Resonant converter current-limiting protection control method, control device and switching power supply

Abstract

The invention discloses a resonant converter current-limiting protection control method, a control device and a switching power supply, and the control method comprises the steps: a resonant current sampling step: obtaining a first voltage signal representing the magnitude of the resonant cavity current of a resonant converter in real time; a current-limiting protection judgment step: comparing the first voltage signal with a set current-limiting threshold value, and judging whether current-limiting protection needs to be carried out or not; a current-limiting protection processing step: if it is judged that current-limiting protection needs to be carried out, resetting the driving pulse width of the currently conducted switch tube, so that the switch tube is switched off, another switch tube in the same switch bridge arm keeps complementary conduction, meanwhile, the working mode is switched to a current-limiting mode, and the internal control quantity is gradually lowered; and a driving control step: the smaller value of the internal control quantity and the external feedback control quantity is taken to control the driving pulse width, and the driving pulse width is set to be a maximum limit value and a minimum limit value. The reliability of the resonant converter can be greatly improved.

Description

Technical Field

[0001] The present invention relates to the technical field of switching converters, and in particular to a resonant converter current limiting protection control method, a control device, and a switching power supply. Background Art

[0002] In recent years, LLC resonant converters have been widely used due to their high efficiency, soft switching, and ability to achieve higher power density. To ensure reliable operation under various operating conditions, especially under special conditions such as output short circuits, resonant current limit control is generally added. That is, when the resonant current exceeds the set limit, the corresponding switch is promptly shut off to prevent the resonant current from further increasing and exceeding the safe operating range of the power device.

[0003] The drawback of the above solution is that, under conditions such as an output short circuit, the continuous triggering of the resonant current wave-by-wave current limiting protection can lead to asymmetry between the positive and negative cycles of the resonant current. This can easily cause transformer saturation and cause a voltage shift in the resonant capacitor, which in turn can cause the switch to lose its soft switching characteristics and risk damage from overvoltage stress. Furthermore, due to the operating characteristics of the LLC resonant converter, the resonant current peak cannot accurately reflect the current power transfer. In this case, the control loop is essentially open-loop, and this abnormal resonant capacitor voltage shift cannot be self-recovered.

[0004] To prevent the LLC resonant converter from being damaged by operating in an abnormal state for a long time, the current control method is usually to trigger the resonant current wave-by-wave current limiting within several consecutive switching cycles, directly shut down all the switches, enter fault rest, and then restart. However, this control method will cause the output voltage or output current of the LLC resonant converter to be interrupted, which is not allowed in some applications with inductive loads such as motors. For applications with inductive loads such as motors, the converter is required to have both constant voltage and constant current, that is, it is in a constant voltage state during normal operation and in a constant current state in situations such as output short circuit to maintain normal operation of the load. Currently, a constant current loop feedback circuit is usually added to the traditional constant voltage loop feedback circuit to meet this application requirement, which increases the cost of peripheral circuit design. Summary of the Invention

[0005] In view of this, the technical problem to be solved by the present invention is to propose a resonant converter current limiting protection control method, a control device and a switching power supply. Without adding a constant current loop feedback circuit, the resonant current wave-by-wave current limiting control combined with the automatic adjustment of the internal control quantity can effectively limit the peak value of the resonant current when an output short circuit fault occurs in the resonant converter, thereby avoiding damage to the switching device. At the same time, the control loop is in closed-loop control, which can automatically correct the resonant voltage offset phenomenon, ensure the soft switching characteristics of the switching tube, and greatly improve the reliability of the resonant converter.

[0006] As a first aspect of the present invention, an embodiment and technical solution of a resonant converter current limiting protection control method is provided as follows:

[0007] A method for controlling current limiting protection of a resonant converter, wherein the resonant converter includes at least one half-bridge switch arm, wherein the half-bridge switch arm is composed of two series-connected switch tubes, wherein the two series-connected switch tubes are driven to maintain complementary conduction, wherein the control method includes:

[0008] A resonant current sampling step of acquiring in real time a first voltage signal representing the magnitude of the resonant cavity current of the resonant converter;

[0009] a current limiting protection judgment step, comparing the first voltage signal with a set current limiting threshold to judge whether current limiting protection is required;

[0010] If current limiting protection is required, the drive pulse width of the currently on switch is reset to turn off the switch, while the other switch in the same switch arm remains complementary and turned on. At the same time, the operating mode is switched to the current limiting mode, and the internal control variable is gradually reduced.

[0011] The drive control step takes the smaller value of the internal control amount and the external feedback control amount to control the drive pulse width, wherein the drive pulse width is set with a maximum and a minimum limit.

[0012] Furthermore, whether current limiting protection is required is determined as follows:

[0013] The current limiting threshold includes a first set threshold and a second set threshold. When the first voltage signal is greater than the first set threshold or less than the second set threshold, it is determined that current limiting protection is required and the current limiting protection process is entered; otherwise, it is determined that current limiting protection is not required and the current working mode is maintained as normal mode.

[0014] Furthermore, the external feedback control quantity is a feedback voltage signal representing the magnitude of the output voltage or output current of the resonant converter. When the output voltage or output current of the resonant converter reaches a desired value, the internal control quantity is greater than the external feedback control quantity.

[0015] Preferably, the maximum limit of the driving pulse width is less than or equal to 0.5 times the first resonant period, wherein the first resonant period is the first series resonant period of the resonant capacitor, resonant inductor and equivalent excitation inductance of the primary winding of the transformer in the resonant cavity.

[0016] Furthermore, when the working mode is switched to the current limiting mode, the following steps are further included:

[0017] The current limiting protection recovery step performs current limiting protection judgment in real time. If the current limiting protection is no longer triggered within a complete switching cycle, the working mode is restored to the normal mode and the internal control amount is gradually increased; otherwise, the current working mode is maintained at the current limiting mode.

[0018] Furthermore, the complete switching cycle refers to two switching tubes connected in series in the same switching bridge arm completing one complementary conduction.

[0019] Furthermore, when working in the normal mode, the driving control steps are followed to implement driving pulse width control.

[0020] As a second aspect of the present invention, the technical solution of the embodiment of the resonant converter current limiting protection control device provided is as follows:

[0021] A resonant converter current limiting protection control device, the resonant converter comprising at least one half-bridge switch arm, the half-bridge switch arm consisting of two series-connected switch tubes, wherein the two series-connected switch tubes are driven to maintain complementary conduction, wherein the control device comprises:

[0022] A current limiting protection judgment circuit is used to receive in real time a first voltage signal representing the magnitude of the resonant cavity current of the resonant converter, and to compare the first voltage signal with a set current limiting threshold to determine whether current limiting protection is required;

[0023] The current limiting protection processing circuit is used to reset the driving pulse width of the currently turned-on switch tube when it is determined that current limiting protection is required, so that the switch tube is turned off, and the other switch tube in the same switch bridge arm remains complementary and turned on. At the same time, the working mode is switched to the current limiting mode, and the internal control variable is gradually reduced;

[0024] The drive control circuit is used to control the drive pulse width according to the smaller value of the internal control amount and the external feedback control amount, wherein the drive pulse width is set to a maximum limit.

[0025] Furthermore, the current limiting protection processing circuit further includes:

[0026] The current limiting protection recovery circuit is used to restore the working mode to the normal mode and gradually increase the internal control amount after working in the current limiting mode if the current limiting protection is no longer triggered within a complete switching cycle;

[0027] The control quantity processing circuit is used to compare the internal control quantity with the external feedback control quantity and output the smaller value between the two to the drive control circuit.

[0028] As a third aspect of the present invention, the technical solution of the embodiment of the switching power supply provided is as follows:

[0029] A switching power supply includes a resonant converter, wherein: it also includes the resonant converter current limiting protection control device described in any one of the second aspects above.

[0030] Based on the above technical solution, compared with the prior art, the present invention has the following beneficial effects:

[0031] (1) Current limiting protection is performed on the complete cycle resonant current, so that both the positive and negative cycle resonant currents are limited to a safe range. At the same time, the two switches in the same bridge arm are kept in complementary conduction, and the maximum and minimum drive pulse widths are limited, so that all switches maintain soft switching characteristics when the current limiting protection is triggered, thereby improving the reliability of the resonant converter.

[0032] (2) By introducing internal control quantity adjustment, the control loop can smoothly transition to a closed-loop control state in the event of an output short circuit without the need for an additional external constant current loop feedback circuit. On the one hand, the resonant capacitor voltage offset can be automatically corrected, and on the other hand, the resonant converter short-circuit constant current output performance can be achieved, and it can self-recover, which can meet the application requirements of inductive loads such as motors, while saving the cost of peripheral circuits. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 A specific flow chart of a resonant converter current limiting protection control method provided by the first aspect of the embodiment of the present invention;

[0034] Figure 2 A circuit structure diagram of a resonant converter current limiting protection control device provided in accordance with the second aspect of the present invention;

[0035] Figure 3 Schematic diagram of the structure of the current limiting processing circuit in the second aspect of the embodiment of the present invention;

[0036] Figure 4 2 is a typical working timing diagram when triggering the resonant current limiting protection according to an embodiment of the present invention;

[0037] Figure 5 This is a timing diagram of the main working waveforms of a prototype device adopting the control method according to an embodiment of the present invention during the output short-circuit constant current process. DETAILED DESCRIPTION

[0038] It should be noted that, unless there is any conflict, the embodiments and features in the embodiments of this application can be combined with each other.

[0039] In order to enable those skilled in the art to better understand the present invention, the following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments in the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts should fall within the scope of protection of this application.

[0040] It should be noted that the terms "first", "second", etc. in the specification and claims of the present application and the above-mentioned drawings are used to distinguish similar objects and are not necessarily used to describe a specific order or sequential order. It should be understood that the data used in this way can be interchanged where appropriate to describe the embodiments of the present application here. In addition, the terms "including" and "having" and any of their variations are intended to cover non-exclusive inclusions, for example, a process, method, system, product or device that includes a series of steps or units is not necessarily limited to those steps or units clearly listed, but may include other steps or units that are not clearly listed or inherent to these processes, methods, products or devices.

[0041] It should be understood that in the specification, claims and drawings, when a step is described as being connected to another step, the step may be directly connected to the other step, or be connected to the other step through a third step; when an element / unit is described as being "connected" to another element / unit, the element / unit may be "directly connected" to the other element / unit, or be "connected" to the other element / unit through a third element / unit.

[0042] In addition, the figures of this disclosure are merely schematic diagrams of the present disclosure and are not necessarily drawn to scale. Identical reference numbers in the figures denote identical or similar parts, and therefore repeated descriptions thereof will be omitted. Some of the blocks shown in the figures are functional entities that do not necessarily correspond to physically or logically separate entities. These functional entities may be implemented using software, in one or more hardware modules or integrated circuits, or in different networks and / or processor devices and / or microcontrollers.

[0043] like Figure 1 FIG. 1 is a flow chart of a method for controlling current limiting protection of a resonant converter according to a first aspect of an embodiment of the present invention. For ease of explanation, only the portion related to this embodiment is shown, which is described in detail as follows:

[0044] A resonant converter current limiting protection control method comprises the following steps:

[0045] S01: sampling the resonant current in real time to obtain a first voltage signal representing the magnitude of the resonant current.

[0046] S02: comparing the first voltage signal with a set current limiting threshold to determine whether current limiting protection is required.

[0047] Specifically, the current limiting threshold includes a first set threshold and a second set threshold. When the first voltage signal is greater than the first set threshold or less than the second set threshold, it is determined that current limiting protection is required, and then the process enters step S03; otherwise, it is determined that current limiting protection is not required, and then the process directly enters step S07, that is, maintaining the current working mode.

[0048] It should be noted that the first set threshold is used to limit the peak value of the resonant current in the positive cycle, and the second set threshold is used to limit the peak value of the resonant current in the negative cycle, wherein the positive cycle refers to the resonant current in the negative cycle. Figure 2 The working cycle when the resonant current flows clockwise in the resonant cavity shown in the figure is negative. Figure 2 In the working cycle when the flow is counterclockwise in the resonant cavity shown, the positive and negative cycles constitute a complete switching cycle, that is, within a complete switching cycle, the two series-connected switching tubes in the same switching bridge arm complete a complementary conduction.

[0049] S03: When current limiting protection is required, the driving pulse width of the currently turned-on switch tube is reset to turn off the switch tube, and the other switch tube in the same switch bridge arm remains complementary to the on state to prevent the resonant current from further increasing and exceeding the safe operating range of the switch tube; at the same time, the operating mode is switched to the current limiting mode, and the internal control amount will be gradually reduced in the current limiting mode.

[0050] S04: taking the smaller value of the internal control quantity and the external feedback control quantity to control the driving pulse width, so as to correct the working state of the resonant cavity and avoid abnormal operation.

[0051] It should be noted that the external feedback control quantity is a feedback voltage signal that characterizes the output voltage or output current of the resonant converter. For constant voltage output applications, it can be obtained through an external constant voltage loop feedback circuit; while the internal control quantity is a control voltage signal constructed internally in the control device of the embodiment of the present invention. When the resonant converter is operating stably, that is, when the output voltage reaches the desired value, the internal control quantity will be clamped to a higher voltage value, so that the internal control quantity is greater than the external feedback control quantity. At this time, the resonant converter is closed-loop controlled by the external constant voltage loop. When the resonant current limiting protection is triggered, the power transmission amount is reduced due to the premature shutdown of the switch tube. At this time, the output voltage will drop slightly. If the resonant current limiting protection is continuously triggered, the transmission power will be limited, the output voltage cannot reach the desired value, the external constant voltage loop will be out of adjustment, and the external feedback control quantity will increase. At this time, by gradually reducing the internal control quantity, when the internal control quantity is less than the external feedback control quantity, the internal control quantity takes over the loop control, so that the control loop can be restored to closed-loop regulation, thereby preventing the resonant capacitor voltage from offsetting. In the process of the internal control quantity gradually decreasing to be less than the external feedback control quantity, in order to prevent the control from being out of adjustment, the maximum value of the driving control pulse width of the switch tube is limited, that is, the maximum value is less than or equal to 0.5 times the first resonant period Tr1, so as to avoid the resonant cavity working in the capacitive region and causing the switch tube to lose the soft switching characteristics. The first resonant period Tr1 is:

[0052]

[0053] In the above formula, π is the circumference of a circle, C r Expressed as the resonant capacitor value, L r Indicates the resonant inductance, L m Indicates the equivalent excitation inductance of the primary winding of the transformer.

[0054] The above steps S01, S02, and S04 are executed every cycle, while steps S03 and S07 are executed every cycle according to the judgment result of step S02. When the working mode is the current limiting mode, the following steps are also included:

[0055] S05: When working in the current limiting mode, on the basis of executing step S02, the number of times the current limiting protection is triggered in a complete cycle will be further recorded to determine whether to exit the current limiting mode. Specifically, if the first voltage signal is not detected to be greater than the first set threshold or less than the second set threshold in a complete cycle, the working mode will be restored to the normal mode, and then step S06 will be entered. Otherwise, step S07 will be entered to maintain the current limiting mode.

[0056] S06: When the working mode returns to normal mode, the internal control amount will be gradually increased.

[0057] It should be noted that no matter which mode is used, the switch tube drive pulse width control is implemented according to step S04. To prevent output fluctuation caused by sudden changes in the drive pulse width, the internal control quantity changes continuously during the switching process between the current limiting mode and the normal mode.

[0058] like Figure 2 FIG. 1 is a circuit diagram of a resonant converter current limiting protection control device according to a second aspect of an embodiment of the present invention. For ease of explanation, only the portion related to this embodiment is shown. In a specific implementation, the structure is implemented as follows:

[0059] The resonant converter 2 includes a switching circuit 20. The switching circuit 20 is composed of two switching transistors connected in series to form a half-bridge structure. The drain of the first switching transistor S1 is connected to the input power supply VIN, the source of the first switching transistor S1 is connected to the drain of the second switching transistor S2, and the source of the second switching transistor S2 is connected to the reference ground GND. The switching circuit 20 is controlled by a control device 21 to generate a periodic square wave voltage to drive the LLC resonant circuit 22 to achieve energy conversion. The LLC resonant circuit 22 includes a resonant inductor L connected in series. r and the equivalent excitation inductance L of the primary winding of transformer 23 m , resonant capacitor C r , resonant inductor L r The other end is connected to the source of the first switch tube S1, and the resonant capacitor C r The other end is connected to the reference ground GND. The two secondary windings of the transformer 23 are connected to the drains of the first synchronous rectifier SR1 and the second synchronous rectifier SR2, respectively, to form a full-wave rectifier circuit. The sources of the first synchronous rectifier SR1 and the second synchronous rectifier SR2 are connected in parallel with the output filter capacitor C. o And the output resistance R o One end of the output filter capacitor C o And the output resistance R o The other end is connected to the middle tap of the two secondary windings of the transformer 23 and serves as the output voltage terminal VOUT of the resonant converter 2. The resonant current sampling circuit 24 is coupled to the series loop of the LLC resonant circuit 22 and is used to sample the resonant current and output a sampling voltage signal V representing the magnitude and change trend of the resonant current in the entire cycle. IR_SAMP The output feedback circuit 25 is connected to the output end of the resonant converter 2 and is used to sample the output voltage and output a feedback voltage signal V representing the magnitude of the output voltage. FB The first input terminal of the control device 21 receives a sampling voltage signal V representing the magnitude and change trend of the full-cycle resonant current. IR_SAMP The second input terminal receives the feedback voltage signal V representing the output voltage. FBThe output end is connected to the switch circuit 20. The control device 21 is based on the sampling voltage signal V IR_SAMP To identify whether to perform current limiting protection, and then according to the internal control amount and feedback voltage signal V FB The driving pulse width is adjusted by the smaller value in , thereby controlling the switching circuit 20 to generate a periodic square wave voltage to drive the LLC resonant circuit 22.

[0060] The control device 21 includes a current limiting protection judgment circuit 201, which is used to receive a sampling voltage signal V that represents the magnitude and change trend of the full-cycle resonant current. IR_SAMP and the sampled voltage signal V IR_SAMP The first set current limiting threshold and the second set current limiting threshold are used to determine whether current limiting protection is required. The current limiting protection processing circuit 202 is used to perform related operations according to the judgment result of the current limiting protection judgment circuit 201. Specifically, when it is determined that current limiting protection is required, the current limiting protection processing circuit 202 first outputs a drive reset signal to the drive control circuit 203 to control the current switching tube drive pulse width reset, so that the switch tube is turned off, and the other switch tube in the same switch bridge arm remains complementary, and at the same time the working mode is switched to the current limiting mode, and the internal control amount is gradually reduced. Figure 3 As shown, the current limiting protection processing circuit 202 also includes a current limiting protection recovery circuit 301, which is used to record the number of times the current limiting protection is triggered in a complete cycle and determine whether to exit the current limiting mode. Specifically, after working in the current limiting mode, if the current limiting protection is not triggered in a complete switching cycle, the working mode is restored to the normal mode and the internal control amount is gradually increased. The control amount processing circuit 302 is used to compare the internal control amount with the feedback voltage signal V FB , and outputs the smaller value of the two to the drive control circuit 203. The drive control circuit 203 is used to receive the internal control amount and the feedback voltage signal V FB The smaller value in the control pulse width is used to control the driving pulse width. Specifically, the internal control amount can be combined with the feedback voltage signal V FB The smaller value in is compared with the charge feedback signal representing the input charge size to control the driving pulse width, wherein the charge feedback signal acquisition circuit is not shown in the diagram.

[0061] It should be noted that when the current limiting protection is triggered, the drive control circuit 203 will also receive the drive reset signal output by the current limiting protection processing circuit 202 to forcibly reset the drive pulse width, so that the actual drive pulse width of the corresponding switch tube is less than the internal control amount and the feedback voltage signal V FB The driving pulse width is obtained by comparing the smaller value of with the charge feedback signal representing the input charge size, thereby limiting the further increase of the resonant current.

[0062] For those skilled in the art, Figure 2The resonant converter shown also includes but is not limited to the following variations:

[0063] (1) Replace the primary switching circuit with a full-bridge structure consisting of two sets of half-bridge switch arms connected in parallel;

[0064] (2) Replace the secondary side rectifier circuit with a bridge rectifier structure consisting of four switching tubes or diodes.

[0065] Figure 4 The following is a typical working sequence diagram of triggering the resonant current limiting protection according to an embodiment of the present invention. Figure 4 To introduce the working principle in detail:

[0066] Where Vo is the output voltage signal of the resonant converter, V IR_SAMP is the resonant current sampling voltage signal, V IR_OCP+ The first set current limit threshold, V IR_OCP- is the second set current limit threshold, GH is the driving signal of the first switch tube S1, GL is the driving signal of the second switch tube S2, V FB is the external feedback voltage signal, V FB_INT is the internal control voltage signal, V CS is the charge feedback signal, HRst is the driving reset signal of the first switch tube S1 when the current limiting protection is triggered, LRst is the driving reset signal of the second switch tube S2 when the current limiting protection is triggered, and CC_MODE is the flag signal representing working in the current limiting mode.

[0067] Before time t1, the resonant converter works in normal mode, the output voltage Vo reaches a steady state, and the resonant current works stably within the set current limit threshold. At this time, the internal control voltage signal V FB_INT is clamped at a higher value, and the driving pulse width is based on the external feedback voltage signal V FB And the charge feedback signal V CS Comparison shows that the driving signal GH of the first switch tube S1 and the driving signal GL of the second switch tube S2 are complementary to each other and have substantially the same driving pulse width.

[0068] At time t1, the resonant converter has an output short circuit fault, and the output voltage Vo begins to drop, causing the external feedback voltage signal V FB It starts to rise, and the resonant current change slope becomes steeper until the resonant current sampling voltage signal V IR_SAMP Greater than the first set current limit threshold V IR_OCP+, the driving reset signal HRst controls the driving signal GH of the first switch tube S1 to reset, limiting the further increase of the resonant current, while the driving signal GL of the second switch tube S2 maintains complementary conduction; at the same time, the current limiting mode flag signal CC_MODE is set high, and the resonant converter enters the current limiting working mode. At this time, the internal control voltage signal V FB_INT Gradually decrease.

[0069] During the time period from t2 to t3, the resonant converter still operates in the current limiting mode, and the internal control voltage signal V FB_INT continues to decrease, while the external feedback voltage signal V FB As the output voltage Vo continues to drop, it continues to rise until it is clamped at a higher value and is in an unregulated state. At this time, the positive and negative cycle resonant currents are asymmetric, which will cause the resonant capacitor voltage to shift. By taking a smaller internal control voltage signal V FB_INT and the charge feedback signal V CS Comparison is used to control the driving pulse width, which can gradually correct the resonant capacitor voltage offset phenomenon. In this process, in order to prevent the resonant converter from operating in the capacitive region, the maximum driving pulse width will be limited. If the maximum driving pulse width limit is reached, the internal control voltage signal V FB_INT The charge feedback signal V CS , and the corresponding drive signal will be forced to reset.

[0070] At time t3, the resonant current sampling voltage signal V IR_SAMP Less than the second set current limit threshold V IR_OCP- , the driving reset signal LRst controls the driving signal GL of the second switch tube S2 to reset, while the driving signal GH of the first switch tube S1 remains complementary. Since the current limiting protection condition is not triggered within a complete cycle, the current limiting mode is maintained after time t3, and the internal control voltage signal V FB_INT Continue to decrease.

[0071] At t4, the output voltage Vo drops below close to 0V, and the external feedback voltage signal V FB Maintains the offset state while the internal control voltage signal V FB_INT When the voltage drops to a smaller value, the control loop is in a closed-loop state, and the resonant current is corrected to a positive and negative symmetrical state.

[0072] At t5, if the current limiting protection condition is not triggered within a complete cycle, the current limiting mode flag signal CC_MODE is reset, and the working mode is restored to the normal mode. At this time, the internal control voltage signal V FB_INT Gradually increase.

[0073] At t6, the current limiting protection condition is triggered again, the current limiting mode flag signal CC_MODE is set high again, and the current limiting working mode is entered again. The internal control voltage signal VFB_INT Gradually decrease.

[0074] Since the control loop is in a closed loop state at this time, the internal control voltage signal V FB_INT The state is repeated between t5 and t6 with small fluctuation, so that the resonant converter works in a constant current output state, which can meet the needs of inductive load applications such as motors.

[0075] In a specific embodiment, Figure 2 The rated output power of the resonant converter is 600W, the input voltage Vin varies from 250V to 375V, and the nominal output voltage is 24V. When the input voltage is 250V, the load is switched between full load and short circuit conditions, and the following is obtained: Figure 5 The experimental waveform shown in the figure, where Vcr is the resonant capacitor voltage, Ir is the resonant capacitor current, and the rest are the same as Figure 4 The same signals have the same reference numerals and are not described in detail. Figure 5 The experimental waveform shows that at time t1, the resonant converter switches from full-load stable operation to output short-circuit state. During the time from t1 to t2, based on the current limiting protection, the resonant current is limited to a safe range, but the resonant capacitor voltage Vcr has an offset phenomenon. Until time t2, the internal control voltage signal V FB_INT By intervening in loop control, the resonant capacitor voltage Vcr is gradually corrected until it returns to normal at time t3. Output short-circuit constant current control is achieved without an external constant current loop feedback circuit during the time period from t3 to t4. At time t4, the output short-circuit fault is removed, and the output voltage Vo begins to gradually recover. During the recovery process, the resonant current Ir and the resonant capacitor voltage Vcr do not deviate. Until time t5, the output voltage Vo returns to normal, and the resonant converter operates stably, thereby proving the effectiveness of the current limiting protection control method of the present invention.

[0076] In the description of the above embodiments, the present invention describes a resonant converter current limiting protection control method, control device and switching power supply. Without adding a constant current loop feedback circuit, the resonant current wave-by-wave current limiting control combined with the internal control quantity automatic adjustment method can effectively limit the peak value of the resonant current when an output short circuit fault occurs in the resonant converter, thereby avoiding damage to the switching device. At the same time, the control loop is in closed-loop control, which can automatically correct the resonant voltage offset phenomenon, ensure the soft switching characteristics of the switching tube, and greatly improve the reliability of the resonant converter.

[0077] It should be noted that the embodiments described above are merely illustrative of the technical solutions and contents of the present invention, and should not be construed as limiting the present invention. Persons skilled in the art will appreciate that improvements and modifications may be made without departing from the spirit and scope of the present invention. However, these improvements and modifications do not deviate from the spirit of the present invention or exceed the scope defined by the appended claims, and should be considered within the scope of protection of the present invention.

Claims

1. A method for controlling current limiting protection of a resonant converter, wherein the resonant converter comprises at least one half-bridge switch arm, wherein the half-bridge switch arm comprises two switches connected in series, wherein the two switches in series are driven to maintain complementary conduction, characterized in that: The control method includes: A resonant current sampling step of acquiring in real time a first voltage signal representing the magnitude of the resonant cavity current of the resonant converter; a current limiting protection judgment step, comparing the first voltage signal with a set current limiting threshold to judge whether current limiting protection is required; If current limiting protection is required, the drive pulse width of the currently on switch is reset to turn off the switch, while the other switch in the same switch arm remains complementary and turned on. At the same time, the operating mode is switched to the current limiting mode, and the internal control variable is gradually reduced. The drive control step takes the smaller value of the internal control amount and the external feedback control amount to control the drive pulse width, wherein the drive pulse width is set to a maximum limit.

2. The control method according to claim 1, characterized in that: The specific methods for judging whether current limiting protection is needed are: The current limiting threshold includes a first set threshold and a second set threshold. When the first voltage signal is greater than the first set threshold or less than the second set threshold, it is determined that current limiting protection is required and the current limiting protection process is entered; otherwise, it is determined that current limiting protection is not required and the current working mode is maintained as normal mode.

3. The control method according to claim 1, characterized in that: The external feedback control quantity is a feedback voltage signal representing the magnitude of the output voltage or output current of the resonant converter. When the output voltage or output current of the resonant converter reaches a desired value, the internal control quantity is greater than the external feedback control quantity.

4. The control method according to claim 1, characterized in that: The maximum limit of the driving pulse width is less than or equal to 0.5 times the first resonant period, wherein the first resonant period is the first series resonant period of the resonant capacitor, resonant inductor and equivalent excitation inductance of the primary winding of the transformer in the resonant cavity.

5. The control method according to claim 1, characterized in that: When the working mode is switched to current limiting mode, it also includes: The current limiting protection recovery step performs current limiting protection judgment in real time. If the current limiting protection is no longer triggered within a complete switching cycle, the working mode is restored to the normal mode and the internal control amount is gradually increased; otherwise, the current working mode is maintained at the current limiting mode.

6. The control method according to claim 5, characterized in that: The complete switching cycle refers to the completion of one complementary conduction of two series-connected switching tubes in the same switching bridge arm.

7. The control method according to claim 5, characterized in that: When working in the normal mode, the driving pulse width control is implemented according to the driving control steps.

8. A current limiting protection control device for a resonant converter, the resonant converter comprising at least one half-bridge switch arm, the half-bridge switch arm consisting of two series-connected switch tubes, wherein the two series-connected switch tubes are driven to maintain complementary conduction, characterized in that: The control device comprises: A current limiting protection judgment circuit is used to receive in real time a first voltage signal representing the magnitude of the resonant cavity current of the resonant converter, and to compare the first voltage signal with a set current limiting threshold to determine whether current limiting protection is required; The current limiting protection processing circuit is used to reset the driving pulse width of the currently turned-on switch tube when it is determined that current limiting protection is required, so that the switch tube is turned off, and the other switch tube in the same switch bridge arm remains complementary and turned on. At the same time, the working mode is switched to the current limiting mode, and the internal control variable is gradually reduced; The drive control circuit is used to control the drive pulse width according to the smaller value of the internal control amount and the external feedback control amount, wherein the drive pulse width is set to a maximum limit.

9. The resonant converter current limiting protection control device according to claim 8, characterized in that: The current limiting protection processing circuit further includes: The current limiting protection recovery circuit is used to restore the working mode to the normal mode and gradually increase the internal control amount after working in the current limiting mode if the current limiting protection is no longer triggered within a complete switching cycle; The control quantity processing circuit is used to compare the internal control quantity with the external feedback control quantity and output the smaller value between the two to the drive control circuit.

10. A switching power supply comprising a resonant converter, characterized in that: It also includes the resonant converter current limiting protection control device according to any one of claims 8 to 9.

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