An easily scalable power device on-state voltage drop online measurement circuit

Abstract

The application discloses an easily-expandable power device conduction voltage drop online measurement circuit, and belongs to the technical field of electric power devices. The circuit comprises a clamping unit and n pressure-bearing units in series, wherein one end of the first pressure-bearing unit in series is used for connecting the collector of a power device to be measured, one end of the last pressure-bearing unit in series is connected with one end of the clamping unit, the other end of the clamping unit is used for connecting the emitter of the power device to be measured, and the two ends of the clamping unit serve as measurement output ends; when the power device to be measured is turned on, the pressure-bearing units are completely turned on, and the clamping unit outputs the conduction voltage drop of the power device to be measured; when the power device to be measured is turned off, the pressure-bearing units bear a value close to the off voltage of the power device, and the clamping unit outputs a clamping value. The circuit extracts the conduction voltage drop of the device to be measured through cooperation of the pressure-bearing units and the clamping unit, and effectively clamps the off voltage; the structure is simple, easy to expand and high in flexibility.

Description

Technical Field

[0001] This invention relates to the field of power device technology, and in particular to an easily expandable online measurement circuit for the on-state voltage drop of power devices. Background Technology

[0002] High-power power electronic converters are core equipment supporting new energy power generation, high-efficiency motor drives, and flexible DC power transmission. As the core sub-component of the converter, the reliability of power semiconductor devices is crucial to the safe and stable operation of the entire converter system. Therefore, real-time monitoring of the health status of power semiconductor devices is of paramount importance.

[0003] On-state voltage drop is a typical characteristic parameter of power semiconductor devices. It is not only a temperature-sensitive electrical parameter, but also related to the degree of degradation of the bonding wires of power semiconductor devices. Therefore, real-time measurement of on-state voltage drop can not only reflect the junction temperature of the power semiconductor device chip, but also be used to sense the aging degree of the device in real time, providing a powerful and effective means for real-time temperature protection, fault early warning and health management of power semiconductor devices.

[0004] Because power semiconductor devices in power electronic converters switch between on and off states in real time, and because these devices need to withstand voltages of hundreds or thousands of volts when off, while their on-state voltage drop is typically less than 4V when on, directly measuring the on-state voltage drop with a large range of measurement systems cannot guarantee accuracy. To accurately measure the on-state voltage drop of power devices, the most widely used method currently is... Figure 1 The dual-diode circuit shown utilizes D2 as a high-voltage blocking diode. When the device under test (DUT) is turned on, the circuit's output is its forward voltage drop, thus allowing for relatively accurate measurement of the power device's forward voltage drop. However, this circuit cannot avoid the influence of temperature drift on the voltage drops of diodes D1 and D2, resulting in a certain degree of temperature drift error. Summary of the Invention

[0005] In view of the shortcomings of the prior art described above, the purpose of this invention is to provide an easily expandable online measurement circuit for the on-state voltage drop of power devices, which solves the problems of the accuracy of the on-state voltage drop measurement circuit for power devices being easily affected by temperature, the difficulty in expansion, and the complexity of the structure.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0007] An easily expandable online measurement circuit for on-state voltage drop of power devices includes a clamping unit and n voltage-bearing units connected in series. One end of the first voltage-bearing unit connected in series is used to connect to the collector of the power device under test, one end of the last voltage-bearing unit connected in series is connected to one end of the clamping unit, and the other end of the clamping unit is used to connect to the emitter of the power device under test. The two ends of the clamping unit serve as measurement output terminals.

[0008] When the device under test (DUT) is turned on, the pressure-bearing unit is fully turned on, and the output of the clamping unit is the on-state voltage drop of the DUT. When the DUT is turned off, the pressure-bearing unit withstands a value close to the off-state voltage of the DUT, and the output of the clamping unit is the clamping value.

[0009] Furthermore, the pressure-bearing unit includes a depletion-mode field-effect transistor (MOSFET), connecting resistors R0 and R1, and a static voltage-equalizing resistor R. M Dynamic voltage equalization resistor R D Dynamic voltage equalization capacitor C D ;

[0010] One end of R1 is connected to the source of the MOSFET, and the other end of R1 is connected to R0 and R1 respectively. M and C D One end of R0 is connected to the gate of the MOSFET, and the other end of C is connected to the gate of the MOSFET. D The other end is connected to R D One end, R D The other end and R M The other end is connected to the drain of the MOSFET.

[0011] Furthermore, in the series of n pressure-bearing units, the other end of R1 of the previous pressure-bearing unit is connected to the drain of the MOSFET of the next pressure-bearing unit, the drain of the MOSFET of the first pressure-bearing unit in series is connected to the collector of the power device under test, and the other end of R1 of the nth pressure-bearing unit in series is connected to the clamping unit.

[0012] Furthermore, combining the transfer characteristic formula I = f(V) satisfied by the leakage current on the MOSFET... GS ) and I = -V GS / R1, by adjusting the resistance value of R1, based on the intersection of the two curves, ensures that the depletion-mode MOSFET operates at a suitable operating point under voltage; where I represents the leakage current, V GS f(.) represents the voltage between the gate and drain of the MOSFET, and f(.) represents the transfer characteristic function.

[0013] Furthermore, in the aforementioned pressure-bearing unit, the selection of the depletion-mode MOSFET and the static voltage-equalizing resistor R... M The process of determining the resistance value includes:

[0014] 2n MOSFETs were randomly selected from the same batch of candidates, and the body diode voltage drop V was measured under the same low current. F,1-2n Determine |V F,max -V F,min Does | < 0.01V hold true, where V F,max V F,min These represent the maximum and minimum body diode voltage drops under low current conditions in 2n depletion-mode MOSFETs, respectively.

[0015] If not, re-select 2n depletion-mode MOSFETs; if yes, select n MOSFETs from the 2n depletion-mode MOSFETs for low-voltage testing, discarding those that withstand a voltage V. DS MOSFETs with a depletion potential of ≈0 are removed from the pool of candidates and replaced by the remaining n depletion potential MOSFETs until n depletion potential MOSFETs that meet the conditions are obtained.

[0016] The n depletion-type field-effect transistors (MOSFETs) obtained in the first round of screening are connected in parallel with a static voltage equalization resistor R with a value in the MΩ range. M Perform a low-pressure test again and calculate the maximum pressure unevenness |V DS,max -V DS,min |=ΔI max *R M , where ΔI max R is the difference between the maximum and minimum leakage current flowing through n depletion-mode MOSFETs. M This is the static equalizing resistance value, V. DS,max V DS,min These represent the maximum and minimum voltages that n depletion-mode MOSFETs can withstand during low-voltage testing, respectively.

[0017] Determine ΔI max *R M <ΔV DS,set Whether it holds true, where ΔV DS,set Let R be the expected maximum static voltage imbalance for n depletion-mode MOSFETs. If so, complete the static voltage equalization test; otherwise, reduce R. M The resistance value can be adjusted, or the depletion-type MOSFET can be replaced from the alternatives.

[0018] Furthermore, the dynamic voltage equalization capacitor C D The value is on the same order of magnitude as the inter-electrode capacitance of the MOSFET, and satisfies R D C D <0.25t p , t p This represents the voltage rise time.

[0019] Furthermore, the clamping unit includes a first Schottky diode D. a1 First Zener diode Z1, second Schottky diode D a2 ;

[0020] The D mentioned a1 The cathode of Z1 is connected to the cathode of Z2, and the anode of Z1 is connected to the cathode of D. a2 The anode is connected and serves as one end of the clamping unit, D a2 Cathode and D a1 The anode is connected and serves as the other end of the clamping unit, with the regulated voltage V of Z1. Z1 It is greater than the on-state voltage drop of the power device under test.

[0021] Furthermore, the clamping unit includes a first Schottky diode D. a1 First Zener diode Z1, second Schottky diode D a2 The second Zener diode, Z2;

[0022] The D mentioned a1 The cathode of Z1 is connected to the cathode of Z2, and the anode of Z1 is connected to the cathode of D. a2 The anode is connected and serves as one end of the clamping unit, D a2 The cathode of Z1 is connected to the cathode of Z2, and the anode of Z2 is connected to D. a1 The anode is connected and serves as the other end of the clamping unit; the regulated voltage V of Z1 and Z2 Z1 V Z2 It is greater than the on-state voltage drop of the power device under test.

[0023] Furthermore, when the clamping unit is connected to the measurement circuit, one end of the clamping unit is connected to the collector of the power device under test, and the other end of the clamping unit is connected to the last pressure-bearing unit in series.

[0024] The beneficial effects of this invention are: the measurement circuit provided by this invention can extract the on-state voltage drop of the device under test by working in cooperation with the pressure bearing unit and the clamping unit, and achieve effective clamping of the off-state voltage; the applicable voltage level of the measurement circuit can be changed by changing the number of pressure bearing units, and the structure is simple, easy to expand, and highly flexible. Attached Figure Description

[0025] Figure 1 It is a traditional dual-diode circuit used to measure the forward voltage drop of power devices;

[0026] Figure 2 This is an online measurement circuit for the on-state voltage drop of power devices, which is easily expandable, as shown in the embodiments of the present invention.

[0027] Figure 3This is a schematic diagram of the components of the pressure-bearing unit shown in an embodiment of the present invention;

[0028] Figure 4 This is a schematic diagram of the components of the clamping unit shown in an embodiment of the present invention;

[0029] Figure 5 This is a schematic diagram illustrating the online measurement of the on-state voltage drop of the device under test (DUT) when it is in a typical double-pulse test circuit, as shown in an embodiment of the present invention.

[0030] Figure 6 This is a schematic diagram of the operating point of a depletion-type MOSFET under load;

[0031] Figure 7 This is a schematic diagram of the operating point of a depletion-type MOSFET when there are certain differences in the static parameters.

[0032] Figure 8 This is a schematic diagram of the stress when two depletion-type MOSFETs with inconsistent static parameters are directly connected in series.

[0033] Figure 9 It uses an equalizing resistor R M A schematic diagram illustrating the stress on a depletion-type MOSFET directly connected in series.

[0034] Figure 10 This is a schematic diagram of the voltage bearing capacity of a depletion-type MOSFET before and after dynamic voltage equalization;

[0035] Figure 11 This is a schematic diagram showing the effect of the on-state voltage drop measurement circuit under dual-pulse testing and the voltage bearing capacity of the depletion-type MOSFET.

[0036] Figure 12 The selection of static characteristic parameters of depletion-mode MOSFETs and static voltage equalization resistor R in the voltage-bearing unit. M Flowchart of resistance values;

[0037] Figure 13 This is a structural diagram of the units connected in series during low-voltage testing, where (a) represents the first round of low-voltage testing and (b) represents the second round of low-voltage testing. Detailed implementation method.

[0038] To make the content of this invention easier to understand, the invention will be further described in detail below with reference to specific embodiments and accompanying drawings.

[0039] To improve measurement accuracy, a measurement circuit needs to be designed to clamp the high voltage of the power device when it is turned off to a lower voltage. To flexibly achieve online measurement of the on-state voltage drop of power devices at different voltage levels, a method for expanding the voltage-bearing unit needs to be defined. Therefore, this invention proposes an easily expandable online measurement circuit for the on-state voltage drop of power devices, the circuit structure of which is as follows: Figure 1The dashed box in the diagram shows a voltage-bearing unit and a clamping unit, whose input terminals are directly connected to the collector (C) and emitter (E) of the IGBT (Internet Protocol Device) under test. During normal operation of the IGBT, the measurement circuit can extract the on-state voltage drop of the IGBT and effectively clamp the off-state voltage through the cooperation of the voltage-bearing unit and the clamping unit. The applicable voltage level of the measurement circuit can be changed by altering the number of voltage-bearing units.

[0040] The pressure-bearing units 1-n (where n is the number of pressure-bearing units) are connected in series. One end of pressure-bearing unit 1 is connected to the collector C of the IGBT under test, and one end of pressure-bearing unit n is connected to one end of the clamping unit. The other end of the clamping unit is connected to the emitter E of the IGBT under test. The two ends of the clamping unit serve as output terminals. When the IGBT under test is turned on, the pressure-bearing units are fully turned on, and the output of the clamping unit is the on-state voltage drop of the IGBT. When the IGBT under test is turned off, the pressure-bearing units withstand a value close to the off-state voltage of the IGBT, and the output of the clamping unit is the clamping value. Therefore, the output of the clamping unit can be maintained as a low-voltage signal, which greatly facilitates the subsequent circuitry in acquiring and analyzing voltage drop information, thus improving measurement accuracy.

[0041] The pressure unit is composed of Figure 3 As shown within the dashed box, the i-th pressure-bearing unit mainly includes a depletion-mode field-effect transistor (MOSFET) M. i (i = 1, 2, 3…n), R0 and R1 are connection resistors, R M R is the static equalizing resistor of the pressure-bearing unit. D C is the dynamic voltage equalization resistor for the pressure-bearing unit. D This is the dynamic voltage equalization capacitor for the voltage-bearing unit. One end of R1 is connected to the source of the MOSFET, and the other end of R1 is connected to R0 and R... M and C D One end of R0 is connected to the gate of the MOSFET, and the other end of C is connected to the gate of the MOSFET. D The other end is connected to R D One end, R D The other end and R M The other end is connected to the drain of the MOSFET; several pressure bearing units are connected in series, the other end of R1 of the previous pressure bearing unit is connected to the drain of the MOSFET of the next pressure bearing unit, the drain of the MOSFET of the first pressure bearing unit is connected to the collector of the power device under test, and the other end of R1 of the nth pressure bearing unit is connected to the clamping unit.

[0042] The clamping unit consists of Figure 4 As shown in (a), it mainly consists of the first Schottky diode D. a1 First Zener diode Z1, second Schottky diode D a2Composition, the first Schottky diode D a1 The cathode of the second Schottky diode is connected to the cathode of the first Zener diode Z1, and the cathode of the second Schottky diode D is connected to the cathode of the first Zener diode Z1. a2 The anode of the second Schottky diode D is connected to the anode of the first Zener diode Z1 and serves as one end of the clamping unit. a2 The cathode and the first Schottky diode D a1 The anode connection serves as the other end of the clamping unit, requiring the Zener diode to maintain a stable voltage V. Z1 Greater than the on-state voltage drop V of the device under test CE,sat When the clamping unit is connected to the measurement circuit, the second Schottky diode D... a2 The anode of the first Zener diode Z1 and the anode of the second Schottky diode D are connected to the collector E of the power device under test (IGBT). a2 The cathode and the first Schottky diode D a1 The anode connection of the pressure-bearing unit n. When the measurement circuit needs to simultaneously measure the voltage drop of the anti-parallel diode of the device under test, it can be used in D. a2 The second Zener diode Z2 is connected in series on the branch line, such as Figure 4 As shown in (b) in D, that is, in D a2 Cathode and D a1 Z2 is connected in series between the anodes of Z2 and D. a2 The cathode of Z2 is connected to the anode of D. a1 The anode is connected and serves as the other end of the clamping unit.

[0043] The device under test (DUT) is in Figure 5 In the typical double-pulse test circuit shown, V DC The circuit uses a high-voltage DC power supply, where C is the bus capacitor connected in parallel, L is the load inductor, and D is a freewheeling diode connected in parallel with the load inductor. The input terminal of the measurement circuit is connected to the collector and emitter of the device under test (DUT). When the DUT is turned on, the voltage V across its terminals... ce,sat Within a few volts, V ce,sat <V z1 The Zener diode did not reach reverse breakdown, and its leakage current I... leak Very small, in the nA range, therefore I leak The voltage drop across R1 in each voltage-bearing unit is negligible, and the depletion-type MOSFET in the voltage-bearing unit remains on, therefore the measuring circuit outputs V. out =V ce,sat -nI leak (R1+R ds,on )≈V ce,sat R ds,onThe resistance of the MOSFET is the on-resistance. When the device under test (DUT) is turned off, the Zener diode Z1 reaches reverse breakdown, its leakage current increases, and a voltage drop is formed across R1. The depletion-mode MOSFET operates in high-impedance mode, the voltage-bearing unit withstands the voltage, and the measurement circuit outputs V. out Clamped in V z1 +V Da1 V out =V z1 +V Da1 .

[0044] The static equalizing resistance R in the pressure-bearing unit is not considered for the time being. M With dynamic voltage equalization resistor R D C D The function of this method is analyzed to determine the operating point of the depletion-type MOSFET under voltage. Under voltage, the current flowing through the depletion-type MOSFET is equal to the Zener breakdown current I of the Zener regulator Z1. z The voltage drop across R1 caused by this current is I. z R1, since the drive current of the high-speed MOSFET is extremely small and can be ignored, therefore the voltage V between the gate G and drain S of the depletion-type MOSFET is... GS For -I z R1, in addition, since the leakage current on the depletion-type MOSFET satisfies its transfer characteristic I = f(V GS ), combined with the relation I = -V gs / R1 can determine the operating point of the depletion-mode MOSFET under voltage, such as Figure 6 As shown, taking the BSS126 depletion-type MOSFET as an example, the transfer characteristics I = f(V) are given for R1 = 2k and R1 = 3.3k respectively. GS ) and I = -V GS The diagram shows the intersection of R1 and R2. Therefore, by adjusting the resistance of R1, the depletion-type MOSFET can be made to operate at its appropriate operating point when under voltage.

[0045] When only depletion-mode MOSFETs are used as the voltage-bearing unit and directly connected in series, the transfer characteristics will differ due to certain differences in their static parameters. For example... Figure 7 I = f1(V) GS ), I = f2(V GS As shown in the figure, if the two MOSFETs can uniformly bear a certain voltage, the operating points of the two depletion-mode MOSFETs should be respectively the same as those on the curve I = -V. GS The intersection of / R, but since the voltage equalization units are directly connected in series, their leakage current is equal in steady state under voltage, which will cause V on the first depletion-mode MOSFET to be affected. dsThe voltage drops sharply, causing its leakage current to equalize with that of the second depletion-mode MOSFET. At this point, the first depletion-mode MOSFET operates in the linear region, and it experiences almost no voltage. Figure 8 As shown in the upper middle, V DS1 and V DS2 These represent the voltage conditions of the two depletion-type MOSFETs, respectively. Figure 8 Below are the gate-source voltages V corresponding to the two depletion-type MOSFETs. GS1 V GS2 .

[0046] Based on the aforementioned problem of uneven voltage bearing in the voltage-bearing unit caused by inconsistent MOSFET static parameters, this invention selects R M As a component for static voltage equalization, such as Figure 3 As shown, unlike traditional power devices connected in series (operating in the cutoff region when turned off), the value of the voltage equalizing resistor is determined differently. Taking the series connection of two units as an example, the voltage equalizing resistor R is discussed below. M The issue of resistor value selection. With a high voltage input, after connecting the equalizing resistor in parallel, the current in the sampling circuit loop satisfies the following equation: I1 + V DS1 / R M =I² + V DS2 / R M Where I1 and I2 are the leakage currents flowing through the MOSFET, due to the voltage equalization resistor R M Due to the current shunting effect, the leakage currents of the two MOSFETs can be different, meaning both MOSFETs can operate at... Figure 7 The operating point shown is where the voltage difference between the two MOSFETs is: ΔV DS =(V DS1 -V DS2 )=(I2-I1)R M Subject to the high-speed MOSFET transfer characteristic curve and I D =-V GS When the curvature of R affects the device characteristics and they are inconsistent, (I2-I1) is around 0.05mA. Therefore, when R... M When the value is in the MΩ range, its ΔV DS Also within tens of volts, to ensure the voltage equalization effect as much as possible, R is taken as... M =1MΩ was used for verification, and the voltage withstand capability of the MOSFET device was obtained as follows: Figure 9 As shown above, at the same time Figure 9 Below are the gate-source voltages of the two MOSFETs, which are consistent with the theoretical analysis.

[0047] When multiple pressure-bearing units are directly connected in series, they can be arranged according to... Figure 12The given process steps determine the static voltage equalization resistor value, where n is the number of voltage-bearing units that need to be connected in series in the measurement circuit. First, depletion-type MOSFETs are screened, where i (i>2n) is the number of candidate signal-level MOSFETs from the same batch. 2n depletion-type MOSFETs are randomly selected, and the voltage drop V of the body diode under the same small current is considered. F,1-2n Take measurements, V F,max V represents the maximum body diode voltage drop under low current conditions among 2n MOSFETs. F,min This represents the minimum body diode voltage drop under low current conditions among 2n MOSFETs.

[0048] Judgment | V F,max -V F,min If the value is less than 0.01V, re-evaluate the body diode voltage drop V of the 2n depletion-type MOSFETs under the same low current. F,1-2n If so, perform a measurement; if so, select n MOSFETs from the 2n MOSFETs for low-voltage testing (the input voltage of the measurement circuit is controlled between 50V and 100V). DS,1-n V represents the voltage across n MOSFETs during low-voltage testing. DS,max V represents the maximum voltage that n MOSFETs can withstand during low-voltage testing. DS,min Given the minimum voltage withstand value of n MOSFETs during low-voltage testing, exclude those with withstand voltage V. DS For MOSFETs with a value approximately equal to 0, substitute them from the remaining n MOSFETs until n MOSFETs that meet the conditions are obtained.

[0049] In this embodiment, during the first round of low-voltage testing, as follows: Figure 13 As shown in (a), a configuration is constructed using only MOSFETs, connecting resistors R0 and R1, and clamping units, as shown in [the diagram]. Figure 2 The measurement circuit shown (without the static equalizing resistor R) M Dynamic voltage equalization resistor R D Dynamic voltage equalization capacitor C D By applying an input voltage of 50V to 100V, a low-voltage test is completed, and n MOSFETs are obtained from the first round of screening.

[0050] Based on the n MOSFETs selected in the first round of screening, and building upon the low-voltage test circuit from the first round, a static voltage equalization resistor R in the MΩ range is connected in parallel with the n MOSFETs. M Perform a low-voltage test again (measuring circuit input voltage controlled between 50V and 100V) and calculate the maximum voltage unevenness |V. DS,max -V DS,min |=ΔI max *R M ΔI maxR is the difference between the maximum and minimum leakage current flowing through n MOSFETs. M This is the static voltage equalization resistor value;

[0051] In this embodiment, during the second round of low-voltage testing, as follows: Figure 13 As shown in (b), a parallel static voltage equalization resistor R is added to the first round of low-voltage test circuit. M , construct as Figure 2 The measurement circuit shown (without the dynamic equalizing resistor R) D Dynamic voltage equalization capacitor C D By applying an input voltage of 50V to 100V, a low-voltage test is completed, and n MOSFETs are obtained from the second round of screening.

[0052] Determine ΔI max *R M <ΔV DS,set Whether it holds true, ΔV DS,set Let R be the expected maximum static voltage imbalance for n MOSFET cells. If so, complete the static voltage equalization test; otherwise, decrease R. M Adjust the resistance value or replace the component with one of the alternatives.

[0053] Based on the aforementioned analysis, all n MOSFETs that have undergone the second screening are now operating in the saturation region. As the input voltage increases, ΔI max ·R M The value remains essentially unchanged, and ΔI is satisfied during low-voltage testing. max ·R M <ΔV DS,set Under these conditions, the static equalization test can be completed.

[0054] When the inter-electrode capacitance of a depletion-mode MOSFET is inconsistent, leading to inconsistent du / dt of its voltage rise, dynamic unevenness will occur during the voltage rise process, such as... Figure 10 As shown above, for this reason, Figure 3 The buffer resistor R in D and buffer capacitor C D It can play a role in dynamic voltage equalization, that is, make the du / dt of the depletion-mode MOSFET approach uniformity and suppress dynamic voltage unevenness, such as Figure 10 As shown below, since the inter-electrode capacitance of the signal-type depletion-mode MOSFET is small, in the pF range, this capacitance is not significantly different from the parasitic capacitance in the actual circuit. Therefore, in order to ignore the influence of the parasitic capacitance in the actual circuit, the capacitance C is... D The value needs to be on the order of magnitude higher than the inter-electrode capacitance of the depletion-mode MOSFET, and can be in the nF range, while satisfying R... D C D <0.25t p , tp This represents the voltage rise time.

[0055] In one specific embodiment of the present invention, the bus voltage is 2kV, and six MOSFETs are connected in series. The static parameters and dynamic parameters of these six MOSFETs are set to be somewhat inconsistent. According to the aforementioned analysis method, the MOSFETs can achieve a better voltage equalization effect, such as... Figure 11 As shown below, good dynamic and static pressure equalization can be achieved. Figure 11 As shown above, the measurement circuit output can accurately extract the on-state voltage drop when the device under test is turned on, and achieve effective clamping when it is turned off.

[0056] The above examples are merely specific embodiments of the present invention. Obviously, the present invention is not limited to the above embodiments and many variations are possible. All variations that can be directly derived or conceived by those skilled in the art from the disclosure of the present invention should be considered within the scope of protection of the present invention.

Claims

1. An easily expandable online measurement circuit for the on-state voltage drop of power devices, characterized in that, It includes a clamping unit and n pressure bearing units connected in series. One end of the first pressure bearing unit connected in series is used to connect to the collector of the power device under test. One end of the last pressure bearing unit connected in series is connected to one end of the clamping unit. The other end of the clamping unit is used to connect to the emitter of the power device under test. The two ends of the clamping unit serve as measurement output terminals. When the device under test (DUT) is turned on, the voltage-bearing unit is fully turned on, and the output of the clamping unit is the on-state voltage drop of the DUT; when the DUT is turned off, the voltage-bearing unit withstands a value close to the off-state voltage of the DUT, and the output of the clamping unit is the clamping value. The pressure-bearing unit includes a depletion-mode MOSFET, connecting resistors R0 and R1, and a static voltage-equalizing resistor R. M Dynamic voltage equalization resistor R D Dynamic voltage equalization capacitor C D ; One end of R1 is connected to the source of the MOSFET, and the other end of R1 is connected to R0 and R1 respectively. M and C D One end of R0 is connected to the gate of the MOSFET, and the other end of C is connected to the gate of the MOSFET. D The other end is connected to R D One end, R D The other end and R M The other end is connected to the drain of the MOSFET; In the aforementioned pressure-bearing unit, the selection of depletion-mode MOSFETs and the static voltage-equalizing resistor R M The process of determining the resistance value includes: 2n MOSFETs were randomly selected from the same batch of candidates, and the body diode voltage drop V was measured under the same low current. F,1-2n Determine |V F,max -V F,min Does | < 0.01V hold true, where V F,max V F,min These represent the maximum and minimum body diode voltage drops under low current conditions in 2n depletion-mode MOSFETs, respectively. If not, re-select 2n depletion-mode MOSFETs; if yes, select n MOSFETs from the 2n depletion-mode MOSFETs for low-voltage testing, and discard those that withstand a voltage V. DS MOSFETs with a depletion potential of ≈0 are removed from the pool of candidates and replaced by the remaining n depletion potential MOSFETs until n depletion potential MOSFETs that meet the conditions are obtained. The n depletion-type field-effect transistors (MOSFETs) obtained in the first round of screening are connected in parallel with a static voltage equalization resistor R with a value in the MΩ range. M Perform a low-pressure test again and calculate the maximum pressure unevenness |V DS,max -V DS,min |=ΔI max *R M , where ΔI max R is the difference between the maximum and minimum leakage current flowing through n depletion-mode MOSFETs. M This is the static voltage equalization resistor value, V DS,max V DS,min These represent the maximum and minimum voltages that n depletion-mode MOSFETs can withstand during low-voltage testing, respectively. Determine ΔI max *R M <ΔV DS,set Whether it holds true, where ΔV DS,set Let R be the expected maximum static voltage imbalance for n depletion-mode MOSFETs. If so, complete the static voltage equalization test; otherwise, reduce R. M The resistance value can be adjusted, or the depletion-type MOSFET can be replaced from the alternatives.

2. The easily expandable online measurement circuit for the on-state voltage drop of power devices according to claim 1, characterized in that, In the series of n pressure-bearing units, the other end of R1 of the previous pressure-bearing unit is connected to the drain of the MOSFET of the next pressure-bearing unit, the drain of the MOSFET of the first pressure-bearing unit is connected to the collector of the power device under test, and the other end of R1 of the nth pressure-bearing unit is connected to the clamping unit.

3. The easily expandable online measurement circuit for the on-state voltage drop of power devices according to claim 1, characterized in that, Combined with the transfer characteristic formula I=f(V) satisfied by the leakage current on the MOSFET GS ) and I=-V GS / R1, by adjusting the resistance value of R1, based on the intersection of the two curves, ensures that the depletion-mode MOSFET operates at a suitable operating point under voltage; where I represents the leakage current, V GS f(.) represents the voltage between the gate and source of the MOSFET, and f(.) represents the transfer characteristic function.

4. The easily expandable online measurement circuit for the on-state voltage drop of power devices according to claim 1, characterized in that, Dynamic voltage equalization capacitor C D The value is on the same order of magnitude as the inter-electrode capacitance of the MOSFET, and satisfies R D C D <0.25t p , t p This represents the voltage rise time.

5. The easily expandable online measurement circuit for the on-state voltage drop of power devices according to claim 1, characterized in that, The clamping unit includes a first Schottky diode D. a1 First Zener diode Z1, second Schottky diode D a2 ; The D mentioned a1 The cathode of Z1 is connected to the cathode of Z2, and the anode of Z1 is connected to the cathode of D. a2 The anode is connected and serves as one end of the clamping unit, D a2 Cathode and D a1 The anode is connected and serves as the other end of the clamping unit, with the regulated voltage V of Z1. Z1 It is greater than the on-state voltage drop of the power device under test.

6. The easily expandable online measurement circuit for the on-state voltage drop of power devices according to claim 1, characterized in that, The clamping unit includes a first Schottky diode D. a1 First Zener diode Z1, second Schottky diode D a2 The second Zener diode, Z2; The D mentioned a1 The cathode of Z1 is connected to the cathode of Z2, and the anode of Z1 is connected to the cathode of D. a2 The anode is connected and serves as one end of the clamping unit, D a2 The cathode of Z1 is connected to the cathode of Z2, and the anode of Z2 is connected to D. a1 The anode is connected and serves as the other end of the clamping unit; the regulated voltage V of Z1 and Z2 Z1 V Z2 It is greater than the on-state voltage drop of the power device under test.

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