An overcurrent protection circuit and overcurrent protection method for a power switch tube

Abstract

The present invention provides an overcurrent protection circuit and an overcurrent protection method for a power switch tube, wherein the overcurrent protection circuit includes a voltage sampling circuit for collecting the desaturation voltage of the power switch tube and outputting it to the first input terminal of a comparator; a reference voltage circuit generates a reference voltage and outputs it to the second input terminal of the comparator; the comparator compares the desaturation voltage with the reference voltage and then outputs a low level or a high level to a power supply shutdown circuit at the output terminal of the driver, controls the on and off of the power supply at the output terminal of the driver, controls the on and off of the gate drive signal at the output terminal of the driver, and thus controls the on and off of the power switch tube through the gate drive circuit. Based on desaturation detection, the present invention directly shuts off the drive signal at the output terminal of the driver, and does not need to go through the control logic inside the driver to shut off the drive signal at the output terminal, thereby quickly shutting off the power switch tube.

Description

Technical Field

[0001] The present invention relates to the technical field of air conditioners, and in particular to an overcurrent protection circuit and an overcurrent protection method for a power switch tube. Background Art

[0002] The frequency conversion technology used by variable frequency air conditioners is realized by using power switch tubes. Power switch tubes can include power devices such as metal oxide semiconductor field effect transistors (MOSFET), insulated gate bipolar transistors (IGBT) or intelligent power modules (IPM). In addition, the realization of frequency conversion is inseparable from the single-chip microcomputer and the power switch tube driver.

[0003] At present, there are two ways to detect overcurrent of power switch tubes. One is to detect the output load current of the switch tube, and the other is to detect the on-voltage of the switch tube based on the saturation characteristics of the power switch tube. After the detection is completed, both methods need to transmit the fault signal to the input end of the driver, and then control the output end to output the shutdown signal according to the internal control logic of the driver. The output end signal of the driver cannot be directly turned off, that is, the end that directly drives the power switch tube. Therefore, the IGBT, MOSFET or IPM cannot be quickly turned off to form a fast protection. Summary of the invention

[0004] The problem solved by the present invention is how to quickly turn off the power switch tube when the power switch tube outputs an overcurrent.

[0005] In order to solve the above problems, the present invention provides an overcurrent protection circuit for a power switch tube, comprising: a driver, a power switch tube, a comparator, a gate driving circuit, a voltage sampling circuit, a reference voltage circuit and a driver output end power supply shutdown circuit; the gate driving circuit is connected to the driver at one end and to the gate of the power switch tube at the other end; the voltage sampling circuit is connected to the power switch tube at one end and to the first input end of the comparator at one end, and is used to collect the desaturation voltage of the power switch tube and output it to the first input end of the comparator; the reference voltage circuit is connected to the second input end of the comparator, and the reference voltage circuit generates a reference voltage and outputs it to the second input end of the comparator; the driver output end power supply shutdown circuit is connected to the output end of the comparator at one end and to the driver at one end, and is used to control the on and off of the driver output end power supply; the comparator compares the desaturation voltage with the reference voltage and outputs a low level or a high level to the driver output end power supply shutdown circuit, controls the on and off of the driver output end power supply, and controls the on and off of the gate driving signal at the driver output end, thereby controlling the on and off of the power switch tube through the gate driving circuit.

[0006] The present invention directly turns off the driving signal at the output end of the driver based on desaturation detection, and does not need to go through the control logic inside the driver to turn off the driving signal at the output end, thereby achieving the purpose of quickly turning off the power switch tube.

[0007] Furthermore, the output terminal of the driver includes a power supply V C , gate drive terminal V G and the common terminal V E .

[0008] Furthermore, the power supply of the comparator and the power supply V of the output end of the driver C The common terminal of the comparator and the common terminal of the driver output are V E Same potential.

[0009] Furthermore, the power switch tube is a metal oxide semiconductor field effect transistor (MOSFET) or an insulated gate bipolar transistor (IGBT).

[0010] Further, the gate drive circuit is composed of an eighth resistor, a ninth resistor and a capacitor, and one end of the eighth resistor is connected to the gate drive terminal V G The ninth resistor has one end connected to the gate of the IGBT or MOSFET and the other end connected to the emitter of the IGBT or the source of the MOSFET. One end of the capacitor is connected to the gate drive terminal V of the IGBT or MOSFET driver. G One end of a ninth resistor is connected to the gate of the IGBT or MOSFET, and the other end is connected to the gate of the IGBT or MOSFET. One end of the ninth resistor is connected to the gate of the IGBT or MOSFET, and the other end is connected to the emitter of the IGBT or the source of the MOSFET.

[0011] The driver's driving signal controls the power switch tube through the gate driving circuit, and the gate driving circuit also plays the role of current limiting and filtering.

[0012] Further, the voltage sampling circuit is composed of a first diode, a seventh resistor, a fifth resistor and a sixth resistor, the cathode of the first diode is connected to the IGBT collector or the MOSFET drain, the anode of the first diode is connected in series with one end of the seventh resistor, the other end of the seventh resistor is connected to the first input end of the comparator, and one end of the fifth resistor is connected to the IGBT or MOSFET gate drive power supply V C One end of a sixth resistor is connected to the first input terminal of the comparator, and the other end is connected to the common terminal V E connect.

[0013] The voltage sampling circuit is used to detect the collector V of the IGBT. C -Emitter V E The voltage between V CE or the drain of the MOSFET V D - Source V S The voltage between V DS and outputs it to the first input terminal of the comparator.

[0014] Furthermore, the reference voltage circuit is composed of a third resistor and a fourth resistor, and one end of the third resistor is connected to the IGBT or MOSFET gate drive power supply V C One end of the fourth resistor is connected to the second input terminal of the comparator, and the other end is connected to the common terminal V E connect.

[0015] The reference voltage circuit outputs a reference voltage to the second input terminal of the comparator after voltage division by the third resistor and the fourth resistor. The reference voltage is equal to the voltage protection value of the power switch tube.

[0016] Furthermore, the driver output power shutoff circuit is composed of a transistor, a first resistor and a second resistor, and the emitter of the transistor is connected to the driver output power supply V C The base of the transistor is connected to the output end of the comparator, and the collector of the transistor is connected to the output end power supply V C Connect one end of the first resistor to the IGBT or MOSFET gate drive power supply V C One end of the second resistor is connected to the output end of the comparator, and the other end is connected to the common terminal V of the driver. E connect.

[0017] If the voltage at the first input terminal is less than the reference voltage at the second output terminal, the comparator outputs a low level. When the comparator outputs a low level, the transistor is in the saturation region, and the transistor is in the on state at this time, which is equivalent to a wire; if the voltage at the first input terminal is greater than the reference voltage at the second output terminal, the comparator outputs a high level. When the comparator outputs a high level, the transistor is in the cut-off region, the transistor is disconnected, and the power supply of the driver output terminal is turned off.

[0018] Furthermore, it also includes a discharge circuit, which is composed of a second diode and a tenth resistor, wherein the anode of the second diode is connected to the gate of the IGBT or MOSFET, the cathode of the second diode is connected in series with one end of the tenth resistor, and the other end of the tenth resistor is connected to the gate drive power supply V C connect.

[0019] When the power switch tube is connected, the second diode in the discharge circuit is in the cut-off state. When the power switch tube is disconnected, a large voltage difference will be generated between the collector and the gate. Since the power switch tube has parasitic capacitance, namely Miller capacitance, this voltage difference will generate parasitic current, namely Miller current, through Miller capacitance. At this time, the second diode is connected, and the Miller current is discharged through the discharge circuit, so that all components are reset.

[0020] The present invention also provides an overcurrent protection method for a power switch tube, based on the overcurrent protection circuit of the power switch tube, comprising the following steps:

[0021] The voltage sampling circuit detects the desaturation voltage of the power switch tube in real time;

[0022] The comparator compares the desaturation voltage with a reference voltage generated by a reference voltage circuit;

[0023] When the desaturation voltage is greater than the reference voltage, the comparator outputs a high level;

[0024] When the comparator outputs a high level, the power supply shutdown circuit at the driver output is disconnected, the power supply at the driver output is disconnected, and the gate drive signal of the power switch tube is disconnected, so that the power switch tube is disconnected. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the provided drawings without paying creative work.

[0026] Figure 1 is a schematic diagram of the overcurrent protection circuit in Example 1;

[0027] Figure 2 This is a schematic diagram of the overcurrent protection method in Example 2.

[0028] Description of reference numerals:

[0029] 100-driver; 101-power switch tube; 102-comparator; 103-gate drive circuit; 105-voltage sampling circuit; 106-reference voltage circuit; 107-driver output power shutdown circuit; 201-transistor; 202-first resistor; 203-second resistor; 204-third resistor; 205-fourth resistor; 206-fifth resistor; 207-sixth resistor; 208-seventh resistor; 209-first diode; 210-eighth resistor; 211-capacitor; 212-ninth resistor; 213-second diode; 214-tenth resistor. DETAILED DESCRIPTION

[0030] At present, there are two ways to protect the power switch tube from overcurrent. One is to detect the output load current of the switch tube. The specific detection principle of this method is that the load current is converted into a voltage signal through a converter, and the signal is amplified by an amplifier and compared with the set threshold signal (the threshold signal corresponds to the current protection value of the switch tube). When it is greater than the threshold voltage, a fault signal is output to the microcontroller, and the microcontroller then sends a shutdown command to the switch tube driver to disconnect the power switch tube, or the fault signal is transmitted to the input end of the switch tube driver, and the output end of the driver is controlled by the internal functional logic of the driver to output a shutdown signal to disconnect the power switch tube.

[0031] Another way is to detect the on-state voltage of the switch tube according to the saturation characteristics of the power switch tube and implement fast desaturation detection in the switch tube. During IGBT overload, the collector-emitter voltage VCE increases rapidly, and the IGBT leaves the saturation state, that is, desaturation. Similarly, during overload for MOSFET, the increase in load current will cause the drain-source voltage VDS to increase rapidly. When the voltage is detected and compared with the set threshold voltage, when it is greater than the threshold voltage, a fault signal is output to the microcontroller, and the microcontroller then issues a shutdown command to the switch driver to disconnect the power switch tube, or transmit it to the input end of the switch tube driver chip, and the output end of the driver is controlled by the internal functional logic of the driver chip to output a shutdown signal to disconnect the power switch tube.

[0032] These two methods cannot quickly shut down the IGBT, MOSFET or IPM to form a fast protection.

[0033] For the two methods of overcurrent detection of power switch tubes, directly detecting the saturation voltage drop of the switch tube in the on state is the most direct and faster than the method of detecting through load current. Therefore, the present invention directly turns off the driver output signal based on the detection of the saturation voltage drop, and does not need to go through the control logic inside the driver to turn off the output signal, thereby achieving the purpose of quickly turning off the power switch tube.

[0034] In order to make the above-mentioned objects, features and advantages of the present invention more clearly understood, the specific embodiments of the present invention are described in detail below in conjunction with the accompanying drawings. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0035] Example 1

[0036] An overcurrent protection circuit for a power switch tube includes: a driver 100, a power switch tube 101, a comparator 102, a gate drive circuit 103, a voltage sampling circuit 105, a reference voltage circuit 106 and a driver output power shutoff circuit 107;

[0037] The gate drive circuit 103 is connected to the driver 100 at one end and to the gate of the power switch tube 101 at another end; the voltage sampling circuit 105 is connected to the power switch tube 101 at one end and to the first input end of the comparator 102 at another end, and is used to collect the desaturation voltage of the power switch tube 101 and output it to the first input end of the comparator 102; the reference voltage circuit 106 is connected to the second input end of the comparator 102, and the reference voltage circuit 106 generates a reference voltage and outputs it to the second input end of the comparator 102; the driver output end power supply shutdown circuit 107 is connected to the output end of the comparator 102 at one end and to the driver 100 at another end, and is used to control the on and off of the driver output end power supply;

[0038] The comparator 102 compares the desaturation voltage with the reference voltage and outputs a low level or a high level to the power supply shutdown circuit 107 at the output end of the driver, controls the on and off of the power supply at the output end of the driver, controls the on and off of the gate drive signal at the output end of the driver 100, and thus controls the on and off of the power switch tube 101 through the gate drive circuit 103.

[0039] The present invention directly turns off the driving signal at the output end of the driver based on desaturation detection, and does not need to go through the control logic inside the driver to turn off the driving signal at the output end, thereby achieving the purpose of quickly turning off the power switch tube.

[0040] The output terminal of the driver 100 includes a power supply V C , gate drive terminal V G and the common terminal V E ;

[0041] The power switch tube 101 is a metal oxide semiconductor field effect transistor (MOSFET) or an insulated gate bipolar transistor (IGBT).

[0042] The IGBT or MOSFET includes a freewheeling diode to provide freewheeling current to the inductive load when the IGBT or MOSFET is turned off.

[0043] The power supply of the comparator 102 and the power supply V of the output terminal of the driver 100 C The common terminal of the comparator 102 and the common terminal of the output terminal of the driver 100 are at the same potential. E Same potential.

[0044] The gate drive circuit 103 is composed of an eighth resistor 210, a ninth resistor 212 and a capacitor 211. One end of the eighth resistor 210 is connected to the gate drive terminal V G The ninth resistor 212 is connected to the gate of the IGBT or MOSFET at one end and connected to the emitter of the IGBT or the source of the MOSFET at the other end. The capacitor 211 is connected to the gate drive terminal V of the IGBT or MOSFET driver 100 at one end and connected to the gate of the IGBT or MOSFET at the other end. G One end of the ninth resistor 212 is connected to the gate of the IGBT or MOSFET, and the other end is connected to the emitter of the IGBT or the source of the MOSFET.

[0045] The driving signal of the driver controls the power switch tube 101 through the gate driving circuit 103, and the gate driving circuit plays the role of current limiting and filtering at the same time.

[0046] The voltage sampling circuit 105 is composed of a first diode 209, a seventh resistor 208, a fifth resistor 206 and a sixth resistor 207. The cathode of the first diode 209 is connected to the collector of the IGBT or the drain of the MOSFET. The anode of the first diode 209 is connected in series with one end of the seventh resistor 208. The other end of the seventh resistor 208 is connected to the first input end of the comparator 102. One end of the fifth resistor 206 is connected to the gate drive power supply V C One end of the sixth resistor 207 is connected to the first input terminal of the comparator 102, and the other end is connected to the common terminal V E connect.

[0047] The voltage sampling circuit 105 is used to detect the collector V of the IGBT. C -Emitter V E The voltage between V CE or the drain of the MOSFET V D - Source V S The voltage between V DS , and outputs it to the first input terminal of the comparator 102.

[0048] When the power switch tube 101 is disconnected, the cathode voltage of the first diode 209 is equal to the bus voltage V ps, that is, the voltage after rectification and filtering is much larger than the anode voltage of the first diode 209. Therefore, the first diode 209 remains disconnected when the power switch tube 101 is disconnected. When the power switch tube 101 is connected, the saturation conduction voltage is very small, the cathode voltage of the first diode 209 is smaller than the anode voltage, and the first diode 209 is turned on. At this time, the voltage at the first input terminal of the comparator 102 is the saturation voltage of the power switch tube 101 plus the conduction voltage of the diode 209 plus the voltage across the resistor 208: V 入1 =V CE / DS +V D209 +V R208 , in order to detect the saturation conduction voltage drop of the power switch tube 101. During the overload period of the power switch tube 101, V CE or V DS Rapidly increases, and at the same time the power switch tube 101 leaves the saturation state, that is, the desaturation state. At this time, V 入1 The size of V CE or V DS size.

[0049] The reference voltage circuit 106 is composed of a third resistor 204 and a fourth resistor 205. One end of the third resistor 204 is connected to the IGBT or MOSFET gate drive power supply V C The fourth resistor 205 is connected to the second input terminal of the comparator 102, and the other end is connected to the common terminal V E connect.

[0050] The reference voltage circuit 106 outputs a reference voltage to the second input terminal of the comparator 102 after voltage division by the third resistor 204 and the fourth resistor 205 . The reference voltage is equal to the voltage protection value of the power switch tube 101 .

[0051] The driver output power shutoff circuit 107 is composed of a transistor 201, a first resistor 202 and a second resistor 203. The emitter of the transistor 201 is connected to the output power supply V C The base of transistor 201 is connected to the output terminal of comparator 102, and the collector of transistor 201 is connected to the output terminal power supply V of driver 100. C Connect one end of the first resistor 202 to the IGBT or MOSFET gate drive power supply V C One end of the second resistor 203 is connected to the output end of the comparator 102, and the other end is connected to the common terminal V of the driver 100. E connect.

[0052] If the first input terminal V 入1If the reference voltage of the first input terminal is less than the reference voltage of the second output terminal, the comparator 102 outputs a low level. When the comparator 102 outputs a low level, the transistor 201 is in the saturation region. The transistor is in the on state at this time, which is equivalent to a wire. If the V 入1 When the voltage of the comparator 102 is greater than the reference voltage of the second output terminal, the comparator 102 outputs a high level. When the comparator 102 outputs a high level, the transistor 201 is in the cut-off region, the transistor 201 is disconnected, and the power supply of the driver output terminal is turned off.

[0053] The protection circuit further includes a discharge circuit 104, which is composed of a second diode 213 and a tenth resistor 214. The anode of the second diode 213 is connected to the gate of the IGBT or MOSFET, the cathode of the second diode 213 is connected in series with one end of the tenth resistor 214, and the other end of the tenth resistor 214 is connected to the gate drive power supply V C connect.

[0054] When the power switch tube 101 is connected, the second diode 213 in the discharge circuit 104 is in the cut-off state. When the power switch tube 101 is disconnected, a large voltage difference will be generated between the collector and the gate. Since the power switch tube 101 has a parasitic capacitor, namely the Miller capacitor, this voltage difference will generate a parasitic current, namely the Miller current, through the Miller capacitor. At this time, the second diode 213 is connected, and the Miller current is discharged through the discharge circuit 104, so that all components are reset.

[0055] Example 2

[0056] A method for overcurrent protection of a power switch tube, based on the overcurrent protection circuit of the power switch tube in embodiment 1,

[0057] Step S1, the voltage sampling circuit 105 detects the desaturation voltage of the power switch tube 101 in real time;

[0058] Step S2, the comparator 102 compares the desaturation voltage with the reference voltage generated by the reference voltage circuit 106;

[0059] Step S3: When the desaturation voltage is greater than the reference voltage, the comparator 102 outputs a high level;

[0060] Step S4, when the comparator 102 outputs a high level, the driver output power shutdown circuit 107 is disconnected, the driver output power is disconnected, and the gate drive signal of the power switch tube 101 is disconnected, so that the power switch tube 101 is disconnected.

[0061] Finally, it should be noted that, in this article, relational terms such as first and second, etc. are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Moreover, the terms "include", "comprise" or any other variants thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or device. In the absence of further restrictions, the elements defined by the sentence "comprise a ..." do not exclude the presence of other identical elements in the process, method, article or device including the elements.

[0062] The above description of the disclosed embodiments enables one skilled in the art to implement or use the present invention. Various modifications to these embodiments will be apparent to one skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to the embodiments shown herein, but rather to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. An overcurrent protection circuit for a power switch tube, characterized in that: include: A driver (100), a power switch tube (101), a comparator (102), a gate drive circuit (103), a voltage sampling circuit (105), a reference voltage circuit (106) and a driver output end power supply shutoff circuit (107); One end of the gate drive circuit (103) is connected to the driver (100), and the other end is connected to the gate of the power switch tube (101); The voltage sampling circuit (105) has one end connected to the power switch tube (101) and one end connected to the first input end of the comparator (102), and is used to collect the desaturation voltage of the power switch tube (101) and output it to the first input end of the comparator (102); The reference voltage circuit (106) is connected to the second input terminal of the comparator (102), and the reference voltage circuit (106) generates a reference voltage and outputs it to the second input terminal of the comparator (102); The driver output end power shutoff circuit (107) has one end connected to the output end of the comparator (102) and one end connected to the driver (100), and is used to control the on and off of the driver output end power supply; The comparator (102) compares the desaturation voltage with the reference voltage and outputs a low level or a high level to the driver output end power shutoff circuit (107), thereby controlling the on and off of the driver output end power supply, and controlling the on and off of the gate drive signal at the output end of the driver (100), thereby controlling the on and off of the power switch tube (101) through the gate drive circuit (103); The power switch tube (101) is a metal oxide semiconductor field effect transistor MOSFET or an insulated gate bipolar transistor IGBT; The gate drive circuit (103) is composed of an eighth resistor (210), a ninth resistor (212) and a capacitor (211), wherein one end of the eighth resistor (210) is connected to a gate drive terminal V G The ninth resistor (212) has one end connected to the gate of the IGBT or the MOSFET and the other end connected to the emitter of the IGBT or the source of the MOSFET. The capacitor (211) has one end connected to the gate drive terminal V of the IGBT or the MOSFET driver (100). G A ninth resistor (212) has one end connected to the gate of the IGBT or the MOSFET and the other end connected to the emitter of the IGBT or the source of the MOSFET; The voltage sampling circuit (105) is composed of a first diode (209), a seventh resistor (208), a fifth resistor (206) and a sixth resistor (207); the cathode of the first diode (209) is connected to the collector of the IGBT or the drain of the MOSFET; the anode of the first diode (209) is connected in series with one end of the seventh resistor (208); the other end of the seventh resistor (208) is connected to the first input end of the comparator (102); one end of the fifth resistor (206) is connected to the gate drive power supply V C One end of a sixth resistor (207) is connected to the first input end of the comparator (102), and the other end is connected to the common end V of the driver (100). E connect; The driver output power shutoff circuit (107) is composed of a transistor (201), a first resistor (202) and a second resistor (203). The emitter of the transistor (201) is connected to the driver (100) output power supply V C The base of the transistor (201) is connected to the output end of the comparator (102), and the collector of the transistor (201) is connected to the output end power supply V of the driver (100). C One end of the first resistor (202) is connected to the IGBT or MOSFET gate drive power supply V C One end of the second resistor (203) is connected to the output end of the comparator (102), and the other end is connected to the common terminal V of the driver (100). E connect.

2. The overcurrent protection circuit of a power switch tube according to claim 1, characterized in that: The power supply of the comparator (102) and the power supply V at the output end of the driver (100) are connected. C The common terminal of the comparator (102) and the common terminal of the output terminal of the driver (100) are at the same potential. E Same potential.

3. The overcurrent protection circuit of a power switch tube according to claim 1, characterized in that: The reference voltage circuit (106) is composed of a third resistor (204) and a fourth resistor (205), one end of the third resistor (204) being connected to the gate drive power supply V C The fourth resistor (205) has one end connected to the second input terminal of the comparator (102) and the other end connected to the common terminal V of the driver (100). E connect.

4. The overcurrent protection circuit of a power switch tube according to claim 1, characterized in that: The device also includes a discharge circuit (104), wherein the discharge circuit (104) is composed of a second diode (213) and a tenth resistor (214), wherein the anode of the second diode (213) is connected to the gate of the IGBT or the MOSFET, the cathode of the second diode (213) is connected in series with one end of the tenth resistor (214), and the other end of the tenth resistor (214) is connected to the gate drive power supply V C connect.

5. A method for overcurrent protection of a power switch tube, characterized in that: The overcurrent protection circuit of the power switch tube according to any one of claims 1 to 4 comprises the following steps: The voltage sampling circuit (105) detects the desaturation voltage of the power switch tube (101) in real time; The comparator (102) compares the desaturation voltage with a reference voltage generated by a reference voltage circuit (106); When the desaturation voltage is greater than the reference voltage, the comparator (102) outputs a high level; When the comparator (102) outputs a high level, the driver output power supply cutoff circuit (107) is disconnected, the driver output power supply is disconnected, and the gate drive signal of the power switch tube (101) is disconnected, so that the power switch tube (101) is disconnected.

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