rectifier tube.

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