An IGBT bus overcurrent detection circuit with adjustable output pulse width

Abstract

The present invention discloses an IGBT bus overcurrent detection circuit with adjustable output pulse width. The current is sampled by a milliohm resistor on the low side of the IGBT bus, and the converted voltage value is amplified by an operational amplifier and compared with a threshold voltage. The output signal of the comparator drives a triode to turn on and controls an isolation optocoupler to output an overcurrent alarm signal. At the same time, after the alarm occurs, the rectification and clamping of a diode are used to reduce the threshold voltage of the comparator, achieving the effects of fast response of the alarm output during overcurrent, delaying the closing of the alarm until the overcurrent completely disappears, and increasing the output pulse width of the alarm signal. It solves the problem of poor anti-interference ability of the hardware detection IGBT overcurrent circuit in the existing scheme.

Description

Technical Field

[0001] The present invention belongs to the field of servo drivers, and particularly relates to an IGBT bus overcurrent detection circuit with adjustable output pulse width. Background Art

[0002] In the product design of servo drivers, the overcurrent detection and protection of IGBTs are the key points to prevent IGBT damage. The short-circuit withstand time of an IGBT itself is generally within 10 μs. Due to the factor of the current loop control period, the software sampling protection method cannot guarantee the protection response when a short-circuit overcurrent occurs. Therefore, a hardware detection method is usually used to handle such alarms.

[0003] Traditional hardware solutions include:

[0004] Method 1: Motor phase current sampling comparison output alarm circuit. This solution monitors the motor output phase current in real time, uses a comparator circuit to set the overcurrent detection threshold, triggers the output alarm when overcurrent occurs, and then interrupts the IGBT conduction to achieve the effect of overcurrent detection and alarm.

[0005] The disadvantages of the motor phase current sampling comparison output alarm circuit are as follows: In practical applications, it is difficult to guarantee the accuracy of the phase current detection sampled by using a Hall sensor or a linear optocoupler plus an operational amplifier simulation circuit. In mass production, the consistency of the actual trigger current threshold of the overcurrent detection circuit is poor, and the anti-interference ability is poor.

[0006] Method 2: IGBT CE-pole oversaturation detection output alarm circuit, which is an active clamping protection; uses a gate driver chip with IGBT oversaturation detection to detect that the IGBT is oversaturated when a short circuit occurs, so that Vce rapidly rises above the circuit-set threshold, triggering and outputting an overcurrent alarm.

[0007] The disadvantages of the IGBT CE-pole oversaturation detection output alarm circuit are as follows: This circuit relies heavily on the accurate and stable value of the IGBT CE-pole saturation voltage Uce sat. For products from different IGBT manufacturers, the circuit parameters need to be adjusted. Otherwise, faults such as false alarms or untimely alarms are likely to occur. The test and verification period of this solution is long, the hardware circuit has poor versatility, has high requirements for the performance of the gate driver chip and IGBT, and the hardware cost is high. Summary of the Invention

[0008] To solve the technical problems existing in the background art, the present invention aims to provide an IGBT bus overcurrent detection circuit with adjustable output pulse width. The current is sampled by a milliohm resistor on the low side of the IGBT bus, and the converted voltage value is amplified by an operational amplifier and compared with a threshold voltage. The output signal of the comparator drives an isolation optocoupler to output an overcurrent alarm. The sampling of the bus current is the most direct way to judge whether there is overcurrent in the IGBT, and the actual detection effect of the circuit has nothing to do with the selection of the IGBT and its drive control circuit components and solutions.

[0009] To solve the technical problems, the technical solution of the present invention is as follows:

[0010] An IGBT bus overcurrent detection circuit with adjustable output pulse width, comprising: a current sampling and amplifying unit, a threshold comparison unit, and an alarm signal output unit;

[0011] The input end of the current sampling and amplifying unit is connected to the IGBT bus, the output signal of the current sampling and amplifying unit is connected to the input end of the threshold comparison unit, and the output end of the threshold comparison unit is connected to the alarm signal output unit;

[0012] The current sampling and amplifying unit is used to sample the current of the IGBT bus, filter and amplify the voltage signal obtained by the current sampling, and output the processed voltage signal to the threshold comparison unit;

[0013] The threshold comparison unit is used to compare the voltage signal input by the current sampling and amplifying unit with its own trigger threshold voltage for overcurrent detection; if the voltage signal is greater than the trigger threshold voltage, that is, after an overcurrent fault alarm occurs, a control signal is sent to turn on the light-emitting diode of the optocoupler of the alarm signal output unit, and at the same time, the trigger threshold voltage for its own overcurrent detection is pulled low; if the voltage signal is less than the trigger threshold voltage, that is, after the overcurrent fault alarm disappears, a control signal is sent to turn off the light-emitting diode of the optocoupler of the alarm signal output unit, and by changing the resistance value of its own resistor R3, the effect of adjustable alarm output pulse width is achieved;

[0014] The alarm signal output unit is used to isolate the control signal sent by the threshold comparison unit and output a digital signal, and after shaping the digital signal, output an overcurrent alarm fault level signal readable by the single-chip microcomputer.

[0015] It can be understood that the current is sampled through the milliohm resistor on the low side of the IGBT busbar. The converted voltage value is amplified by an operational amplifier and compared with the threshold voltage. The output signal of the comparator drives the triode to turn on to control the isolation optocoupler to output an overcurrent alarm signal. At the same time, after the alarm occurs, the rectification and clamping of the diode are used to reduce the threshold voltage of the comparator, achieving the effects of fast response of the alarm output during overcurrent, delaying the closing of the alarm until the overcurrent completely disappears, and increasing the output pulse width of the alarm signal. It solves the problem of poor anti-interference ability of the hardware detection IGBT overcurrent circuit in the existing solution.

[0016] Further, the current sampling and amplifying unit includes: a sampling resistor RES1, an operational amplifier U3A, a resistor R2, a resistor R7, a resistor R8, a resistor R9, a resistor R12, a capacitor C1, and a capacitor C7;

[0017] Both ends of the sampling resistor RES1 are connected to the input end and the output end of the IGBT busbar. One end of the resistor R8 is simultaneously connected to one end of the sampling resistor RES1 and grounded. One end of the resistor R9 is connected to the other end of the sampling resistor RES1. The other end of the resistor R9 is connected to pin 2 of the operational amplifier U3A. The other end of the resistor R8 is connected to pin 3 of the operational amplifier U3A. Pin 4 of the operational amplifier U3A is connected to -15V voltage. Pin 8 of the operational amplifier U3A is connected to +15V voltage. Pin 1 of the operational amplifier U3A is connected to one end of the resistor R7. One end of the capacitor C1 and one end of the resistor R2 are simultaneously connected to pin 3 of the operational amplifier U3A. The other end of the capacitor C1 is connected to the other end of the resistor R2. The other end of the resistor R2 is grounded. One end of the resistor R12 and one end of the capacitor C7 are simultaneously connected to pin 2 of the operational amplifier U3A. The other ends of the resistor R12 and the capacitor C7 are simultaneously connected to one end of the resistor R7.

[0018] Further, the threshold comparison unit includes: a comparator U3B, a voltage reference source UW1, a zener diode DZ1, a triode Q1, a Schottky diode DK1, a resistor R1, a resistor R3, a resistor R5, a resistor R10, a resistor R11, a resistor R13, a resistor R14, a capacitor C3, a capacitor C6, and a capacitor C8;

[0019] The other end of the resistor R7 is connected to pin 5 of the comparator U3B. Pin 6 of the comparator U3B is simultaneously connected to one end of the resistor R14 and port 1 of the Schottky diode DK1. Port 2 of the Schottky diode DK1 is connected to one end of the resistor R3. The other end of the resistor R3 is simultaneously connected to one ends of the resistor R5 and the resistor R1. The other end of the resistor R1 is connected to the +15V voltage. The other end of the resistor R5 is connected to the collector of the triode Q1. The other end of the resistor R14 is simultaneously connected to one end of the resistor R13, one end of the capacitor C8, and pins 1 and 2 of the voltage reference source UW1. The other end of the resistor R13 is grounded. The other end of the capacitor C8 is simultaneously connected to pin 3 of the voltage reference source UW1 and grounded. Pin 7 of the comparator U3B is connected to one end of the resistor R10. The other end of the resistor R10 is connected to the output end of the voltage stabilizing diode DZ1. The input end of the voltage stabilizing diode DZ1 is simultaneously connected to one end of the resistor R11 and the base of the triode Q1. The other end of the resistor R11 and the emitter of the triode Q1 are simultaneously connected to the -15V voltage. Pin 8 of the comparator U3B is simultaneously connected to the +15V voltage and one end of the capacitor C3. The other end of the capacitor C3 is grounded. Pin 4 of the comparator U3B is simultaneously connected to the -15V voltage and one end of the capacitor C6. The other end of the capacitor C6 is grounded.

[0020] Further, the alarm signal output unit includes: an optocoupler U1, a logic AND gate U2, a resistor R4, a capacitor C2, a capacitor C4, and a capacitor C5;

[0021] The other end of the resistor R1 is connected to pin 2 of the optocoupler U1. The other end of the resistor R5 is connected to pin 3 of the optocoupler U1. Pin 8 of the optocoupler U1 is connected to pin 7 of the optocoupler U1. Pin 8 of the optocoupler U1 and pin 7 of the optocoupler U1 are simultaneously connected to the +5V voltage. One end of the resistor R4 is simultaneously connected to pin 8 of the optocoupler U1 and pin 7 of the optocoupler U1. The other end of the resistor R4 is simultaneously connected to pin 6 of the optocoupler U1, one end of the capacitor C5, and pins 1 and 2 of the logic AND gate U2. One end of the capacitor C4 is simultaneously connected to pin 8 of the optocoupler U1 and pin 7 of the optocoupler U1. The other end of the capacitor C4 and the other end of the capacitor C5 are simultaneously connected to pin 5 of the optocoupler U1. Pin 5 of the optocoupler U1 is grounded; pin 3 of the logic AND gate U2 is grounded. Pin 5 of the logic AND gate U2 is connected to the +5V voltage. One end of the capacitor C2 is connected to pin 5 of the logic AND gate U2. The other end of the capacitor C2 is grounded.

[0022] Further, the resistor R9 and the resistor R12 simultaneously control the amplification ratio of the operational amplifier U3A; the capacitor C7 and the resistor R12 form a filtering module to filter the noise in the sampled voltage of the sampling resistor RES1.

[0023] Further, the voltage reference source UW1 and the resistor R13 form a reference voltage, which serves as the trigger threshold voltage for overcurrent detection;

[0024] The reference voltage signal and the voltage signal output by the current sampling and amplifying unit are input into the comparator U3B after passing through the resistor R7 and the resistor R8. When the voltage signal output by the current sampling and amplifying unit is greater than the trigger threshold voltage for overcurrent detection, the output of pin 7 of the comparator U3B starts to turn on. When the voltage signal output by the current sampling and amplifying unit exceeds the stable voltage Vz of the zener diode DZ1, the triode Q1 is turned on and the optocoupler U1 is turned on.

[0025] Further, after the optocoupler U1 is turned on, the voltage of pin 2 of the optocoupler U1 is: the sum of the collector-emitter voltage drop Vce of the triode Q1 and the forward conduction voltage drop Vf of the light-emitting diode in the optocoupler U1 when it is turned on;

[0026] The trigger threshold voltage for overcurrent detection at pin 6 of the comparator U3B is clamped to the voltage of pin 2 of the optocoupler U1 plus the forward voltage drop Vf of the Schottky diode DK through the circuit composed of the Schottky diode DK1 with a low forward conduction voltage drop and the resistor R3; at this time, the output of pin 7 of the comparator U3B continues to output, keeping the light-emitting diode of the optocoupler U1 turned on until the voltage signal output by the current sampling and amplifying unit drops to the clamped reference level at pin 6 of the comparator U3B, and then the output of pin 7 of the comparator U3B is turned off and the light-emitting diode of the optocoupler U1 is turned off.

[0027] Further, the logic AND gate U2 shapes the overcurrent alarm signal sent by the optocoupler U1 and outputs the overcurrent alarm signal, namely / OCL_O.

[0028] Further, the current value of the IGBT bus is Ibus, and the voltage value Vres = Ibus * Rres obtained by the sampling resistor RES1 collecting the current Ibus; the operational amplifier U3A outputs the amplified voltage signal Vop = Vres * R12 / R9, that is, Vop = Ibus * Rres * R12 / R9;

[0029] The trigger threshold voltage VH for overcurrent detection of the comparator U3B at this time th - = Vref = 2.495V. When Vop > VH th - that is when, the overcurrent alarm is triggered and output;

[0030] After the overcurrent alarm is triggered and output, the trigger threshold voltage for overcurrent detection of the comparator U3B is clamped, and the clamped voltage

[0031] When the IGBT output is turned off and Vop drops to Vop < VL th at this time, the alarm output ends.

[0032] Further, the logic AND gate U2 adopts the 74 series logic AND gate U2.

[0033] It can be understood that the IGBT bus is the source of IGBT power output. Detecting the IGBT bus current through a sampling resistor is the most direct way to detect whether there is overcurrent in the IGBT. The operational amplifier circuit can amplify the voltage signal obtained by resistor sampling, reduce the power loss of the resistor, and reduce the negative impact caused by the increase in the temperature of the resistor itself. At the same time, it can improve the detection range of the current. A reasonable filtering circuit weakens the interference caused by the introduced noise in the circuit to the detection circuit. The circuit of the threshold comparison unit automatically reduces the comparison reference voltage after triggering overcurrent until the overcurrent is eliminated and the pulse output of the alarm signal is turned off. This mechanism greatly improves the reliability of the detection circuit.

[0034] Compared with the prior art, the advantages of the present invention are as follows:

[0035] The present invention samples the current through a milliohm resistor on the low side of the IGBT bus. The converted voltage value is amplified by an operational amplifier and compared with the threshold voltage. The output signal of the comparator drives an isolation optocoupler to output an overcurrent alarm; sampling the bus current is the most direct detection of whether there is overcurrent in the IGBT; the actual detection effect of the circuit is independent of the selection of IGBT and its drive control circuit components and schemes.

[0036] The present invention has strong anti-interference ability. When the output current triggers the overcurrent threshold in on-site applications, the comparator delays the output turn-off time of the comparator by automatically changing the comparison reference voltage, so that the alarm output circuit outputs a sufficient signal pulse width to be captured by the subsequent circuit; after the overcurrent disappears, the trigger threshold for the next alarm automatically returns to the reference level signal generated by the voltage reference source; therefore, the threshold value for each overcurrent trigger is only related to the reference voltage generated by the voltage reference source, and the trigger thresholds of the circuits of different products are highly consistent. Brief Description of the Drawings

[0037] Figure 1 The principle block diagram of an IGBT bus overcurrent detection circuit with adjustable output pulse width according to the present invention;

[0038] Figure 2 The connection diagram of an IGBT bus overcurrent detection circuit with adjustable output pulse width according to the present invention;

[0039] Figure 3 The simulation diagram before pulse width adjustment of the present invention;

[0040] Figure 4 The simulation diagram after pulse width adjustment of the present invention. Detailed Embodiments

[0041] The following describes the specific embodiments of the present invention in conjunction with the embodiments:

[0042] It should be noted that the structures, ratios, sizes, etc. shown in 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. Any modification of the structure, change of the proportional relationship, or adjustment of the size, without affecting the effects that the present invention can produce and the purposes that can be achieved, should still fall within the scope covered by the technical content disclosed in the present invention.

[0043] At the same time, the terms such as "upper", "lower", "left", "right", "middle", and "one" cited in this specification are only for the convenience of clear narration and are not used to limit the scope of implementation of the present invention. The change or adjustment of their relative relationship, without substantial change in the technical content, should also be regarded as the scope in which the present invention can be implemented.

[0044] Embodiment 1

[0045] An IGBT bus overcurrent detection circuit with adjustable output pulse width includes: a current sampling and amplifying unit, a threshold comparison unit, and an alarm signal output unit;

[0046] The input end of the current sampling and amplifying unit is connected to the IGBT bus, the output end signal of the current sampling and amplifying unit is connected to the input end of the threshold comparison unit, and the output end signal of the threshold comparison unit is connected to the alarm signal output unit;

[0047] The current sampling and amplifying unit is used to sample the current of the IGBT bus, filter and amplify the voltage signal obtained by the current sampling, and output the processed voltage signal to the threshold comparison unit;

[0048] The threshold comparison unit is used to compare the voltage signal input by the current sampling and amplifying unit with its own trigger threshold voltage for overcurrent detection; if the voltage signal is greater than the trigger threshold voltage, that is, after an overcurrent fault alarm occurs, a control signal is sent to turn on the light-emitting diode of the optocoupler of the alarm signal output unit, and at the same time, its own trigger threshold voltage for overcurrent detection is pulled low; if the voltage signal is less than the trigger threshold voltage, that is, after the overcurrent fault alarm disappears, a control signal is sent to turn off the light-emitting diode of the optocoupler of the alarm signal output unit, and by changing the resistance value of its own resistor R3, the effect of adjustable pulse width of the alarm output is achieved;

[0049] The alarm signal output unit is used to isolate the control signal sent by the threshold comparison unit and output a digital signal, and after shaping the digital signal, output an overcurrent alarm fault level signal readable by the single-chip microcomputer.

[0050] It can be understood that the current is sampled through the milliohm resistor on the low side of the IGBT busbar. The converted voltage value is amplified by an operational amplifier and then compared with the threshold voltage. The output signal of the comparator drives the triode to turn on and controls the isolation optocoupler to output an overcurrent alarm signal. At the same time, after the alarm occurs, the rectification and clamping of the diode are used to reduce the threshold voltage of the comparator, achieving the effects of fast response of the alarm output during overcurrent, delaying the closing of the alarm until the overcurrent completely disappears, and increasing the output pulse width of the alarm signal. It solves the problem of poor anti-interference ability of the hardware detection IGBT overcurrent circuit in the existing solution.

[0051] Further, the current sampling and amplifying unit includes: a sampling resistor RES1, an operational amplifier U3A, resistors R2, R7, R8, R9, R12, a capacitor C1, and a capacitor C7;

[0052] Both ends of the sampling resistor RES1 are connected to the input end and the output end of the IGBT busbar. One end of the resistor R8 is simultaneously connected to one end of the sampling resistor RES1 and grounded. One end of the resistor R9 is connected to the other end of the sampling resistor RES1. The other end of the resistor R9 is connected to pin 2 of the operational amplifier U3A. The other end of the resistor R8 is connected to pin 3 of the operational amplifier U3A. Pin 4 of the operational amplifier U3A is connected to a -15V voltage. Pin 8 of the operational amplifier U3A is connected to a +15V voltage. Pin 1 of the operational amplifier U3A is connected to one end of the resistor R7. One end of the capacitor C1 and one end of the resistor R2 are simultaneously connected to pin 3 of the operational amplifier U3A. The other end of the capacitor C1 is connected to the other end of the resistor R2, and the other end of the resistor R2 is grounded. One end of the resistor R12 and one end of the capacitor C7 are simultaneously connected to pin 2 of the operational amplifier U3A. The other ends of the resistor R12 and the capacitor C7 are simultaneously connected to one end of the resistor R7.

[0053] Further, the threshold comparison unit includes: a comparator U3B, a voltage reference source UW1, a zener diode DZ1, a triode Q1, a Schottky diode DK1, resistors R1, R3, R5, R10, R11, R13, R14, capacitors C3, C6, and a capacitor C8;

[0054] The other end of the resistor R7 is connected to pin 5 of the comparator U3B. Pin 6 of the comparator U3B is connected to one end of the resistor R14 and port 1 of the Schottky diode DK1 at the same time. Port 2 of the Schottky diode DK1 is connected to one end of the resistor R3. The other end of the resistor R3 is connected to one end of the resistor R5 and the resistor R1 at the same time. The other end of the resistor R1 is connected to the +15V voltage. The other end of the resistor R5 is connected to the collector of the triode Q1. The other end of the resistor R14 is connected to one end of the resistor R13, one end of the capacitor C8, and pins 1 and 2 of the voltage reference source UW1 at the same time. The other end of the resistor R13 is grounded. The other end of the capacitor C8 is connected to pin 3 of the voltage reference source UW1 and grounded at the same time. Pin 7 of the comparator U3B is connected to one end of the resistor R10. The other end of the resistor R10 is connected to the output end of the voltage regulator diode DZ1. The input end of the voltage regulator diode DZ1 is connected to one end of the resistor R11 and the base of the triode Q1 at the same time. The other end of the resistor R11 and the emitter of the triode Q1 are connected to the -15V voltage at the same time.

[0055] Further, the alarm signal output unit includes: an optocoupler U1, a logic AND gate U2, a resistor R4, a capacitor C2, a capacitor C4, and a capacitor C5;

[0056] The other end of the resistor R1 is connected to pin 2 of the optocoupler U1. The other end of the resistor R5 is connected to pin 3 of the optocoupler U1. Pin 8 of the optocoupler U1 is connected to pin 7 of the optocoupler U1. Pin 8 of the optocoupler U1 and pin 7 of the optocoupler U1 are connected to the +5V voltage at the same time. One end of the resistor R4 is connected to pin 8 of the optocoupler U1 and pin 7 of the optocoupler U1 at the same time. The other end of the resistor R4 is connected to pin 6 of the optocoupler U1, one end of the capacitor C5, and pins 1 and 2 of the logic AND gate U2 at the same time. One end of the capacitor C4 is connected to pin 8 of the optocoupler U1 and pin 7 of the optocoupler U1 at the same time. The other end of the capacitor C4 and the other end of the capacitor C5 are connected to pin 5 of the optocoupler U1 at the same time. Pin 5 of the optocoupler U1 is grounded; Pin 3 of the logic AND gate U2 is grounded. Pin 5 of the logic AND gate U2 is connected to the +5V voltage. One end of the capacitor C2 is connected to pin 5 of the logic AND gate U2. The other end of the capacitor C2 is grounded.

[0057] Further, the resistors R9 and R12 control the amplification ratio of the operational amplifier U3A at the same time; the capacitor C7 and the resistor R12 form a filtering module to filter out the noise in the sampled voltage of the sampling resistor RES1.

[0058] Further, the voltage reference source UW1 and the resistor R13 form a reference voltage, which is used as the trigger threshold voltage for overcurrent detection;

[0059] The reference voltage signal and the voltage signal output by the current sampling and amplifying unit are input into the comparator U3B after passing through the resistor R7 and the resistor R8. When the voltage signal output by the current sampling and amplifying unit is greater than the trigger threshold voltage for overcurrent detection, the output of pin 7 of the comparator U3B starts to turn on. When the voltage signal output by the current sampling and amplifying unit exceeds the stable voltage Vz of the zener diode DZ1, the triode Q1 is turned on and the optocoupler U1 is turned on.

[0060] Further, when the optocoupler U1 is turned on, the voltage of pin 2 of the optocoupler U1 is: the sum of the CE voltage drop Vce of the triode Q1 and the forward conduction voltage drop Vf of the light-emitting diode in the optocoupler U1 when it is turned on;

[0061] The trigger threshold voltage for overcurrent detection at pin 6 of the comparator U3B is clamped to the voltage of pin 2 of the optocoupler U1 plus the forward voltage drop Vf of the Schottky diode DK through the circuit composed of the Schottky diode DK1 with a low forward conduction voltage drop and the resistor R3; at this time, the output of pin 7 of the comparator U3B continues to output, keeping the light-emitting diode of the optocoupler U1 turned on until the voltage signal output by the current sampling and amplifying unit drops to the clamped reference level at pin 6 of the comparator U3B, and then the output of pin 7 of the comparator U3B is turned off and the light-emitting diode of the optocoupler U1 is turned off.

[0062] Further, the logic AND gate U2 shapes the overcurrent alarm signal emitted by the optocoupler U1 and outputs the overcurrent alarm signal, namely / OCL_O.

[0063] Further, the current value of the IGBT bus is Ibus, and the voltage value Vres = Ibus * Rres obtained by the sampling resistor RES1 for sampling the current Ibus; the operational amplifier U3A outputs the amplified voltage signal Vop = Vres * R12 / R9, that is, Vop = Ibus * Rres * R12 / R9;

[0064] The trigger threshold voltage VH for overcurrent detection of the comparator U3B at this time th - = Vref = 2.495V. When Vop > VH th - that is when, the overcurrent alarm is triggered and output;

[0065] After the overcurrent alarm is triggered and output, the trigger threshold voltage for overcurrent detection of the comparator U3B is clamped, and the clamped voltage

[0066] When the IGBT output is turned off and Vop drops to Vop < VL th then, the alarm output ends.

[0067] Further, the logic AND gate U2 uses a 74-series logic AND gate U2.

[0068] It can be understood that the IGBT bus is the source of IGBT power output. Detecting the IGBT bus current through a sampling resistor is the most direct way to detect whether there is overcurrent in the IGBT. The operational amplifier circuit can amplify the voltage signal obtained by resistor sampling, reduce the power loss of the resistor, and reduce the negative impact caused by the increase in the temperature of the resistor itself. At the same time, it can improve the detection range of the current. A reasonable filtering circuit weakens the interference caused by the introduced noise in the circuit to the detection circuit. The circuit of the threshold comparison unit automatically reduces the comparison reference voltage after triggering overcurrent until the overcurrent is eliminated and the pulse output of the alarm signal is turned off. This mechanism greatly improves the reliability of the detection circuit.

[0069] Embodiment 2:

[0070] In this embodiment, the current is sampled by a milliohm resistor on the low side of the IGBT bus. The converted voltage value is amplified by an operational amplifier and compared with the threshold voltage. The output signal of the comparator drives an isolation optocoupler to output an overcurrent alarm. Sampling the bus current is the most direct detection of whether there is overcurrent in the IGBT. The actual detection effect of the circuit has nothing to do with the selection of IGBT and its drive control circuit components and schemes.

[0071] The anti-interference ability of the present invention is relatively strong. When the output current in on-site application triggers the overcurrent threshold, the comparator delays the turn-off time of the output by automatically changing the comparison reference voltage, so that the alarm output circuit outputs a sufficient signal pulse width to be captured by the subsequent circuit. After the overcurrent disappears, the trigger threshold for the next alarm automatically returns to the reference level signal generated by the voltage reference source. Therefore, the threshold value for each overcurrent trigger is only related to the reference voltage generated by the voltage reference source, and the trigger thresholds of the circuits of different products have high consistency.

[0072] The circuit principle block diagram is as Figure 1 shown. The bus overcurrent detection circuit consists of three parts: a current sampling and amplifying unit, a threshold comparison unit, and an alarm signal output unit;

[0073] The circuit schematic diagram is as Figure 2 shown. The current sampling and amplifying unit consists of a sampling resistor R6 with a low resistance value and the circuit of operational amplifier U3A. Resistors R9 and R12 determine the amplification ratio Gain of the operational amplifier circuit. Capacitor C7 and resistor R12 form a filtering circuit to filter out the noise in the sampling circuit. The filtering delay is set to 1.3uS (this parameter can be fine-tuned according to the test results in actual application to achieve the best filtering effect within the effective protection response of the circuit).

[0074] The threshold comparison unit is the core unit that triggers the output alarm after overcurrent. The voltage reference source UW1 and the resistor R13 form a reference voltage, which serves as the trigger threshold voltage for overcurrent detection. This voltage signal and the current sampling signal voltage output by the operational amplifier circuit are input to the 5th and 6th pins of the comparator U3B through resistors R7 and R8. When the voltage signal amplified by the current sampling is greater than the overcurrent trigger threshold voltage of the comparator U3B-6 pin, the output of the comparator U3B-7 pin is turned on. After exceeding the stable voltage Vz of the voltage regulator DZ1, the transistor Q1 is turned on, and then the optocoupler U1 is turned on. After the optocoupler U1 is turned on, the level of pin 2 is the CE diode voltage drop Vce of the transistor Q1 plus the forward conduction voltage drop Vf of the light-emitting diode in the optocoupler U1. The circuit composed of Schottky diode DK1 with low forward voltage drop and resistor R3 clamps the reference level of comparator pin 6 to the voltage of pin U1-2 plus the forward voltage drop Vf of Schottky diode DK. At this time, pin 7 of comparator U3B continues to output, keeping the light-emitting diode of optocoupler U turned on, until the voltage signal of the sampling bus current operational amplification is reduced to the reference level after the clamping of comparator U3B-6 pin at this time, and pin 7 of comparator U3B turns off the output, and the light-emitting diode of optocoupler U1 turns off. This part of the circuit can ensure that the comparison reference threshold voltage of the comparator is automatically clamped to a lower comparison reference threshold voltage after triggering overcurrent while setting the trigger value, so as to maintain the continuous output of the alarm during the overcurrent generation period and ensure the output pulse width of the alarm, which is the core of this circuit.

[0075] The alarm signal output unit is composed of an optocoupler U1 and a 74 series logic AND gate U2. The optocoupler U1 is a high-speed isolation optocoupler with an isolation voltage of 5000Vrms to ensure safety requirements. Pin 7 of the optocoupler U1 is connected to the isolated system power supply +5V, and the output signal of pin 6 is connected to the R4 pull-up resistor to the system power supply +5V. The output signal is connected to pins 1 and 2 of the logic AND gate U2. The logic AND gate U2 shapes the signal and outputs the overcurrent alarm signal " / OCL_O".

[0076] The current value of the IGBT bus is Ibus, and the sampling resistor Rres1 (ie, resistor Rres) collects the current to obtain a voltage value Vres=Ibus*Rres; the operational amplifier U3A outputs an amplified voltage signal Vop=Vres*R12 / R9, ie, Vop=Ibus*Rres*R12 / R9.

[0077] At this time, the comparator overcurrent trigger threshold reference voltage VH th -=Vref=2.495V,when Vop>VH th - when When the overcurrent alarm is triggered, the output

[0078] After the overcurrent alarm output is triggered, the reference voltage is clamped and the voltage after clamping

[0079] When the post-stage circuit shuts off the IGBT output and Vop drops to Vop < VL th the alarm output ends.

[0080] Circuit simulation: Through circuit simulation, in the same simulated overcurrent environment, by changing the resistance value of resistor R5, the threshold VL th - of the comparator is changed to achieve the effect of extending the pulse width of the OCL alarm output; the actual application test results are consistent with the simulation results.

[0081] As Figure 3 shown, when designing R5 = 100 Kohm, VL th - = 2.34V and the OCL alarm pulse width is 0.21 mS;

[0082] As Figure 4 shown, when designing R5 = 7.5 Kohm, VL th - = 0.6V and the OCL alarm pulse width is 0.28 mS.

[0083] The preferred embodiments of the present invention have been described in detail above, but the present invention is not limited to the above embodiments. Within the scope of knowledge possessed by those of ordinary skill in the art, various changes can be made without departing from the gist of the present invention.

[0084] Many other changes and modifications can be made without departing from the concept and scope of the present invention. It should be understood that the present invention is not limited to specific embodiments, and the scope of the present invention is defined by the appended claims.

Claims

1. An IGBT bus overcurrent detection circuit with adjustable output pulse width, characterized in that, Including: A current sampling and amplifying unit, a threshold comparison unit, and an alarm signal output unit; The input end of the current sampling and amplifying unit is connected to the IGBT busbar, the output end signal of the current sampling and amplifying unit is connected to the input end of the threshold comparison unit, and the output end signal of the threshold comparison unit is connected to the alarm signal output unit; The current sampling and amplifying unit is used to sample the current of the IGBT busbar, filter and amplify the voltage signal obtained by the current sampling, and output the processed voltage signal to the threshold comparison unit; The threshold comparison unit is used to compare the voltage signal input by the current sampling and amplifying unit with the trigger threshold voltage of its own overcurrent detection; if the voltage signal is greater than the trigger threshold voltage, that is, after an overcurrent fault alarm occurs, a control signal is sent to turn on the light-emitting diode of the optocoupler of the alarm signal output unit, and at the same time, the trigger threshold voltage of its own overcurrent detection is pulled low; if the voltage signal is less than the trigger threshold voltage, that is, after the overcurrent fault alarm disappears, a control signal is sent to turn off the light-emitting diode of the optocoupler of the alarm signal output unit, and by changing the resistance value of its own resistor, the effect of adjustable alarm output pulse width is achieved; The alarm signal output unit is used to isolate the control signal sent by the threshold comparison unit and output a digital signal, and after shaping the digital signal, output an overcurrent alarm fault level signal readable by the single-chip microcomputer.

2. The IGBT bus overcurrent detection circuit with adjustable output pulse width according to claim 1, characterized in that, The current sampling and amplifying unit includes: a sampling resistor RES1, an operational amplifier U3A, a resistor R2, a resistor R7, a resistor R8, a resistor R9, a resistor R12, a capacitor C1, and a capacitor C7; Both ends of the sampling resistor RES1 are connected to the input end and the output end of the IGBT busbar, one end of the resistor R8 is simultaneously connected to one end of the sampling resistor RES1 and grounded, one end of the resistor R9 is connected to the other end of the sampling resistor RES1, the other end of the resistor R9 is connected to the 2nd pin of the operational amplifier U3A, the other end of the resistor R8 is connected to the 3rd pin of the operational amplifier U3A, the 4th pin of the operational amplifier U3A is connected to -15V voltage, the 8th pin of the operational amplifier U3A is connected to +15V voltage, the 1st pin of the operational amplifier U3A is connected to one end of the resistor R7, one end of the capacitor C1 and the resistor R2 are simultaneously connected to the 3rd pin of the operational amplifier U3A, the other end of the capacitor C1 is connected to the other end of the resistor R2, and the other end of the resistor R2 is grounded; one end of the resistor R12 and the capacitor C7 are simultaneously connected to the 2nd pin of the operational amplifier U3A, and the other ends of the resistor R12 and the capacitor C7 are simultaneously connected to one end of the resistor R7.

3. An IGBT bus overcurrent detection circuit with adjustable output pulse width according to claim 2, characterized in that The threshold comparison unit includes: a comparator U3B, a voltage reference source UW1, a zener diode DZ1, a triode Q1, a Schottky diode DK1, a resistor R1, a resistor R3, a resistor R5, a resistor R10, a resistor R11, a resistor R13, a resistor R14, a capacitor C3, a capacitor C6, and a capacitor C8; The other end of the resistor R7 is connected to pin 5 of the comparator U3B. Pin 6 of the comparator U3B is simultaneously connected to one end of the resistor R14 and port 1 of the Schottky diode DK1. Port 2 of the Schottky diode DK1 is connected to one end of the resistor R3. The other end of the resistor R3 is simultaneously connected to one ends of the resistor R5 and the resistor R1. The other end of the resistor R1 is connected to the +15V voltage. The other end of the resistor R5 is connected to the collector of the triode Q1. The other end of the resistor R14 is simultaneously connected to one end of the resistor R13, one end of the capacitor C8, and pins 1 and 2 of the voltage reference source UW1. The other end of the resistor R13 is grounded. The other end of the capacitor C8 is simultaneously connected to pin 3 of the voltage reference source UW1 and grounded. Pin 7 of the comparator U3B is connected to one end of the resistor R10. The other end of the resistor R10 is connected to the output end of the voltage regulator diode DZ1. The input end of the voltage regulator diode DZ1 is simultaneously connected to one end of the resistor R11 and the base of the triode Q1. The other end of the resistor R11 and the emitter of the triode Q1 are simultaneously connected to the -15V voltage. Pin 8 of the comparator U3B is simultaneously connected to the +15V voltage and one end of the capacitor C3. The other end of the capacitor C3 is grounded. Pin 4 of the comparator U3B is simultaneously connected to the -15V voltage and one end of the capacitor C6. The other end of the capacitor C6 is grounded.

4. An IGBT bus overcurrent detection circuit with adjustable output pulse width according to claim 3, characterized in that, The alarm signal output unit includes: an optocoupler U1, a logic AND gate U2, a resistor R4, capacitors C2, C4, and C5; The other end of the resistor R1 is connected to pin 2 of the optocoupler U1. The other end of the resistor R5 is connected to pin 3 of the optocoupler U1. Pin 8 of the optocoupler U1 is connected to pin 7 of the optocoupler U1. Pin 8 and pin 7 of the optocoupler U1 are simultaneously connected to the +5V voltage. One end of the resistor R4 is simultaneously connected to pin 8 and pin 7 of the optocoupler U1. The other end of the resistor R4 is simultaneously connected to pin 6 of the optocoupler U1, one end of the capacitor C5, and pins 1 and 2 of the logic AND gate U2. One end of the capacitor C4 is simultaneously connected to pin 8 and pin 7 of the optocoupler U1. The other end of the capacitor C4 and the other end of the capacitor C5 are simultaneously connected to pin 5 of the optocoupler U1. Pin 5 of the optocoupler U1 is grounded; Pin 3 of the logic AND gate U2 is grounded. Pin 5 of the logic AND gate U2 is connected to the +5V voltage. One end of the capacitor C2 is connected to pin 5 of the logic AND gate U2. The other end of the capacitor C2 is grounded.

5. The IGBT bus overcurrent detection circuit with adjustable output pulse width according to claim 2, wherein, The resistors R9 and R12 simultaneously control the amplification ratio of the operational amplifier U3A; The capacitor C7 and the resistor R12 form a filtering module to filter the noise in the sampled voltage of the sampling resistor RES1.

6. An IGBT bus overcurrent detection circuit with adjustable output pulse width according to claim 4, characterized in that, The voltage reference source UW1 and the resistor R13 form a reference voltage as the trigger threshold voltage for overcurrent detection; The voltage signal output by the reference voltage and current sampling and amplification unit is input to the comparator U3B after passing through resistors R7 and R8. When the voltage signal output by the current sampling and amplification unit is greater than the trigger threshold voltage for overcurrent detection, the output of pin 7 of the comparator U3B starts to turn on. When the voltage signal output by the current sampling and amplification unit exceeds the stable voltage Vz of the zener diode DZ1, the triode Q1 is turned on and the optocoupler U1 is turned on.

7. An IGBT bus overcurrent detection circuit with adjustable output pulse width according to claim 6, characterized in that, When the optocoupler U1 is turned on, the voltage of pin 2 of the optocoupler U1 is: the sum of the CE voltage drop Vce of the triode Q1 and the forward conduction voltage drop Vf of the light-emitting diode in the optocoupler U1 when it is turned on; The trigger threshold voltage for overcurrent detection at pin 6 of the comparator U3B is clamped to the voltage of pin 2 of the optocoupler U1 plus the forward voltage drop Vf of the Schottky diode DK through the circuit composed of the Schottky diode DK1 with a low forward conduction voltage drop and the resistor R3; at this time, the output of pin 7 of the comparator U3B continues to output, keeping the light-emitting diode of the optocoupler U1 turned on until the voltage signal output by the current sampling and amplification unit drops to the clamped reference level at pin 6 of the comparator U3B, and then the output of pin 7 of the comparator U3B is turned off and the light-emitting diode of the optocoupler U1 is turned off.

8. An IGBT bus overcurrent detection circuit with adjustable output pulse width according to claim 4, characterized in that, The logic AND gate U2 shapes the overcurrent alarm signal sent by the optocoupler U1 and outputs the overcurrent alarm signal, namely / OCL_O.

9. An IGBT bus overcurrent detection circuit with adjustable output pulse width according to claim 7, characterized in that The current value of the IGBT bus is Ibus, and the voltage value Vres = Ibus * Rres obtained by the sampling resistor RES1 collecting the current Ibus; the operational amplifier U3A outputs the amplified voltage signal Vop = Vres * R12 / R9, that is, Vop = Ibus * Rres * R12 / R9; At this time, the trigger threshold voltage VH for overcurrent detection of the comparator U3B th - = Vref = 2.495V. When Vop > VH th - that is - the overcurrent alarm trigger output is generated; After the overcurrent alarm trigger output, the trigger threshold voltage of the overcurrent detection of comparator U3B is clamped, and the voltage after clamping When the IGBT output is turned off and Vop drops to Vop < VL th the alarm output ends.

10. An IGBT bus overcurrent detection circuit with adjustable output pulse width according to claim 7, characterized in that, The logic AND gate U2 uses the 74 series logic AND gate U2.

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