An IGBT soft turn-off circuit based on pulse width recognition

Abstract

The present invention provides an IGBT soft turn-off circuit based on pulse width recognition. This IGBT soft turn-off circuit realizes the soft turn-off of the IGBT by recognizing the pulse width. Different from the existing technology where multiple isolation transformers are used for joint control, this solution only uses one isolation transformer to achieve the soft turn-off of the IGBT, and can realize the switching between soft turn-off and turn-off, with low circuit devices and strong system reliability.

Description

Technical Field

[0001] The present invention relates to the field of IGBT control, and particularly to an IGBT soft turn-off circuit based on pulse width recognition. Background Art

[0002] IGBT (Insulated Gate Bipolar Transistor), also known as insulated gate bipolar transistor, is a composite fully controlled voltage-driven power semiconductor device composed of BJT and MOS, which has the advantages of high input impedance of MOSFET and low conduction voltage drop of GTR. Therefore, it is more and more widely used in power electronic equipment. However, the time that IGBT can withstand short circuit is very short. When a short circuit occurs, the maximum current far exceeds the rated value, the power consumption per unit time is also much higher than the normal working state, and directly turning off the IGBT will generate a very high turn-off spike voltage. In order to suppress the voltage spike generated when the IGBT is turned off, the common methods at present are to adopt a soft turn-off strategy and add a clamping circuit. However, the latter requires additional devices, increases the cost, and is also prone to failure after multiple operations. In comparison, the soft turn-off strategy means slowly reducing the gate voltage of the IGBT, and then using a negative voltage to turn off normally when the current drops to a certain value.

[0003] However, in a conventional IGBT drive circuit, as Figure 1 shown, the input signal PWM_IN passes through a level conversion circuit and then drives an isolation transformer through two drivers Driver. A positive pulse is generated at the rising edge of the primary side of the isolation transformer, and a negative pulse is generated at the falling edge. After being transmitted through the isolation transformer to the secondary side, the secondary side converts the high and low levels of the input signal PWM_IN into secondary side on (ON), off (OFF) signals through a detection circuit to control the turn-on and turn-off of the IGBT, but it cannot transmit a soft turn-off signal. At this time, a complex and expensive clamping circuit needs to be configured.

[0004] In some other solutions, the soft turn-off can be achieved by setting multiple isolation transformers. As Figure 2 shown, the input signal PWM_IN passes through a level conversion circuit and then drives an isolation transformer through a driver Driver. When turning on, a positive pulse is generated at both ends of the first isolation transformer at its rising edge. When turning off, first a negative pulse is generated at the falling edge by the second isolation transformer to perform the first soft turn-off, and then a negative pulse is generated by the first isolation transformer to perform the second turn-off. The secondary side converts the high and low levels of the input signal PWM_IN into secondary side on (ON), soft turn-off (SOLTOFF), off (OFF) signals through a detection circuit to control the turn-on and turn-off of the IGBT. Two transformers are used to isolate and transmit 3 command signals. However, this method requires multiple isolation transformers, and the increase in the number of isolation transformers also increases the cost. Summary of the Invention

[0005] The object of the present invention is to provide an IGBT soft turn-off circuit based on pulse width recognition. The IGBT soft turn-off circuit determines whether to adopt a soft turn-off strategy based on pulse width recognition technology, and completes the soft turn-off strategy of the circuit when necessary, with strong low-system reliability of circuit devices.

[0006] In order to achieve any of the above invention objects, an IGBT soft turn-off circuit based on pulse width recognition includes: a level conversion circuit, a driving module, an isolation transformer, a voltage dividing circuit, a comparison module, a detection circuit, and a control module. The level conversion circuit is connected to the isolation transformer through the driving module. The isolation transformer is connected to the input ends of the comparison module and the detection circuit through the voltage dividing circuit, and the input end and the output end of the comparison module are connected to the detection circuit. The output end of the detection circuit is connected to the control module. When the level is at the falling edge, the driving module drives the isolation transformer to generate a width pulse. The comparison module obtains the divided voltage level corresponding to the width pulse and the reference level generated by the detection circuit, compares to obtain the pulse width of the width pulse, and the detection circuit selects the control module according to the pulse width.

[0007] In some embodiments, the driving module respectively includes an upper driver and a lower driver. The output ends of the level conversion circuit are respectively connected to the upper driver and the lower driver, and the upper driver and the lower driver are respectively connected to both ends of the primary excitation winding of the isolation transformer.

[0008] In some embodiments, when the level is at the falling edge, the width pulse is a positive pulse.

[0009] In some embodiments, the voltage dividing circuit is connected to the negative input end of the comparison module, and the detection circuit is connected to the positive input end of the comparison module.

[0010] In some embodiments, the voltage dividing circuit includes a first voltage dividing resistor and a second voltage dividing resistor. The first resistor and the second voltage dividing resistor are connected in series, and the first voltage dividing resistor and the second voltage dividing resistor are respectively connected to both ends of the secondary induced winding of the isolation transformer. The two end points of the first voltage dividing resistor and the second voltage dividing resistor are connected to the input end of the detection circuit, and the end point between the second voltage dividing resistor and the second voltage dividing resistor is connected to the negative input end of the comparison module.

[0011] In some embodiments, the detection circuit selects the control module according to the relationship between the comparison pulse width Twidth, the turn-off width threshold Twidth1, and the soft turn-off width threshold Twidth2.

[0012] In some embodiments, the control module includes a turn-on module, a turn-off module, and a soft turn-off module.

[0013] Compared with the prior art, the IGBT soft turn-off circuit based on pulse width recognition provided by the present technical solution only requires one isolation transformer to simultaneously transmit turn-on, turn-off, and soft turn-off instructions, reducing the number of isolation transformers, lowering the circuit manufacturing cost, and improving the reliability of the system. In this solution, when the circuit needs to be turned off, the primary signal generates a pulse with a variable width at the falling edge of the primary side of the isolation transformer. The secondary side receives the changing pulse, and the recognition module recognizes the width of the pulse to determine whether to directly execute the turn-off strategy or first execute the turn-off strategy and then the soft turn-off strategy, thereby realizing the simultaneous transmission of turn-on, turn-off, and soft turn-off instructions, achieving the purpose of fewer components, lower cost, and system reliability. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 is a circuit diagram of an IGBT drive circuit in the prior art that fails to execute the soft turn-off instruction.

[0015] Figure 2 is a circuit diagram of an IGBT drive circuit in the prior art with multiple isolation transformers.

[0016] Figure 3 is a schematic circuit diagram of an IGBT drive circuit based on pulse width recognition according to an embodiment of the present invention.

[0017] Figure 4 is based on Figure 3 the signal transmission schematic diagram of the IGBT drive circuit based on pulse width recognition in

[0018] In the figure: 10 - level conversion circuit, 20 - drive module, 21 - upper driver, 22 - lower driver, 30 - isolation transformer, 31 - primary excitation winding, 32 - secondary induction winding, 40 - voltage division circuit, 41 - first voltage division resistor, 42 - second voltage division resistor, 50 - comparison module, 60 - detection circuit, 70 - control module, 71 - turn-on module, 72 - turn-off module, 73 - soft turn-off module. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0019] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention belong to the scope of protection of the present invention.

[0020] It should be noted that the schematic diagrams, device models, and timing waveforms drawn in the drawings of this specification are only used to cooperate with the content disclosed in the specification for those familiar with this technology to understand and read, and are not used to limit the implementation conditions of the present invention. Therefore, they do not have substantial technical significance. Any modification of the structure, change in the proportional relationship, adjustment of the size, change in the RC value parameter, change in the device model, cyclic conversion of the logical state, or overall transformation of the logical state should still fall within the scope covered by the technical content disclosed in the present invention without affecting the effects that the present invention can produce and the purposes that can be achieved.

[0021] This technical solution provides an IGBT soft turn-off circuit based on pulse width recognition. This IGBT soft turn-off circuit realizes IGBT soft turn-off by recognizing the pulse width. Different from the existing technology where multiple isolation transformers are jointly controlled, this solution only uses one isolation transformer to realize IGBT soft turn-off, and can realize the switching between soft turn-off and turn-off, with strong low-system reliability of circuit devices.

[0022] Specifically, the IGBT soft turn-off circuit includes a level conversion circuit 10, a driving module 20, an isolation transformer 30, a voltage dividing circuit 40, a comparison module 50, a detection circuit 60, and a control module 70. Among them, the level conversion circuit 10 is connected to both ends of the isolation transformer 30 through the driving module 20. The isolation transformer 30 is connected to the input ends of the comparison module 50 and the detection circuit 60 through the voltage dividing circuit 40. The input end and the output end of the comparison module 50 are both connected to the detection circuit 60, and the output end of the detection circuit 60 is connected to the control module 70. When the level is at the falling edge, the driving module 20 drives the isolation transformer 30 to generate a width pulse. The comparison module 50 obtains the divided voltage level corresponding to the width pulse and the reference level generated by the detection circuit 60, compares to obtain the pulse width of the width pulse, and the detection circuit 60 selects the control module 70 according to the pulse width.

[0023] Specifically, the driving module 20 includes an upper driver 21 and a lower driver 22 respectively. The output end of the level conversion circuit 10 is respectively connected to the upper driver 21 and the lower driver 22, and the upper driver 21 and the lower driver 22 are respectively connected to both ends of the primary excitation winding 31 of the isolation transformer 30.

[0024] The primary signal PWM_IN is input to the input end of the level conversion circuit 10. The function of the level conversion circuit 10 is to convert it into the corresponding level according to the primary signal PWM_IN. When the instruction of the primary signal PWM_IN is to turn on the circuit, the corresponding level rises from low level to high level at this time. When the instruction of the primary signal PWM_IN is to turn off the circuit, the corresponding level drops from high level to low level at this time. Since the level conversion circuit 10 is a conventional circuit, the specific circuit structure is not elaborated in this solution.

[0025] The output terminals of the level conversion circuit 10 are respectively connected to the upper driver 21 and the lower driver 22. The function of the driving module 20 is to drive the isolation transformer 30. There is a capacitor between the upper driver 21 and the isolation transformer 30. When the level is at the rising edge, the driving module 20 drives the primary excitation winding 31 of the isolation transformer 30 to generate a pulse. When the level is at the falling edge, the driving module 20 drives the primary excitation winding 31 of the isolation transformer 30 to generate a pulse with a variable width. In this solution, if the positive pulse is selected for shutdown, it is convenient for the comparison module 50 to select single - power supply. Therefore, when the level is at the rising edge, the driving module 20 drives the primary excitation winding 31 to generate a sub - pulse.

[0026] When a short - circuit fault occurs in the IGBT, the driving module 20 will receive the fault information and then execute different pulse widths. That is, at this time, for different circuit shutdown situations, the primary excitation winding 31 of the isolation transformer 30 will generate pulses with different widths, and then the shutdown state can be judged and executed by identifying the pulses with different widths.

[0027] Particularly, the width of the variable - width positive pulse does not exceed the saturation magnetic density of the magnetic core.

[0028] In this solution, the driving module 20 is selected as a driver, and the model can be CPLD + driver IC or a dedicated ASIC chip. In this solution, CPLD + driver IC is adopted.

[0029] It should be particularly emphasized that only one isolation transformer 30 is required in this solution to complete the change of three instructions. The variable - width positive pulse generated by the primary excitation winding 31 of the isolation transformer 30 is transmitted to the secondary side of the isolation transformer 30, so that the secondary side of the isolation transformer 30 can make targeted instruction judgments.

[0030] The function of the voltage - dividing circuit 40 is to make the voltage input to the comparison module 50 not exceed the power supply voltage and add a resistor, so that the LC oscillation of the secondary - side inductance of the isolation transformer 30 and the distributed capacitance of the isolation transformer 20 can be reduced, forming an RLC damped oscillation.

[0031] Specifically, in the embodiment of this solution, the voltage - dividing circuit 40 includes a first voltage - dividing resistor 41 and a second voltage - dividing resistor 42. The first resistor 41 and the second voltage - dividing resistor 42 are connected in series, and the first voltage - dividing resistor 41 and the second voltage - dividing resistor 42 are respectively connected to both ends of the secondary - side induction winding 32 of the isolation transformer 30. The two end - points of the first voltage - dividing resistor 41 and the second voltage - dividing resistor 42 are connected to the input end of the detection circuit 60, and the end - point between the second voltage - dividing resistor 41 and the second voltage - dividing resistor 42 is connected to the input end of the comparison module 50.

[0032] Among them, the first voltage-dividing resistor 41 and the second voltage-dividing resistor 42 satisfy the following conditions: the sum of the first voltage-dividing resistor 41 and the second voltage-dividing resistor 42 is less than 1K, and the resistance distribution between the first voltage-dividing resistor 41 and the second voltage-dividing resistor 42 can be selected according to the specific turns ratio of the isolation transformer 30 and the reference level of the comparison module 50.

[0033] The input side of the comparison module 50 is respectively connected to the voltage-dividing circuit 40 and the detection circuit 60, and the output side of the comparison module 50 is also connected to the detection circuit 60. Specifically, in an embodiment, the voltage-dividing circuit 40 is connected to the negative input terminal of the comparison module 50, and the detection circuit 60 is connected to the positive input terminal of the comparison module 50. At this time, the divided voltage level of the voltage-dividing circuit 40 and the reference level generated by the detection circuit 60 are input to the comparison module 50 for comparison.

[0034] The comparison module 50 can obtain the pulse width of the level change pulse by comparing the divided voltage level and the reference level. Specifically, if a certain part of the divided voltage level does not conform to the reference level, that part of the divided voltage level is recorded, and then a pulse with a specific width can be obtained. In this solution, the comparison module 50 selects a comparator.

[0035] The detection circuit 60 identifies the pulse width Twidth of the width pulse. The high-speed CPLD is used in the detection circuit 60 to collect the pulse width, and then the accurate pulse width can be obtained. In addition, the detection circuit 60 judges the type of the execution control module 70 according to the comparison of the pulse width Twidth, the turn-off width threshold Twidth1, and the soft turn-off width threshold Twidth2.

[0036] Among them, when the pulse width Twidth is less than the turn-off width threshold Twidth1, the turn-off instruction is executed; when the pulse width Twidth is greater than the turn-off width threshold Twidth1 and less than the soft turn-off width threshold Twidth2, the soft turn-off instruction is first executed, and then the turn-off instruction is executed.

[0037] The control module 70 includes a turn-on module 71, a turn-off module 72, and a soft turn-off module 73. The detection circuit 60 executes different control instructions to turn on or off the corresponding control module 70. In this solution, the turn-on module 71 includes a turn-on triode and a turn-on resistor connected to the turn-on triode. The turn-off module 72 includes a turn-off triode and a turn-off resistor connected to the turn-off triode. The soft turn-off module 73 includes a soft turn-off triode and a soft turn-off resistor connected to the soft turn-off triode. Among them, the turn-on resistor, the turn-off resistor, and the soft turn-off resistor are connected in parallel, and one end of the soft turn-off triode is grounded.

[0038] Specifically, the working principle of this IGBT soft turn-off circuit is as follows:

[0039] When the IGBT circuit needs to be turned on, the input level of the input primary signal PWM_IN changes from low level to high level. At this time, a negative pulse is generated in the primary excitation winding 31 of the isolation transformer 30. Correspondingly, the secondary induction winding of the isolation transformer 30 receives this negative pulse, and the detection circuit 60 executes the turn-on instruction according to this negative pulse.

[0040] When the IGBT circuit needs to be turned off, the input level of the input primary signal PWM_IN changes from high level to low level. At this time, a positive pulse with a certain width is generated in the primary excitation winding 31 of the isolation transformer 30. The secondary induction winding of the isolation transformer 30 receives this positive pulse, enters the comparison module 50 through the voltage division circuit 40. The comparison module 50 compares the divided voltage level corresponding to this positive pulse with the reference level provided by the detection circuit 60 to obtain the width of this positive pulse. The detection circuit 60 identifies this width and compares this width with the judgment threshold to determine whether to execute the turn-off instruction or first execute the soft turn-off instruction.

[0041] The present invention is not limited to the above best implementation manner. Anyone can obtain other various forms of products under the inspiration of the present invention. However, no matter what changes are made in its shape or structure, as long as it has a technical solution identical or similar to the present application, it falls within the protection scope of the present invention.

Claims

1. An IGBT soft turn-off circuit based on pulse width recognition, Characterized in that, It includes: A level conversion circuit (10), a driving module (20), an isolation transformer (30), a voltage dividing circuit (40), a comparison module (50), a detection circuit (60) and a control module (70), Wherein the level conversion circuit (10) is connected to the isolation transformer (30) through the driving module (20), The isolation transformer (30) is connected to the input ends of the comparison module (50) and the detection circuit (60) through the voltage dividing circuit (40), and the input end and the output end of the comparison module (50) are connected to the detection circuit (60), and the output end of the detection circuit (60) is connected to the control module (70); The control module (70) includes a turn-on module (71), a turn-off module (72) and a soft turn-off module (73); Wherein when the level is at the falling edge, the driving module (20) drives the isolation transformer (30) to generate a width pulse, the comparison module (50) obtains the divided voltage level corresponding to the width pulse and the reference level generated by the detection circuit (60), compares to obtain the pulse width of the width pulse, and the detection circuit (60) selects the control module (70) according to the pulse width; Wherein, the detection circuit (60) selects the control module (70) according to the relationship between the comparison pulse width Twidth, the turn-off width threshold Twidth1 and the soft turn-off width threshold Twidth2; Wherein, the detection circuit (60) selects the control module (70) according to the relationship between the comparison pulse width Twidth, the turn-off width threshold Twidth1 and the soft turn-off width threshold Twidth2, including: when the pulse width Twidth is less than the turn-off width threshold Twidth1, execute the turn-off instruction; when the pulse width Twidth is greater than the turn-off width threshold Twidth1 and less than the soft turn-off width threshold Twidth2, first execute the soft turn-off instruction and then execute the turn-off instruction; The high-speed CPLD is adopted in the detection circuit (60) to collect the pulse width.

2. The IGBT soft turn-off circuit based on pulse width recognition according to claim 1, Characterized in that, The driving module (20) respectively includes an upper driver (21) and a lower driver (22), the output end of the level conversion circuit (10) is respectively connected to the upper driver (21) and the lower driver (22), and the upper driver (21) and the lower driver (22) are respectively connected to both ends of the primary excitation winding (31) of the isolation transformer (30).

3. The IGBT soft turn-off circuit based on pulse width recognition according to claim 1, Characterized in that, When the level is at the falling edge, the width pulse is a positive pulse.

4. The IGBT soft turn-off circuit based on pulse width recognition according to claim 1, Characterized in that, Both the voltage dividing circuit (40) and the detection circuit (60) are connected to the input end of the comparison module (50).

5. The IGBT soft turn-off circuit based on pulse width recognition according to claim 1, Characterized in that, The voltage-dividing circuit (40) includes a first voltage-dividing resistor (41) and a second voltage-dividing resistor (42), wherein the first resistor (41) and the second voltage-dividing resistor (42) are connected in series, and the first voltage-dividing resistor (41) and the second voltage-dividing resistor (42) are respectively connected to both ends of the secondary induction winding (32) of the isolation transformer (30). The two end points of the first voltage-dividing resistor (41) and the second voltage-dividing resistor (42) are connected to the input end of the detection circuit (60), and the end point between the second voltage-dividing resistor (41) and the second voltage-dividing resistor (42) is connected to the input end of the comparison module (50).

6. The IGBT soft turn-off circuit based on pulse width identification according to claim 5, characterized in that, the sum of the first voltage-dividing resistor (41) and the second voltage-dividing resistor (42) is less than 1K.

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