Synchronous rectification control system based on half-bridge LLC resonant converter

Abstract

The invention relates to the technical field of half-bridge LLC resonant converters, in particular to a synchronous rectification control system based on a half-bridge LLC resonant converter, which comprises a main control unit, a half-bridge driver and a control circuit, and is characterized in that the half-bridge driver and the control circuit are both in communication connection with the main control unit; the control circuit comprises a rectification circuit, and the rectification circuit is in communication connection with the main control unit through a zero-crossing detector. According to the invention, a main control unit controls a rectification circuit to switch working modes of asymmetric resonant half-bridge flyback and symmetric half-bridge resonant forward, a high-power working range of 30-48V is put on LLC resonant half-bridge forward, wide-range voltage stabilization and adjustment are realized through a mode of adjusting frequency by a zero-crossing detector, the cost is high, and the size is large. And meanwhile, the problem that the characteristic output range of the LLC is small in working, and the problems that the conversion efficiency is low and the ripple current is large in an output scene are solved.

Description

Technical Field

[0001] The invention relates to a rectification control system, in particular to a synchronous rectification control system based on a half-bridge LLC resonant converter, and belongs to the technical field of half-bridge LLC resonant converters. Background Art

[0002] The control of LLC synchronous rectification drive is more complicated than hard-switching half-bridge, full-bridge, forward and other topologies. However, LLC is different in that its synchronous rectification drive is not only related to the primary side drive, but also will produce asymmetric resonant half-bridge current.

[0003] The asymmetric resonant half-bridge flyback converter AHB is used in the isolated DC-DC field. The output voltage is controlled by adjusting the duty cycle of the high-end switch of the half-bridge switch. By using the duty cycle adjustment method, it is more suitable for working in a wide input and output range. It has a wider gain adjustment capability than the symmetrical half-bridge resonant forward converter LLC, so it is suitable for applications that require a wide output range. The traditional transformer secondary side has only one winding and a diode for rectification. When the output power of the converter is increased to more than 200W, it will also be limited by the performance of the flyback converter. When the output voltage is above 30V, the output power is already greater than 150W. In this case, the efficiency of using AHB leaves the optimal efficiency working range, but the characteristics of LLC make it difficult to adapt to a wide output range.

[0004] Therefore, it is urgent to improve the rectification system of the half-bridge LLC resonant converter to solve the above-mentioned problems. Summary of the invention

[0005] The purpose of the present invention is to provide a synchronous rectification control system based on a half-bridge LLC resonant converter, which switches the working modes of asymmetric resonant half-bridge flyback and symmetric half-bridge resonant forward by controlling the rectification circuit through a main control unit, places a high-power working range of 30 to 48V on the LLC resonant half-bridge forward, and realizes wide-range voltage stabilization and regulation by adjusting the frequency through a zero-crossing detector, but solves the problems of high cost and large volume, and at the same time solves the problem of small working range of LLC characteristic output, as well as low conversion efficiency and large ripple current in output scenarios.

[0006] In order to achieve the above object, the main technical solutions adopted by the present invention include:

[0007] A synchronous rectification control system based on a half-bridge LLC resonant converter comprises a main control unit, a half-bridge drive and a control circuit. The half-bridge drive and the control circuit are both connected to the main control unit in communication. The main control unit controls the half-bridge drive to rectify the control circuit. The circuit is simple, the manufacturing cost is low, and the rectification efficiency is high.

[0008] The control circuit includes a rectifier circuit, a triode Q1 and a triode Q2 are arranged in series on the rectifier circuit, the triode Q1 and the triode Q2 are both connected to the half-bridge driver in communication, the triode Q1 is electrically connected to the transistor Tr through the inductor L1, the transistor Tr is electrically connected to the triode Q3, the triode Q3 is connected in parallel with a diode D1 and a capacitor C2, the diode D1 and the capacitor C2 are connected in parallel to establish a communication connection with the main control unit through a voltage loop, and the triode Q3 is connected to the main control unit through a driver driver;

[0009] The rectifier circuit establishes a communication connection with the main control unit via a zero-crossing detector;

[0010] By switching the asymmetric resonant half-bridge flyback and symmetric half-bridge resonant forward working modes through the triode Q3 switch in the rectifier circuit, when a wide range of about ten times 5 to 48V is required, the high-power working range of 30 to 48V can be placed on the LLC resonant half-bridge forward, and wide-range voltage regulation and adjustment can be achieved by adjusting the frequency, solving the problems of high cost and large size of the current LLC+BUCK two-stage solution, and solving the problems of low conversion efficiency and large ripple current of the AHB solution in higher power output scenarios;

[0011] Among them, it is constructed by a resettable integrator. In the circuit, a fixed current source can be used to charge the capacitor. When resetting, the voltage on the capacitor is released by turning on the switch to achieve reset. In digital control, it can be achieved by a counter that accumulates at a fixed beat. When resetting, the value of the counter is cleared. There are two reset signals for the integrator, which are the mark of the resonant current crossing the zero point and the mark of automatic reset when the output value of the integrator is greater than the set value.

[0012] The input of the integrator is the output of the voltage loop. This input is used to determine the rising speed of the output value of the integrator. It can be simply understood that when the input value is higher, the output value of the integrator increases faster, and the time required to reach the automatic reset point is shorter;

[0013] On the contrary, when the input of the integrator is smaller, the output increases more slowly and the time required to reach the automatic reset point is longer.

[0014] The control method of the control system is as follows:

[0015] S01, after the power supply is connected, the transistor Q1 and the transistor Q2 are driven by the half-bridge driver to rectify the connected power supply;

[0016] S02, switching the working modes of asymmetric resonant half-bridge flyback and symmetric half-bridge resonant forward through the transistor Q3 switch on the control circuit, specifically:

[0017] When a wide range of about ten times 5 to 48V is required, the high-power operating range of 30 to 48V can be placed on the LLC resonant half-bridge forward, and wide-range voltage regulation and regulation can be achieved by adjusting the frequency;

[0018] Then, the medium and low power working range of 5 to 30V is placed on the AHB asymmetric resonant flyback excitation, and the wide output range is adjusted by adjusting the duty cycle and frequency. The combined working mode of the two converters is used to achieve about 10 times the output voltage regulation and full range ZVS high efficiency operation;

[0019] S03, resetting the output of the integrator by using the zero-crossing signal through a zero-crossing detector, and then automatically resetting the integrator after the output of the integrator reaches the set half-bridge switch on time length;

[0020] S04, then use the time length of the two automatic resets of the integrator as the driving signal of HG and LG of the half-bridge switch tube, and realize it by performing secondary frequency division through the D trigger, and then increase the dead time of HG and LG, and then output it to the driving module to drive the actual half-bridge switch tube to work;

[0021] S05. In LLC working mode, the main control unit turns on the secondary switch transistor Q3, so that both windings of the secondary side of the transformer can work in rectification mode. At this time, the resonant half-bridge realizes frequency modulation control by controlling the switch on time after the resonant current passes through zero to achieve closed-loop regulation of the output voltage.

[0022] Preferably, a shunt resistor Rsen and a capacitor C1 are connected in series between the transistor Q2 and the inductor L1, and one end of the zero-crossing detector is connected between the shunt resistor Rsen and the capacitor C1;

[0023] In the half-bridge control circuit, transistors Q1 and Q2 are turned on alternately in one cycle, that is, the duty cycle is 50%, so VA is a square wave with an amplitude equal to Vin, and its Fourier series expansion is;

[0024]

[0025] Its fundamental component is;

[0026]

[0027] where f sw is the switching frequency, Vo.FHA is the fundamental component of the square wave voltage input to the resonant cavity, and accordingly, the output voltage of the resonant cavity is also a square wave;

[0028]

[0029] Its fundamental component is;

[0030]

[0031] Where Ψ is the phase shift of the output voltage relative to the input voltage, which is actually zero. In traditional switching power supplies, magnetic components are usually used to achieve filtering, energy storage and transmission. The higher the operating frequency of the switching device, the smaller the size of the magnetic component can be, and the easier it is to achieve miniaturization, lightweight and low cost of the power supply device. However, the increase in switching frequency will correspondingly increase the switching loss of the switching device, so soft switching technology came into being. To achieve ideal soft switching, the best situation is to turn off and turn on the switch when the voltage and current are zero at the same time, so that the loss will be truly zero. To achieve this goal, resonance technology must be used;

[0032] According to the circuit principle, inductors and capacitors connected in series or in parallel can form a resonant circuit, so that when the power supply is a DC power supply, the current in the circuit changes according to the sinusoidal law. Since the current or voltage changes according to the sinusoidal law, there is a zero point. If the switching device is turned on or off at this time, the loss generated is zero.

[0033] Preferably, a diode D2 is connected in series to the transistor Q3, and a load Rload is connected in parallel to the capacitor C2.

[0034] Preferably, the rectifier circuit is sequentially connected with a low-pass filter circuit, an operational amplifier circuit and a voltage sampling circuit, the low-pass filter circuit is provided with a resistor R1, the resistor R1 is grounded via a capacitor C3, the negative electrode pin of the operational amplifier circuit is electrically connected to the voltage sampling circuit, and the voltage sampling circuit is connected in parallel with a diode D3 and a resistor R4 via the resistor R3;

[0035] The voltage sampling circuit collects the drain voltage of the synchronous rectifier MOS tube, which is recorded as VSR1 after passing through the operational amplifier circuit and the low-pass filter circuit. VSR1 is converted into a digital voltage through the analog-to-digital converter ADC0 and stored in the main control unit. In each switching cycle, the turn-off time of the synchronous rectifier MOS tube on the secondary side of the LLC resonant converter is adjusted in real time. The self-adaptive ability is strong, the turn-off time is more accurate, and the turn-off point of the synchronous rectifier MOS tube is adjusted to stabilize it at its current zero point, which effectively reduces the conduction and reverse conduction of the body diode and improves the working efficiency of the converter.

[0036] Preferably, the zero-crossing detector includes a diode D4, a diode D5, a diode D6 and a diode D7 connected in sequence, and the models of the diode D4, the diode D5, the diode D6 and the diode D7 are all 1N4007. The diode D4 is connected to a resistor R5 and a resistor R6 arranged in parallel, and the models of the resistor R5 and the resistor R6 are both 47K and 3W.

[0037] Preferably, the diode D5 and the diode D6 are electrically connected to an optocoupler OPTOCOUPLER-NPN, and a resistor R7 is electrically connected to pin 5 of the optocoupler OPTOCOUPLER-NPN. The circuit provides a pulse output at each zero voltage reference of the sine wave, and the 4N25 optocoupler is kept turned on during two positive cycles because the full-bridge circuit converts the negative cycle into a positive cycle. When the optocoupler is turned on, the output will be zero because the output will be the reference ground. When the sine wave passes through zero, the optocoupler is turned off, and a pulse with a Vcc amplitude appears at the output end;

[0038] The zero crossing detector detects the number of times the input signal crosses the zero value or zero voltage level. A zero detector is basically a comparator circuit that compares the input sinusoidal signal or sine wave signal with the zero voltage level.

[0039] The detected voltage changes from positive level to negative level and from negative level to positive level. When the input voltage crosses the zero level to high level or high level to zero, the output of the zero crossing detector changes.

[0040] Preferably, the implementation method of the LLC frequency control module is:

[0041] It is constructed by a resettable integrator. In the circuit, a fixed current source can be used to charge the capacitor. When resetting, the voltage on the capacitor is released by turning on the switch to achieve reset. In digital control, it can be achieved by a counter that accumulates at a fixed beat. When resetting, the value of the counter is cleared. There are two reset signals for the integrator, which are the mark of the resonant current crossing the zero point and the mark of automatic reset when the output value of the integrator is greater than the set value.

[0042] The input of the integrator is the output of the voltage loop. This input is used to determine the rising speed of the output value of the integrator. It can be simply understood that when the input value is higher, the output value of the integrator increases faster, and the time required to reach the automatic reset point is shorter;

[0043] On the contrary, when the input of the integrator is smaller, the output increases more slowly and the time required to reach the automatic reset point is longer.

[0044] The switching logic of the two controllers is:

[0045] When the dimensionless number of the voltage loop control output is 0.55, the corresponding maximum rising slope of the integrator output value is the maximum switching frequency of the LLC converter. If the output voltage is also lower than 30V, when both conditions are met, after a period of threshold determination, the AHB control mode is switched.

[0046] When both HG and LG are in the off state, the secondary transformer winding switch tube Q3 is pulled down. If the output voltage is higher than 30V and the duty cycle of the high-end switch tube drive signal HG is greater than 45% in the AHB mode, both are established at the same time and after a period of threshold judgment, it is converted to the LLC mode of symmetrical switching.

[0047] The present invention has at least the following beneficial effects:

[0048] 1. The main control unit controls the rectifier circuit to switch the working modes of asymmetric resonant half-bridge flyback and symmetric half-bridge resonant forward, and places the high-power working range of 30-48V on the LLC resonant half-bridge forward. The frequency is adjusted by the zero-crossing detector to achieve wide-range voltage regulation and regulation. The problems of high cost and large size are solved, and at the same time, the problem of small working range of LLC characteristic output, as well as low conversion efficiency and large ripple current in output scenarios are solved.

[0049] 2. Using resonance technology, according to the circuit principle, inductors and capacitors can be connected in series or in parallel to form a resonant circuit, so that when the power supply is a DC power supply, the current in the circuit changes according to the sinusoidal law. Since the current or voltage changes according to the sinusoidal law, there is a zero point. If the switching device is turned on or off at this time, the loss generated is zero.

[0050] 3. The voltage sampling circuit collects the drain voltage of the synchronous rectifier MOS tube. The drain voltage is recorded as VSR1 after passing through the operational amplifier circuit and the low-pass filter circuit. VSR1 is converted into a digital voltage through the analog-to-digital converter ADC0 and stored in the main control unit. In each switching cycle, the turn-off time of the synchronous rectifier MOS tube on the secondary side of the LLC resonant converter is adjusted in real time. It has strong adaptive ability and more accurate turn-off time. The turn-off point of the synchronous rectifier MOS tube is adjusted to stabilize it at its current zero point, effectively reducing the conduction and reverse conduction of the body diode and improving the working efficiency of the converter.

[0051] 4. Zero crossing detector detects the number of times the input signal crosses zero value or zero voltage level. Zero detector is basically a comparator circuit that compares the input sinusoidal signal or sine wave signal with zero voltage level and detects voltage changes from positive level to negative level and from negative level to positive level. When the input voltage crosses zero level to high level or high level to zero, the output of zero crossing detector changes. BRIEF DESCRIPTION OF THE DRAWINGS

[0052] The drawings described herein are used to provide a further understanding of the present application and constitute a part of the present application. The illustrative embodiments of the present application and their descriptions are used to explain the present application and do not constitute an improper limitation on the present application. In the drawings:

[0053] Figure 1 It is a structural diagram of the present invention;

[0054] Figure 2 is the electrical schematic diagram of the present invention;

[0055] Figure 3 A circuit diagram of the present invention;

[0056] Figure 4 It is a schematic diagram of zero-crossing detection of the present invention;

[0057] Figure 5 It is a zero-crossing detection circuit diagram of the present invention;

[0058] Figure 6 is a partial circuit diagram of the present invention;

[0059] Figure 7 is the LLC flow chart of the present invention;

[0060] Figure 8 This is the AHB mode diagram of the present invention.

[0061] In the figure, 1-main control unit, 2-half-bridge driver, 3-control circuit, 301-rectifier circuit, 302-low-pass filter circuit, 303-operational amplifier circuit, 304-voltage sampling circuit, 4-zero-crossing detector, 5-driver, 6-voltage loop. DETAILED DESCRIPTION

[0062] The following will describe the implementation methods of the present application in detail with the help of accompanying drawings and examples, so that the implementation process of how the present application uses technical means to solve technical problems and achieve technical effects can be fully understood and implemented accordingly.

[0063] like Figure 1-Figure 8 As shown, the synchronous rectification control system based on the half-bridge LLC resonant converter provided in this embodiment includes a main control unit 1, a half-bridge driver 2 and a control circuit 3. The half-bridge driver 2 and the control circuit 3 are both connected to the main control unit 1 in communication. The main control unit 1 controls the half-bridge driver 2 to rectify the control circuit 3. The circuit is simple, the manufacturing cost is low, and the rectification efficiency is high.

[0064] The control circuit 3 includes a rectifier circuit 301, on which a triode Q1 and a triode Q2 are arranged in series, and both the triode Q1 and the triode Q2 establish a communication connection with the half-bridge driver 2, the triode Q1 is electrically connected to the transistor Tr through the inductor L1, the transistor Tr is electrically connected to the triode Q3, the triode Q3 is connected in parallel with a diode D1 and a capacitor C2, the diode D1 and the capacitor C2 are connected in parallel and establish a communication connection with the main control unit 1 through a voltage loop 6, the triode Q3 establishes a communication connection with the main control unit 1 through a driver 5, and the rectifier circuit 301 establishes a communication connection with the main control unit 1 through a zero-crossing detector 4;

[0065] By switching the asymmetric resonant half-bridge flyback and symmetric half-bridge resonant forward working modes through the triode Q3 switch tube on the rectifier circuit 301, when a wide range of about ten times of 5 to 48V is required to be output, a high-power working range of 30 to 48V can be placed on the LLC resonant half-bridge forward, and wide-range voltage regulation and adjustment can be achieved by adjusting the frequency, solving the problems of high cost and large size of the current LLC+BUCK two-stage solution, and solving the problems of low conversion efficiency and large ripple current of the AHB solution in a higher power output scenario;

[0066] Among them, Figure 4 It is constructed by a resettable integrator. In the circuit, a fixed current source can be used to charge the capacitor. When resetting, the voltage on the capacitor is released by turning on the switch to achieve reset. In digital control, it can be achieved by a counter that accumulates at a fixed beat. When resetting, the value of the counter is cleared. There are two reset signals for the integrator, which are the mark of the resonant current crossing the zero point and the mark of automatic reset when the output value of the integrator is greater than the set value.

[0067] The input of the integrator is the output of the voltage loop. This input is used to determine the rising speed of the output value of the integrator. It can be simply understood that when the input value is higher, the output value of the integrator increases faster, and the time required to reach the automatic reset point is shorter;

[0068] On the contrary, when the input of the integrator is smaller, the output increases more slowly and the time required to reach the automatic reset point is longer.

[0069] In such Figure 7 and Figure 8 In the switching logic, when the dimensionless number of the control output of the voltage loop 6 is 0.55, the corresponding maximum rising slope of the output value of the integrator, that is, the maximum switching frequency of the LLC converter, and if the output voltage is also lower than 30V, when both are established at the same time, after a period of threshold judgment, it is switched to the AHB control mode;

[0070] When both HG and LG are in the off state, the secondary transformer winding switch Q3 is pulled down. If the output voltage is higher than 30V, and the duty cycle of the high-end switch drive signal HG is greater than 45% in the AHB mode, both are established at the same time and after a period of threshold judgment, it is converted to the LLC mode of symmetrical switching;

[0071] The control method of the control system is as follows:

[0072] S01, after the power supply is connected, the transistor Q1 and the transistor Q2 are driven by the half-bridge driver 2 to rectify the connected power supply;

[0073] S02, switching the working modes of asymmetric resonant half-bridge flyback and symmetric half-bridge resonant forward through the transistor Q3 switch on the control circuit 3, specifically:

[0074] When a wide range of about ten times 5 to 48V is required, the high-power operating range of 30 to 48V can be placed on the LLC resonant half-bridge forward, and wide-range voltage regulation and regulation can be achieved by adjusting the frequency;

[0075] Then, the medium and low power working range of 5 to 30V is placed on the AHB asymmetric resonant flyback excitation, and the wide output range is adjusted by adjusting the duty cycle and frequency. The combined working mode of the two converters is used to achieve about 10 times the output voltage regulation and full range ZVS high efficiency operation;

[0076] S03, using the zero-crossing signal through the zero-crossing detector 4 to reset the output of the integrator, and then the integrator automatically resets after the output of the integrator reaches the set half-bridge switch on time length;

[0077] S04, then use the time length of the two automatic resets of the integrator as the driving signal of HG and LG of the half-bridge switch tube, and realize it by performing secondary frequency division through the D trigger, and then increase the dead time of HG and LG, and then output it to the driving module to drive the actual half-bridge switch tube to work;

[0078] S05. In LLC working mode, the main control unit 1 turns on the secondary switch transistor Q3, so that both windings of the secondary side of the transformer can work in rectification mode. At this time, the resonant half-bridge realizes frequency modulation control by controlling the switch on time after the resonant current passes through zero to achieve closed-loop regulation of the output voltage.

[0079] In this embodiment, if Figure 1 As shown, a shunt resistor Rsen and a capacitor C1 are connected in series between the transistor Q2 and the inductor L1, and one end of the zero-crossing detector 4 is connected between the shunt resistor Rsen and the capacitor C1;

[0080] In the half-bridge control circuit, transistors Q1 and Q2 are turned on alternately in one cycle, that is, the duty cycle is 50%, so VA is a square wave with an amplitude equal to Vin, and its Fourier series expansion is;

[0081]

[0082] Its fundamental component is;

[0083]

[0084] where f sw is the switching frequency, Vo.FHAt is the fundamental component of the square wave voltage input to the resonant cavity, and accordingly, the output voltage of the resonant cavity is also a square wave;

[0085]

[0086] Its fundamental component is;

[0087]

[0088] Where Ψ is the phase shift of the output voltage relative to the input voltage, which is actually zero;

[0089] In traditional switching power supplies, magnetic components are usually used to achieve filtering, energy storage and transmission. The higher the operating frequency of the switching device, the smaller the size of the magnetic component can be, and the easier it is to achieve miniaturization, lightweight and low cost of the power supply device. However, the increase in switching frequency will correspondingly increase the switching loss of the switching device, so soft switching technology came into being. To achieve ideal soft switching, the best situation is to turn off and turn on the switch when the voltage and current are zero at the same time, so that the loss will be truly zero. To achieve this goal, resonance technology must be used;

[0090] According to the circuit principle, inductors and capacitors connected in series or in parallel can form a resonant circuit, so that when the power supply is a DC power supply, the current in the circuit changes according to the sinusoidal law. Since the current or voltage changes according to the sinusoidal law, there is a zero point. If the switching device is turned on or off at this time, the loss generated is zero.

[0091] Further, such as Figure 1 and Figure 2As shown, a diode D2 is connected in series to the triode Q3, a load Rload is arranged in parallel to the capacitor C2, a low-pass filter circuit 302, an operational amplifier circuit 303 and a voltage sampling circuit 304 are sequentially connected to the rectifier circuit 301, a resistor R1 is arranged on the low-pass filter circuit 302, and the resistor R1 is grounded through the capacitor C3, the negative electrode pin of the operational amplifier circuit 303 is electrically connected to the voltage sampling circuit 304, and a diode D3 and a resistor R4 are connected in parallel to the voltage sampling circuit 304 through the resistor R3, and the voltage sampling circuit 304 collects synchronous The drain voltage of the rectifier MOS tube is recorded as VSR1 after passing through the operational amplifier circuit 303 and the low-pass filter circuit 302. VSR1 is converted into a digital voltage through the analog-to-digital converter ADC0 and stored in the main control unit 1. In each switching cycle, the turn-off time of the synchronous rectifier MOS tube on the secondary side of the LLC resonant converter is adjusted in real time. The adaptive ability is strong and the turn-off time is more accurate. The turn-off point of the synchronous rectifier MOS tube is adjusted to stabilize it at its current zero-crossing point, which effectively reduces the conduction and reverse conduction of the body diode and improves the working efficiency of the converter.

[0092] Furthermore, if Figure 5 As shown, the zero-crossing detector 4 includes a diode D4, a diode D5, a diode D6 and a diode D7 connected in sequence, the models of the diode D4, the diode D5, the diode D6 and the diode D7 are all 1N4007, the diode D4 is connected to a resistor R5 and a resistor R6 arranged in parallel, the models of the resistor R5 and the resistor R6 are both 47K and 3W, the diode D5 and the diode D6 are electrically connected to a photocoupler OPTOCOUPLER-NPN, and the pin 5 of the photocoupler OPTOCOUPLER-NPN is electrically connected to a resistor R7;

[0093] The zero-crossing detection circuit on the zero-crossing detector 4 is as follows Figure 5 The circuit provides a pulse output on every zero voltage reference of the sine wave, utilizing the 4N25 optocoupler to remain on during the two positive cycles, as the full bridge circuit converts the negative cycles into positive cycles, when the optocoupler is on, the output will be zero, as the output will be referenced to ground, at the zero crossing of the sine wave, the optocoupler is off, and a pulse of Vcc amplitude appears at the output;

[0094] The zero crossing detector detects the number of times the input signal crosses the zero value or zero voltage level. A zero detector is basically a comparator circuit that compares the input sinusoidal signal or sine wave signal with the zero voltage level.

[0095] The detected voltage changes from positive level to negative level and from negative level to positive level. When the input voltage crosses the zero level to high level or high level to zero, the output of the zero crossing detector changes.

[0096] For example, certain words are used in the specification and claims to refer to specific components. Those skilled in the art should understand that hardware manufacturers may use different terms to refer to the same component. This specification and claims do not use differences in names as a way to distinguish components, but use differences in the functions of components as the criteria for distinction. For example, "including" mentioned throughout the specification and claims is an open term, so it should be interpreted as "including but not limited to". "Approximately" means that within an acceptable error range, those skilled in the art can solve technical problems within a certain error range and basically achieve technical effects.

[0097] It should be noted that the terms "include", "comprises" or any other variations thereof are intended to cover non-exclusive inclusion, so that a product or system including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such product or system. In the absence of more restrictions, the elements defined by the sentence "comprises a ..." do not exclude the existence of other identical elements in the product or system including the elements.

[0098] The above description shows and describes several preferred embodiments of the present invention, but as mentioned above, it should be understood that the present invention is not limited to the form disclosed herein, and should not be regarded as excluding other embodiments, but can be used in various other combinations, modifications and environments, and can be modified within the scope of the invention concept described herein through the above teachings or the technology or knowledge of the relevant field. Changes and variations made by those skilled in the art do not depart from the spirit and scope of the present invention, and should be within the scope of protection of the claims attached to the present invention.

Claims

1. A synchronous rectification control system based on a half-bridge LLC resonant converter, comprising a main control unit (1), a half-bridge driver (2) and a control circuit (3), characterized in that: The half-bridge driver (2) and the control circuit (3) both establish communication connections with the main control unit (1); The control circuit (3) comprises a rectifier circuit (301), on which a triode Q1 and a triode Q2 are arranged in series, the triode Q1 and the triode Q2 both establish a communication connection with the half-bridge driver (2), the triode Q1 is electrically connected to a transistor Tr via an inductor L1, the transistor Tr is electrically connected to a triode Q3, the triode Q3 is connected in parallel with a diode D1 and a capacitor C2, the diode D1 and the capacitor C2 are connected in parallel and establish a communication connection with the main control unit (1) via a voltage loop (6), and the triode Q3 establishes a communication connection with the main control unit (1) via a driver driver (5); The rectifier circuit (301) establishes a communication connection with the main control unit (1) via a zero-crossing detector (4); The control method of the control system is as follows: S01, after the power supply is connected, the transistor Q1 and the transistor Q2 are driven by the half-bridge driver (2) to rectify the connected power supply; S02, switching the working modes of asymmetric resonant half-bridge flyback and symmetric half-bridge resonant forward by using the transistor Q3 switch on the control circuit (3), specifically: When a wide range of about ten times 5 to 48V is required, the high-power operating range of 30 to 48V can be placed on the LLC resonant half-bridge forward, and wide-range voltage regulation and regulation can be achieved by adjusting the frequency; Then, the medium and low power working range of 5 to 30V is placed on the AHB asymmetric resonant flyback excitation, and the wide output range is adjusted by adjusting the duty cycle and frequency. The combined working mode of the two converters is used to achieve about 10 times the output voltage regulation and full range ZVS high efficiency operation; S03, using the zero-crossing signal through the zero-crossing detector (4) to reset the output of the integrator, and then automatically resetting the integrator after the output of the integrator reaches the set half-bridge switch on time length; S04, then use the time length of the two automatic resets of the integrator as the driving signal of HG and LG of the half-bridge switch tube, and realize it by performing secondary frequency division through the D trigger, and then increase the dead time of HG and LG, and then output it to the driving module to drive the actual half-bridge switch tube to work; S05. In the LLC working mode, the main control unit (1) turns on the secondary switch transistor Q3, so that both windings of the secondary side of the transformer can work in the rectification mode. At this time, the resonant half bridge realizes frequency modulation control by controlling the switch on time after the resonant current passes through zero, thereby realizing closed-loop regulation of the output voltage.

2. A synchronous rectification control system based on a half-bridge LLC resonant converter according to claim 1, characterized in that: A shunt resistor Rsen and a capacitor C1 are connected in series between the transistor Q2 and the inductor L1, and one end of the zero-crossing detector (4) is connected between the shunt resistor Rsen and the capacitor C1; In the half-bridge control circuit, transistors Q1 and Q2 are turned on alternately in one cycle, that is, the duty cycle is 50%, so VA is a square wave with an amplitude equal to Vin, and its Fourier series expansion is; Its fundamental component is; where f sw is the switching frequency, Vo.FHA(t) is the fundamental component of the square wave voltage input to the resonant cavity, and accordingly, the output voltage of the resonant cavity is also a square wave; Its fundamental component is; Where Ψ is the phase shift of the output voltage relative to the input voltage, which is actually zero.

3. A synchronous rectification control system based on a half-bridge LLC resonant converter according to claim 1, characterized in that: The diode D2 is connected in series to the transistor Q3, and a load Rload is connected in parallel to the capacitor C2.

4. A synchronous rectification control system based on a half-bridge LLC resonant converter according to claim 1, characterized in that: The rectifier circuit (301) is sequentially connected to a low-pass filter circuit (302), an operational amplifier circuit (303) and a voltage sampling circuit (304).

5. A synchronous rectification control system based on a half-bridge LLC resonant converter according to claim 4, characterized in that: The low-pass filter circuit (302) is provided with a resistor R1, and the resistor R1 is grounded via a capacitor C3.

6. A synchronous rectification control system based on a half-bridge LLC resonant converter according to claim 4, characterized in that: The negative electrode pin of the operational amplifier circuit (303) is electrically connected to the voltage sampling circuit (304), and the voltage sampling circuit (304) is connected in parallel with a diode D3 and a resistor R4 via a resistor R3.

7. A synchronous rectification control system based on a half-bridge LLC resonant converter according to claim 1, characterized in that: The zero-crossing detector (4) comprises a diode D4, a diode D5, a diode D6 and a diode D7 connected in sequence, the models of the diode D4, the diode D5, the diode D6 and the diode D7 are all 1N4007, the diode D4 is connected to a resistor R5 and a resistor R6 arranged in parallel, the models of the resistor R5 and the resistor R6 are both 47K and 3W.

8. A synchronous rectification control system based on a half-bridge LLC resonant converter according to claim 1, characterized in that: The diode D5 and the diode D6 are electrically connected to a photocoupler OPTOCOUPLER-NPN, and a resistor R7 is electrically connected to a pin 5 of the photocoupler OPTOCOUPLER-NPN.

9. A synchronous rectification control system based on a half-bridge LLC resonant converter according to claim 1, characterized in that: The implementation method of the LLC frequency control module is: It is constructed by a resettable integrator. In the circuit, a fixed current source can be used to charge the capacitor. When resetting, the voltage on the capacitor is released by turning on the switch to achieve reset. In digital control, it can be achieved by a counter that accumulates at a fixed beat. When resetting, the value of the counter is cleared. There are two reset signals for the integrator, which are the mark of the resonant current crossing the zero point and the mark of automatic reset when the output value of the integrator is greater than the set value. The input of the integrator is the output of the voltage loop. This input is used to determine the rising speed of the output value of the integrator. It can be simply understood that when the input value is higher, the output value of the integrator increases faster, and the time required to reach the automatic reset point is shorter; On the contrary, when the input of the integrator is smaller, the output increases more slowly and the time required to reach the automatic reset point is longer.

10. A synchronous rectification control system based on a half-bridge LLC resonant converter according to claim 9, characterized in that: The switching logic of the two controllers is: When the dimensionless number of the control output of the voltage loop (6) is 0.55, the corresponding maximum rising slope of the output value of the integrator is the maximum switching frequency of the LLC converter. If the output voltage is also lower than 30V, when both conditions are met, after a period of threshold determination, the control mode is switched to the AHB control mode. When both HG and LG are in the off state, the secondary transformer winding switch tube Q3 is pulled down. If the output voltage is higher than 30V and the duty cycle of the high-end switch tube drive signal HG is greater than 45% in the AHB mode, both are established at the same time and after a period of threshold judgment, it is converted to the LLC mode of symmetrical switching.

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