WO2013078851A1

WO2013078851A1 - Current-limiting protection method and device for resonance circuit

Info

Publication number: WO2013078851A1
Application number: PCT/CN2012/077449
Authority: WO
Inventors: 万正海; 王明金; 李俊凯; 张伟
Original assignee: 中兴通讯股份有限公司
Priority date: 2011-12-02
Filing date: 2012-06-25
Publication date: 2013-06-06
Also published as: CN103138590A; CN103138590B

Abstract

Disclosed are a current-limiting protection method and device for a resonance circuit. The method comprises: detecting in a resonance circuit a voltage between two ends of a sampling resistor through which a resonance current flows; when it is detected in the current resonance period that the voltage between two ends of the sampling resistor is greater than a preset threshold value, blocking the drive of the resonance circuit; when the next pulse width modulation period arrives, switching the resonance circuit from a constant voltage mode to an output current-limiting mode. The present invention adopts a strategy that an LLC resonant converter immediately enters the current-limiting mode in control upon detecting the pulse-by-pulse current limit, so that the primary current quickly drops below the threshold value, thereby solving the technical problem that the voltage stress of the full-bridge diode exceeds the limit during the continuous pulse-by-pulse current limit, and improving the reliability of the switch power supply and power devices.

Description

TECHNICAL FIELD The present invention relates to the field of communications, and in particular, to a method and device for current-limiting protection of a resonant circuit. BACKGROUND High efficiency, high power and high density are an important development trend of power electronic products. Full-bridge LLC (single-port network containing inductors, resistors and capacitors) resonant DC/DC (DC-to-DC) converters rely on their conversion efficiency and The outstanding advantages of power density have been favored by many people in the switching power supply industry. At present, for a full-bridge LLC resonant DC/DC converter, when a wave-by-wave current limitation occurs, the four drives of the full-bridge tube of the LLC converter are blocked, and the four drives are re-enabled after a period of time. When the wave-by-wave current limiting occurs, the four drivers of the full-bridge tube are immediately blocked, and the full-bridge LLC resonant circuit will enter a self-resonant state. When the lower tube of the full bridge over the forearm is freewheeling, if the wave-by-wave current limiting action has been completed at this time, it is necessary to restart the four drives of the full bridge tube of the LLC converter. If the drive corresponding to V1 and V4 is turned on, due to the reverse recovery current of V2, VI and V2 will have a common phenomenon, and the voltage stress of V2 will be abnormal; in the same way, when the down tube of the full bridge lagging arm is freewheeling, If the wave-by-wave current limiting action has been completed at this time, it is necessary to restart the four drives of the full-bridge of the LLC converter. If the drives corresponding to V2 and V3 are turned on, since V4 has reverse recovery current, then V3, V4 will have a common phenomenon, and the voltage stress of V4 will be abnormal. In view of the above-mentioned problem that the voltage stress of the full bridge tube may exceed the standard when the drive is restarted after the end of the wave-by-wave current limit, especially the problem that the pressure of the full-bridge switch tube exceeds the standard repeatedly caused by the continuous wave-by-wave current limit, no effective solution has been proposed yet. plan. SUMMARY OF THE INVENTION The present invention provides a current limiting protection method and device for a resonant circuit to at least solve the technical problem of excessive voltage stress of a full bridge tube caused by continuous wave-by-wave current limiting in the prior art. According to one aspect of the present invention, there is provided a current limiting protection method for a resonance circuit, including: detecting a voltage across a sampling resistor through which a resonance current flows in a resonance circuit; detecting that the voltage across the sampling resistor is greater than a predetermined threshold in the current resonance period When the time, the drive of the resonant circuit is blocked; when the next pulse width modulation cycle arrives, the resonant circuit is switched from the constant voltage mode to the output current limiting mode. Preferably, the step of switching the resonant circuit from the constant voltage mode to the output current limiting mode includes: when detecting that the output signal level of the comparator of the resonant circuit is inverted, connecting the current loop output signal of the previous resonant period to the upper The current loop error signal of a resonant period is cleared; the pulse width modulation signal used to switch the resonant circuit from the constant voltage mode to the output current limiting mode is generated according to the current loop output signal of the current resonant period. Preferably, the step of blocking the driving of the resonant circuit includes: blocking the driving of a pair of tubes corresponding to the direction of the resonant current. Preferably, the predetermined threshold includes: a first predetermined threshold and a second predetermined threshold; the sampling resistor includes: a first sampling resistor and a second sampling resistor; the tube driving includes: a first pair of tube driving and a second pair of tube driving, Wherein, the step of blocking the driving of a pair of tubes corresponding to the direction of the resonance current includes: when the voltage across the first sampling resistor is greater than a first predetermined threshold, blocking the driving of the first pair of tubes; when the voltage across the second sampling resistor is greater than At the second predetermined threshold, the drive of the second pair of tubes is blocked. Preferably, after the drive of the resonant circuit is blocked, the current-limiting protection method of the resonant circuit further includes: when the next resonant period of the current resonant period arrives, judging whether the primary side of the resonant circuit has overcurrent; if the primary side of the resonant circuit does not If there is overcurrent, the driver will be unlocked. Preferably, the step of detecting the voltage across the sampling resistor through which the resonant current flows includes: converting the resonant current through a current transformer; rectifying the converted resonant current through a rectifier; and after the rectified resonant current flows through the The voltage at both ends of the sampling resistor is sampled to obtain the voltage at both ends of the sampling resistor. According to another aspect of the present invention, there is provided a current limiting protection device for a resonance circuit, including: a detection unit configured to detect the voltage across a sampling resistor through which a resonance current flows in the resonance circuit; and a blocking unit configured to be in the current resonance period When it detects that the voltage across the sampling resistor is greater than the predetermined threshold, the drive of the resonant circuit is blocked; the switching unit is set to switch the resonant circuit from the constant voltage mode to the output current limiting mode when the next pulse width modulation period arrives. Preferably, the switching unit includes: a clearing module, which is configured to compare the current loop output signal of the previous resonance period with the current loop error of the previous resonance period when it is detected that the output signal level of the comparator of the resonance circuit is inverted The signal is cleared; the generating module is set to generate a pulse width modulation signal for switching the resonant circuit from the constant voltage mode to the output current limiting mode according to the current loop output signal of the current resonance period. Preferably, the blocking unit includes: a blocking module configured to block a pair of tube driving corresponding to the direction of the resonance current when it is detected that the voltage across the sampling resistor is greater than a predetermined threshold in the current resonance period. Preferably, the predetermined threshold includes: a first predetermined threshold and a second predetermined threshold; the sampling resistor includes: a first sampling resistor and a second sampling resistor; the tube driving includes: a first pair of tube driving and a second pair of tube driving, The blockade module includes: a first blockade submodule, which is set to block the drive of the first pair of tubes when the voltage across the first sampling resistor is greater than a first predetermined threshold; and the second blockade submodule is set to block the drive of the second pair of tubes When the voltage at both ends is greater than the second predetermined threshold, the second pair of tube driving is blocked. Preferably, the resonant circuit current-limiting protection device further includes: a judging unit, set to judge whether an overcurrent occurs on the primary side of the resonant circuit when the next resonant period of the current resonant period arrives; the unblocking unit is set to be at the resonance When there is no overcurrent on the primary side of the circuit, the drive is unblocked. In the present invention, by adding the strategy of making the LLC resonant converter immediately enter the current-limiting loop in control after the wave-by-wave current limiting is detected in the smart unit, the primary current is quickly reduced to within the threshold, which solves the problem of continuous wave-by-wave current limiting. The technical problem that the voltage stress of the full-bridge tube exceeds the standard caused by the wave current limitation has improved the reliability of the switching power supply and power devices. Further, by detecting the current direction of the resonant current, when the resonant current exceeds the current protection threshold, a pair of pairs of tubes are blocked according to the detected current direction to achieve the wave-by-wave current limiting protection of the LLC resonant circuit, which solves the problem in the prior art. Due to the delay problem caused by the need to block the four drives of the full bridge tube during the wave-by-wave current limiting, the technical effect of realizing fast response to the loop after wave-by-wave is achieved. BRIEF DESCRIPTION OF THE DRAWINGS The drawings described here are used to provide a further understanding of the present invention and constitute a part of the application. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention, and do not constitute an improper limitation of the present invention. In the drawings: Figure 1 is a block diagram of a preferred structure of a current limiting protection device for a resonant circuit according to an embodiment of the present invention; Figure 2 is another preferred structure of a current limiting protection device for a resonant circuit according to an embodiment of the present invention Block diagram; Figure 3 is a schematic diagram of a circuit for current limiting protection of a resonant circuit according to an embodiment of the present invention; Figure 4 is another preferred structural block diagram of a current limiting protection device for a resonant circuit according to an embodiment of the present invention; Another preferred structural block diagram of the resonant circuit current limiting protection device according to the embodiment of the present invention; Fig. 6 is another preferred structural block diagram of the resonant circuit current limiting protection device according to the embodiment of the present invention; Fig. 7 is according to the present invention Another preferred structural block diagram of the resonant circuit current-limiting protection device of the embodiment; FIG. 8 is a preferred flowchart of the resonant circuit current-limiting protection method according to an embodiment of the present invention; Fig. 9 is a schematic diagram of a driving waveform when the primary side is over-current according to an embodiment of the present invention; Fig. 10 is another preferred structural block diagram of a current limiting protection device for a resonant circuit according to an embodiment of the present invention. DETAILED DESCRIPTION Hereinafter, the present invention will be described in detail with reference to the drawings and in conjunction with the embodiments. It should be noted that the embodiments in the application and the features in the embodiments can be combined with each other if there is no conflict. Embodiment 1 As shown in FIG. 1, this embodiment provides a preferred current limiting protection device for a resonance circuit. The device includes: a detection unit 102 configured to detect the voltage across the sampling resistor through which the resonance current flows in the resonance circuit; The blocking unit 104 is configured to block the driving of the resonant circuit when it is detected that the voltage across the sampling resistor is greater than a predetermined threshold during the current resonance period; the switching unit 106 is configured to switch all the signals when the next pulse width modulation period arrives. The resonant circuit is switched from the constant voltage mode to the output current limiting mode. In the above-mentioned preferred embodiment, by adding the strategy of making the LLC resonant converter immediately enter the current limiting loop in control after the wave-by-wave current limiting is detected in the smart unit, the primary current is quickly reduced to the threshold value, which solves the problem. The technical problem of excessive voltage stress of the full bridge tube caused by continuous wave-by-wave current limiting has improved the reliability of switching power supplies and power devices. In a preferred embodiment of the present invention, as shown in FIG. 2, the blocking unit 104 includes: a blocking module 202, which is configured to block communication with the A pair of tube drives corresponding to the direction of the resonant current. By detecting the current direction of the resonant current, when the resonant current exceeds the current protection threshold, a pair of tube drives are blocked according to the detected current direction to achieve the wave-by-wave current limiting protection of the LLC resonant circuit. The delay problem caused by the need to block the four drives of the full bridge tube when the wave current is limited, achieves the technical effect of realizing a fast response to the loop after the wave. Specifically, as shown in Figure 3, the resonant current passes through a current transformer (CT) from a high frequency AC value to a DC effective value, then flows through a rectifier for rectification, and finally samples the voltage across the sampling resistor. Preferably, taking the Ik current direction in Figure 3 as positive, the current flowing through the sampling resistor R2 is the positive resonant current, and the current flowing through the sampling resistor R3 is the negative resonant current. By sampling the voltage across R2 and R3, The magnitude of the corresponding resonant current can be obtained, so that the detection of positive and negative resonant currents is realized. Preferably, when _R2 exceeds the predetermined threshold Vref, the driving of V2 and V3 is blocked; when V _R3 exceeds the predetermined threshold Vref, the driving of VI and V4 is blocked, thereby achieving the purpose of wave-by-wave current limiting. In a preferred embodiment, as shown in FIG. 4, the switching unit 106 includes: a zero clearing module 402, configured to change the previous resonance period when the output signal level of the comparator of the resonance circuit is inverted The current loop output signal of the current loop and the current loop error signal of the previous resonance period are cleared; the generating module 404 is configured to generate the current loop output signal of the current resonance period for switching the resonance circuit from the constant voltage mode to Output pulse width modulation signal in current limiting mode. In this preferred embodiment, the method of forcibly switching to the output current limiting mode is adopted, which improves the conversion from the constant voltage mode to the current limiting mode through natural loop selection in the prior art, and generally requires 10 pulse width modulation periods. The above conditions can completely enter the working mode of output current limiting. When the current exceeds the predetermined threshold, the effect that the resonant circuit can enter the working mode of output current limiting in the next pulse width modulation cycle makes the primary current quickly drop to Within the threshold, the technical problem of excessive voltage stress of the full bridge tube caused by continuous wave-by-wave current limiting is solved, and the reliability of switching power supplies and power devices is improved. Specifically, based on the circuit diagram shown in FIG. 3, the voltages _R2 and ₃ sampled by the sampling resistor are compared with a predetermined threshold (fixed voltage value Vref). As shown in Figure 5: When _{the value of R2} is greater than Vref, the level of Vol output by the comparator will flip; after the smart unit detects the level flip, it will be forced by the controller when the next pulse width modulation cycle arrives. The working mode of the LLC resonant converter is switched from the constant voltage working mode to the output current limiting mode, so that the LLC resonant converter does not need to be completed after 10 pulse width modulation cycles due to natural selection through the loop as in the prior art. Enter the working mode of output current limit, thereby improving the efficiency of switching current limit. Similarly, when _{the value of 3} is greater than Vref, the level of Vol output by the comparator will also be inverted, which will not be repeated here. This embodiment also provides a preferred unblocking method to unblock the drive after the current of the resonant circuit returns to normal. In a preferred embodiment of the present invention, as shown in FIG. 6, the resonant circuit current limiting protection device further includes: a judging unit 602, configured to judge whether the primary side of the resonant circuit arrives when the next resonant period of the current resonant period arrives Overcurrent occurs; the unblocking unit 604 is configured to unblock the drive when there is no overcurrent on the primary side of the resonant circuit. The present invention also provides a preferred method for sampling the voltage across the sampling resistor, so as to accurately sample the required voltage, so as to realize the judgment of whether the current exceeds the threshold value. In a preferred embodiment of the present invention, the detection unit 102 is further configured to convert the resonant current through a current transformer (CT), and rectify the converted resonant current through a rectifier; after the rectification Voltage sampling is performed on both ends of the sampling resistor through which the resonant current flows to obtain the voltage across the sampling resistor. In a preferred embodiment of the present invention, preferably, the above-mentioned predetermined threshold includes but is not limited to at least one of the following: a first predetermined threshold and a second predetermined threshold; the above-mentioned sampling resistor includes but is not limited to at least one of the following: A sampling resistor and a second sampling resistor; the above-mentioned pair of tube driving includes but not limited to at least one of the following: The first pair For the tube driving and the second pair of tube driving, as shown in FIG. 7, the blocking module 202 includes: a first blocking sub-module 702, configured to block the first pair when the voltage across the first sampling resistor is greater than a first predetermined threshold Drive the tube; the second blockade sub-module 704 is configured to block the drive of the second pair of tubes when the voltage across the second sampling resistor is greater than a second predetermined threshold. Embodiment 2 Based on the devices and circuits shown in 1-7, the present invention also provides a preferred current-limiting protection method for resonant circuits. As shown in FIG. 8, the method specifically includes the following steps: Step S802: detecting in the resonant circuit The voltage across the sampling resistor through which the resonant current flows; Step S804: When it is detected that the voltage across the sampling resistor is greater than the predetermined threshold during the current resonance period, the drive of the resonance circuit is blocked; Step S806: When the next pulse width modulation period arrives, the The resonant circuit switches from constant voltage mode to output current limiting mode. In the above-mentioned preferred embodiment, by adding the strategy of making the LLC resonant converter immediately enter the current limiting loop in control after the wave-by-wave current limiting is detected in the smart unit, the primary current is quickly reduced to the threshold value, which solves the problem. The technical problem of excessive voltage stress of the full bridge tube caused by continuous wave-by-wave current limiting has improved the reliability of switching power supplies and power devices. In a preferred embodiment, the step of blocking the driving of the resonant circuit includes: blocking the driving of a pair of tubes corresponding to the direction of the resonant current. By detecting the current direction of the resonant current, when the resonant current exceeds the current protection threshold, a pair of tube drives are blocked according to the detected current direction to achieve the wave-by-wave current limiting protection of the LLC resonant circuit. The delay problem caused by the need to block the four drives of the full bridge tube when the wave current is limited, achieves the technical effect of realizing a fast response to the loop after the wave. Specifically, as shown in Figure 3, the resonant current passes through a current transformer (CT) from a high frequency AC value to a DC effective value, then flows through a rectifier for rectification, and finally samples the voltage across the sampling resistor. Preferably, taking the Ik current direction in Figure 3 as positive, the current flowing through the sampling resistor R2 is the positive resonant current, and the current flowing through the sampling resistor R3 is the negative resonant current. By sampling the voltage across R2 and R3, The magnitude of the corresponding resonant current can be obtained, so that the detection of positive and negative resonant currents is realized. Preferably, when _R2 exceeds the predetermined threshold Vref, the driving of V2 and V3 is blocked; when V _R3 exceeds the predetermined threshold Vref, the driving of VI and V4 is blocked, thereby achieving the purpose of wave-by-wave current limiting. In a preferred embodiment, the step of switching the resonant circuit from the constant voltage mode to the output current limiting mode includes: when it is detected that the output signal level of the comparator of the resonant circuit is inverted, turning the previous resonance The periodic current loop output signal and the current loop error signal of the previous resonant period are cleared; according to the current loop output signal of the current resonant period, a signal for switching the resonant circuit from the constant voltage mode to the output current limiting mode is generated Pulse width modulation signal. In this preferred embodiment, the method of forcibly switching to the output current limiting mode is adopted, which improves the conversion from the constant voltage mode to the current limiting mode through natural loop selection in the prior art. Generally, 10 pulse width modulation periods are required. The above conditions can completely enter the working mode of output current limiting. When the current exceeds the predetermined threshold, the effect that the resonant circuit can enter the working mode of output current limiting in the next pulse width modulation cycle makes the primary current quickly drop to Within the threshold, the technical problem of excessive voltage stress of the full bridge tube caused by continuous wave-by-wave current limiting is solved, and the reliability of switching power supplies and power devices is improved. Specifically, based on the circuit diagram shown in FIG. 3, the voltages _R2 and ₃ sampled by the sampling resistor are compared with a predetermined threshold (fixed voltage value Vref). As shown in Figure 5: When _{the value of R2} is greater than Vref, the level of Vol output by the comparator will flip; after the smart unit detects the level flip, it will be forced by the controller when the next pulse width modulation cycle arrives. The working mode of the LLC resonant converter is switched from the constant voltage working mode to the output current limiting mode, so that the LLC resonant converter does not need to be completed after 10 pulse width modulation cycles due to natural selection through the loop as in the prior art. Enter the working mode of output current limit, thereby improving the efficiency of switching current limit. Similarly, when _{the value of 3} is greater than Vref, the level of Vol output by the comparator will also be inverted, which will not be repeated here. In a preferred embodiment, the foregoing predetermined threshold includes but is not limited to at least one of the following: a first predetermined threshold and a second predetermined threshold; the sampling resistor includes but is not limited to at least one of the following: a first sampling resistor and a second Sampling resistor; the pair of tube driving includes but is not limited to at least one of the following: a first pair of tube driving and a second pair of tube driving, wherein the step of blocking a pair of tube driving corresponding to the direction of the resonant current includes : When the voltage across the first sampling resistor is greater than a first predetermined threshold, block the drive of the first pair of tubes; when the voltage across the second sampling resistor is greater than a second predetermined threshold, block the second Pair to tube drive. In a preferred embodiment of the present invention, after blocking the drive of the resonant circuit, the current limiting protection method of the resonant circuit further includes: determining the origin of the resonant circuit when the next resonant period of the current resonant period arrives. Whether there is overcurrent on the side; if there is no overcurrent on the primary side of the resonant circuit, the drive is unblocked. In a preferred embodiment of the present invention, the step of detecting the voltage across the sampling resistor through which the resonant current flows includes: converting the resonant current through a current transformer; converting the converted current through a rectifier The resonant current is rectified; voltage sampling is performed on both ends of the sampling resistor through which the rectified resonant current flows to obtain the voltage across the sampling resistor. Embodiment 3 The present invention provides a preferred embodiment to further explain the present invention, but it is worth noting that this preferred embodiment is only for better describing the present invention, and does not constitute an improper limitation of the present invention. Hereinafter, the present invention will be further described in detail through specific embodiments in conjunction with the accompanying drawings. As shown in FIG. 3, an LLC resonant circuit includes a resonant inductor Lr, a main transformer T, a resonant capacitor Cr, main power switching devices VI, V2, V3, and V4, and secondary power Schottky diodes D1 and D2. The resonant current detection circuit includes: a current transformer CT1, a magnetic reset resistance R1 of CT1, and diodes D3, D4, D5, and D6. Preferably, the diode uses a fast recovery diode or a Schottky diode and the current sampling resistors R2 and R3. The resonance circuit is connected to the DC input voltage Vin, the main power switching devices VI, V2, V3, and V4 have body diodes, and the secondary side of the transformer of the LLC resonance circuit is connected to the output voltage Vo. The LLC resonant circuit can realize the zero voltage turn-on (ZVS) of the main power device and the zero current turn-off (ZCS) of the secondary diode by controlling the switching frequency of the main power switching devices VI, V2, V3, and V4, which is beneficial to reduce The switching loss of power devices in order to improve the efficiency of the entire machine. In order to protect the components in the main topology circuit from overcurrent, it is necessary to detect the current in the main topology circuit. As shown in Figure 3: The current detection device of the LLC resonant circuit, preferably, the resonant current is ILr, the direction of the current is positive as shown by the arrow in the figure, the turns ratio of CT1 is n, and the resonant current is transformed by CT1, n -I2) = I _L rln, preferably, the resonance current is changed from a high-frequency AC value to a DC effective value for detection, which makes the detection more convenient. The rectifier is then used to rectify the converted resonant current, the rectified current flows through the sampling resistor, and the voltage across the sampling resistor is sampled to obtain the size of the resonant current flowing through the sampling resistor. Through this preferred embodiment, the current detection device can detect the forward resonant current: _R2 = (/^ / «) *R2. The reverse resonance current can also be detected: V _R3 = (I _Lr I) * Ri. When V _R2 exceeds the set value Vref, the drive of V2 and V3 is blocked; when V _R3 exceeds the set value Vref, the drive of VI and V4 is blocked. The specific realization of the drive blockade is shown in Figure 5. When _R2 or _R3 exceeds the set value Vref, the corresponding drive enable unit enable pin level will be reversed, as shown in Figure 9. At this time, the corresponding PWM wave will be blocked during this pulse width modulation period, and the blocking will continue until At the beginning of the next resonant period; when the next resonant period arrives, judge whether the primary side overcurrent occurs in the resonant circuit. If the primary side current limit does not occur in the resonant circuit, the pair of blocked pairs will be blocked in the next pulse width modulation period. The driver unlocks and resumes normal operation. Preferably, the comparator output signals Vol and Vo2 are sent to the intelligent unit shown in FIG. 5 at the same time. As shown in Figure 10, the intelligent unit includes: a feedback voltage loop and a feedback current loop. Among them, the feedback voltage loop and the feedback current loop work in parallel, the voltage loop plays a role of stabilizing, and the current loop plays a role of current limiting. Both the voltage loop and the current loop adopt the PI (proportional-integral) control method. Among them, the expression of current loop PI control is as follows: I _out (k) = I _out (k-\) + K _p ^ err{k) + K _t * err(k-1), where is the current cycle current loop Output, /. „_ 1) is the output of the current loop of the previous cycle, enik, is the current loop error of the current cycle, and err^-l) is the current loop error of the previous cycle. The intelligent unit detects the input levels of Vol and Vo2, and when the intelligent unit After detecting that the level of the comparator output signal Vol or Vo2 is inverted, the intelligent unit _{clears the output of the previous cycle current loop / OTi} -l) and the previous cycle current loop error err-1). At this time, the current loop The output has only one error proportional component, and the output value is very small. Since the loop compares the output in the feedback voltage loop and the feedback current loop and selects the smaller one for output, the resonant circuit will work in current limiting mode at this time, and Since the output component of the feedback current loop is very small, the output current can be limited to a small value. Therefore, the energy provided to the outside by the LLC resonant converter is also very small, and the current on the primary side of the resonant converter circuit will also decay rapidly. , Plays a role in protecting the resonant circuit. In addition, since the current loop has the function of integrating and accumulating, the output of the current loop will gradually increase, and finally reach a stable current limit value. In this preferred embodiment, the above steps are adopted The problem of excessive voltage stress of the full-bridge tube caused by continuous wave-by-wave current limiting is basically solved. Preferably, the voltage stress of the full-bridge tube is less than the rated voltage of the switch tube. As can be seen from the above description, the traditional LLC full The bridge resonant current detection circuit generally can only detect the magnitude of the resonant current, but cannot determine the direction of the current, so that it is necessary to turn off the driving of the four switching tubes of the full bridge when the current is limited by the wave. In addition, in the prior art, due to LLC The special topological structure of the full bridge causes the voltage stress of the full bridge tube to seriously exceed the standard after continuous wave-by-wave current limiting, which will cause the switch tube to be damaged due to voltage stress. Compared with the traditional LLC full-bridge resonant current detection circuit, the present invention The positive and negative resonant currents of the LLC full bridge can be detected, so that only the driving of the full bridge tube to the tube needs to be turned off during the wave-by-wave cycle. In addition, the present invention also solves the problem that the voltage stress of the full-bridge tube caused by continuous wave-by-wave current limiting is seriously exceeded. This problem greatly improves the reliability of the full bridge tube. Obviously, those skilled in the art should understand that the above-mentioned modules or steps of the present invention can be implemented by a general computing device, and they can be concentrated on a single calculation. On the device, or distributed on a network composed of multiple computing devices, optionally, they can be implemented by program codes executable by the computing device, so that they can be stored in the storage device and executed by the computing device, and In some cases, the steps shown or described can be performed in a different order than here, or they can be fabricated into individual integrated circuit modules, or multiple modules or steps of them can be fabricated into a single integrated circuit module In this way, the present invention is not limited to any specific combination of hardware and software. The foregoing descriptions are only preferred embodiments of the present invention and are not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and changes. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A current limiting protection method for resonant circuits, including:

Detect the voltage across the sampling resistor through which the resonant current flows in the resonant circuit;

When detecting that the voltage across the sampling resistor is greater than a predetermined threshold in the current resonant period, block the driving of the resonant circuit;

When the next pulse width modulation cycle arrives, the resonant circuit is switched from the constant voltage mode to the output current limiting mode.

2. The method according to claim 1, wherein the step of switching the resonant circuit from a constant voltage mode to an output current limiting mode comprises:

When it is detected that the output signal level of the comparator of the resonance circuit is inverted, clear the current loop output signal of the previous resonance cycle and the current loop error signal of the previous resonance cycle to zero;

According to the current loop output signal of the current resonance period, a pulse width modulation signal for switching the resonance circuit from a constant voltage mode to an output current limiting mode is generated.

3. The method according to claim 1, wherein the step of blocking the driving of the resonance circuit comprises: blocking a pair of tube driving corresponding to the direction of the resonance current.

4. The method according to claim 3, wherein the predetermined threshold value comprises: a first predetermined threshold value and a second predetermined threshold value; the sampling resistor comprises: a first sampling resistor and a second sampling resistor; the pair of tube driving It includes: a first pair of tube driving and a second pair of tube driving, wherein the step of blocking a pair of tube driving corresponding to the direction of the resonance current includes:

When the voltage across the first sampling resistor is greater than a first predetermined threshold, blocking the driving of the first pair of tubes;

When the voltage across the second sampling resistor is greater than the second predetermined threshold, the second pair of tube driving is blocked.

5. The method according to claim 1, wherein after blocking the driving of the resonant circuit, the method further comprises:

When the next resonant period of the current resonant period arrives, judging whether an overcurrent occurs on the primary side of the resonant circuit;

If there is no overcurrent on the primary side of the resonant circuit, the drive is unblocked. The method according to any one of claims 1 to 5, wherein the step of detecting the voltage across the sampling resistor through which the resonance current flows comprises:

Converting the resonant current through a current transformer;

Rectifying the converted resonant current through a rectifier;

Voltage sampling is performed on both ends of the sampling resistor through which the rectified resonance current flows to obtain the voltage across the sampling resistor. A current-limiting protection device for a resonance circuit includes:

The detection unit is configured to detect the voltage across the sampling resistor through which the resonant current flows in the resonant circuit; the blocking unit is configured to block the voltage across the sampling resistor when the voltage across the sampling resistor is greater than a predetermined threshold in the current resonant period Drive

The switching unit is configured to switch the resonant circuit from the constant voltage mode to the output current limiting mode when the next pulse width modulation period arrives. 7. The device according to claim 7, wherein the switching unit comprises: a clearing module configured to, when detecting that the output signal level of the comparator of the resonant circuit is inverted, change the current of the previous resonant period The loop output signal and the current loop error signal of the previous resonance cycle are cleared;

The generating module is configured to generate a pulse width modulation signal for switching the resonant circuit from a constant voltage mode to an output current limiting mode according to the current loop output signal of the current resonance period. 7. The device according to claim 7, wherein the blocking unit comprises: a blocking module, configured to block a signal corresponding to the direction of the resonant current when the voltage across the sampling resistor is detected to be greater than a predetermined threshold in the current resonance period Driven by a pair of tubes. The device according to claim 9, wherein the predetermined threshold value includes: a first predetermined threshold value and a second predetermined threshold value; the sampling resistor includes: a first sampling resistor and a second sampling resistor; and the pair of tube driving includes: The first pair of tube drives and the second pair of tube drives, wherein the lockout module includes:

A first blockade sub-module, configured to block the drive of the first pair of tubes when the voltage across the first sampling resistor is greater than a first predetermined threshold;

The second blocking sub-module is configured to block the driving of the second pair of tubes when the voltage across the second sampling resistor is greater than a second predetermined threshold.

1. The device according to any one of claims 7-10, further comprising: a judging unit, configured to judge whether the primary side of the resonant circuit comes when the next resonant period of the current resonant period arrives Excessive current;

The unblocking unit is set to unblock the drive when there is no overcurrent on the primary side of the resonant circuit.