LLC power supply input overvoltage protection circuit and overvoltage protection method

Abstract

The present invention provides an LLC power supply input overvoltage protection circuit and an overvoltage protection method, wherein the circuit includes an overvoltage detection circuit, a switch tube off-state voltage equalization circuit, and a control circuit. The circuit is composed of simple components and can accurately and reliably protect the circuit according to the preset threshold value. It can ensure that when the input power supply voltage is twice the limit voltage that the switch tube can withstand, the switch tube will not explode due to overvoltage, so it can be used in ultra-high voltage applications. Using the most basic circuit principles, through ingenious and reasonable design and repeated experimental verification, it is not only extremely reliable, but also one of the simplest and lowest-cost circuit solutions at present.

Description

Technical Field

[0001] The present invention relates to the technical field of electronic circuits, and in particular to an LLC power supply input overvoltage protection circuit and an overvoltage protection method. Background Art

[0002] As a kind of soft switch, the resonant switching converter has the advantages of high operating frequency, low loss, high efficiency and small size. The LLC resonant switching converter has gained wide attention and application in the field of high-frequency switching because of its advantages such as being able to realize ZVS turn-on of the primary switch tube and ZCS turn-off of the rectifier diode within the full load range, easy magnetic integration and wide input voltage range.

[0003] STMicroelectronics' L6599 chip occupies half of the market share in the field of control chips for half-bridge resonant power supplies with its advantages of high adjustment efficiency, saving heat sinks, saving space, good output intermodulation, low withstand voltage of output rectifier tubes, and low EMI caused by primary soft switching. LLC topology belongs to a soft switching circuit, and the surge voltage caused by the switch tube shutdown is small, which makes the switch tube not easily damaged by overvoltage during normal operation. However, in industrial applications, the input voltage of the converter often exceeds the breakdown voltage of the switching device due to overvoltage operation, resulting in machine explosion. In the face of this situation, the most direct way is to increase the breakdown voltage of the switch tube, or to use a switch tube with a higher withstand voltage, but this will increase the cost and volume on the one hand, and reduce the working efficiency of the switching power supply on the other hand. Therefore, it is necessary to adopt overvoltage protection measures for the switching power supply.

[0004] In the existing overvoltage protection patents for switching power supplies, after input overvoltage is detected, a method of stopping the switching power supply chip from working is generally adopted, for example:

[0005] CN201310466813, when the input DC voltage is detected to be over-voltage, the supply voltage of the switching power supply chip is pulled down, so that the switching power supply chip is lower than its minimum operating voltage and stops working; CN201611154552, detects the output voltage of the auxiliary winding to determine whether the DC input is over-voltage, and CN201711120437, detects the current slope to determine whether the DC input is over-voltage, and generates a protection signal to stop the switching power supply chip when the DC input over-voltage is detected. These measures cannot still play a protective role when the input voltage exceeds the breakdown voltage of the switch tube, because in this case, as long as the switch tube still bears the entire input voltage, it will be damaged even if it does not work.

[0006] Other patents use a method of disconnecting the circuit from the input power supply after detecting input overvoltage, for example:

[0007] CN201110451970, after detecting overvoltage on the AC input side, controls the relay to make the circuit free from overvoltage. This solution increases the volume and cost, and the relay action time is too long, which cannot meet the needs of operational overvoltage protection.

[0008] CN201310121503 and CN201310134796, after detecting that the input DC voltage is over-voltage, control the access switch to disconnect, so that the input DC voltage does not continue to increase. This solution requires the use of power switch elements that can be quickly shut down and have high withstand voltage and current, which increases the cost of the circuit.

[0009] It can be seen that there are two problems with the existing switching voltage input power supply overvoltage protection: first, it cannot play an effective protective role when the input voltage exceeds the breakdown voltage of the switch tube; second, it requires additional power switching elements, increasing the circuit cost.

[0010] Therefore, providing an LLC power supply input overvoltage protection circuit and an overvoltage protection method has high value and significance. Summary of the invention

[0011] In view of the defects in the prior art, an object of the present invention is to provide an LLC power supply input overvoltage protection circuit and an overvoltage protection method.

[0012] According to the present invention, an LLC power supply input overvoltage protection circuit includes a half-bridge, a filter capacitor, an overvoltage detection circuit, a switch tube off-state voltage equalization circuit and a control circuit;

[0013] The half bridge includes two field effect transistors, which are respectively referred to as a first field effect transistor and a second field effect transistor; one of the source of the first field effect transistor and the drain of the second field effect transistor is connected to the positive electrode of the DC bus, and the other is connected to the negative electrode of the DC bus; the drain of the first field effect transistor and the source of the second field effect transistor are both connected to the midpoint of the half bridge arm;

[0014] The filter capacitor is connected to the positive pole of the DC bus and the negative pole of the DC bus respectively;

[0015] The overvoltage detection circuit includes at least three signal terminals, which are respectively connected to the DC bus positive electrode, the DC bus negative electrode, and the control circuit;

[0016] The switch tube off-state voltage equalizing circuit comprises at least four signal terminals, which are respectively connected to the positive pole of the DC bus, the negative pole of the DC bus, the filter capacitor, and the midpoint of the half-bridge arm;

[0017] The control circuit includes at least three lead terminals, which are respectively connected to the gate of the first field effect transistor, the gate of the second field effect transistor, and the overvoltage detection circuit.

[0018] Preferably, the LLC power supply input overvoltage protection circuit further includes a main transformer;

[0019] One side of the main transformer is connected to the load circuit, and the other side includes a first port and a second port; the first port is connected to the midpoint of the half-bridge arm; the second port is connected to the positive pole of the DC bus or the negative pole of the DC bus.

[0020] Preferably, the LLC power supply input overvoltage protection circuit further includes an auxiliary power supply; the auxiliary power supply includes an input filter capacitor, an output filter capacitor and a voltage stabilizing chip;

[0021] The voltage stabilizing chip includes three signal terminals, which are respectively recorded as an input terminal, an output terminal, and a common terminal; the input terminal and the output terminal are respectively connected to the positive electrode of the input filter capacitor and the positive electrode of the output filter capacitor; the common terminal is grounded; the negative electrode of the input filter capacitor and the negative electrode of the output filter capacitor are both grounded.

[0022] Preferably, the overvoltage LC circuit detection circuit includes any one or any combination of a resistor voltage divider circuit, a reference voltage circuit, a hysteresis comparison circuit and an anti-interference circuit;

[0023] The resistor voltage divider circuit and the reference voltage circuit are independently connected to the input end of the hysteresis comparator circuit; the output end of the hysteresis comparator circuit is connected to the anti-interference circuit.

[0024] Preferably, the control circuit includes a main chip, a high-voltage floating drive transformer and peripheral configuration parameters;

[0025] One of the first field effect transistor and the second field effect transistor is connected to the main chip through a high-voltage floating drive transformer, and the other is directly connected to the main chip;

[0026] The high-voltage floating drive transformer allows a voltage range of 500V to 1000V;

[0027] The peripheral configuration parameters refer to the circuit elements necessary for the operation of the control circuit, including any one or any combination of an oscillation circuit, a soft start circuit, an overcurrent protection circuit, a drive circuit, and a voltage stabilization control circuit.

[0028] Preferably, the switch-off-state voltage-equalizing circuit comprises a resistor voltage-dividing circuit.

[0029] Preferably, the reference voltage circuit includes a pull-up resistor R301, an output filter capacitor C303 and a voltage stabilizing source U301;

[0030] The reference electrode and cathode of the voltage stabilizing source are electrically connected to the two ends of the output filter capacitor C303 respectively; the anode of the voltage stabilizing source is electrically connected to the output node; and one end of the pull-up resistor R301 is electrically connected to the output node.

[0031] Preferably, the overvoltage detection circuit includes a first resistor R401, a second resistor R402, a third resistor R403, a fourth resistor R404, a fifth resistor R405, a sixth resistor R406, a seventh resistor R407, a first capacitor C401, a first diode D401 and a comparator U401;

[0032] The input terminal VIN is connected to the ground via the first resistor R401 and the second resistor R402 in sequence, and the area between the first resistor R401 and the second resistor R402 is recorded as the first node; one end of the first capacitor C401 is electrically connected to the first node, and the other end is connected to the ground; the two ends of the fourth resistor R404 are respectively recorded as the second node and the third node; one end of the third resistor R403 is electrically connected to the second node, and the other end is electrically connected to the reference terminal VREF; one end of the fifth resistor R405 is electrically connected to the third node, and the other end is electrically connected to the power supply terminal VCC; the power supply terminal VCC is connected to the ground via the sixth resistor R406 and the seventh resistor R407 in sequence, and the area between the sixth resistor R406 and the seventh resistor R407 is recorded as the fourth node; the fourth node is electrically connected to the voltage detection terminal LINE; the two ends of the first diode D401 are respectively electrically connected to the third node and the fourth node; the three ports of the comparator U401 are respectively electrically connected to the first node, the second node, and the third node.

[0033] According to the present invention, a method for protecting an LLC power supply input overvoltage includes:

[0034] Overvoltage detection step: receiving two signals, namely, a voltage input signal obtained by resistor voltage division and a preset voltage threshold signal generated by a reference circuit voltage, and then comparing the two signals through a hysteresis comparator circuit; if the voltage input signal is greater than the preset voltage threshold signal, the comparator outputs a low level; if the voltage input signal is not greater than the preset voltage threshold signal, the comparator outputs a high level, and the level signal output by the comparator flows into the control circuit through an anti-interference circuit;

[0035] Control steps: Receive the level signal output by the comparator. If the received signal is at a low level, the output of the drive signal is turned off, the switch tube is disconnected, and the input of the power supply is cut off; if the received signal is at a high level, the output of the drive signal is turned on and the power supply works normally.

[0036] Preferably, the LLC power supply input overvoltage protection method further includes:

[0037] Switch tube off-state voltage equalization step: When the switch tube is turned off, the input power supply voltage is evenly divided through the resistor voltage divider circuit to prevent the switch tube from receiving voltage shock before it stabilizes. Compared with the prior art, the present invention has the following beneficial effects:

[0038] 1. The LLC power input overvoltage protection circuit provided by the present invention has the advantages of simple structure, high reliability and strong versatility;

[0039] 2. The LLC power input overvoltage protection circuit and overvoltage protection method provided by the present invention avoid the interference of high-voltage signals on the chip through the ingenious design of the detection circuit, and avoid the common problem in the prior art, that is, when overvoltage occurs, the drive signal of the control circuit is not turned off quickly enough, thereby causing various complex working conditions (in the case of overvoltage, any interference may cause the drive signal to be abnormal, thereby causing power supply damage. If the chip is used to directly detect the input voltage, it may be interfered by it and cannot turn off the drive signal in time);

[0040] 3. The LLC power supply input overvoltage protection circuit and overvoltage protection method provided by the present invention cooperate with each other, and use two switch tubes in series of the main circuit half bridge to jointly bear the input DC voltage, so there is no need to add additional switch tubes, reducing the use of components, saving space and reducing product costs;

[0041] 4. The LLC power supply input overvoltage protection circuit and overvoltage protection method provided by the present invention can play an effective protective role when the input voltage exceeds the breakdown voltage of the switch tube, and does not require additional power switch components. It enhances the reliability of power supply overvoltage protection, expands the voltage application range, and can greatly improve the reliability of the designed product;

[0042] 5. The LLC power input overvoltage protection circuit and overvoltage protection method provided by the present invention involve circuits that have been cleverly designed and strictly verified. They use the most basic circuit principles, so the circuits are extremely reliable and highly accurate, and can enhance the ability of the half-bridge circuit to withstand overvoltages. They can enable the switch tube to withstand a voltage twice its own withstand voltage when not working, and effectively solve the problem of power supply overvoltage explosion using the simplest circuit. The circuit uses very few components, which can effectively reduce production costs, save design space, and improve the reliability of the entire machine. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] Other features, objects and advantages of the present invention will become more apparent from the detailed description of non-limiting embodiments made with reference to the following drawings:

[0044] Figure 1 A schematic diagram of an overvoltage protection scheme in an embodiment of the present invention;

[0045] Figure 2A schematic diagram of an auxiliary power supply circuit in one embodiment of the present invention;

[0046] Figure 3 A schematic diagram of a reference voltage circuit in an embodiment of the present invention;

[0047] Figure 4 A schematic diagram of an overvoltage detection circuit according to an embodiment of the present invention;

[0048] Figure 5 It is a schematic diagram of a switch tube off-state voltage equalizing circuit and a control circuit in one embodiment of the present invention;

[0049] Figure 6 FIG. 1 is a schematic diagram of an overall circuit when used in an embodiment of the present invention. DETAILED DESCRIPTION

[0050] The present invention is described in detail below in conjunction with specific embodiments. The following embodiments will help those skilled in the art to further understand the present invention, but are not intended to limit the present invention in any form. It should be noted that, for those of ordinary skill in the art, several changes and improvements can also be made without departing from the concept of the present invention. These all belong to the protection scope of the present invention.

[0051] According to the present invention, an LLC power supply input overvoltage protection circuit includes a half-bridge, a filter capacitor, an overvoltage detection circuit, a switch tube off-state voltage equalization circuit and a control circuit;

[0052] The half bridge includes two field effect transistors, which are respectively referred to as a first field effect transistor and a second field effect transistor; one of the source of the first field effect transistor and the drain of the second field effect transistor is connected to the positive electrode of the DC bus, and the other is connected to the negative electrode of the DC bus; the drain of the first field effect transistor and the source of the second field effect transistor are both connected to the midpoint of the half bridge arm;

[0053] The filter capacitor is connected to the positive pole of the DC bus and the negative pole of the DC bus respectively;

[0054] The overvoltage detection circuit includes at least three signal terminals, which are respectively connected to the DC bus positive electrode, the DC bus negative electrode, and the control circuit;

[0055] The switch tube off-state voltage equalizing circuit comprises at least four signal terminals, which are respectively connected to the positive pole of the DC bus, the negative pole of the DC bus, the filter capacitor, and the midpoint of the half-bridge arm;

[0056] The control circuit includes at least three lead terminals, which are respectively connected to the gate of the first field effect transistor, the gate of the second field effect transistor, and the overvoltage detection circuit.

[0057] The LLC power supply input overvoltage protection circuit also includes a main transformer;

[0058] One side of the main transformer is connected to the load circuit, and the other side includes a first port and a second port; the first port is connected to the midpoint of the half-bridge arm; the second port is connected to the positive pole of the DC bus or the negative pole of the DC bus.

[0059] The LLC power supply input overvoltage protection circuit also includes an auxiliary power supply; the auxiliary power supply includes an input filter capacitor, an output filter capacitor and a voltage stabilizing chip;

[0060] The voltage stabilizing chip includes three signal terminals, which are respectively recorded as an input terminal, an output terminal, and a common terminal; the input terminal and the output terminal are respectively connected to the positive electrode of the input filter capacitor and the positive electrode of the output filter capacitor; the common terminal is grounded; the negative electrode of the input filter capacitor and the negative electrode of the output filter capacitor are both grounded.

[0061] The overvoltage LC circuit detection circuit includes any one or any combination of a resistor voltage divider circuit, a reference voltage circuit, a hysteresis comparison circuit and an anti-interference circuit;

[0062] The resistor voltage divider circuit and the reference voltage circuit are independently connected to the input end of the hysteresis comparator circuit; the output end of the hysteresis comparator circuit is connected to the anti-interference circuit.

[0063] The control circuit includes a main chip, a high-voltage floating drive transformer and peripheral configuration parameters;

[0064] One of the first field effect transistor and the second field effect transistor is connected to the main chip through a high-voltage floating drive transformer, and the other is directly connected to the main chip;

[0065] The high-voltage floating drive transformer allows a voltage range of 500V to 1000V;

[0066] The peripheral configuration parameters refer to the circuit elements necessary for the operation of the control circuit, including any one or any combination of an oscillation circuit, a soft start circuit, an overcurrent protection circuit, a drive circuit, and a voltage stabilization control circuit.

[0067] The switch tube off-state voltage equalizing circuit includes a resistor voltage dividing circuit.

[0068] The reference voltage circuit includes a pull-up resistor R301, an output filter capacitor C303 and a voltage stabilizing source U301;

[0069] The reference electrode and cathode of the voltage stabilizing source are electrically connected to the two ends of the output filter capacitor C303 respectively; the anode of the voltage stabilizing source is electrically connected to the output node; and one end of the pull-up resistor R301 is electrically connected to the output node.

[0070] The overvoltage detection circuit includes a first resistor R401, a second resistor R402, a third resistor R403, a fourth resistor R404, a fifth resistor R405, a sixth resistor R406, a seventh resistor R407, a first capacitor C401, a first diode D401 and a comparator U401;

[0071] The input terminal VIN is connected to the ground via the first resistor R401 and the second resistor R402 in sequence, and the area between the first resistor R401 and the second resistor R402 is recorded as the first node; one end of the first capacitor C401 is electrically connected to the first node, and the other end is connected to the ground; the two ends of the fourth resistor R404 are respectively recorded as the second node and the third node; one end of the third resistor R403 is electrically connected to the second node, and the other end is electrically connected to the reference terminal VREF; one end of the fifth resistor R405 is electrically connected to the third node, and the other end is electrically connected to the power supply terminal VCC; the power supply terminal VCC is connected to the ground via the sixth resistor R406 and the seventh resistor R407 in sequence, and the area between the sixth resistor R406 and the seventh resistor R407 is recorded as the fourth node; the fourth node is electrically connected to the voltage detection terminal LINE; the two ends of the first diode D401 are respectively electrically connected to the third node and the fourth node; the three ports of the comparator U401 are respectively electrically connected to the first node, the second node, and the third node.

[0072] According to the present invention, a method for protecting an LLC power supply input overvoltage includes:

[0073] Overvoltage detection step: receiving two signals, namely, a voltage input signal obtained by resistor voltage division and a preset voltage threshold signal generated by a reference circuit voltage, and then comparing the two signals through a hysteresis comparator circuit; if the voltage input signal is greater than the preset voltage threshold signal, the comparator outputs a low level; if the voltage input signal is not greater than the preset voltage threshold signal, the comparator outputs a high level, and the level signal output by the comparator flows into the control circuit through an anti-interference circuit;

[0074] Control steps: Receive the level signal output by the comparator. If the received signal is at a low level, the output of the drive signal is turned off, the switch tube is disconnected, and the input of the power supply is cut off; if the received signal is at a high level, the output of the drive signal is turned on and the power supply works normally.

[0075] The LLC power supply input overvoltage protection method further includes:

[0076] Switch tube off-state voltage equalization step: When the switch tube is turned off, the input power supply voltage is evenly divided through the resistor voltage divider circuit to prevent the switch tube from receiving voltage shock before it stabilizes. Compared with the prior art, the present invention has the following beneficial effects:

[0077] Furthermore, a preferred example of the present invention relates to an LLC power supply input overvoltage protection method and circuit, including an overvoltage detection circuit, a switch tube off-state voltage equalization circuit, and a control circuit. The circuit is composed of simple components and can accurately and reliably protect the circuit according to the preset threshold value. It can ensure that when the input power supply voltage is twice the limit voltage that the switch tube can withstand, the switch tube will not explode due to overvoltage, so it can be used in ultra-high voltage applications. Using the most basic circuit principles, through ingenious and reasonable design and repeated experimental verification, it is not only extremely reliable, but also one of the simplest and lowest-cost circuit solutions currently available.

[0078] The preferred embodiments of the present invention involve the following terms:

[0079] LLC: A single-port network containing inductors, capacitors, and resistors. When the port voltage and current waveforms have the same phase at certain operating frequencies, the circuit is said to resonate. A circuit that can resonate is called a resonant circuit.

[0080] Overvoltage protection: Overvoltage protection is a protection method that disconnects the power supply or reduces the voltage of the controlled equipment when the voltage of the protected circuit exceeds the predetermined maximum value.

[0081] A preferred example of the present invention provides an overvoltage protection circuit characterized by comprising an overvoltage detection circuit, a switch-off state voltage equalizing circuit, and a control circuit.

[0082] The overvoltage detection circuit includes a resistor voltage divider circuit, a reference voltage circuit, a hysteresis comparator circuit, and an anti-interference circuit. The working mode of the overvoltage detection circuit is: first, the resistor voltage divider obtains the voltage signal, and the reference circuit voltage generates a preset voltage threshold, and then the two signals are compared through the hysteresis comparator circuit. If the voltage is over, the comparator outputs a low level, and if it is not over, the comparator outputs a high level, and then the comparator output flows into the control circuit through the anti-interference circuit. The function of the anti-interference circuit is that the signal can only be transmitted to the control circuit when the comparator output voltage is low, avoiding the interference of the high level on the control circuit.

[0083] The control circuit includes the main control chip, necessary peripheral configuration parameters and a high-voltage floating drive transformer. The purpose of using the transformer is to enable the upper tube of the bridge arm to obtain a floating high-voltage drive signal.

[0084] The circuits of the preferred example of the present invention cooperate with each other and utilize the switch tube of the main circuit to shut off the input power supply, so there is no need to add additional switch tubes, which reduces the use of components, saves space, and reduces product costs.

[0085] The switch tube off-state voltage equalization circuit is composed of a resistor voltage divider circuit, and its working method is: when the switch tube is suddenly turned off, the input power supply voltage is evenly divided by resistors R1 and R3, and the bridge arm midpoint voltage is made equal to 1 / 2 of the power supply voltage through R2, which can effectively prevent the switch tube from obtaining a safe voltage before it is stable, and can effectively enhance the overvoltage level that the power supply can withstand.

[0086] The function of the overvoltage detection circuit is to detect the input voltage and determine whether it exceeds the preset overvoltage threshold. The circuit can determine whether there is overvoltage and whether the overvoltage fault has been resolved. This can effectively prevent the circuit from continuously operating at the overvoltage point and generating a high peak voltage, thereby avoiding circuit damage. The use of a diode can effectively prevent the comparator output from interfering with the main circuit when it is at a high level. Figure 1 As shown, the overvoltage detection circuit mainly consists of three signal terminals, which are respectively connected between the positive and negative poles of the DC bus and the control circuit.

[0087] The switch-off state voltage-equalizing circuit uses the resistor voltage-dividing principle to evenly divide the DC bus voltage after the switch is turned off. Figure 1 As shown, the switch tube off-state voltage stabilization circuit mainly has four terminals, which are respectively connected to the positive and negative poles of the DC bus, the midpoint of the capacitor, and the midpoint of the half-bridge arm.

[0088] The control circuit is mainly composed of the LLC power supply main control chip. There are many types of control chips on the market, but the basic principles and functions are basically the same. When the chip detects that the signal sent by the detection circuit is overvoltage, the chip will turn off the output of the drive signal, disconnect the switch tube, and cut off the input of the power supply. When it is detected that the signal given by the detection circuit is overvoltage recovery or not overvoltage, the chip will turn on the output of the drive signal again, and the power supply will continue to work normally. There are three lead terminals related to the control circuit and overvoltage protection. They are respectively connected to the overvoltage detection circuit and the upper and lower tube gate drivers, such as Figure 1 shown.

[0089] The technical difficulty of the present invention is that when overvoltage occurs, the driving signal of the control circuit must be turned off very cleanly, otherwise various complex working conditions may occur. In the case of overvoltage, any interference may cause the driving signal to be abnormal, thereby causing power supply damage. If the chip is used to directly detect the input voltage, it may be interfered by it and fail to turn off the driving signal in time.

[0090] An overvoltage protection method provided by the present invention includes the following processes:

[0091] The amplitude of the input voltage of the LLC power supply circuit is obtained through the overvoltage detection circuit, and compared with the preset overvoltage threshold to determine whether the circuit input voltage is overvoltage.

[0092] After judgment, the processed signal is input to the control circuit. If the signal is an overvoltage signal, the signal input to the control circuit is a low-level signal, which will force the control circuit to turn off the power supply. If the signal is determined to be not overvoltage, the signal input to the control circuit is a high-level signal. Due to the presence of a diode, this signal will not affect the normal operation of the control circuit.

[0093] When the power is turned off, the switch tube off-state voltage equalization circuit is activated, so that the upper and lower tubes of the switch tube share the input power voltage in a 1:1 ratio, enhancing the voltage-bearing ability of the half-bridge circuit.

[0094] Furthermore, the present embodiment is an overvoltage protection circuit of a resonant power supply based on L6599, including an overvoltage detection circuit, a switch tube off-state voltage equalization circuit, and a control circuit.

[0095] 1) In order to provide power for each circuit, this example designs an auxiliary power supply, which mainly provides power for the chips used in this system. This part is mainly composed of a simple DCDC step-down voltage regulator chip. In this invention, the main chip used is 78L15. With the cooperation of the external circuit, 78L15 can output a stable 15V power supply after internal conversion of the input voltage. The circuit is as follows Figure 2 As shown:

[0096] Among them, C201 and C202 are input and output filter capacitors respectively. If the input voltage allows, VIN can be the system input voltage or the power supply voltage provided by other devices. Here, VCC is a positive 15V output.

[0097] 2) The overvoltage detection circuit includes a reference voltage circuit and a hysteresis comparator circuit

[0098] The reference voltage circuit can generate a relatively accurate and stable voltage for us to set the overvoltage protection threshold. This part of the circuit mainly uses the TL431 that can output accurate voltage. With the cooperation of the peripheral circuit, it can output various accurate voltages. Figure 3 As shown, R301 is a pull-up resistor, C303 is an output filter capacitor, and VREF is an output reference voltage, which is mainly used by the detection circuit.

[0099] Overvoltage detection circuit: The function of this part of the circuit is to detect the input voltage and determine whether it exceeds the preset overvoltage threshold. The overvoltage threshold can be set by R401 and R402. C401 is a high-frequency filter capacitor, and the overvoltage value and the voltage value at which the circuit resumes normal operation can be set by selecting appropriate R403, R404, and R405. This can effectively prevent the circuit from continuously operating at the overvoltage point and generating a higher peak voltage, thereby avoiding circuit damage. Figure 4As shown. Among them, LM393 is a voltage comparator, VREF is generated by the reference voltage circuit, and the diode D401 is used here to prevent interference to the main circuit when the comparator output is a high level. The control chip used in the present invention is L6599, and its voltage detection pin is the 7th pin (LINE pin), and its pin signal is named LINE signal. R406 and R407 provide a normal working LINE signal. Only when the voltage amplitude of the LINE signal is within a certain range can our control chip work normally. If it is lower or higher than this range, our control chip will stop working. When no overvoltage is detected, the comparator outputs a high level. When overvoltage occurs, the comparator outputs a low level, which is what we call the "0" potential. At this time, the diode is forward-conducted, and the LINE signal is pulled down, forcing the LINE signal amplitude to be lower than the normal range, thereby shutting down the chip output. The overvoltage protection threshold and recovery value can be set by the following formula:

[0100]

[0101]

[0102] 3) The control circuit is mainly composed of the peripheral circuit of the control chip L6599. The circuit diagram is as follows Figure 5 As shown. Among them, L6599 is the control chip of the circuit system of the present invention, which drives the two switch tubes of the half-bridge main circuit through HVG and LVG, and determines whether to turn off the output of the two drive signals of HVG and LVG according to the LINE signal. Because the solution involved in the present invention only involves overvoltage protection, the L6599 in the figure is actually a simplified pin.

[0103] The switch tube off-state voltage equalization circuit consists of Figure 5 In the circuit, R501, R502 and R503 are composed. The resistance values ​​of R501 and R503 should be consistent and much larger than the load. R502 can select a suitable value, which can also be consistent with the other two resistors. When the switch tube is not working, R501 and R502 divide the voltage, and the resistance value of R501 should be consistent with that of R503. When the switch tube is turned off, under the bridge connection of R502, If R501=R503, then Where V bus is the voltage value of the DC bus.

[0104] In the description of the present application, it should be understood that the terms "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", etc., indicating orientations or positional relationships, are based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present application and simplifying the description, and do not indicate or imply that the referred device or element must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as a limitation on the present application.

[0105] The above describes the specific embodiments of the present invention. It should be understood that the present invention is not limited to the above specific embodiments, and those skilled in the art can make various changes or modifications within the scope of the claims, which does not affect the essence of the present invention. In the absence of conflict, the embodiments of the present application and the features in the embodiments can be combined with each other arbitrarily.

Claims

1. An LLC power supply input overvoltage protection circuit, characterized in that: It includes a half bridge, a filter capacitor, an overvoltage detection circuit, a switch tube off-state voltage equalization circuit and a control circuit; The half bridge includes two field effect transistors, which are respectively referred to as a first field effect transistor and a second field effect transistor; one of the source of the first field effect transistor and the drain of the second field effect transistor is connected to the positive electrode of the DC bus, and the other is connected to the negative electrode of the DC bus; the drain of the first field effect transistor and the source of the second field effect transistor are both connected to the midpoint of the half bridge arm; The filter capacitor is connected to the positive pole of the DC bus and the negative pole of the DC bus respectively; The overvoltage detection circuit includes at least three signal terminals, which are respectively connected to the positive pole of the DC bus, the negative pole of the DC bus, and the control circuit; The switch tube off-state voltage equalizing circuit comprises at least four signal terminals, which are respectively connected to the positive pole of the DC bus, the negative pole of the DC bus, the filter capacitor, and the midpoint of the half-bridge arm; The control circuit includes at least three lead terminals, which are respectively connected to the gate of the first field effect transistor, the gate of the second field effect transistor, and the overvoltage detection circuit; The overvoltage detection circuit includes any one or any combination of a resistor voltage divider circuit, a reference voltage circuit, a hysteresis comparison circuit and an anti-interference circuit; The resistor divider circuit and the reference voltage circuit are independently connected to the input terminal of the hysteresis comparator circuit; the output terminal of the hysteresis comparator circuit is connected to the anti-interference circuit; The overvoltage detection circuit includes a first resistor R401, a second resistor R402, a third resistor R403, a fourth resistor R404, a fifth resistor R405, a sixth resistor R406, a seventh resistor R407, a first capacitor C401, a first diode D401 and a comparator U401; The input terminal VIN is connected to the ground via the first resistor R401 and the second resistor R402 in sequence, and the area between the first resistor R401 and the second resistor R402 is recorded as the first node; one end of the first capacitor C401 is electrically connected to the first node, and the other end is connected to the ground; the two ends of the fourth resistor R404 are respectively recorded as the second node and the third node; one end of the third resistor R403 is electrically connected to the second node, and the other end is electrically connected to the reference terminal VREF; one end of the fifth resistor R405 is electrically connected to the third node, and the other end is electrically connected to the power supply terminal VCC; the power supply terminal VCC is connected to the ground via the sixth resistor R406 and the seventh resistor R407 in sequence, and the area between the sixth resistor R406 and the seventh resistor R407 is recorded as the fourth node; the fourth node is electrically connected to the voltage detection terminal LINE; the two ends of the first diode D401 are respectively electrically connected to the third node and the fourth node; the three ports of the comparator U401 are respectively electrically connected to the first node, the second node, and the third node.

2. The LLC power supply input overvoltage protection circuit according to claim 1, characterized in that: The LLC power supply input overvoltage protection circuit also includes a main transformer; One side of the main transformer is connected to the load circuit, and the other side includes a first port and a second port; the first port is connected to the midpoint of the half-bridge arm; the second port is connected to the positive pole of the DC bus or the negative pole of the DC bus.

3. The LLC power supply input overvoltage protection circuit according to claim 1, characterized in that: The LLC power supply input overvoltage protection circuit also includes an auxiliary power supply; the auxiliary power supply includes an input filter capacitor, an output filter capacitor and a voltage stabilizing chip; The voltage stabilizing chip includes three signal terminals, which are respectively recorded as an input terminal, an output terminal, and a common terminal; the input terminal and the output terminal are respectively connected to the positive electrode of the input filter capacitor and the positive electrode of the output filter capacitor; the common terminal is grounded; the negative electrode of the input filter capacitor and the negative electrode of the output filter capacitor are both grounded.

4. The LLC power supply input overvoltage protection circuit according to claim 1, characterized in that: The control circuit includes a main chip, a high-voltage floating drive transformer and peripheral configuration parameters; One of the first field effect transistor and the second field effect transistor is connected to the main chip through a high-voltage floating drive transformer, and the other is directly connected to the main chip; The high-voltage floating drive transformer allows a voltage range of 500V to 1000V; The peripheral configuration parameters refer to the circuit elements necessary for the operation of the control circuit, including any one or any combination of an oscillation circuit, a soft start circuit, an overcurrent protection circuit, a drive circuit, and a voltage stabilization control circuit.

5. The LLC power supply input overvoltage protection circuit according to claim 1, characterized in that: The switch tube off-state voltage equalizing circuit includes a resistor voltage dividing circuit.

6. The LLC power supply input overvoltage protection circuit according to claim 1, characterized in that: The reference voltage circuit includes a pull-up resistor R301, an output filter capacitor C303 and a voltage stabilizing source U301; The reference electrode and cathode of the voltage stabilizing source are electrically connected to the two ends of the output filter capacitor C303 respectively; the anode of the voltage stabilizing source is electrically connected to the output node; and one end of the pull-up resistor R301 is electrically connected to the output node.

7. A method for implementing the LLC power supply input overvoltage protection circuit of claim 1, characterized in that: include: Overvoltage detection step: receiving two signals, namely, a voltage input signal obtained by resistor voltage division and a preset voltage threshold signal generated by a reference circuit voltage, and then comparing the two signals through a hysteresis comparator circuit; if the voltage input signal is greater than the preset voltage threshold signal, the comparator outputs a low level; if the voltage input signal is not greater than the preset voltage threshold signal, the comparator outputs a high level, and the level signal output by the comparator flows into the control circuit through an anti-interference circuit; Control steps: Receive the level signal output by the comparator. If the received signal is at a low level, the output of the drive signal is turned off, the switch tube is disconnected, and the input of the power supply is cut off; if the received signal is at a high level, the output of the drive signal is turned on and the power supply works normally.

8. The method of the LLC power supply input overvoltage protection circuit according to claim 7, characterized in that: The LLC power supply input overvoltage protection method further includes: Steps for equalizing the voltage in the off-state of the switch tube: When the switch tube is turned off, the input power supply voltage is evenly divided through a resistor voltage divider circuit to prevent the switch tube from receiving voltage shock before it stabilizes.

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