CN115201651A - An on-state voltage drop online monitoring circuit and device for power devices - Google Patents

Abstract

The invention relates to an on-state voltage drop on-line monitoring circuit and a device for a power device, which comprise a same-direction proportional operation circuit and a test current source I _sense Diode D ₁ High-voltage-resistant ultrafast recovery diode D ₂ A clamping branch circuit formed by connecting a plurality of clamping diodes in series, and an anti-parallel bleeder diode D ₅ (ii) a The same direction proportional operation circuit comprises an operational amplifier and a resistor R ₁ Resistance R ₂ (ii) a First clamping diode D on the clamping branch ₃ Anode of the diode is connected with the same-direction input end of the operational amplifier of the same-direction proportional operation circuit and the diode D ₁ Cathode, high voltage resistant ultrafast recovery diode D ₂ The anode of (2); last clamping diode D ₄ The cathode of the transistor is connected with the source electrode or the emitter electrode of the tested device; the anti-parallel bleeder diode D ₅ Anode and last clamping diode D ₄ Is connected with the cathode of the diode D ₅ Is connected to the first clamping diode D ₃ Of (2) an anode. The circuit reducesThe circuit reliability is enhanced while the cost is low.

Description

An on-state voltage drop online monitoring circuit and device for power devices

technical field

The invention belongs to the field of state monitoring and reliability evaluation of power semiconductor devices, and is mainly used for on-line monitoring of on-state voltage drop of power semiconductor devices, and further can be used for junction temperature information extraction and reliability evaluation.

Background technique

Power semiconductor devices are one of the most critical components in power electronic converters, and their safe operation is critical to the robustness and reliability of power electronic converter systems. According to the power electronic system reliability research report, the power device is the component with the highest failure rate in the converter system, accounting for about 35%. In recent years, silicon carbide (SiC) materials have attracted more and more attention in the power electronics industry due to their excellent physical and electrical properties. Most likely to replace the currently widely used silicon (Si) IGBT devices. However, the performance of SiC power devices in practical applications is far from reaching its theoretical performance, which is partly due to the limitations of state sensing technologies such as electricity, magnetism, and heat. Therefore, online monitoring of electrical parameters can realize full utilization of apparent capacity of SiC power devices and safe operation in complex limit situations.

The on-state voltage drop of power devices (such as V _CE of IGBT, V _DS-on and V _SD of MOSFET) is widely used in device junction temperature monitoring and life prediction, and is an indispensable parameter for device state monitoring and loss calculation. With the development of power converters to high frequency, high power and high density, in order to realize real-time monitoring of the state of power devices, the monitoring of on-state voltage drop should meet the requirements of online linearity, safety and accuracy. Due to the existence of the overdrive problem and the limitation of dynamic range, measurement equipment such as oscilloscopes cannot accurately extract the on-state voltage at the steady-state time during the switching process, which is not conducive to integration. Therefore, a dedicated on-state voltage drop online monitoring circuit is required to realize cost-reducing and high-precision online monitoring of the on-state voltage of power devices.

In order to solve the defect of online monitoring of on-state voltage drop by measuring instruments, the invention patent with the application number of 202010694635.1 proposes an on-state voltage drop on-line monitoring circuit with a diode blocking large current, but it uses a NOT gate, a second drive module and an additional on-state voltage drop. The switching device provides a path for the test current. When used, the additional switching device needs to have synchronous reverse control with the device under test, which increases the complexity of the control and increases the application cost. The invention patent with the application number of 201611049398.3 proposes an on-state voltage drop clamp on-line monitoring circuit, but its clamping branch consists of a diode isolated power supply in series. In Figure 1 of the patent, when the upper tube under test is turned on, To achieve accurate monitoring of the on-state voltage drop, all the test current I _sense needs to pass through D ₂ and D ₁ and then enter the upper tube; if the 15V power supply is not set, part of the test current I _sense will be shunted through D ₃ and D ₄ , resulting in The I _senses of D ₂ and D ₁ are not equal, which destroys the predetermined conditions of the operation circuit, resulting in inaccurate monitoring; after setting the power supply, when the upper tube is turned on, a voltage of 15V is provided, so that the cathode potential of D ₄ and D ₃ is higher than that of the anode, Avoid shunting, and it is well known in the art that the power supply needs to choose an expensive isolated power supply with high common-mode transient immunity, otherwise common-mode interference will be introduced, causing the circuit output to oscillate. The circuit output will oscillate, and the output waveform cannot be used.

Therefore, a low-cost, high-precision, and simple-to-control on-state voltage drop online monitoring circuit needs to be proposed.

SUMMARY OF THE INVENTION

In order to solve the shortcomings existing in the prior art, the present invention aims to provide an on-state voltage drop online monitoring circuit and device for power devices, which provides a technical support for the reliability research of power devices, which can reduce the cost. On the premise of simple control, the higher voltage when the device under test is turned off is clamped to a lower voltage circuit, and the voltage across the power device is monitored within a smaller voltage range, thereby ensuring the device under test. On-state voltage drop monitoring accuracy.

The technical scheme adopted in the present invention is:

In a first aspect, the present invention provides an on-state voltage drop on-line monitoring circuit for power devices, including a proportional operation circuit in the same direction, a test current source I _sense , a diode D ₁ , and a high-voltage ultra-fast recovery diode D ₂ ; the The same-direction proportional operation circuit includes an operational amplifier, a resistor R ₁ , and a resistor R ₂ ; it is characterized in that the on-state voltage drop online monitoring circuit further includes a clamping branch formed by a plurality of clamping diodes in series, an anti-parallel leakage diode D ₅ , the on-state voltage drop of all clamping diodes on the clamping branch minus the on-state voltage drop of a single clamping diode is not less than the theoretical maximum on-state voltage drop of the device under test; the first clamp on the clamping branch The anode of diode _D3 is connected to the non-inverting input terminal of the operational amplifier of the proportional operation circuit, the cathode of diode D1, the anode of high _- voltage ultrafast recovery diode D2 _; the cathode of the last clamping diode _D4 is connected to the source of the device under test _The anode of the anti _- parallel bleeder diode D5 is connected to the cathode of the last clamp diode D4, and the cathode of the anti _- parallel bleeder diode D5 is connected to the anode of the first clamp diode _D3 .

The power device to be tested is a SiC MOSFET or an IGBT, an anti-parallel diode is provided on the IGBT, and an on-state voltage drop online monitoring circuit is connected in parallel between the emitter (E) and the collector (C) of the IGBT.

In a second aspect, the present invention provides an apparatus for measuring the forward or/and reverse on-state voltage drop of a device under test by applying the above-mentioned on-state voltage drop online monitoring circuit for a power device.

The device is a double-pulse circuit, with two devices under test, each device under test is connected in parallel with an on-state voltage drop online monitoring circuit, including gate drive, busbar capacitance, busbar voltage V _DC , device under test; busbar voltage, The circuit composed of busbar capacitance, inductive load and the device under test will carry large voltage and current, which is called the main power circuit; the devices under test used are Q ₁ and Q ₂ respectively; the gate drive is connected to the drive circuit, and the drive circuit is The circuit that provides the control signal to the switch tube, the gate drive outputs the drive signal to control the switch of the lower tube _Q2 , the driving frequency is 50~ _300kHZ , the gate of the upper tube Q1 is low level or floating, only in the freewheeling stage by Its body diode works, and the test current source I _sense of the on _- state voltage drop online monitoring circuit connected to the upper tube Q1 and the source or emitter connection position of the device under test are connected to the drain or collector of the lower tube _Q2 ; The test current source I _sense of the on-state voltage drop online monitoring circuit connected with the lower tube Q ₂ and the connection position of the source or emitter of the SiC MOSFET under test are grounded; the upper tube Q ₁ is connected in parallel with the inductive load, and the gate of the lower tube Q ₂ Connect the gate drive; the bus voltage and bus capacitance are connected in parallel between the upper tube Q1 and the lower tube _{Q2 ;}

When the driving signal outputs a high level, the lower tube _Q2 is turned on, the bus voltage V _DC forms a closed loop with the inductive load L _load and the lower tube _Q2 , and the voltage across the lower tube _Q2 is its on-state voltage drop. When the circuit outputs a low level, the lower tube _Q2 is turned off. At this time, the inductive load L _load continues to discharge the upper tube Q1, and the current passes through the body diode or the anti _- parallel diode _of the upper tube Q1 to form _a closed loop. The terminal voltage is the voltage drop across its body diode or anti-parallel diode.

Compared with the prior art, the beneficial technical effects of the present invention are:

(1) The present invention is used for the on-state voltage drop online monitoring circuit of power devices, and proposes a method of using multiple diodes in series as the clamping branch, which optimizes the monitoring error caused by the traditional single-diode clamping branch and solves the problem of double diodes. The problem of the output waveform oscillation caused by the series power supply as a clamping branch reduces the cost and enhances the reliability of the circuit.

(2) The present invention is used for the on-state voltage drop on-line monitoring circuit of power devices. During the monitoring process, the voltage of the non-inverting input terminal of the operational amplifier has a voltage peak at the time of conduction. The reason is that the switching voltage of the device under test is overshoot and clamping It is caused by the reverse recovery current of the branch, and the negative voltage overshoot may cause the monitoring circuit to work in an abnormal condition, reducing the reliability of the entire on-state voltage drop online monitoring circuit. The present invention proposes an anti _- parallel bleeder diode D5 in the clamping branch to suppress the voltage spike existing in the clamping branch. There is a large voltage spike when the bleeder diode is set, and the voltage spike is greatly reduced after the bleeder diode is set, which proves that the effect of suppressing the voltage spike is obvious.

(3) For a MOSFET device, the body diode-related parameters included in its own structure can also characterize the junction temperature information and aging degree of the MOSFET. The circuit proposed by the present invention can monitor the voltage drop of the on-state voltage, and can also monitor the voltage drop of the body diode when the MOSFET is freewheeling, so as to realize an on-state voltage drop online monitoring circuit to extract two different voltage parameters (the forward direction of the MOSFET on-state voltage drop and its body diode voltage drop). The same on-state voltage drop online monitoring circuit is used to separately monitor the devices under test at different positions, so as to monitor the forward on-state voltage drop and/or the body diode voltage drop of the switch tube with freewheeling function.

(4) The present invention is used for the on-state voltage drop online monitoring circuit of the power device, which is simple, reliable, has high monitoring accuracy, can isolate high voltage, and can be used normally in the converter. The actual verification shows that the on-state voltage drop online monitoring circuit proposed by the present invention can work normally at a maximum switching frequency of 300 kHz, while the operating frequency of the traditional on-state voltage drop online monitoring circuit is all tens of kHz.

In summary, the present invention provides an on-state voltage drop online monitoring circuit of a power device based on multi-diode series clamping. Reliability also reduces costs. In addition, after a plurality of clamping diodes are connected in series in the present application, no additional special power supply is required, and the shunt can also be suppressed, the cost is reduced, and the stability of the monitoring circuit is improved.

Description of drawings

FIG. 1 is a circuit topology diagram of an on-state voltage drop on-line monitoring circuit for power devices according to the present invention.

FIG. 2 is a connection diagram when the on-state voltage drop online monitoring circuit for power devices of the present invention is applied in the following examples.

Figure 3 shows the monitoring results of forward on-state voltage drop and body diode voltage drop of SiC MOSFET, in which (a) is the output result of MOSFET forward on-state voltage drop monitoring, and (b) is the monitoring result of body diode voltage drop during reverse freewheeling of MOSFET Output the result.

FIG. 4 is a physical diagram of the power main circuit and the proposed on-state voltage drop online monitoring circuit in the embodiment.

FIG. 5 is a comparison diagram of the effect of the voltage waveform of the co-directional input terminal when the anti-parallel bleeder diode is not set and when the anti-parallel bleeder diode is set.

Detailed ways

In order to facilitate the understanding of the present invention, the accompanying drawings will be given below to describe the present application in all aspects. Preferred embodiments of the present application are shown in the accompanying drawings. However, the present invention can be implemented in different scenarios or structures, and is not limited to the embodiments shown herein.

The circuit topology of the on-state voltage drop on-line monitoring circuit used in the power device of the present invention is shown in Figure 1. In this embodiment, the device under test is a SiC MOSFET as an example for description, including a series of clamping diodes composed of multiple clamping diodes. A clamping branch, a co-directional proportional operation circuit (processing circuit), an anti-parallel bleeder diode D ₅ , a test current source I _sense , a diode D ₁ , a high-voltage resistant ultra-fast recovery diode D ₂ ; the co-directional proportional calculation circuit includes operational amplifier, resistor R ₁ , resistor R ₂ ;

The value of the on-state voltage drop of all clamping diodes on the clamping branch minus the on-state voltage drop of a single clamping diode is not less than the theoretical maximum on-state voltage drop of the device under test; the first clamping diode on the clamping branch D ₃ The anode is connected to the non-inverting input terminal of the operational amplifier of the same-direction proportional operation circuit, the cathode _of the diode D1, and the anode of the high-voltage ultra _- fast recovery diode D2, which provides a path for the test current and stabilizes the operational amplifier when it is turned off. For the function of voltage clamping, the cathode of the last clamping diode D4 is connected to the source of the SiC MOSFET under test to provide a complete closed loop as the test current source I _{sense ;} the anode of the anti _- parallel bleed diode D5 is connected to the last _The cathode of a clamping diode D4 is connected, and the cathode of the anti _- parallel bleeder diode D5 is connected to the anode of the first clamping diode _D3 , which provides a path for the reverse recovery current and suppresses the reverse recovery voltage. , the anti _- parallel bleeder diode D5 can eliminate the reverse overshoot of the switching voltage of the device under test, and at the same time bleed the reverse recovery current of multiple clamp diodes connected in series, so as to suppress the voltage spike at the same input terminal of the operational amplifier.

_The cathode of the high-voltage ultrafast recovery diode D2 is connected to the drain terminal of the SiC MOSFET under test, preventing the load current from entering the processing circuit, and the anode is connected to the non-inverting input of the operational amplifier. The cathode of the diode D ₁ is connected to the non-inverting input terminal of the operational amplifier, and its anode is connected to one end of the resistor R ₁ and the output terminal of the test current source I _sense to provide a path for the test current; the other end of the resistor R ₁ is connected to the inverse of the operational amplifier. to the input. _One end of the resistor R2 is connected to the inverting input of the operational amplifier, and the other end is connected to the output of the operational amplifier to provide a loop for the feedback signal. The reference ground of the test current source I _sense , which provides a small test current, is the source of the SiC MOSFET under test, which can avoid the risk of short circuit caused by non-common ground connection.

The clamping diodes of the clamping branch are ultra-fast recovery diodes, and a plurality of clamping diodes are connected in series in sequence according to the sequence in which the cathode of the previous clamping diode is connected to the anode of the next clamping diode.

In Figure 1, Q ₂ is the SiC MOSFET under test; I _sense is the test current source, which provides a stable milliamp test current. Both D ₂ and D ₄ use high-voltage ultra-fast recovery diodes. High breakdown voltage can only work in high voltage environment, select high-voltage ultra-fast recovery diode, its reverse recovery time is short (nanosecond level), the reverse recovery current is small, and the breakdown voltage is high, which is higher than the measured When the device is turned off, the high voltage at both ends will separate the high current of the power main circuit (the high current loop where the device under test is located, which is the prior art) from the processing circuit, preventing the high current of the power part from entering the processing circuit, which plays a role in Protect the role of the post-processing circuit.

In the on-state voltage drop online monitoring circuit, when the device under test is turned off, the clamping branch clamps the voltage at the same-inverting input terminal of the op amp to a low voltage level to realize the function of voltage regulation clamping. The clamping branch is followed by a proportional operation circuit in the same direction, in which R ₁ and R ₂ use high-precision resistors with the same low resistance value. High precision means that the accuracy is higher than 0.1%. R ₂ is used as a feedback resistor. If the resistance value is too high, the feedback will be delayed and the operational amplifier will self-oscillate and affect the quality of the output waveform. At the same time, the resistance values of R ₁ and R ₂ should be the same, so that the output value of the proportional operation circuit in the same direction is equal to the on-state voltage drop value of the device under test.

The test current source I _sense is used for on-state voltage drop online monitoring and testing. The test current source I _sense is composed of a voltage regulator chip in series with a regulating resistor to output a constant small test current, and the output current value can be changed by adjusting the resistance value. The voltage regulator chip outputs the test current, and the power supply including the test current source I _sense and the operational amplifier is realized by a power module with isolation function. The power module with isolation function is a common isolated power module, and does not require expensive high common mode. The isolated power supply with transient immunity can also avoid the interference problem caused by common ground.

According to the actual needs of the present invention, the number of series-connected clamping diodes in the clamping branch should be adjusted to obtain an appropriate clamping voltage, and the number of clamping diodes is the value of the clamping voltage divided by the forward voltage drop value of a single clamping diode. The obtained number of , plus one, the forward voltage drop of all the clamping diodes on the clamping branch is equal. In this application, the clamping voltage can be adjusted according to the number of clamping diodes. The theoretically highest on-state voltage drop of the device under test is fixed, and the value of the on-state voltage drop of all clamping diodes minus the on-state voltage drop of a single clamping diode is not less than The theoretical maximum on-state voltage drop of the device under test to realize the function of voltage regulator clamp.

Example

This embodiment is implemented in the built double-pulse circuit, which has two devices under test, and each device under test is connected in parallel with an on-state voltage drop online monitoring circuit of the present application. Build a double-pulse hardware platform as shown in Figure 4, the hardware platform includes gate drive, busbar capacitance, busbar voltage V _DC , device under test and the on-state voltage drop online monitoring circuit proposed by the present invention. The circuit composed of busbar voltage, busbar capacitance, inductive load and the SiC MOSFET under test will carry large voltage and current, which is called the power main circuit. The device under test used is two SiC MOSFETs Q ₁ and Q ₂ respectively. The circuit connection mode of the embodiment is shown in FIG. 2 . The gate drive is connected to a drive circuit, and the drive circuit is a circuit that provides a control signal to the switch tube. The gate drive outputs the drive signal to control the switch of the lower tube _Q2 , the driving frequency is _50-300kHZ , the gate of the upper tube Q1 is low level or floating, and its body diode works only in the freewheeling stage. In this embodiment, the clamping voltage is set to about 4V, and seven clamping diodes are set.

When the driving signal outputs a high level, the lower tube _Q2 is turned on, the bus voltage V _DC forms a closed loop with the inductive load L _load and the lower tube _Q2 , and the voltage across the lower tube _Q2 is its on-state voltage drop. When the drive circuit outputs a low level, the lower tube _Q2 is turned off, and the inductive load L _load continues to discharge to the upper tube Q1, and the current passes through the body diode _of the upper tube Q1 to form _a closed loop. At this time, the voltage across the upper tube _Q1 is the voltage drop across its body diode.

When the on-state voltage drop online monitoring circuit proposed by the present invention is connected in parallel at both ends of the lower tube, the on-state voltage drop of the lower tube Q2 can be monitored when the lower tube _Q2 is turned on. The output value of the on-state voltage drop online monitoring circuit is the on-state voltage drop value of the lower tube _Q2 when the lower tube _Q2 is turned on; when it is turned off, the output value is the clamping voltage value set by the clamping branch.

When the on-state voltage drop online monitoring circuit is connected to both ends of the lower tube _Q2 , the on-state voltage drop of the conduction of the lower tube _Q2 can be monitored. The on-state voltage drop monitoring circuit proposed by the present invention monitors the on-state voltage drop _{VDS -} monitoring of the device under test. The output of the monitoring circuit is its on-state voltage drop value, and when the lower tube _Q2 is turned off, the output value of the monitoring circuit is the clamping voltage value to realize the function of voltage regulator clamping. When the on-state voltage drop online monitoring circuit measures the voltage drop of the body diode, the measurement principle is basically the same as that of the forward voltage drop of the switching tube.

When the on-state voltage drop online monitoring circuit is connected to both ends of the upper transistor Q1, the on _- state voltage drop of the body diode when the reverse freewheeling current _of the upper transistor Q1 is monitored can be monitored. The on-state voltage drop on-line monitoring circuit proposed by the present invention monitors the on-state voltage drop V _SD of the body diode of the upper tube Q1 _- the monitoring result is shown in (b) of FIG. 3 . During freewheeling, the output value of the on-state voltage drop monitoring circuit is the reverse voltage drop of the body diode of the upper tube Q1, which is _a negative value, and its absolute value is the on-state voltage drop of the body diode of the upper tube Q1 _; At the moment, the output value is the clamp voltage to realize the function of voltage regulator clamp. In Figure 3, I _load is the current waveform passing through the inductive load L _load , V _g is the driving waveform of the lower tube _Q2 , V _DS is the voltage between the drain and the source, and V _SD is the voltage between the source and the drain voltage between.

The output voltage of the proportional operation circuit in the same direction is the voltage drop of the body diode of the upper tube under test and the on-state voltage drop of the lower tube, respectively. When the tested SiC MOSFET is turned on, the output of the operation circuit is its on-state voltage drop value, and when the tested SiC MOSFET is turned off, the output of the operation circuit is the set clamping voltage value. The voltage signal is input into the digital processing unit for processing, so as to realize the extraction of the state information of the device under test.

It can be seen from Figure 3 that the on-state voltage drop online monitoring circuit can output the on-state voltage drop value when the device under test is turned on, and the output waveform has small peaks and good quality. It shows that the monitoring value of the on-state voltage drop monitored by the on-state voltage drop online monitoring circuit of the present invention is accurate, and the good waveform quality can improve the reliability of the on-state voltage drop monitoring circuit. When the device under test is turned off, the on-state voltage drop The drop-line monitoring circuit can clamp the high voltage at both ends to a low voltage level, which improves the safety of the monitoring circuit and greatly improves the monitoring accuracy. Through example verification, the circuit proposed by the present invention can run at the 300kHZ switching frequency set by the signal generator, and meets the monitoring requirements of wide bandgap power devices.

It can be seen from FIG. 4 that the on-state voltage drop on-line monitoring circuit proposed by the present invention occupies a small space and is easy to integrate, and can be integrated into a driving circuit or inside a power module in the future. The module of the on-state voltage drop online monitoring circuit can be made 4cm or even smaller, and can be integrated on the driver board in future applications, which can further reduce the occupied space.

Figure ₅ (a) is the voltage waveform of the non-inverting input terminal of the operational amplifier when the anti-parallel bleeder diode D5 is not set. The dotted circle in the figure marks the voltage spike there, which is caused by the switching voltage overshoot and reverse recovery. _The peak value of the voltage at this place caused by the current is too large, there is a risk of damaging the processing current, which is not conducive to the guarantee of the reliability of the monitoring circuit. overshoot. Figure ₅ (b) shows the voltage waveform of the non-inverting input terminal of the operational amplifier when the anti _- parallel bleeder diode D5 is set. This voltage overshoot is suppressed.

What is not described in the present invention applies to the prior art.

Claims (8)

1. An on-line voltage drop monitoring circuit for power device comprises a homodromous proportional operation circuit and a test current source I _sense Diode D ₁ High-voltage-resistant ultrafast recovery diode D ₂ (ii) a The same direction proportional operation circuit comprises an operational amplifier and a resistor R ₁ Resistance R ₂ (ii) a The on-line voltage drop monitoring circuit is characterized by further comprising a clamping branch formed by serially connecting a plurality of clamping diodes and an anti-parallel bleeder diode D ₅ Subtracting the on-state voltage drop value of a single clamping diode from the on-state voltage drops of all the clamping diodes on the clamping branch circuit, wherein the theoretical highest on-state voltage drop of the tested device is not less than the theoretical highest on-state voltage drop of the tested device; first clamping diode D on the clamping branch ₃ Anode of the diode is connected with the same-direction input end of the operational amplifier of the same-direction proportional operational circuit and the diode D ₁ Cathode, high voltage resistant ultrafast recovery diodeD ₂ The anode of (2); last clamping diode D ₄ The cathode of the transistor is connected with the source electrode or the emitter electrode of the tested device; the anti-parallel bleeder diode D ₅ Anode and last clamping diode D ₄ Is connected with the cathode of the diode D ₅ Is connected to the first clamping diode D ₃ Of (2) an anode.

2. The on-state voltage drop on-line monitoring circuit for power device as claimed in claim 1, wherein the anti-parallel bleeder diode D ₅ The reverse overshoot of the switching voltage of the device to be tested can be eliminated, and the reverse recovery current of the plurality of clamping diodes connected in series is discharged so as to inhibit the voltage spike of the equidirectional input end of the operational amplifier.

3. The on-line voltage drop monitoring circuit for power device as claimed in claim 1, wherein the high voltage tolerant ultrafast recovery diode D ₂ The cathode of the operational amplifier is connected with a drain electrode or a collector electrode terminal of the tested device to prevent load current from entering the processing circuit, and the anode of the operational amplifier is connected with the homodromous input end of the operational amplifier; diode D ₁ The cathode of the operational amplifier is connected with the same-direction input end of the operational amplifier, and the anode of the operational amplifier is connected with the resistor R ₁ And a test current source I _sense The output terminal of (2) provides a pass for the test current; resistance R ₁ The other end of the first resistor is connected to the inverting input end of the operational amplifier; resistance R ₂ One end of the operational amplifier is connected with the reverse input end of the operational amplifier, and the other end of the operational amplifier is connected with the output end of the operational amplifier to provide a loop for a feedback signal; test current source I for providing test small current _sense The reference ground of the device to be tested is the source electrode or the emitter electrode of the device to be tested, and the risk of short circuit caused by non-common ground connection is avoided.

4. The on-state voltage drop on-line monitoring circuit for the power device as claimed in claim 1, wherein the clamping diodes of the clamping branch are ultrafast recovery diodes, and the plurality of clamping diodes are connected in series in the order of connecting the cathode of the previous clamping diode to the anode of the next clamping diode.

5. The on-state voltage drop on-line monitoring circuit for the power device as claimed in claim 1, wherein when the on-state voltage drop on-line monitoring circuit is turned off, the clamping branch clamps the voltage at the non-inverting input terminal of the operational amplifier to a low voltage level, so as to realize a voltage stabilizing and clamping function; the clamp branch is connected with a homodromous proportional operation circuit at the back, wherein R ₁ And R ₂ Selecting high-precision resistors, R, of the same low resistance ₁ 、R ₂ The resistance values should be the same so that the output value of the same direction proportional operation circuit is equal to the on-state voltage drop value of the tested device.

6. The on-line voltage drop monitoring circuit for the power device as claimed in claim 1, wherein the device to be tested is a SiCSMOSFET or an IGBT, an anti-parallel diode is arranged on the IGBT, and the on-line voltage drop monitoring circuit is connected between an emitter (E) and a collector (C) of the IGBT in parallel.

7. An apparatus, characterized in that the apparatus uses the on-state voltage drop on-line monitoring circuit for power device as claimed in any one of claims 1-6 to measure the forward or/and reverse on-state voltage drop of the device under test.

8. The device of claim 7, wherein the device is a double pulse circuit having two devices under test, and an on-state voltage drop on-line monitoring circuit is connected in parallel to each device under test, and comprises a gate driver, a bus capacitor, and a bus voltage V _DC A device under test; a circuit formed by the bus voltage, the bus capacitor, the inductive load and the tested device can carry large voltage and large current, and is called a power main circuit; the devices to be tested used are respectively Q ₁ 、Q ₂ (ii) a The grid drive is connected with a drive circuit, the drive circuit is a circuit for providing a control signal for the switching tube, and the grid drive outputs the drive signal to control the lower tube Q ₂ The switch (2) has a driving frequency of 50-300 kHZ and a high-tube Q ₁ The gate of which is given a low level, or floating, only during the freewheeling phase by its body diode,and the upper pipe Q ₁ Test current source I of connected on-state voltage drop on-line monitoring circuit _sense And the source electrode or the emitter electrode of the tested device is connected with the lower tube Q ₂ Is connected to the drain or collector of; and a lower tube Q ₂ Test current source I of connected on-state voltage drop on-line monitoring circuit _sense The source electrode or emitter electrode connecting position of the tested device is grounded; upper tube Q ₁ Parallel inductive load, lower tube Q ₂ The grid of the grid is connected with the grid driver; the bus voltage and the bus capacitor are connected in parallel on the upper tube Q ₁ And a lower tube Q ₂ To (c) to (d);

when the driving signal outputs a high level, the lower tube Q ₂ On, bus voltage V _DC And an inductive load L _load And a lower tube Q ₂ Form a closed loop when the lower tube Q ₂ The voltage at both ends is the on-state voltage drop, and when the driving circuit outputs a low level, the lower tube Q ₂ Is turned off when the inductive load L _load Continuously upward pipe Q ₁ Discharging, current passing through the upper tube Q ₁ The body diode or the anti-parallel diode form a closed loop, and the tube Q is arranged at the moment ₁ The voltage at both ends is the voltage drop of the body diode or the anti-parallel diode.

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