Fast protection circuit and method based on short circuit at the output end of LLC circuit

Abstract

The present invention discloses a fast protection circuit and method based on the short circuit of the output end of an LLC circuit, including: a resonant cavity current detection circuit, which is composed of a mutual inductor T5, a diode D78, a diode D79, a resistor R288, a resistor R289, a resistor R290 and a resistor R291; an isolation diode D29, the resonant cavity current detection circuit is connected to the positive electrode of the isolation diode D29, the negative electrode of the isolation diode D29 is connected to the second end of a resistor R86, the first end of the resistor R86 is connected to the first end of a capacitor C208, and the resistor R86 and the capacitor C208 form an overcurrent protection time constant. It solves the short circuit protection under the full range of operating frequencies of the LLC, and performs current retraction during long-term short circuits, reducing voltage, current and temperature stresses, thereby improving the reliability of power devices, and is particularly applicable to LLC circuits with wide frequency regulation requirements for input and output voltage regulation.

Description

Technical Field

[0001] The present invention relates to the field of power electronics technology, and particularly relates to a fast protection circuit and method based on the short - circuit of the output end of an LLC circuit. Background Art

[0002] At present, the methods for LLC output short - circuit protection include output - end current - limiting protection, analog chip OCP protection, primary - side diode clamping, DSP control protection, resonant - cavity current detection fast protection + DSP - controlled output short - circuit retraction protection. However, there are still the following disadvantages: 1. Output - end current - limiting protection can usually only handle protection during normal operation. For situations such as output short - circuit startup, immediate short - circuit under no - load, etc., it cannot provide fast protection and needs to cooperate with primary - side clamping diodes for protection. The reaction of secondary - side protection to the primary - side takes time, and during this time, the MOS tube may have been damaged. 2. The OCP protection method of analog chips (such as NCP1396 & 1399, etc.) usually also detects the resonant - cavity current for protection; however, the sensitivity of adjusting the recovery time after control protection is not high, and in the case of long - term short - circuit, the temperature rise of each power device will be maintained at a high level for a long time, which will reduce the reliability of the module. Adding short - circuit retraction requires additional devices and changes to the PCB layout and the original size. 3. The DSP control method is also one of the most widely used methods at present, but it is limited by the sampling rate and protection speed, and there are limitations in the operating frequency. For example, the utility model of a fast digital short - circuit protection circuit based on LLC output current with the patent application number CN201922498116.3 cannot meet the requirements of fast protection while minimizing misoperation, and cannot start the machine normally after the short - circuit is restored to within the rated load, and cannot reduce the voltage, current, and temperature stress of power devices after long - term short - circuit. Summary of the Invention

[0003] The main purpose of the present invention is to provide a fast protection circuit and method based on the short - circuit of the output end of an LLC circuit, which can effectively solve the problems in the background art.

[0004] To achieve the above - mentioned purpose, the technical solution adopted by the present invention is as follows:

[0005] A fast protection circuit based on the short - circuit of the output end of an LLC circuit, comprising:

[0006] A resonant - cavity current detection circuit, which is composed of a mutual inductor T5, a diode D78, a diode D79, a resistor R288, a resistor R289, a resistor R290, and a resistor R291;

[0007] Isolation diode D29, the resonant cavity current detection circuit is connected to the positive electrode of the isolation diode D29, the negative electrode of the isolation diode D29 is connected to the second end of the resistor R86, the first end of the resistor R86 is connected to the first end of the capacitor C208, and the resistor R86 and the capacitor C208 form an overcurrent protection time constant.

[0008] Further, it further includes a comparator U49, and the first end of the resistor R86 and the first end of the capacitor C208 are connected to the P5 terminal of the comparator U49.

[0009] Further, it further includes a resistor R85 and a resistor R297. The first end of the resistor R85 is connected to the first end of the resistor R297. The first end of the resistor R85 and the first end of the resistor R297 are connected to the P6 terminal of the comparator U49. The resistor R85 and the resistor R297 form an arbitrary reference voltage value to output an OCP action signal.

[0010] Further, the second ends of the resistor R288, the resistor R289, the resistor R290, and the resistor R291 are connected to the ground terminal DGND. The second ends of the resistor R288, the resistor R289, the resistor R290, and the resistor R291 are respectively connected to the positive electrodes of two diodes. The negative electrodes of the two diodes are respectively connected to the 3-terminal and 4-terminal of the current transformer T5. The negative electrodes of the two diodes are also respectively connected to the positive electrodes of the diode D79 and the diode D78. The negative electrodes of the diode D79 and the diode D78 are connected to the first ends of the resistor R288, the resistor R289, the resistor R290, and the resistor R291 and the positive electrode of the diode D29.

[0011] Further, the second end of the resistor R297 is connected to the ground terminal DGND. The ground terminal of the comparator U49 is connected to the ground terminal DGND. The output terminal of the comparator U49 is connected to the power supply VCC through the resistor R83. The output terminal of the comparator U49 is connected to the OCPM terminal. The resistor R86 is connected to the first end of the resistor R296. The second end of the resistor R296 is connected to the OCPM, the first end of the resistor R83, and the output terminal of the comparator U49. The second end of the capacitor C208 is connected to the ground terminal DGND. The resistor R85 is connected to VREF. The VCC terminal of the comparator U49 is connected to the power supply VCC. The second end of the resistor R83 is connected to the VCC terminal of the comparator and the second end of the capacitor C44. The first end of the capacitor C44 is connected to the ground terminal DGND.

[0012] According to another aspect of the embodiments of the present invention, there is provided a fast protection method for short circuit at the output end of an LLC circuit based on the above-mentioned fast protection circuit for short circuit at the output end of the LLC circuit, including the following steps:

[0013] According to the circuit parameters, calculate the peak current Im of the resonant cavity when the output is short-circuited, Im = Vin / (f*Lr);

[0014] Adjust the turns ratio of the T5 current transformer or the resistance values of the current detection resistors R288 - R291 to obtain a more appropriate voltage signal, which is sent to the non-inverting terminal of U49 through the isolation diode;

[0015] Quickly output a flip signal to flip the level of the enable pin of the drive chip, and at the same time send it to the DSP to perform wave blocking protection and control the time to resume wave generation.

[0016] Further, it further includes the following steps:

[0017] When the output is instantaneously short-circuited, the first to act is the hardware signal. When a peak current arrives, the resonant cavity current passes through the current transformer T5, making the voltage of P5 of U49 higher than the voltage of the P6 pin, and the OCP signal immediately flips to a high level output.

[0018] Further, it further includes the following steps:

[0019] Receive the OCP signal and start to control wave generation, including the wave generation frequency, wave generation period, and hiccup time at N cycles.

[0020] Further, it further includes the following steps:

[0021] When it is detected that the short-circuit state persists, that is, the output current continuously exceeds the rated current value and the output voltage is lower than the first voltage, the given IDA value of the output current slowly drops to 1 / 6 of the current value;

[0022] When the voltage slowly recovers above the second voltage, gradually recover IDA to the rated current given value.

[0023] Further, the first voltage is 25V and the second voltage is 20V.

[0024] Compared with the prior art, the present invention has the following beneficial effects:

[0025] Solve the short-circuit protection at all operating frequencies of the LLC, and perform current retraction during long-term short-circuit, reducing voltage, current, and temperature stress, thereby improving the reliability of power devices, and is particularly suitable for LLC circuits with wide frequency regulation requirements for voltage regulation at the input and output. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1The circuit diagram of a fast protection circuit based on the short - circuit of the output end of an LLC circuit provided by an embodiment of the present invention.

[0027] Figure 2 The circuit diagram of a fast protection circuit based on the short - circuit of the output end of an LLC circuit provided by an embodiment of the present invention.

[0028] Figure 3 The output short - circuit waveform of a fast protection circuit based on the short - circuit of the output end of an LLC circuit provided by an embodiment of the present invention

[0029] Figure 4 The expanded view of the output short - circuit waveform of a fast protection circuit based on the short - circuit of the output end of an LLC circuit provided by an embodiment of the present invention

[0030] Figure 5 The short - circuit waveform under low input voltage of a fast protection circuit based on the short - circuit of the output end of an LLC circuit provided by an embodiment of the present invention

[0031] In the figure: a, input voltage; b, drive; c, resonant cavity current. Detailed implementation manners

[0032] To make the objectives, technical solutions and advantages of the present invention clearer, the present invention will be further described in detail below in conjunction with the detailed implementation manners and with reference to the accompanying drawings. It should be understood that these descriptions are exemplary only and are not intended to limit the scope of the present invention. In addition, in the following description, the descriptions of well - known structures and technologies are omitted to avoid unnecessarily confusing the concepts of the present invention.

[0033] It should be noted that the terms "first", "second", etc. in the specification, claims and drawings of this application are used to distinguish similar objects and do not necessarily need to describe a specific order or sequence. It should be understood that such terms can be interchanged under appropriate circumstances so that the embodiments of the present application described here can be implemented in an order different from those illustrated or described here. In addition, the terms "include" and "have" and any variations thereof are intended to cover non - exclusive inclusion. For example, a process, method, system, product or device that includes a series of steps or units does not necessarily have to be limited to those steps or units clearly listed, but may include other steps or units not clearly listed or inherent to these process, method, product or device.

[0034] Now, exemplary embodiments according to the present application will be described in more detail with reference to the accompanying drawings. However, these exemplary embodiments can be implemented in many different forms and should not be construed as being limited only to the embodiments set forth herein. It should be understood that these embodiments are provided so that the disclosure of the present application is thorough and complete, and the concept of these exemplary embodiments is fully conveyed to those of ordinary skill in the art. In the drawings, for clarity, the thickness of layers and regions may be exaggerated, and the same reference numerals are used to denote the same devices, and thus their descriptions will be omitted.

[0035] According to Figures 1-5 , a fast protection circuit based on the short - circuit of the output end of an LLC circuit is provided, including:

[0036] A resonant - cavity current detection circuit, which is composed of a transformer T5, diodes D78, D79, resistors R288, R289, R290, and R291;

[0037] An isolation diode D29, the resonant - cavity current detection circuit is connected to the positive electrode of the isolation diode D29, the negative electrode of the isolation diode D29 is connected to the second end of a resistor R86, the first end of the resistor R86 is connected to the first end of a capacitor C208, and the resistor R86 and the capacitor C208 form an over - current protection time constant.

[0038] Among them, a comparator U49 is further included, and the first end of the resistor R86 and the first end of the capacitor C208 are connected to the P5 terminal of the comparator U49.

[0039] Among them, resistors R85 and R297 are further included. The first end of the resistor R85 is connected to the first end of the resistor R297. The first end of the resistor R85 and the first end of the resistor R297 are connected to the P6 terminal of the comparator U49. The resistor R85 and the resistor R297 form an arbitrary reference voltage value and output an OCP action signal.

[0040] Among them, the second ends of the resistors R288, R289, R290, and R291 are connected to the ground terminal DGND. The second ends of the resistors R288, R289, the resistors R290, and the resistors R291 are respectively connected to the positive electrodes of two diodes. The negative electrodes of the two diodes are respectively connected to the 3 - terminal and 4 - terminal of the transformer T5. The negative electrodes of the two diodes are also respectively connected to the positive electrodes of the diode D79 and the diode D78. The negative electrodes of the diode D79 and the diode D78 are connected to the first ends of the resistors R288, R289, R290, and R291 and the positive electrode of the diode D29.

[0041] Among them, the second end of the resistor R297 is connected to the ground terminal DGND, the ground terminal of the comparator U49 is connected to the ground terminal DGND, the output terminal of the comparator U49 is connected to the power supply VCC through the resistor R83, the output terminal of the comparator U49 is connected to the OCPM terminal, the resistor R86 is connected to the first end of the resistor R296, the second end of the resistor R296 is connected to the OCPM, the first end of the resistor R83, and the output terminal of the comparator U49, the second end of the capacitor C208 is connected to the ground terminal DGND, the resistor R85 is connected to VREF, the VCC terminal of the comparator U49 is connected to the power supply VCC, the second end of the resistor R83 is connected to the VCC terminal of the comparator and the second end of the capacitor C44, and the first end of the capacitor C44 is connected to the ground terminal DGND.

[0042] Based on another aspect of the embodiment of the present invention, there is provided a fast protection method for short circuit at the output end of an LLC circuit based on the above-mentioned fast protection circuit for short circuit at the output end of the LLC circuit, including the following steps:

[0043] According to the circuit parameters, calculate the peak current Im of the resonant cavity when the output is short-circuited as Im = Vin / (f*Lr);

[0044] Adjust the turns ratio of the T5 current transformer or the resistance values of the current detecting resistors R288-R291 to obtain a more appropriate voltage signal, and send it to the non-inverting input terminal of U49 through the isolation diode;

[0045] Quickly output a flip signal to make the enable pin level of the drive chip flip, and at the same time send it to the DSP to perform wave blocking protection and control the time for resuming wave generation.

[0046] Among them, the following steps are further included:

[0047] When the output is instantaneously short-circuited, the first action is a hardware signal. When a peak current arrives, the resonant cavity current passes through the current transformer T5, making the voltage of P5 of U49 higher than the voltage of the P6 pin, and the OCP signal immediately flips to a high level output.

[0048] Among them, the following steps are further included:

[0049] Upon receiving the OCP signal, start controlling the wave generation, including the wave generation frequency, wave generation period, and hiccup time at N periods.

[0050] Among them, the following steps are further included:

[0051] When it is detected that the short-circuit state persists, that is, the output current continuously exceeds the rated current value and the output voltage is lower than the first voltage, the given IDA value of the output current slowly drops to 1 / 6 of the current value;

[0052] When the voltage slowly recovers above the second voltage, the IDA is gradually restored to the rated current setting.

[0053] Among them, the first voltage is 25V and the second voltage is 20V.

[0054] Primary side peak fast overcurrent protection; the control enable pin of the hardware UCC27524 is connected to OCP to control the UCC27524 to generate waves; the software DSP (TMS320F28377S) receives the OCP signal and controls the DR1 and DR2 corresponding to the GPIO of the DSP to generate waves; the above double overcurrent protection is achieved; after a long-term short circuit, the current retraction is increased to reduce the device stress.

[0055] The LLC circuit has the maximum peak current at the moment of startup and short circuit; the purpose of current protection is to control the current at this time not to exceed the maximum peak current of the MOS tube and the corresponding pulse width time, and after a long-term short circuit, to reduce the electrical stress of the power device.

[0056] The composition of the primary side short circuit protection circuit: as Figure 1 shown, the current detection circuit of the resonant cavity is composed of the transformer T5, D78, D79 and R288 - R291; D29 is an isolation diode (to make the time constant of R86 and C208 more accurate. There are more spike interferences caused by the LLC circuit in the hiccup state, and D29 can play a certain isolation role); R86 and C208 form the overcurrent protection time constant; U49 is a comparator; R85 and R297 form an arbitrary reference voltage value; the output OCP action signal;

[0057] According to the circuit parameters, the peak current of the resonant cavity at output short circuit is calculated as: Im = Vin / (f * Lr); due to the circuit parasitic parameters, the actual peak current may deviate; adjust the turns ratio of the T5 transformer or the resistance value of the current detection resistors R288 - R291 to obtain a more appropriate voltage signal, which is sent to the non-inverting terminal of U49 through the isolation diode; quickly output a flip signal to make Figure 2 the enable pin level of the driving chip in flip, and at the same time it is also sent to the DSP to perform wave blocking protection and control the time to resume wave generation;

[0058] The working principle is divided into three levels, where 1 and 2 are transient responses, and 3 is the delayed protection response of 1 and 2.

[0059] 1. Output instantaneous short circuit; the first to act is the hardware signal. When a peak current arrives, the resonant cavity current passes through the transformer T5, making the voltage of P5 of U49 higher than the voltage of the P6 pin, and the OCP signal immediately flips to a high level output, as Figure 2Fast protection of the U86\U87 drive chip in it; (It is very difficult to obtain good protection effect by adjusting R86 and C208. Even with the isolation diode D29, either the adjustment is too sensitive, or the protection time is too long, or it cannot self-recover when the output is loaded with a short circuit, and it cycles and hiccups; the current during hiccupping is even larger than the current during short circuit. Because the drive chip does not participate in the loop control, it is impossible to control parameters such as the wave generation period, frequency, and soft start time. After N cycles, the MOS tube will inevitably be damaged due to the continuous peak current impact that it cannot bear.) Therefore, the first-level hardware protection is to quickly respond to a short circuit and block the wave first.

[0060] 2. At the same time, the software also receives the OCP signal and starts to control the wave generation, including the wave generation frequency, wave generation period, and hiccupping time at N cycles. It can control the entire resonant cavity more precisely.

[0061] 3. When it is detected that the short circuit state persists, that is, the output current continuously exceeds the rated current value and the output voltage is lower than 25V (this voltage can be modified to a lower value, which helps to increase the depth of current limiting. When modified to a higher value, the depth of current limiting is reduced.), the given IDA value of the output current slowly drops to about 1 / 6 of the current value, thus well reducing the current during short circuit; when the voltage slowly recovers to above 20V (make a hysteresis, this value can be matched and changed in the same way as 25V), gradually recover IDA to the rated current given value.

[0062] Utilize the enable pin of the drive chip and cooperate with DSP control to better adapt to the short circuit protection at the output end of the LLC circuit with wide range of input and output (wide frequency adjustment range, and the peak current is the largest during low-frequency short circuit).

[0063] Solve the short circuit protection under the full range of operating frequencies of the LLC, and perform current retraction during long-term short circuit to reduce voltage, current, and temperature stress, thereby improving the reliability of power devices. It is especially suitable for LLC circuits with wide frequency adjustment requirements for voltage regulation at the input and output.

[0064] The above has described the present invention with reference to the embodiments of the present disclosure. However, these embodiments are only for the purpose of illustration and not for limiting the scope of the present invention. The scope of the present invention is defined by the appended claims and their equivalents. Without departing from the scope of the present invention, those skilled in the art can make various substitutions and modifications, and these substitutions and modifications should all fall within the scope of the present invention.

Claims

1. A fast protection circuit based on the short circuit of the LLC circuit output terminal, Characterized in that, Comprising: A resonant cavity current detection circuit, which is composed of a transformer T5, a diode D78, a diode D79, a resistor R288, a resistor R289, a resistor R290 and a resistor R291; An isolation diode D29, the resonant cavity current detection circuit is connected to the positive pole of the isolation diode D29, the negative pole of the isolation diode D29 is connected to the second end of a resistor R86, the first end of the resistor R86 is connected to the first end of a capacitor C208, and the resistor R86 and the capacitor C208 form an overcurrent protection time constant; The second ends of the resistor R288, the resistor R289, the resistor R290 and the resistor R291 are connected to the ground terminal DGND, the second ends of the resistor R288, the resistor R289, the resistor R290 and the resistor R291 are respectively connected to the positive poles of two diodes, the negative poles of the two diodes are respectively connected to the 3-terminal and 4-terminal of the transformer T5, and the negative poles of the two diodes are also respectively connected to the positive poles of the diode D79 and the diode D78, and the negative poles of the diode D79 and the diode D78 are connected to the first ends of the resistor R288, the resistor R289, the resistor R290 and the resistor R291 and the positive pole of the diode D29; Wherein, the working principle of the fast protection circuit based on the short circuit of the LLC circuit output terminal is: when it is detected that the short circuit state continues, that is, the output current continuously exceeds the rated current value and the output voltage is lower than the first rated voltage value, the output current given IDA value slowly drops to 1 / 6 of the current value; When the voltage slowly recovers above the second rated voltage value, IDA gradually recovers to the rated current given value.

2. The fast protection circuit based on the short circuit of the LLC circuit output terminal according to claim 1, Characterized in that, It further includes a comparator U49, and the first ends of the resistor R86 and the capacitor C208 are connected to the P5 terminal of the comparator U49.

3. The fast protection circuit based on the short circuit of the LLC circuit output terminal according to claim 2, Characterized in that, It further includes a resistor R85 and a resistor R297. The first end of the resistor R85 is connected to the first end of the resistor R297. The first ends of the resistor R85 and the resistor R297 are connected to the P6 terminal of the comparator U49. The resistor R85 and the resistor R297 form an arbitrary reference voltage value to output an OCP action signal.

4. The fast protection circuit based on the short circuit of the LLC circuit output terminal according to claim 3, Characterized in that, The second end of the resistor R297 is connected to the ground terminal DGND. The ground terminal of the comparator U49 is connected to the ground terminal DGND. The output terminal of the comparator U49 is connected to the power supply VCC through the resistor R83. The output terminal of the comparator U49 is connected to the OCPM terminal. The resistor R86 is connected to the first end of the resistor R296. The second end of the resistor R296 is connected to the OCPM, the first end of the resistor R83, and the output terminal of the comparator U49. The second end of the capacitor C208 is connected to the ground terminal DGND. The resistor R85 is connected to VREF. The VCC terminal of the comparator U49 is connected to the power supply VCC. The second end of the resistor R83 is connected to the VCC terminal of the comparator and the second end of the capacitor C44. The first end of the capacitor C44 is connected to the ground terminal DGND.

5. The fast protection method for short - circuit at the output end of the LLC circuit based on the fast protection circuit for short - circuit at the output end of the LLC circuit according to any one of claims 1 - 4, characterized in that, it includes the following steps: According to the circuit parameters, calculate the peak current Im of the resonant cavity when there is an output short - circuit: Im = Vin / (f*Lr); Adjust the turns ratio of the T5 current transformer or the resistance values of the current - detecting resistors R288 - R291 to obtain an appropriate voltage signal, which is sent to the non - inverting terminal of U49 through the isolation diode; Quickly output a flip signal to flip the level of the enable pin of the drive chip, and also send it to the DSP to perform wave - blocking protection and control the time for resuming wave - sending.

6. The fast protection method for short - circuit at the output end of the LLC circuit according to claim 5, characterized in that, it further includes the following steps: For an instantaneous output short - circuit, the first - acting signal is a hardware signal. When a peak current arrives, the resonant - cavity current passes through the current transformer T5, making the voltage at P5 of U49 higher than the voltage at the P6 pin, and the OCP signal immediately flips to a high - level output.

7. The fast protection method for short - circuit at the output end of the LLC circuit according to claim 6, characterized in that, it further includes the following steps: Upon receiving the OCP signal, start to control the wave - sending, including the wave - sending frequency, the wave - sending period, and the hiccup time at N cycles.

8. The fast protection method for short - circuit at the output end of the LLC circuit according to claim 7, characterized in that, the first rated voltage value is 25V, and the second rated voltage value is 20V.

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