Circuit structure for realizing IGBT follow current and on-state voltage drop extraction by multiplexing Cascode diode

Abstract

The invention discloses a circuit structure for realizing IGBT follow current and on-state voltage drop extraction by multiplexing Cascode diodes, and belongs to the technical field of power semiconductor devices. The circuit structure comprises a cascade diode structure connected in parallel between a collector electrode and an emitter electrode of an IGBT to be tested; the low-voltage clamping circuit is connected in parallel with the two ends of the low-voltage silicon Schottky barrier diode in the structure; the cascode diode structure is formed by connecting a high-voltage normally-on silicon carbide junction field effect transistor and a low-voltage silicon Schottky barrier diode in a cascode manner; the low-voltage clamping circuit consists of a resistor and two voltage stabilizing diodes which are reversely connected in series; when the IGBT is turned off, the high-voltage blocking function is automatically achieved, when the IGBT is turned on, a follow current path is automatically formed, a signal corresponding to the on-state voltage drop of the IGBT is synchronously output from the low-voltage clamping circuit, and meanwhile the functions of a follow current diode and an on-state voltage measuring circuit are achieved. According to the invention, the circuit structure is simplified, the cost and the loss are reduced, and the high-speed and high-precision measurement requirements of the on-state voltage drop of the IGBT are met.

Description

Technical Field

[0001] This invention belongs to the field of power semiconductor device technology, specifically relating to a circuit structure that uses multiplexed Cascode diodes to realize IGBT freewheeling and on-state voltage drop extraction. Background Technology

[0002] As a mainstream new power semiconductor device, the silicon (Si) insulated gate bipolar transistor (IGBT) is widely used in power electronics fields such as electric vehicles, motor frequency conversion speed regulation, and distributed photovoltaic inverters due to its advantages such as low saturation voltage drop, low power loss, and high input impedance. However, IGBTs themselves lack reverse conduction capability, and a free-wheeling diode (FWD) must be connected in anti-parallel between the collector and emitter to ensure normal circuit operation under inductive loads and other conditions. Meanwhile, the on-state voltage drop of the IGBT (… V on_ds The on-state voltage (OVMC) is a key indicator reflecting the aging degree of a device. To prevent sudden failures caused by aging, this parameter needs to be extracted in real time through an on-state voltage measurement circuit.

[0003] In order to extract V on_ds Traditional solutions typically require an additional independent OVMC outside the IGBT main power circuit. However, this traditional discrete design approach has the following significant drawbacks: First, structurally, FWD and OVMC usually exist as independent modules, resulting in complex circuit topology, a large number of components, and a large layout space, which is not conducive to the miniaturization and integration of the system.

[0004] Secondly, in terms of cost and performance, standalone OVMCs often require additional precision sampling resistors, isolation operational amplifiers, or dedicated measurement chips, which increases system cost and power consumption. At the same time, in order to ensure measurement safety, OVMCs need to withstand the same high-voltage isolation requirements as the main circuit, which further increases cost and design difficulty.

[0005] Finally, in terms of performance matching, discrete designs struggle to simultaneously optimize freewheeling and measurement performance. For example, the characteristics of a fast recovery diode chosen to achieve fast freewheeling may conflict with the requirements of high-precision voltage measurement; and parasitic parameters introduced by the measurement circuit may affect the switching speed of the main circuit.

[0006] Therefore, traditional discrete solutions cannot simultaneously meet the requirements of simplifying circuit structure, reducing overall cost and losses, and improving circuit performance. V on_dsThis invention addresses the combined need for high-speed (fast response) and high-precision (small error) measurements. It is specifically proposed to overcome the shortcomings of the existing technologies mentioned above. Summary of the Invention

[0007] The technical problem to be solved by this invention is to address the shortcomings of the prior art by providing a circuit structure for extracting IGBT freewheeling current and on-state voltage drop using a multiplexed Cascode diode. This structure simultaneously realizes the functions of the freewheeling diode and on-state voltage measurement circuit during IGBT operation. It solves the problems of complex circuit structure, numerous high-voltage components, high system cost and losses, complex driving and control, and difficulty in simultaneously meeting high-speed and high-precision measurement requirements caused by the separate design of the freewheeling diode and on-state voltage measurement circuit in traditional solutions. While simplifying the circuit structure, it also effectively meets the requirements of high-speed and high-precision measurement. V on_ds The need for high-speed, high-precision, and low-cost measurement.

[0008] The present invention adopts the following technical solution: A circuit structure for extracting IGBT freewheeling current and on-state voltage drop using multiplexed Cascode diodes includes a common-gate common-source diode structure and a low-voltage clamping circuit. The common-gate common-source diode structure is connected in parallel between the collector and emitter of the IGBT under test; The low-voltage clamping circuit is connected in parallel across the low-voltage silicon Schottky barrier diode in the common-gate common-source diode structure to achieve voltage clamping and on-state voltage drop signal extraction. The common-gate common-source diode structure is configured to provide high-voltage blocking when the IGBT under test is turned off and to form a freewheeling path when the IGBT under test is turned on. The low-voltage clamping circuit is configured to output a signal voltage corresponding to the on-state voltage drop of the IGBT under test when the IGBT under test is turned on, thereby realizing the multiplexing of the freewheeling function and the on-state voltage extraction function.

[0009] Preferably, the common-gate common-source diode structure includes a high-voltage normally-through junction field-effect transistor (JFET) and a low-voltage silicon Schottky barrier diode; the gate and source of the high-voltage normally-through JFET are connected together and connected to the anode of the low-voltage silicon Schottky barrier diode; the drain of the high-voltage normally-through JFET and the cathode of the low-voltage silicon Schottky barrier diode serve as the two ends of the common-gate common-source diode structure, respectively.

[0010] Preferably, the high-voltage normally-through junction field-effect transistor is a silicon carbide junction field-effect transistor.

[0011] Preferably, the low-voltage Schottky barrier diode is a silicon Schottky barrier diode.

[0012] Preferably, the low-voltage clamping circuit includes a resistor and two Zener diodes; the two Zener diodes are connected in reverse series and then in series with the resistor to form a series branch, which is connected in parallel across the low-voltage Schottky barrier diode.

[0013] Preferably, the two Zener diodes have different Zener voltage values.

[0014] Preferably, the common connection point between the resistor and the two Zener diodes serves as the output terminal of the on-state voltage drop signal.

[0015] Preferably, the circuit structure has two operating modes: a freewheeling diode operating mode and an on-state voltage measurement circuit operating mode, and the mode switching is automatically completed based on the on / off state of the IGBT.

[0016] Preferably, the common-gate common-source diode structure has a forward voltage drop in freewheeling mode that is lower than that of a silicon carbide Schottky diode with the same rated parameters, and has no reverse recovery current.

[0017] Preferably, when the IGBT is turned off, the silicon carbide junction field-effect transistor in the common-gate common-source diode structure is cut off, the low-voltage silicon Schottky barrier diode is reverse biased, and the Zener diode in the low-voltage clamping circuit remains in a clamping state, sharing the high voltage between the collector and emitter of the IGBT.

[0018] Compared with the prior art, the present invention has at least the following beneficial effects: A circuit structure using multiplexed Cascode diodes to extract IGBT freewheeling current and on-state voltage drop is presented. Through the collaborative design of a common-gate common-source diode structure and a low-voltage clamping circuit, it overcomes the limitations of traditional discrete FWD and OVMC layouts, achieving dual-function multiplexing. The common-gate common-source diode is connected in parallel to the IGBT collector-emitter junction, and the low-voltage clamping circuit is connected in parallel across a low-voltage silicon Schottky barrier diode. This allows for automatic switching of operating modes based on the IGBT's on / off state without the need for an additional control module. This fundamentally simplifies the circuit architecture, reduces the number of components and connection complexity, lowers assembly and drive costs, and ensures that freewheeling and measurement functions do not interfere with each other. This lays the structural foundation for subsequent performance optimization and fully meets the integrated requirements of IGBT state monitoring.

[0019] Furthermore, the gate and source of the high-voltage normally-on junction field-effect transistor (JFET) are connected together and then to the anode of the SBD, with the drain and the cathode of the SBD serving as the two ends of the structure. This connection method allows the device characteristics to complement each other: the normally-on JFET ensures the rapid formation of a low-resistance freewheeling path when the IGBT is turned on, while the common-gate, common-source structure enhances the high-voltage blocking capability when the IGBT is turned off. This connection not only ensures low loss during freewheeling but also provides a stable carrier for extracting the on-state voltage drop signal, avoiding the shortcomings of a single device in simultaneously meeting high-voltage tolerance and signal sensitivity, thus providing a reliable physical basis for structural reuse.

[0020] Furthermore, SiC JFETs exhibit excellent high-voltage and high-temperature resistance, stably handling the high-voltage blocking task during IGBT turn-off and avoiding the risk of low-voltage device breakdown. Simultaneously, SiC material has low on-resistance, low power consumption during freewheeling, and fast switching speed, enabling the circuit to achieve a dynamic response of 130ns. Compared to traditional silicon-based devices, its normally-on characteristics are better suited for automatic mode switching, requiring no additional drive signal to change the operating mode according to the IGBT's on / off state, further improving circuit reliability and integration.

[0021] Furthermore, Si SBDs have a low forward conduction voltage, which reduces freewheeling circuit losses and improves system efficiency. The absence of reverse recovery current avoids the electromagnetic interference and additional losses caused by the reverse recovery of traditional freewheeling diodes, optimizing circuit electromagnetic compatibility. At the same time, Si SBD technology is mature and cost-controllable, and when paired with SiC JFETs, they form a complementary high- and low-voltage device combination, ensuring freewheeling performance while controlling overall cost.

[0022] Furthermore, the branch formed by the resistor and two reverse-connected Zener diodes not only limits the output voltage range through the clamping characteristics of the Zener diodes to prevent signal overload, but also limits the loop current through the resistor, protecting the Zener diodes from overcurrent damage. This structure eliminates the need for complex active components, achieving accurate signal extraction solely through a combination of passive components. It simplifies circuit design while reducing power consumption, ensuring a high degree of consistency between the output signal and the IGBT's on-state voltage drop, thus guaranteeing high-precision measurements.

[0023] Furthermore, by using differentiated combinations of regulated voltage values, the actual range of the IGBT's on-state voltage drop is precisely matched. The specification uses 15V and 3.3V Zener diodes, which can be flexibly adapted according to the IGBT's rated parameters, avoiding the problem that a single regulated voltage value cannot cover the measurement range or that the clamping accuracy is insufficient. After different regulated voltage values ​​are connected in reverse series, it can both clamp the signal at the upper limit to prevent the signal from exceeding the range and stabilize the signal baseline at the lower limit, ensuring that the extracted voltage signal truly reflects the IGBT's on-state voltage drop, improving measurement accuracy, and enhancing the circuit's compatibility with IGBTs of different specifications.

[0024] Furthermore, optimizing the signal extraction path by limiting the location of the signal output terminal improves measurement convenience and accuracy. The common connection point of the resistor and two Zener diodes serves as the output terminal, allowing direct acquisition of the stable signal after clamping and current limiting, eliminating the need for additional voltage dividers or converters and reducing signal transmission loss and interference. This design enables close connection between the signal output and the measurement circuit, shortening the transmission path, reducing the impact of electromagnetic interference on the measurement results, and simplifying the connection of subsequent testing equipment, thus enhancing the circuit's practicality and operability.

[0025] Furthermore, the operating modes and automatic switching characteristics are clearly defined, achieving intelligent mode switching without the need for additional control signals or driving devices. Based on the automatic switching logic of the IGBT's on / off state, manual intervention or complex control algorithms are avoided, simplifying the circuit drive system and reducing the failure rate. Seamless integration between freewheeling mode and measurement mode ensures uninterrupted freewheeling protection and status monitoring throughout the IGBT's operation, adapting to real-time requirements under dynamic operating conditions while reducing control costs and improving the circuit's adaptability in complex power electronic systems.

[0026] Furthermore, the performance advantages of the limited freewheeling mode lie in overcoming the performance bottlenecks of traditional SiC Schottky diodes. Lower forward voltage means lower freewheeling losses and higher system efficiency; the absence of reverse recovery current avoids voltage spikes and electromagnetic interference during reverse recovery, improving circuit stability and reliability. This characteristic makes the circuit perform better in high-frequency switching scenarios, adapting it to high-frequency operating conditions such as electric vehicles and photovoltaic inverters, while reducing electromagnetic interference to surrounding devices, lowering the complexity of system EMC design, and expanding the range of application scenarios.

[0027] Furthermore, when the IGBT is turned off, the SiC JFET is cut off, the SBD is reverse biased, and the Zener diode remains clamped, thus reasonably distributing the high voltage between the IGBT collector and emitter and preventing low-voltage devices from breaking down due to overvoltage. This design eliminates the need for an additional high-voltage protection module, achieving passive protection through the existing circuit structure. This simplifies the circuit, improves reliability, ensures long-term stable operation of devices under high-voltage conditions, reduces failure risk and maintenance costs, and extends system lifespan.

[0028] In summary, the circuit structure of this invention effectively unifies the IGBT freewheeling function and on-state voltage measurement function through structural reuse, taking into account the requirements of high precision, fast response and circuit simplification, and has significant advantages in engineering applications and promotional value.

[0029] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Attached Figure Description

[0030] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the following description of the relative embodiments will be briefly introduced. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0031] Figure 1 The circuit schematic for extracting IGBT freewheeling current and on-state voltage drop by using multiplexed Cascode diodes; Figure 2 This is an equivalent model diagram of the FWD operating mode of the circuit of the present invention; Figure 3 This is an equivalent model diagram of the OVMC operating mode of the circuit of the present invention; Figure 4 This is a schematic diagram of the actual structure layout of the circuit prototype of the present invention; Figure 5 The following are typical waveform comparison diagrams of the circuit of the present invention in the FWD working state, where (a) is the forward conduction characteristic curve and (b) is the reverse recovery characteristic curve. Figure 6 The following are typical waveform comparison diagrams of the circuit of the present invention in the OVMC working state, where (a) is the measurement error curve and (b) is the dynamic response characteristic curve. Detailed Implementation

[0032] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0033] In the description of this invention, it should be understood that the terms "center," "longitudinal," "lateral," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "one side," "one end," and "one side," etc., indicating orientation or positional relationships based on the orientation or positional relationships shown in the accompanying drawings, are only for the convenience of describing the invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of the invention. Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Thus, a feature defined with "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this invention, unless otherwise stated, "a plurality of" means two or more.

[0034] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0035] It should be understood that, when used in this specification and the appended claims, the terms "comprising" and "including" indicate the presence of the described features, integrals, steps, operations, elements and / or components, but do not exclude the presence or addition of one or more other features, integrals, steps, operations, elements, components and / or collections thereof.

[0036] It should also be understood that the terminology used in this specification is for the purpose of describing particular embodiments only and is not intended to limit the invention. As used in this specification and the appended claims, the singular forms “a,” “an,” and “the” are intended to include the plural forms unless the context clearly indicates otherwise.

[0037] It should also be further understood that the term "and / or" as used in this specification and the appended claims refers to any combination of one or more of the associated listed items and all possible combinations, and includes such combinations.

[0038] The accompanying drawings illustrate various structural schematic diagrams according to embodiments disclosed in this invention. These drawings are not to scale, and some details have been enlarged for clarity, and some details may have been omitted. The shapes of the various regions and layers shown in the drawings, as well as their relative sizes and positional relationships, are merely exemplary and may deviate from reality due to manufacturing tolerances or technical limitations. Furthermore, those skilled in the art can design regions / layers with different shapes, sizes, and relative positions as needed.

[0039] This invention provides a circuit structure for extracting IGBT freewheeling current and on-state voltage drop using multiplexed Cascode diodes. It combines the IGBT freewheeling circuit with the on-state voltage measurement circuit, proposing a novel circuit structure composed of a common-gate common-source diode and a low-voltage clamping circuit. The common-gate common-source diode is multiplexed to achieve both freewheeling current and on-state voltage extraction. This invention simplifies the circuit structure, eliminates the need for additional active components, has good compatibility, reduces circuit cost and losses, and makes it possible to integrate power devices with the measurement circuit. The circuit structure of this invention can optimize IGBT aging test circuits, meeting the requirements of IGBT aging test circuits. V on_ds It meets the requirements of high speed and high precision in measurement, and has good integration and strong compatibility.

[0040] Please see Figure 1This invention discloses a circuit structure for IGBT freewheeling and on-state voltage drop extraction using a multiplexed Cascode diode. The structure includes a Cascode Diode and a Low-Voltage Clamping Circuit (LVCC). A high-voltage normally-conducting silicon carbide (SiC) junction field-effect transistor (JFET) and a low-voltage silicon (Si) Schottky barrier diode (SBD) are connected in a common-gate, common-source configuration to form a Cascode Diode structure, which is then connected in parallel across the collector and emitter of the IGBT module. A small resistor (R1) is connected in series with two reverse-connected Zener diodes (Dz1, Dz2) to form a Low-Voltage Clamping Circuit (LVCC) structure, which is then connected in parallel across the Schottky barrier diode to achieve voltage clamping and signal extraction functions. The overall structure of the Cascode Diode and LVCC multiplexes the Cascode Diode to realize the functions of a freewheeling diode and an on-state voltage measurement circuit.

[0041] When the IGBT is off, the circuit performs the high-voltage blocking function. At this time, the JFET is cut off, the SBD is reverse biased, and the Zener diode in the LVCC remains clamped, thus sharing the high voltage between the collector and emitter and effectively preventing breakdown of low-voltage devices. When the IGBT is on, the JFET enters the on state, and current flows through the SBD to form a freewheeling path. Simultaneously, the LVCC outputs a signal voltage corresponding to the IGBT's on-state voltage drop, achieving multiplexing of the freewheeling and on-state voltage extraction functions.

[0042] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. The components of the embodiments of the present invention described and shown in the accompanying drawings can generally be arranged and designed in various different configurations. Therefore, the following detailed description of the embodiments of the present invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

[0043] Please see Figure 2 and Figure 3The figures show the equivalent circuit models for FWD and OVMC operation, respectively. Equivalent analysis reveals that in freewheeling mode, the current path primarily passes through the SBD and JFET, resulting in a low forward voltage drop and no reverse recovery issue. In on-state voltage measurement mode, the LVCC effectively limits the output voltage, ensuring the measured voltage matches the actual on-state voltage drop of the IGBT. Therefore, the circuit of this invention can automatically switch between the two operating modes without requiring additional control signals or active driving devices, resulting in a simple and reliable circuit structure.

[0044] The operating mode of this circuit is entirely determined autonomously by the state of the external power circuit, realizing passive intelligent switching.

[0045] When the IGBT is turned off, its collector (C) potential rapidly rises to a high voltage, which is applied across the entire Cascode diode structure. Since the JFET is normally-on, its gate-source is pulled low by the anode potential of the SBD, but its drain-source withstands the high voltage, effectively turning the JFET off; the SBD withstands a reverse voltage. At this time, the Zener diodes (Dz1, Dz2) in the LVCC quickly turn on because the forward voltage exceeds their regulation value, clamping the voltage across the SBD at (Vz1 + Vz2), effectively protecting the low-voltage SBD. The circuit is equivalent to... Figure 2 The blocking model shown.

[0046] When the IGBT is turned on, its collector-emitter voltage drops to the saturation voltage drop Vce(sat), which is much lower than (Vz1 + Vz2). At this time, the Zener diodes Dz1 and Dz2 are cut off due to insufficient forward voltage; the gate-source voltage of the JFET is provided by the forward conduction voltage drop of the SBD (approximately 0.7~1V), allowing it to conduct fully; the SBD is forward biased. Current flows through the JFET and SBD to form a freewheeling path. Simultaneously, because the Zener diode branch is cut off, the voltage across the SBD (approximately equal to Vce(sat)) is almost entirely applied to resistor R1 and the cut-off Zener diode branch. A low-voltage measurement signal proportional to Vce(sat) can be extracted from the common point of R1 and Dz1 / Dz2. The circuit is equivalent to... Figure 3 The measurement model shown.

[0047] Figure 3 The equivalent of the IGBT in the middle is its on-state voltage drop. V on_ds The common-gate common-source diode structure is equivalent to a linear transmission channel. Because the SiC JFET is conducting and the SBD is forward conducting, it can transmit... V on_ds The signal; the low-voltage clamping circuit is equivalent to a current-limiting resistor + bidirectional clamping unit. R1 limits the branch current, and Dz1 (15V) and Dz2 (3.3V) are connected in reverse series to form a bidirectional clamp, ensuring that the output voltage Vo is limited to the range of 0-18.3V, and is consistent with...V on_ds Linear correspondence. The signal transmission path is labeled in the model: IGBT's... V on_ds The signal is transmitted to both ends of the SBD through a common-gate common-source structure. After being processed by the clamping circuit, Vo is output from the common connection point of R1 and the Zener diode. This signal can be directly acquired by the detection equipment, demonstrating the simplicity and accuracy of the measurement circuit.

[0048] Please see Figure 4 The figure shows the physical structure of the prototype circuit of this invention. At the bottom of the figure is an aluminum heat sink (100mm × 80mm × 10mm). A SiIGBT module (package size 50mm × 40mm) is fixed to the left side of the heat sink. The collector (C) and emitter (E) terminals are led out from the upper right corner of the module. A common-gate common-source diode structure is connected in parallel between the collector and emitter. This structure uses a surface-mount package (size 20mm × 15mm) and is attached to the surface of the heat sink via a thermal pad. A small PCB board (size 30mm × 20mm) is fixed to the right side of the heat sink. The resistor R1 of the low-voltage clamping circuit and the Zener diodes Dz1 and Dz2 are soldered to the PCB board. The PCB board is connected to the anode and cathode of the Si IGBT in the common-gate common-source diode structure via wires. A reserved test interface (Vo) is located at the edge of the PCB board for easy connection to testing equipment. The figure also marks the positions of the fixing bolts and wire connection points of each component, clearly showing the assembly relationship and spatial layout of the prototype, ensuring assembly repeatability. In the experiment, a 1200V / 33A SiC JFET (model UJ3N120065K3S) and a 40V / 30A Si SBD (model RB228NS-40) were selected to form a Cascode Diode; Zener diode D Z1 D Z2 The BZX84C15LT1 (Vz=15V) and BZX84C3V3 (Vz=3.3V) resistors are selected respectively, and the resistor R1 is 250Ω. This parameter configuration can achieve stable freewheeling characteristics and high-precision voltage measurement under typical operating conditions.

[0049] The specific embodiments of the present invention are intended to describe in detail the circuit assembly, parameter selection, working process and performance verification, so as to ensure that those skilled in the art can repeat the implementation.

[0050] (1) Component selection and assembly A common-gate, common-source diode structure was constructed using a 1200V / 33A high-voltage normally-conducting SiC JFET (model UJ3N120065K3S) and a 40V / 30A Si SBD (model RB228NS-40). The gate and source of the SiC JFET were shorted together with a metal wire to form a common terminal, which was then soldered to the anode of the Si SBD. The drain of the SiC JFET and the cathode of the Si SBD served as the two terminals of the structure. The entire structure was packaged in a surface-mount package to reduce the mounting size. The low-voltage clamping circuit used a 250Ω metal film resistor (R1) and two Zener diodes (Dz1 and Dz2) with voltage regulation values ​​of 15V (model BZX84C15LT1) and 3.3V (model BZX84C3V3), respectively. The cathodes of Dz1 and Dz2 were reverse-connected to form a reverse series circuit, and then connected in series with R1 through copper foil traces on a printed circuit board (PCB) to form a complete branch.

[0051] The common-gate common-source diode structure is bolted to the collector and emitter terminals of the IGBT module (a 1200V / 50A SiIGBT module is selected), ensuring that the contact resistance at the connection point is less than 5mΩ. The low-voltage clamping circuit is directly connected in parallel to the anode and cathode of the Si SBD via PCB traces. A test interface is reserved at the common connection point of resistor R1 and the two Zener diodes for connecting an oscilloscope or data acquisition unit. The entire circuit and the IGBT module are fixed together on an aluminum heat sink, the surface of which is coated with thermal grease to ensure that the device operating temperature does not exceed 125℃.

[0052] (2) Detailed description of the work process Freewheeling diode (FWD) operating mode: When the IGBT is turned off, the reverse current generated by the inductive load needs to form a discharge path. At this time, the SiC JFET remains in the off state due to the high voltage after the IGBT is turned off, the Si SBD is reverse biased, and Dz1 and Dz2 in the low-voltage clamping circuit are in the clamping state, which distributes the high voltage between the collector and emitter of the IGBT across the SiC JFET and the clamping circuit, preventing the Si SBD from breaking down. When the IGBT is turned on, the gate-source voltage difference of the SiC JFET meets the conduction condition, and it quickly enters the low-resistance conduction state. The reverse current forms a freewheeling path through the drain of the SiC JFET → source → anode of the Si SBD → cathode, realizing the discharge of load energy.

[0053] On-state voltage measurement (OVMC) operating modes: When the IGBT is turned on, the on-state voltage drop between its collector and emitter is transmitted to the Si SBD terminals through the common-gate common-source diode structure. The low-voltage clamping circuit limits the output voltage range through the voltage regulation characteristics of Dz1 and Dz2, ensuring that the output signal corresponds linearly to the IGBT on-state voltage drop. Resistor R1 limits the loop current to prevent overcurrent of the Zener diode. Through the test interface at the common connection point, a stable voltage signal corresponding to Von_ds can be directly acquired, achieving high-precision measurement.

[0054] (3) Performance verification The experimental tests were conducted at room temperature (25℃), with the IGBT operating frequency at 10kHz and the load current at 10A. The test results showed that in freewheeling mode, the forward voltage drop was 1.2V, lower than the 1.5V of a SiC Schottky diode with the same rating, and there was no reverse recovery current. In measurement mode, the voltage measurement error was 0.3mV, the relative error was 0.15‰, and the dynamic response time was 128ns, meeting the design requirements. Under light load (2A load current), the system efficiency increased from 89% in the traditional discrete solution to 94%, verifying the circuit's high efficiency and reliability.

[0055] The present invention also provides the following alternative embodiments, in which the core structure remains unchanged, but only the device parameters or models are adjusted, and the same function can still be achieved: Example 1: Component Model Replacement The high-voltage normally-operated SiC JFET is replaced with the 1200V / 40A model (UJ4N120070K3S), and the low-voltage Si SBD is replaced with the 40V / 45A model (RB230NS-40). In the low-voltage clamping circuit, resistor R1 is a 200Ω metal film resistor, Zener diode Dz1 is a 12V type (BZX84C12LT1), and Dz2 is a 3V type (BZX84C3LT1).

[0056] With a freewheeling forward voltage drop of 1.1V, a measurement error of 0.4mV, a dynamic response of 132ns, and a 4% improvement in efficiency under light load, it is suitable for scenarios with higher current.

[0057] Example 2: Parameter Optimization and Replacement The high-voltage normally-continuous SiC JFET uses the 1700V / 33A model (UJ3N170065K3S), which is compatible with high-voltage IGBT modules. In the low-voltage clamping circuit, resistor R1 is selected as 300Ω, Zener diode Dz1 is selected as 18V, and Dz2 is selected as 4V.

[0058] It can withstand 1700V high voltage interruption, with a measurement error of 0.45mV, and is suitable for high voltage power electronic systems (such as high voltage photovoltaic inverters).

[0059] Please see Figure 5 and Figure 6 Typical waveforms obtained from the experiment Figure 5 For comparison of experimental waveforms during FWD operation, the test conditions were an ambient temperature of 25°C and a load current of 10A, to visually demonstrate the performance difference between the circuit of this invention and a traditional freewheeling diode. Figure 5 Figure (a) shows the forward conduction characteristic curve, with the horizontal axis representing the freewheeling current (A) and the vertical axis representing the forward voltage drop (V). The figure contains three curves: Preposed Circuit represents the circuit of this invention, Si FRD represents a traditional silicon-based fast recovery diode, and SiC SBD represents a silicon carbide Schottky diode with the same rated parameters. As can be seen from the curve trends, at a rated freewheeling current of 10A, the forward voltage drop of the circuit of this invention is only 1.2V, lower than the 1.5V of SiC SBD and the 1.8V of Si FRD; and as the current increases, the voltage drop growth rate of the circuit of this invention is gradual, indicating that it possesses low conduction loss characteristics over a wide current range, effectively reducing system freewheeling energy consumption, and is particularly suitable for energy loss control requirements under high-frequency switching conditions.

[0060] Figure 5 Figure (b) shows the reverse recovery characteristic curves, with the horizontal axis representing time (in ns) and the vertical axis representing reverse recovery current (in A). The Si FRD curve in the figure exhibits a significant reverse recovery current peak (approximately 5 A) and a reverse recovery time as long as 150 ns. This is an inherent defect of traditional silicon-based diodes due to the minority carrier storage effect, which leads to additional losses and electromagnetic interference. In contrast, the Preposed Circuit curve shows no reverse recovery current peak, and the reverse current rapidly decays to zero. This indicates that the circuit of this invention, through the complementary characteristics of the common-gate common-source diode structure, completely eliminates the reverse recovery problem, significantly reducing electromagnetic interference (EMI), simplifying system EMC design, and simultaneously avoiding the impact of reverse recovery voltage spikes on the IGBT, thus improving circuit reliability.

[0061] Figure 6 This is a typical waveform comparison diagram of the circuit of the present invention in the working state of the on-state voltage measurement circuit (OVMC). The test conditions are an ambient temperature of 25℃ and an IGBT operating frequency of 10kHz, which is used to verify the accuracy of the on-state voltage drop measurement and the dynamic response performance.

[0062] Figure 6Figure (a) shows the measurement error curve, with the horizontal axis representing the IGBT on-state current (A) and the vertical axis representing the on-state voltage drop measurement error (mV). The Preposed Circuit curve in the figure shows that within a wide current range of 2A-15A, the measurement error of the circuit of this invention is consistently controlled within 0.5mV, with a maximum relative error not exceeding 0.2‰. In contrast, the traditional OVMC circuit (not labeled in the figure, refer to existing technology data) generally exhibits a measurement error greater than 1mV under the same operating conditions, and the error increases sharply when the current deviates from the rated value. This waveform demonstrates that the circuit of this invention, through precise clamping of the low-voltage clamping circuit and signal transmission design, achieves high-precision measurement of the on-state voltage drop, exhibits excellent error stability, accurately reflects the aging state of the IGBT, and provides reliable data support for device fault early warning.

[0063] Figure 6 Figure (b) shows the dynamic response characteristic curve, with the horizontal axis representing time (in ns) and the vertical axis representing the output signal voltage (in V). The VCE curve in the figure represents the actual on-state voltage drop waveform between the IGBT collector and emitter, and the Vo curve represents the measurement signal waveform extracted by the circuit of this invention. It can be seen that when the IGBT is turned on (approximately 50 ns), the Vo signal rapidly follows the VCE waveform, rising from 0V to a stable value corresponding to VCE, with a dynamic response time of only 130 ns (the time difference from signal initiation to stabilization). In contrast, the dynamic response time of traditional OVMC circuits typically exceeds 200 ns, exhibiting significant signal delay. This waveform verifies the high-speed response characteristics of the circuit of this invention, which can adapt to the dynamic measurement requirements of IGBT high-frequency conduction (e.g., above 10kHz), ensuring accurate capture of the on-state voltage drop signal even under rapid switching conditions, and avoiding measurement distortion caused by response lag. It can be seen that the forward voltage drop of the circuit of this invention in freewheeling mode is lower than that of a SiC Schottky diode with the same rating, and there is no reverse recovery current. In on-state voltage extraction mode, the output voltage waveform is highly consistent with the collector-emitter voltage of the IGBT, indicating high measurement accuracy. Test results show that the voltage measurement error of the circuit of this invention is less than 0.5mV, the relative error does not exceed 0.2‰, and the dynamic response time is about 130ns, which can meet the requirements of high precision and fast measurement.

[0064] Compared to the traditional discrete design of FWD and OVMC, this invention requires only a single high-voltage JFET to achieve both freewheeling and on-state voltage extraction functions, reducing the number of high-voltage devices by more than 50%, simplifying the structure and drive connections, and lowering overall cost and losses. System efficiency is improved by approximately 3%–5% under light load conditions, demonstrating good potential for modular integration.

[0065] In summary, this invention presents a circuit structure for IGBT freewheeling and on-state voltage drop extraction using multiplexed Cascode diodes. Through the multiplexing design of a common-gate common-source diode structure and a low-voltage clamping circuit, the functions of IGBT freewheeling and on-state voltage drop extraction are unified. Compared to traditional discrete solutions, this simplifies the circuit structure, reduces high-voltage components by more than 50%, eliminates the need for additional active driver devices, lowers costs and system losses, and improves efficiency by 3%~5% under light load. In freewheeling mode, the forward voltage drop is low, there is no reverse recovery current, the on-state voltage drop measurement error is less than 0.5mV, the relative error does not exceed 0.2‰, and the dynamic response is approximately 130ns, balancing high speed and high precision requirements. Simultaneously, it can share the high voltage when the IGBT is turned off, protecting low-voltage components. It boasts strong integration and compatibility, making it suitable for scenarios such as electric vehicles and photovoltaic inverters, and possesses significant engineering application value.

[0066] The above content is only for illustrating the technical concept of the present invention and should not be construed as limiting the scope of protection of the present invention. Any modifications made to the technical solution based on the technical concept proposed in this invention shall fall within the scope of protection of the claims of this invention.

Claims

1. A circuit structure for extracting IGBT freewheeling current and on-state voltage drop using multiplexed Cascode diodes, characterized in that, Includes a common-gate common-source diode structure and a low-voltage clamping circuit; The common-gate common-source diode structure is connected in parallel between the collector and emitter of the IGBT under test; The low-voltage clamping circuit is connected in parallel across the low-voltage silicon Schottky barrier diode in the common-gate common-source diode structure to achieve voltage clamping and on-state voltage drop signal extraction. The common-gate common-source diode structure is configured to provide high-voltage blocking when the IGBT under test is turned off and to form a freewheeling path when the IGBT under test is turned on. The low-voltage clamping circuit is configured to output a signal voltage corresponding to the on-state voltage drop of the IGBT under test when the IGBT under test is turned on, thereby realizing the multiplexing of the freewheeling function and the on-state voltage extraction function.

2. The circuit structure for extracting IGBT freewheeling current and on-state voltage drop using multiplexed Cascode diodes according to claim 1, characterized in that, The common-gate common-source diode structure includes a high-voltage normally-through junction field-effect transistor (JFET) and a low-voltage silicon Schottky barrier diode (SSD). The gate and source of the high-voltage normally-through JFET are connected together and connected to the anode of the low-voltage SSD. The drain of the high-voltage normally-through JFET and the cathode of the low-voltage SSD serve as the two ends of the common-gate common-source diode structure.

3. The circuit structure for extracting IGBT freewheeling and on-state voltage drop using multiplexed Cascode diodes according to claim 2, characterized in that, The high-voltage normally-through junction field-effect transistor is a silicon carbide junction field-effect transistor.

4. The circuit structure for extracting IGBT freewheeling current and on-state voltage drop using multiplexed Cascode diodes according to claim 2, characterized in that, The low-voltage Schottky barrier diode is a silicon Schottky barrier diode.

5. The circuit structure for extracting IGBT freewheeling current and on-state voltage drop using multiplexed Cascode diodes according to claim 1, characterized in that, The low-voltage clamping circuit includes a resistor and two Zener diodes; the two Zener diodes are connected in reverse series and then in series with the resistor to form a series branch, which is connected in parallel across the low-voltage Schottky barrier diode.

6. The circuit structure for extracting IGBT freewheeling current and on-state voltage drop using multiplexed Cascode diodes according to claim 5, characterized in that, The two Zener diodes have different Zener voltage values.

7. The circuit structure for extracting IGBT freewheeling current and on-state voltage drop using multiplexed Cascode diodes according to claim 5, characterized in that, The common connection point between the resistor and the two Zener diodes serves as the output terminal of the on-state voltage drop signal.

8. The circuit structure for extracting IGBT freewheeling current and on-state voltage drop using multiplexed Cascode diodes according to claim 1, characterized in that, The circuit structure has two operating modes: a freewheeling diode operating mode and an on-state voltage measurement circuit operating mode. The mode switching is automatically completed based on the on / off state of the IGBT.

9. The circuit structure for extracting IGBT freewheeling current and on-state voltage drop using multiplexed Cascode diodes according to claim 8, characterized in that, The common-gate common-source diode structure has a lower forward voltage drop in freewheeling mode than a silicon carbide Schottky diode with the same rated parameters, and has no reverse recovery current.

10. The circuit structure for extracting IGBT freewheeling current and on-state voltage drop using a multiplexed Cascode diode according to any one of claims 1 to 9, characterized in that, When the IGBT is turned off, the silicon carbide junction field-effect transistor in the common-gate common-source diode structure is cut off, the low-voltage silicon Schottky barrier diode is reverse biased, and the Zener diode in the low-voltage clamping circuit remains in the clamping state, sharing the high voltage between the collector and emitter of the IGBT.

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