Output short-circuit protection module of LLC converter and LLC converter

Abstract

The utility model discloses an LLC converter output short circuit protection module and an LLC converter, the LLC converter comprises an LLC power level driver, a resonant cavity, a transformer and a secondary side switch circuit which are connected in sequence, and the resonant cavity comprises a resonant inductor and a resonant capacitor. The output short-circuit protection module comprises a resonant inductor voltage detection circuit, an output current sampling circuit, an output voltage sampling circuit and a control unit; and the control unit is used for updating a built-in protection threshold according to the output voltage and the output current, comparing the voltage of the resonant inductor with the protection threshold, and judging that the LLC converter triggers output short-circuit protection according to a comparison result. The circuit utilizes output current surge and output voltage drop caused by output short circuit of the LLC converter and resonant inductor voltage surge caused by loop regulation, so that a driving signal is quickly turned off, and the purpose of protecting a power device is achieved.

Description

Technical Field

[0001] The utility model belongs to the field of switching power supplies, and particularly relates to an output short-circuit protection circuit, which realizes quickly turning off the driving signal when the LLC converter has an output short circuit, so as to achieve the purpose of protecting power devices. Background Art

[0002] LLC resonant converters are often used in high-power switching power supplies. Once there is an output short circuit, the excitation inductor will quickly saturate, resulting in damage to the power supply. Therefore, it is necessary to make a pre-judgment and fast response to the output short circuit, and quickly turn off the driving signal after the output short circuit occurs. With the improvement of the power density and isolation insulation requirements of the power supply, a simple solution with a small circuit area is needed to achieve a pre-judgment and fast response to the output short circuit. The prior art proposed "A Circuit for Improving the Short-Circuit Protection Sensitivity of a High-Power LLC Controller" (Patent No.: CN209642554U), which uses the voltage of the auxiliary winding of the resonant inductor to represent the voltage of the resonant inductor. When the voltage of the resonant inductor rises above the threshold, the overvoltage protection of the driving chip is directly triggered to cut off the driving signal, realizing output short-circuit protection and achieving the purpose of protecting power devices. However, this scheme using a single resonant inductor voltage threshold is very easy to be mis-triggered. For example, when switching from light no-load to full load, or when the input voltage changes, the circuit gain will change, which will cause the voltage of the resonant inductor to rise, resulting in mis-triggering of the short-circuit protection. Summary of the Utility Model

[0003] The utility model aims to overcome at least one defect (shortcoming) in the above prior art, and provides an output short-circuit protection module and an LLC converter for the LLC converter, so as to solve the problems of slow detection of the output short circuit of the LLC converter and mis-triggering when switching to full load in other output short-circuit protection circuits. The module monitors the voltage of the resonant inductor, the output current and the output voltage through a control unit, and can accurately distinguish the situations of the LLC converter switching to full load and short circuit through an algorithm. Without mis-triggering, it can predict the occurrence of the output short circuit, make a pre-judgment and fast response, quickly turn off the driving signal, protect the power devices, and ensure normal use under other working conditions.

[0004] To achieve the above purpose, the utility model adopts the following technical solutions:

[0005] In a first aspect, an output short-circuit protection module for an LLC converter is provided. The LLC converter includes an LLC power stage driver, a resonant cavity, a transformer, and a secondary side switching circuit connected in sequence. The resonant cavity includes a resonant inductor and a resonant capacitor. The output short-circuit protection module includes: a resonant inductor voltage detection circuit, an output current sampling circuit, an output voltage sampling circuit, and a control unit. The resonant inductor voltage detection circuit is configured to detect the voltage of the resonant inductor and output it to the control unit. The output current sampling circuit is configured to sample the output current of the LLC converter and output it to the control unit. The output voltage sampling circuit is configured to sample the output voltage of the LLC converter and output it to the control unit. The control unit is configured to update a built-in protection threshold according to the output voltage and the output current. The control unit is further configured to compare the voltage of the resonant inductor with the protection threshold and determine whether the LLC converter triggers output short-circuit protection according to the comparison result. If so, the driving signal for the LLC power stage driver is cut off.

[0006] Preferably, the resonant inductor voltage detection circuit includes a first resistor R1, a second resistor R2, a first capacitor C1, a first diode D1, and an auxiliary winding. The auxiliary winding is coupled to the resonant inductor. One end of the auxiliary winding is connected to the anode of the first diode D1. The other end of the auxiliary winding is connected to one end of the first capacitor C1 and one end of the second resistor R2 and then grounded. The cathode of the first diode D1 is connected to the other end of the first capacitor C1 and one end of the first resistor R1. After the other end of the first resistor R1 is connected to the other end of the second resistor R2, it serves as the output end of the resonant inductor voltage detection circuit and is connected to the input end of the control unit.

[0007] Preferably, the output current sampling circuit is further configured to perform differential amplification on the output current and then output it to the control unit.

[0008] Preferably, the output current sampling circuit includes a third resistor R3, a first operational amplifier U1, a third resistor R3, a fourth resistor R4, a fifth resistor R5, a sixth resistor R6, and a seventh resistor R7. The third resistor R3 is connected in series between the secondary side switching circuit and the output end of the LLC converter. One end of the third resistor R3 is connected to one end of the fourth resistor R4, and the other end of the third resistor R3 is connected to one end of the sixth resistor R6. The other end of the fourth resistor R4 is connected to one end of the fifth resistor R5 and the positive input terminal of the first operational amplifier U1. The other end of the fifth resistor R5 is grounded. The other end of the sixth resistor is connected to one end of the seventh resistor R7 and the negative input terminal of the first operational amplifier U1. After the other end of the seventh resistor R7 is connected to the output terminal of the first operational amplifier U1, it serves as the output end of the output current sampling circuit and is connected to the input end of the control unit.

[0009] Preferably, the output voltage sampling circuit includes an eighth resistor R8 and a ninth resistor R9; one end of the eighth resistor R8 is connected to the output end of the LLC converter, and after the other end of the eighth resistor R8 is connected to one end of the ninth resistor R9, it serves as the output end of the output voltage sampling circuit and is connected to the input end of the control unit.

[0010] Preferably, the control unit is a single-chip microcomputer with an analog-to-digital conversion function.

[0011] Second aspect, there is provided an output short-circuit protection module for an LLC converter. The LLC converter includes an LLC power stage driver, a resonant cavity, a transformer, and a secondary side switching circuit connected in sequence. The resonant cavity includes a resonant inductor and a resonant capacitor. The output short-circuit protection module includes: a resonant inductor voltage detection circuit, an output current sampling circuit, an output voltage sampling circuit, and a control unit. The resonant inductor voltage detection circuit includes a first resistor R1, a second resistor R2, a first capacitor C1, a first diode D1, and an auxiliary winding. The auxiliary winding is coupled to the resonant inductor. One end of the auxiliary winding is connected to the anode of the first diode D1. The other end of the auxiliary winding is connected to one end of the first capacitor C1 and one end of the second resistor R2 and then grounded. The cathode of the first diode D1 is connected to the other end of the first capacitor C1 and one end of the first resistor R1. After the other end of the first resistor R1 is connected to the other end of the second resistor R2, it serves as the output end of the resonant inductor voltage detection circuit and is connected to the first input end of the control unit. The output current sampling circuit includes a third resistor R3, a first operational amplifier U1, a third resistor R3, a fourth resistor R4, a fifth resistor R5, a sixth resistor R6, and a seventh resistor R7. The third resistor R3 is connected in series between the secondary side switching circuit and the output end of the LLC converter. One end of the third resistor R3 is connected to one end of the fourth resistor R4, and the other end of the third resistor R3 is connected to one end of the sixth resistor R6. The other end of the fourth resistor R4 is connected to one end of the fifth resistor R5 and the positive input end of the first operational amplifier U1. The other end of the fifth resistor R5 is grounded. The other end of the sixth resistor is connected to one end of the seventh resistor R7 and the negative input end of the first operational amplifier U1. After the other end of the seventh resistor R7 is connected to the output end of the first operational amplifier U1, it serves as the output end of the output current sampling circuit and is connected to the second input end of the control unit. The output voltage sampling circuit includes an eighth resistor R8 and a ninth resistor R9. One end of the eighth resistor R8 is connected to the output end of the LLC converter. After the other end of the eighth resistor R8 is connected to one end of the ninth resistor R9, it serves as the output end of the output voltage sampling circuit and is connected to the third input end of the control unit. The control unit is configured to update the built-in protection threshold according to the output voltage sampled by the output voltage sampling circuit and the output current of the output current sampling circuit. The control unit is further configured to compare the voltage detected by the resonant inductor voltage detection circuit with the protection threshold, and determine whether the LLC converter triggers output short-circuit protection according to the comparison result. If so, the driving signal for the LLC power stage driver is cut off.

[0012] Third aspect, there is provided an LLC converter, including an LLC power stage driver, a resonant cavity, a transformer, and a secondary side switching circuit connected in sequence, and further including the output short-circuit protection module as described above.

[0013] Compared with the prior art, the beneficial effects of the present utility model are as follows: By collecting the output current and output voltage, the voltage threshold of the resonant inductor during output short circuit is updated in real time, so as to anticipate the occurrence of output short circuit without false triggering to switch to full load, thereby making a pre-emptive and rapid response, quickly turning off the drive signal, protecting the power device while ensuring normal use under other working conditions. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 It is a schematic block diagram of the output short-circuit protection module circuit of the present utility model.

[0015] Figure 2 It is a schematic block diagram of the output short-circuit protection module circuit according to the first embodiment of the present utility model. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0016] The present utility model and its beneficial effects will be further described in detail below in conjunction with the specific embodiments and the drawings of the specification. However, the specific embodiments of the present utility model are not limited thereto.

[0017] As Figure 1 shown, it is a schematic block diagram of the output short-circuit protection module in this embodiment. In this embodiment, an output short-circuit protection module for an LLC converter is provided. The LLC converter includes an LLC power stage drive, a resonant cavity, a transformer, and a secondary side switching circuit connected in sequence. The resonant cavity includes a resonant inductor and a resonant capacitor. The output short-circuit protection module includes: a resonant inductor voltage detection circuit 1, an output current sampling circuit 2, an output voltage sampling circuit 3, and a control unit. The resonant inductor voltage detection circuit 1 is used to detect the voltage of the resonant inductor and output it to the control unit. The output current sampling circuit 2 is used to sample the output current of the LLC converter and output it to the control unit. The output voltage sampling circuit 3 is used to sample the output voltage of the LLC converter and output it to the control unit. The control unit is used to update the built-in protection threshold according to the output voltage and output current. The control unit is also used to compare the voltage of the resonant inductor with the protection threshold, and judge whether the LLC converter triggers output short-circuit protection according to the comparison result. If so, the drive signal to the LLC power stage drive is cut off.

[0018] Specifically, the LLC power stage driver can be a full-bridge circuit or a half-bridge circuit, and the secondary side switching circuit can be a full-bridge rectifier circuit or a full-wave rectifier circuit, which is not limited herein; in this embodiment, the LLC power stage driver is a half-bridge circuit and the secondary side switching circuit is a full-wave rectifier circuit as an example for illustration; specifically, the LLC power stage driver includes MOS transistor Q1 and MOS transistor Q2, the transformer includes a primary winding, a first secondary winding, and a second secondary winding, the secondary side switching circuit includes diode D2, diode D3, and capacitor C3, the drain of MOS transistor Q1 is used to connect to the input voltage Vin, the gate of MOS transistor Q1 is connected to the first output terminal of the control unit, the source of MOS transistor Q1 is connected to the drain of MOS transistor Q2 and the same-name terminal of the resonant inductor T1, the gate of MOS transistor Q2 is connected to the second output terminal of the control unit, the source of MOS transistor Q2 is connected to one end of capacitor C2 and then grounded, the different-name terminal of the resonant inductor T1 is connected to the same-name terminal of the primary winding, and the different-name terminal of the primary winding is connected to the other end of capacitor C2; the same-name terminal of the first secondary winding is connected to the anode of diode D2, the cathode of diode D2 is connected to the cathode of diode D3 and one end of capacitor C3 and then connected to the output terminal Vo, the different-name terminal of the first secondary winding is connected to the same-name terminal of the second secondary winding and the other end of capacitor C3 and then grounded, and the different-name terminal of the second secondary winding is connected to the anode of diode D3.

[0019] As Figure 2 shown, as a specific implementation of the resonant inductor voltage detection circuit 1, the resonant inductor voltage detection circuit 1 includes a first resistor R1, a second resistor R2, a first capacitor C1, a first diode D1, and an auxiliary winding; the auxiliary winding is coupled to the resonant inductor, one end of the auxiliary winding is connected to the anode of the first diode D1, the other end of the auxiliary winding is connected to one end of the first capacitor C1 and one end of the second resistor R2 and then grounded, the cathode of the first diode D1 is connected to the other end of the first capacitor C1 and one end of the first resistor R1, and after the other end of the first resistor R1 is connected to the other end of the second resistor R2, it serves as the output terminal of the resonant inductor voltage detection circuit 1 and is connected to the input terminal of the control unit.

[0020] Specifically, the input terminal of the control unit includes a first input terminal, a second input terminal, and a third input terminal, and the output terminal of the resonant inductor voltage detection circuit 1 is connected to the first input terminal of the control unit; the resonant inductor voltage detection circuit indirectly collects the resonant inductor voltage by adding a set of auxiliary windings to the resonant inductor for coupled connection.

[0021] As a specific embodiment of the output current sampling circuit 2, the output current sampling circuit 2 is further configured to differentially amplify the output current and then output it to the control unit. Specifically, the output current sampling circuit 2 includes a third resistor R3, a first operational amplifier U1, a third resistor R3, a fourth resistor R4, a fifth resistor R5, a sixth resistor R6, and a seventh resistor R7. The third resistor R3 is connected in series between the secondary side switching circuit and the output terminal of the LLC converter. One end of the third resistor R3 is connected to one end of the fourth resistor R4, and the other end of the third resistor R3 is connected to one end of the sixth resistor R6. The other end of the fourth resistor R4 is connected to one end of the fifth resistor R5 and the positive input terminal of the first operational amplifier U1. The other end of the fifth resistor R5 is grounded. The other end of the sixth resistor is connected to one end of the seventh resistor R7 and the negative input terminal of the first operational amplifier U1. After the other end of the seventh resistor R7 is connected to the output terminal of the first operational amplifier U1, it serves as the output terminal of the output current sampling circuit 2 and is connected to the input terminal of the control unit.

[0022] Specifically, one end of the third resistor R3 is connected to the cathode of the diode D2 and one end of the capacitor C3, and the other end of the third resistor R3 is connected to the output terminal Vo.

[0023] As a specific embodiment of the output voltage sampling circuit 3, the output voltage sampling circuit 3 includes an eighth resistor R8 and a ninth resistor R9. One end of the eighth resistor R8 is connected to the output terminal of the LLC converter. After the other end of the eighth resistor R8 is connected to one end of the ninth resistor R9, it serves as the output terminal of the output voltage sampling circuit 3 and is connected to the input terminal of the control unit.

[0024] Specifically, one end of the eighth resistor R8 is connected to the other end of the third resistor R3 and the output terminal Vo.

[0025] In the specific implementation process, the control unit is a single-chip microcomputer with an analog-to-digital conversion function, and the input terminals of the control unit are all analog-to-digital conversion interfaces. The working principle of the output short-circuit protection module in this embodiment is as follows:

[0026] The gates of the MOS transistors Q1 and Q2 are connected to the drive interface of the control unit through isolation drive.

[0027] When the module is working, the output voltage is collected and divided by the eighth resistor R8 and the ninth resistor R9 and sent to the control unit. The output current is collected by the sampling resistor, differentially amplified by the first operational amplifier U1 and then sent to the control unit. The control unit calculates the voltage gain of the LLC converter at this time according to the built-in algorithm, estimates the change trend of the resonant inductor voltage and the protection threshold when output short circuit occurs through model fitting, and updates the protection threshold of the resonant inductor voltage in real time. The detected voltage of the resonant inductor is compared with the protection threshold. Once the voltage of the resonant inductor exceeds the protection threshold, the output short circuit protection is triggered, and the driving signals of the MOS transistor Q1 and the MOS transistor Q2 are cut off. If the voltage of the resonant inductor does not exceed the threshold, the protection is not triggered. At this time, the LLC converter switches from light load to heavy load, which does not affect the normal operation of the LLC. By collecting the output current and the output voltage, the threshold of the resonant inductor voltage during output short circuit is updated in real time. This circuit utilizes the sudden increase in output current, the drop in output voltage and the sudden increase in resonant inductor voltage caused by loop regulation when output short circuit occurs in the LLC converter to predict the occurrence of output short circuit without false triggering of switching to full load, so as to make a pre-judgmental fast response and quickly turn off the driving signal. While protecting the power devices, it can also ensure normal use under other working conditions. The circuit principle is simple and the process is simple. With fewer devices and a relatively simple control idea, it can achieve the effect of quickly protecting power devices when output short circuit occurs, and can be widely applied in the product development of LLC resonant converter switching power supply circuits.

[0028] It should be noted that the above are only the preferred embodiments of the present invention. It should be pointed out that the above preferred embodiments should not be regarded as a limitation of the present invention. It should also be recognized that the present invention can be applied in other more extensive ranges. According to the above content of the present invention, using the ordinary technical knowledge and conventional means in the art, without departing from the above basic technical idea of the present invention, the present invention can also be modified, replaced or changed in other various forms, and these modifications, replacements or changes all fall within the scope of the protection of the rights of the present invention.

Claims

1. An output short-circuit protection module for an LLC converter, the LLC converter comprising an LLC power stage driver, a resonant cavity, a transformer and a secondary switch circuit connected in sequence, the resonant cavity comprising a resonant inductor and a resonant capacitor, characterized in that: The output short-circuit protection module includes: a resonant inductor voltage detection circuit, an output current sampling circuit, an output voltage sampling circuit, and a control unit; the resonant inductor voltage detection circuit is used to detect the voltage of the resonant inductor and output it to the control unit; the output current sampling circuit is used to sample the output current of the LLC converter and output it to the control unit; the output voltage sampling circuit is used to sample the output voltage of the LLC converter and output it to the control unit; the control unit is used to update the built-in protection threshold according to the output voltage and the output current; the control unit is also used to compare the voltage of the resonant inductor with the protection threshold, and determine whether the LLC converter triggers output short-circuit protection based on the comparison result, and if so, cut off the drive signal to the LLC power stage.

2. The output short-circuit protection module of the LLC converter according to claim 1, characterized in that: The resonant inductor voltage detection circuit includes a first resistor R1, a second resistor R2, a first capacitor C1, a first diode D1 and an auxiliary winding; the auxiliary winding is coupled to the resonant inductor, one end of the auxiliary winding is connected to the anode of the first diode D1, the other end of the auxiliary winding is connected to one end of the first capacitor C1 and one end of the second resistor R2 and then grounded, the cathode of the first diode D1 is connected to the other end of the first capacitor C1 and one end of the first resistor R1, the other end of the first resistor R1 is connected to the other end of the second resistor R2, and then connected as the output end of the resonant inductor voltage detection circuit to the input end of the control unit.

3. The output short-circuit protection module of the LLC converter according to claim 1, characterized in that: The output current sampling circuit is also used to perform differential amplification on the output current and then output the amplified output current to the control unit.

4. The output short-circuit protection module of the LLC converter according to claim 3, characterized in that: The output current sampling circuit includes a third resistor R3, a first operational amplifier U1, a third resistor R3, a fourth resistor R4, a fifth resistor R5, a sixth resistor R6, and a seventh resistor R7; the third resistor R3 is connected in series between the secondary side switch circuit and the output end of the LLC converter, one end of the third resistor R3 is connected to one end of the fourth resistor R4, and the other end of the third resistor R3 is connected to one end of the sixth resistor R6; the other end of the fourth resistor R4 is connected to one end of the fifth resistor R5 and the positive input end of the first operational amplifier U1; the other end of the fifth resistor R5 is grounded; the other end of the sixth resistor is connected to one end of the seventh resistor R7 and the reverse input end of the first operational amplifier U1; after the other end of the seventh resistor R7 is connected to the output end of the first operational amplifier U1, it is connected to the input end of the control unit as the output end of the output current sampling circuit.

5. The output short circuit protection module of the LLC converter according to claim 1, characterized in that: The output voltage sampling circuit includes an eighth resistor R8 and a ninth resistor R9; one end of the eighth resistor R8 is connected to the output end of the LLC converter, and the other end of the eighth resistor R8 is connected to one end of the ninth resistor R9, and then connected to the input end of the control unit as the output end of the output voltage sampling circuit.

6. The output short-circuit protection module of the LLC converter according to any one of claims 1 to 5, characterized in that: The control unit is a single chip microcomputer with analog-to-digital conversion function.

7. An output short-circuit protection module for an LLC converter, the LLC converter comprising an LLC power stage driver, a resonant cavity, a transformer and a secondary switch circuit connected in sequence, the resonant cavity comprising a resonant inductor and a resonant capacitor, characterized in that: The output short circuit protection module includes: a resonant inductor voltage detection circuit, an output current sampling circuit, an output voltage sampling circuit, and a control unit; the resonant inductor voltage detection circuit includes a first resistor R1, a second resistor R2, a first capacitor C1, a first diode D1 and an auxiliary winding; the auxiliary winding is coupled to the resonant inductor, one end of the auxiliary winding is connected to the anode of the first diode D1, the other end of the auxiliary winding is connected to one end of the first capacitor C1 and one end of the second resistor R2 and then grounded, the cathode of the first diode D1 is connected to the other end of the first capacitor C1 and the first resistor R1, and the other end of the first resistor R1 is connected to the other end of the second resistor R2, and then the output end of the resonant inductor voltage detection circuit is connected to the first input end of the control unit; the output current sampling circuit includes a third resistor R3, a first operational amplifier U1, a third resistor R3, a fourth resistor R4, a fifth resistor R5, a sixth resistor R6, and a seventh resistor R7; the third resistor R3 is connected in series between the secondary switch circuit and the output end of the LLC converter, one end of the third resistor R3 is connected to one end of the fourth resistor R4, and the other end of the third resistor R3 is connected to the sixth resistor R6. The output voltage sampling circuit includes an eighth resistor R8 and a ninth resistor R9; one end of the eighth resistor R8 is connected to the output end of the LLC converter, and the other end of the eighth resistor R8 is connected to one end of the ninth resistor R9, and then connected to the third input end of the control unit as the output end of the output voltage sampling circuit; the control unit is used to update the built-in protection threshold according to the output voltage sampled by the output voltage sampling circuit and the output current sampled by the output current sampling circuit; the control unit is also used to compare the voltage detected by the resonant inductor voltage detection circuit with the protection threshold, and judge whether the LLC converter triggers the output short circuit protection according to the comparison result, and if so, cut off the driving signal for driving the LLC power stage.

8. An LLC converter, comprising an LLC power stage driver, a resonant cavity, a transformer and a secondary switch circuit connected in sequence, characterized in that: It also includes an output short circuit protection module as described in any one of claims 1 to 7.

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