Circuit and method for measuring drain-source on-resistance of a power switching device during operation

Abstract

The present invention discloses a circuit for measuring the drain-source on-resistance of a power switch device during operation, comprising: a low-voltage DC source for supplying power to the primary coil of a transformer and providing current when the power switch device under test is conducting; a transformer for boosting voltage; a first power switch device connected in series with the primary coil of the transformer to provide an original varying current to the primary coil of the transformer; a second power switch device for discharging the voltage on the capacitor in a soft-switching mode; and the power switch device under test. The present invention can measure the source-drain on-resistance of the power switch device under test when operating in both soft-switching and hard-switching modes, and can measure the power switch device under test with different speeds of change of the drain voltage over time (dv / dt).

Description

Technical Field

[0001] The present invention relates to a measurement circuit, mainly used for measuring the drain-source on-resistance of a power semiconductor switching device during operation. Background Art

[0002] The switching technologies of power switching devices are divided into two types: hard switching and soft switching. Hard switching means that during the entire switching process of a power switching device (switching from "on" to "off" or from "off" to "on"), the current flowing through the power switching device × the voltage across the power switching device ≠ 0, that is, the power is not 0. Soft switching means that during the entire switching process of a power switching device, the current flowing through the power switching device × the voltage across the power switching device = 0, that is, one of the current and voltage is 0 and the power is 0.

[0003] The source-drain on-resistance of a semiconductor device (such as a metal-oxide-semiconductor field-effect transistor MOSFET) refers to the resistance value between the drain and the source of the semiconductor device during operation (in the on-state), abbreviated as Rds or Rdson. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to provide a circuit for measuring the drain-source on-resistance of a power semiconductor switching device during operation, which can measure the source-drain on-resistance of the power semiconductor switching device in two working modes: hard switching and soft switching.

[0005] To solve the above technical problems, the present invention discloses a circuit for measuring the drain-source on-resistance of a power switch device during operation, including the following components. A low-voltage DC source, on the one hand, supplies power to the primary coil of the transformer, and on the other hand, supplies current to the power switch device under test when it is conducting through a series-connected resistor one and diode three. A transformer for boosting voltage; the first end of the secondary coil of the transformer is connected to the drain of the power switch device under test through a series-connected diode one and diode two to provide a drain voltage for the power switch device under test; the second end of the secondary coil of the transformer is grounded. A power switch device one is connected in series with the primary coil of the transformer to provide an original varying current to the primary coil of the transformer; the second end of the primary coil of the transformer is grounded through the power switch device one. The drain of the power switch device two is connected to the cathode of diode one, and the source of the power switch device two is grounded; a capacitor is connected between the drain and source of the power switch device two; the power switch device two is used to discharge the voltage on the capacitor in the soft-switching mode; the capacitor is used to stabilize the drain voltage of the power switch device two and the drain voltage of the power switch device under test. The source of the power switch device under test is grounded through resistor two, and a load resistor or an actual load is connected between the drain and source of the power switch device under test. The anode of diode four is connected to the anode of diode three, and the cathode of diode four is connected to the drain of the power switch device two. This is Embodiment One of the present invention.

[0006] Optionally, diode two is omitted. This is a variant implementation of Embodiment One of the present invention.

[0007] Optionally, diode two and diode four are omitted. This is Embodiment Three of the present invention.

[0008] Optionally, diode one, diode two, and diode four are omitted, and at the same time, the second end of the secondary coil of the transformer is changed to be grounded through the power switch device one. This is Embodiment Five of the present invention.

[0009] Further, the second end of the primary coil of the transformer and the first end of the secondary coil are of the same name.

[0010] Optionally, the only low-voltage DC source is split into two low-voltage DC sources; the split low-voltage DC source one is only used to supply power to the primary coil of the transformer, and the split low-voltage DC source two is only used to supply current to the power switch device under test when it is conducting. This is Embodiment Two, Embodiment Four, and Embodiment Six of the present invention.

[0011] Further, the drain breakdown voltage of the power switch device two is higher than or equal to the drain breakdown voltage of the power switch device under test.

[0012] Further, the breakdown voltages of the four diodes are all higher than or equal to the breakdown voltage of the drain terminal of the power switch device under test; the rated currents of Diode 1 and Diode 2 are the same as those of Power Switch Device 2 or the power switch device under test; the rated currents of Diode 3 and Diode 4 are the same as those of the power switch device under test.

[0013] The present invention also discloses a method for measuring the drain-source on-resistance of a power switch device during operation, including the following steps. Step S1: All power switch devices are turned off, then Power Switch Device 2 is turned on to discharge the energy in the secondary coil of the transformer and the capacitor, and then Power Switch Device 2 is turned off. Step S2: Power Switch Device 1 is turned on to raise the drain voltage of the power switch device under test to the required value. Step S3: Power Switch Device 1 is turned off, and the capacitor stabilizes the drain voltages of Power Switch Device 2 and the power switch device under test. Step S4: Power Switch Device 2 is turned on, and the drain voltage of the power switch device under test becomes 0. Step S5: The power switch device under test is turned on. At this time, Power Switch Device 2 is also turned on, and the drain voltage of the power switch device under test is 0. Step S6: Power Switch Device 2 is turned off, and Diode 3 starts to work to measure the voltage Vcs across both ends of Resistor 2 connected to the source of the power switch device under test. Step S7: The power switch device under test is turned off, and the measurement is completed. Step S8: Calculate the drain-source on-resistance Rdson1 of the power switch device under test in the soft-switching mode according to the formula Rdson1 = (Vdc - Vd - Vcs) ÷ Vcs ÷ Rcs; Vdc represents the voltage value of the low-voltage DC source; if there are two low-voltage DC sources, Vdc represents the voltage value of the second low-voltage DC source that provides current when the power switch device under test is turned on; Vd represents the voltage drop across both ends of Diode 3, and the calculation method is: first calculate Vcs ÷ Rcs as the current value flowing through Diode 3, and then obtain the voltage drop across both ends of Diode 3 according to the IV curve of Diode 3; Rcs represents the resistance value of Resistor 2.

[0014] The present invention also discloses a method for measuring the drain-source on-resistance of a power switch device during operation, including the following steps. Step S1: All power switch devices are turned off, then power switch device two is turned on to discharge the energy in the secondary coil of the transformer and the capacitor, and then power switch device two is turned off. Step S2: Power switch device one is turned on to raise the drain voltage of the power switch device under test to the required value. Step S3: Power switch device one is turned off, and the capacitor stabilizes the drain voltage of power switch device two and the drain voltage of the power switch device under test. Step S4a: The power switch device under test is turned on, diode three starts to work, and the voltage Vcs across both ends of resistor two connected to the source of the power switch device under test is measured. Step S5a: The power switch device under test is turned off, and then power switch device two is turned on for a period of time and then turned off, and the measurement is completed. Step S6a: Calculate the drain-source on-resistance Rdson2 of the power switch device under test in the hard-switching mode according to the formula Rdson2 = (Vdc - Vd - Vcs) ÷ Vcs ÷ Rcs; Vdc represents the voltage value of the low-voltage DC source; if there are two low-voltage DC sources, Vdc represents the voltage value of the second low-voltage DC source that provides current when the power switch device under test is turned on; Vd represents the voltage drop across both ends of diode three, and the calculation method is: first calculate Vcs ÷ Rcs as the current value flowing through diode three, and then obtain the voltage drop across both ends of diode three according to the IV curve of diode three; Rcs represents the resistance value of resistor two.

[0015] The technical effects achieved by the present invention are: It can measure the drain-source on-resistance of the power switch device under test in both soft-switching and hard-switching modes, and can measure the power switch device under test with different speeds of change of drain voltage over time (dv / dt). BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 It is a schematic circuit diagram of Embodiment 1 of the measurement circuit proposed by the present invention.

[0017] Figure 2 It is a schematic circuit diagram of Embodiment 2 of the measurement circuit proposed by the present invention.

[0018] Figure 3 It is a schematic circuit diagram of Embodiment 3 of the measurement circuit proposed by the present invention.

[0019] Figure 4 It is a schematic circuit diagram of Embodiment 4 of the measurement circuit proposed by the present invention.

[0020] Figure 5 It is a schematic circuit diagram of Embodiment 5 of the measurement circuit proposed by the present invention.

[0021] Figure 6 It is a schematic circuit diagram of Embodiment 6 of the measurement circuit proposed by the present invention.

[0022] Figure 7 It is a schematic flow chart of the first embodiment of the measurement method proposed by the present invention (the power switch device under test is in the soft-switching mode).

[0023] Figure 8 It is a logic schematic diagram of the gate voltages of three power switch devices during the measurement process in the soft-switching mode of the present invention.

[0024] Figure 9 It is a schematic flow chart of the second embodiment of the measurement method proposed by the present invention (the power switch device under test is in the hard-switching mode).

[0025] Figure 10 It is a logic schematic diagram of the gate voltages of three power switch devices during the measurement process in the hard-switching mode of the present invention.

[0026] Explanation of the reference numerals in the figure: DC, DC1, and DC2 are low-voltage DC sources; T1 is a transformer; D1 to D4 are diodes; Q1 to Q3 are power switch devices; R1, Rcs, and RL are resistors; Vdrain is the drain voltage of the power switch device under test. Specific Embodiments

[0027] Please refer to Figure 1 , which is the first embodiment of the circuit for measuring the drain-source on-resistance of a power switch device during operation proposed by the present invention. The measurement circuit of this first embodiment includes a low-voltage DC source DC, a transformer T1, four diodes D1 to D4, three power switch devices Q1 to Q3, three resistors R1, Rcs, and RL, and a capacitor C.

[0028] On the one hand, the positive pole of the low-voltage DC source DC is connected to the first end of the primary coil of the transformer T1, and the second end of the primary coil of the transformer T1 is grounded through the first power switch device Q1, that is, the second end of the primary coil of the transformer T1 is connected to the drain of the first power switch device Q1, and the source of the first power switch device Q1 is grounded; the low-voltage DC source DC is used to supply power to the primary coil of the transformer T1. On the other hand, the positive pole of the low-voltage DC source DC is also connected to the drain of the power switch device under test Q3 through the series-connected first resistor R1 and the third diode D3 in the forward direction, so as to provide current when the power switch device under test Q3 is conducting.

[0029] The first end of the secondary coil of the transformer T1 is connected to the drain of the power switch device Q3 to be measured through the forward diode D1 and the forward diode D2 connected in series. The second end of the secondary coil of the transformer T1 is grounded. The diode D2 can be omitted. The second end of the primary coil of the transformer T1 and the first end of the secondary coil are the same-name terminals. The transformer T1 is mainly used for boosting to perform a withstand voltage stress test on the power switch device Q3 to be measured. "Withstand voltage stress" refers to the ability to withstand voltage, that is, the ability to withstand the drain voltage Vdrain. By controlling the voltage change of the low-voltage DC source DC and the on-time of the power switch device Q1, the voltage generated by the secondary coil of the transformer T1 can be controlled, that is, the drain voltage Vdrain of the power switch device Q3 to be measured can be controlled. Then, by controlling the on and off of the power switch device Q2 and the on and off of the power switch device Q3 to be measured, the soft-switching and hard-switching modes of the power switch device Q3 to be measured can be easily controlled.

[0030] The power switch device Q1 needs to withstand a large current and generally a MOSFET can be used. This measurement circuit generally measures high-voltage power switch devices, such as greater than 300V. The current measurement can be very wide, and this measurement circuit can be used from the mA level to more than 100A. The power switch device Q1 mainly provides the original varying current for the primary coil of the transformer T1. When the power switch device Q1 is turned on, the transformer T1 starts to work, and the secondary coil of the transformer T1 starts to rise to a high voltage according to the primary coil. When the power switch device Q1 is turned off, the secondary coil of the transformer T1 also drops to a low voltage.

[0031] The drain of the power switch device Q2 is connected to the cathode of the diode D1, and the source of the power switch device Q2 is grounded. A capacitor C is connected between the drain and the source of the power switch device Q2. The withstand voltage (drain voltage) of the power switch device Q2 needs to be higher than or equal to the withstand voltage of the power switch device Q3 to be measured to prevent breakdown, and generally a MOSFET can be used. The power switch device Q2 is mainly used to discharge the voltage on the capacitor C in the soft-switching mode. The capacitor C is mainly used to stabilize the drain voltage of the power switch device Q2 and the drain voltage Vdrain of the power switch device Q3 to be measured.

[0032] The source of the power switch device Q3 to be measured is grounded through the resistor Rcs. A load resistor RL is connected between the drain and the source of the power switch device Q3 to be measured to simulate the load. The load resistor RL can be omitted.

[0033] The anode of the diode D4 is connected to the anode of the diode D3, and the cathode of the diode D4 is connected to the drain of the power switch device Q2. The diode D1 is a freewheeling diode for preventing current backflow. If the diode D2 exists, it is also for preventing current backflow and effectively reducing the change of the drain voltage over time (dv / dt). When the power switch device Q2 is turned on, due to the existence of the diode D2, there will still be a voltage on the power switch device Q3 to be measured, and its drain voltage Vdrain will slowly decrease until it drops to the voltage of the low-voltage DC source DC, and then the current flows through the low-voltage DC source DC through the power switch device Q3 to be measured, taking into account the power switch device Q3 to be measured with a relatively small change of the drain voltage over time. The diode D3 is a freewheeling diode. The diode D3 needs to know (for example, measured in advance) the IV (current-voltage) curve for subsequent calculations. The combination of the diode D2 and the diode D3 is used to make the change of the drain voltage Vdrain of the switch device Q3 to be measured smoother. The diode D4 is a freewheeling diode and is also for preventing current backflow. The breakdown voltages of the diodes D1, D2, and D3 need to be higher than or equal to the drain voltage Vdrain of the power switch device Q3 to be measured, that is, higher than or equal to the breakdown voltage of the power switch device Q3 to be measured. Therefore, the diodes D1, D2, and D3 generally need to use exactly the same diodes. The breakdown voltage of the diode D4 also needs to be higher than or equal to the breakdown voltage of the power switch device Q3 to be measured. The rated currents of the diodes D1 and D2 (i.e., the rated values of the currents that the diodes can pass through) can be the same as those of the power switch device Q2 or the same as those of the power switch device Q3 to be measured. The rated currents of the diodes D3 and D4 need to be the same as those of the power switch device Q3 to be measured.

[0034] Please refer to Figure 2 , which is the second embodiment of the circuit for measuring the drain-source on-resistance of a power switch device during operation proposed by the present invention. The difference between the second embodiment and the first embodiment is only that: the single low-voltage DC source DC in the first embodiment is split into two low-voltage DC sources DC1 and DC2. The low-voltage DC source DC1 is only used to supply power to the primary coil of the transformer T1, so the requirement for the output voltage accuracy is reduced, and at the same time, the interference to the entire measurement circuit is reduced. The low-voltage DC source DC2 is only used to provide a large current when the power switch device Q3 to be measured is turned on, so the requirement for the output voltage magnitude is reduced.

[0035] Please refer to Figure 3, This is the third embodiment of the circuit for measuring the drain-source on-resistance of a power switch device during operation. The only difference between the third embodiment and the first embodiment is that the diode D2 and the diode D4 in the first embodiment are omitted. The diode D2 and the diode D4 in the first embodiment are used to prevent the drain voltage Vdrain of the power switch device Q3 under test from changing too quickly. If Vdrain changes too quickly, that is, the drain voltage changes with time (dv / dt) too quickly, it will cause the power switch device Q3 under test to oscillate and even damage the power switch device Q3 under test. Since two diodes are omitted, the third embodiment will have a large error in measuring the power switch device under test with a large change in drain voltage over time.

[0036] Please refer to Figure 4 , This is the fourth embodiment of the circuit for measuring the drain-source on-resistance of a power switch device during operation. The only difference between the fourth embodiment and the third embodiment is that the single low-voltage DC source DC in the third embodiment is split into two low-voltage DC sources DC1 and DC2. The low-voltage DC source DC1 is only used to supply power to the primary coil of the transformer T1, and the low-voltage DC source DC2 is only used to provide a large current when the power switch device Q3 under test is conducting. The fourth embodiment has both the advantages of the second embodiment and the disadvantages of the third embodiment.

[0037] Please refer to Figure 5 , This is the fifth embodiment of the circuit for measuring the drain-source on-resistance of a power switch device during operation. The only difference between the fifth embodiment and the first embodiment is that the diode D1, the diode D2, and the diode D4 in the first embodiment are omitted, and at the same time, the second end of the secondary coil of the transformer T1 is changed to be connected to the drain of the power switch device Q1, that is, the second end of the secondary coil of the transformer T1 is changed to be grounded through the power switch device Q1. Since three diodes are omitted, the fifth embodiment will have a large error in measuring the power switch device under test with a large change in drain voltage over time, and the error is even larger than that of the third embodiment.

[0038] Please refer to Figure 6 , This is the sixth embodiment of the circuit for measuring the drain-source on-resistance of a power switch device during operation. The only difference between the sixth embodiment and the fifth embodiment is that the single low-voltage DC source DC in the fifth embodiment is split into two low-voltage DC sources DC1 and DC2. The low-voltage DC source DC1 is only used to supply power to the primary coil of the transformer T1, and the low-voltage DC source DC2 is only used to provide a large current when the power switch device Q3 under test is conducting. The sixth embodiment has both the advantages of the second embodiment and the disadvantages of the fifth embodiment.

[0039] Please refer to Figure 7, the method for measuring the source-drain on-resistance of the power switch device Q3 under test when it operates in the soft-switching mode by the measurement circuits of the above respective embodiments includes the following steps. The logics of the gate voltages Q1_G, Q2_G, and Q3_G of the three power switch devices Q1, Q2, and Q3 are as Figure 8 shown, where the high level indicates that the power switch device is turned on, and the low level indicates that the power switch device is turned off.

[0040] Step S1: All power switch devices are turned off, and the entire measurement circuit does not work. Then, the power switch device two Q2 is turned on to discharge the energy in the secondary coil of the transformer T1 and the capacitor C, and then the power switch device two Q2 is turned off.

[0041] Step S2: The power switch device one Q1 is turned on to raise the drain voltage Vdrain of the power switch device Q3 under test to the required value.

[0042] Step S3: The power switch device one Q1 is turned off, and the capacitor C stabilizes the drain voltage of the power switch device two Q2 and the drain voltage Vdrain of the power switch device Q3 under test.

[0043] Step S4: The power switch device two Q2 is turned on. Due to the presence of the load resistor RL (or the actual load), the drain voltage Vdrain of the power switch device Q3 under test will become 0. If the diode two D2 is omitted, the drain voltage Vdrain of the power switch device Q3 under test becomes 0 at a faster speed, and in this process, it is required that the change of the drain voltage with time (dv / dt) is smaller; if the change of the drain voltage with time is larger, it may damage the power switch device Q3 under test. If the diode two D2 exists, due to the parasitic capacitance effect, the drain voltage Vdrain of the power switch device Q3 under test will take some time to become 0; it is applicable to the power switch device Q3 under test with a larger change of the drain voltage with time.

[0044] Step S5: The power switch device Q3 under test is turned on. Since the power switch device two Q2 is also turned on, the drain voltage Vdrain of the power switch device Q3 under test is 0. At this time, the power switch device two Q2 and the power switch device Q3 under test are turned on simultaneously for a certain period of time, mainly to ensure that the drain voltage Vdrain of the power switch device Q3 under test is 0.

[0045] Step S6: The power switch device two Q2 is turned off, and the diode three D3 starts to work, that is, there is a current flowing through the diode three D3 to the drain of the power switch device Q3 under test, and the voltage Vcs across the two ends of the resistor two Rcs connected to the source of the power switch device Q3 under test is measured.

[0046] Step S7: The power switch device Q3 under test is turned off, and the measurement is completed.

[0047] Step S8: Calculate the source-drain on-resistance of the power switch device Q3 under test when it operates in the soft-switching mode according to the formula Rdson1 = (Vdc - Vd - Vcs) ÷ Vcs ÷ Rcs. Rdson1 represents the source-drain on-resistance of the power switch device Q3 under test when it operates in the soft-switching mode. Vdc represents the voltage value of the low-voltage DC source DC. If there are two low-voltage DC sources, Vdc represents the voltage value of the low-voltage DC source two DC2 that supplies current when the power switch device Q3 under test is turned on. Vd represents the voltage drop across both ends of the diode three D3. The calculation method is as follows: First, calculate Vcs ÷ Rcs as the current value flowing through the diode three D3, and then obtain the voltage drop across both ends of the diode three D3 according to the known IV curve of the diode three D3. Vcs ÷ Rcs represents the current flowing through the power switch device Q3 under test, and the current flowing through the diode three D3 is the same as it. Rcs represents the resistance value of the resistor two Rcs.

[0048] Please refer to Figure 9 , the measurement method of the source-drain on-resistance of the power switch device Q3 under test in the hard-switching mode by the measurement circuits of the above various embodiments includes the following steps. The logic of the gate voltages Q1_G, Q2_G, and Q3_G of the three power switch devices Q1, Q2, and Q3 is as Figure 10 shown, where a high level indicates that the power switch device is turned on, and a low level indicates that the power switch device is turned off.

[0049] Step S1: All power switch devices are turned off, and the entire measurement circuit does not work. Then, the power switch device two Q2 is turned on to discharge the energy in the secondary coil of the transformer T1 and the capacitor C, and then the power switch device two Q2 is turned off.

[0050] Step S2: The power switch device one Q1 is turned on to raise the drain voltage Vdrain of the power switch device Q3 under test to the required value.

[0051] Step S3: The power switch device one Q1 is turned off, and the capacitor C stabilizes the drain voltage of the power switch device two Q2 and the drain voltage Vdrain of the power switch device Q3 under test.

[0052] Step S4a: The power switch device Q3 under test is turned on, and the diode three D3 starts to work, that is, current flows through the diode three D3 to the drain of the power switch device Q3 under test, and measure the voltage Vcs across both ends of the resistor two Rcs connected to the source of the power switch device Q3 under test.

[0053] Step S5a: The power switch device Q3 under test is turned off. To discharge the energy in the entire measurement circuit, the power switch device two Q2 is turned on for a period of time and then turned off, and the measurement is completed.

[0054] Step S6a: Calculate the source-drain on-resistance of the power switch device Q3 under test when operating in the hard-switching mode according to the formula Rdson2 = (Vdc - Vd - Vcs) ÷ Vcs ÷ Rcs. Rdson2 represents the source-drain on-resistance of the power switch device Q3 under test when operating in the hard-switching mode. Vdc represents the voltage value of the low-voltage DC source DC. If there are two low-voltage DC sources, Vdc represents the voltage value of the low-voltage DC source two DC2 that provides current when the power switch device Q3 under test is turned on. Vd represents the voltage drop across the two ends of the diode three D3, and the calculation method is as follows: First, calculate Vcs ÷ Rcs as the current value flowing through the diode three D3, and then obtain the voltage drop across the two ends of the diode three D3 according to the known IV curve of the diode three D3. Vcs ÷ Rcs represents the current flowing through the power switch device Q3 under test, and the current flowing through the diode three D3 is the same as it. Rcs represents the resistance value of the resistor two Rcs.

[0055] The measurement circuit proposed by the present invention has the following beneficial effects. First, this measurement circuit only uses a small number of power switch devices. Through different combinations, it can test the source-drain on-resistance of the power switch device under test when operating in two modes: soft-switching and hard-switching. Moreover, when the input voltage is low, it can measure the source-drain on-resistance of the power switch device under test with high voltage and large current, and can take into account the power switch devices under test with different speeds of change of the drain voltage over time (dv / dt). Second, this measurement circuit is particularly suitable for the situation where the drain voltage stress of the power switch device under test changes violently. For example, within 100 ns, the drain voltage of the power switch device under test changes from 600 V to 0 V, and the current changes from 0 A to 10 A, etc., and measure the source-drain on-resistance during operation. Third, this measurement circuit has extremely strong versatility and can be applied to different types of power switch devices under test. Once the parameters of the transformer are fixed and the gate voltage control logic of the power switch device Q1 is fixed, this measurement circuit will have built-in current limiting protection, with strong safety and is not easy to damage the power switch device under test. Fourth, this measurement circuit is easy to operate. Even when testing a power switch device under test with high voltage, there is no need for a high-voltage power supply, avoiding various safety problems caused by the high-voltage power supply. At the same time, by adjusting the conduction time of the power switch device Q1 and the size of the capacitor C, and reasonably designing the transformer, the withstand voltage stress of the power switch device under test can be accurately adjusted, simplifying the test steps.

[0056] The above is only the preferred embodiment of the present invention and is not used to limit the present invention. For those skilled in the art, the present invention can have various changes and modifications. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A circuit for measuring the drain-source on-resistance of a power switching device during operation, characterized in that, The measurement circuit includes the following components; A low-voltage DC source that supplies power to the primary coil of the transformer on one hand and supplies current to the power switch device under test when it is conducting through resistor one and diode three in series on the other hand; A transformer for boosting voltage; The first end of the secondary coil of the transformer is connected to the drain of the power switch device under test through diode one and diode two in series to provide the drain voltage for the power switch device under test; The second end of the secondary coil of the transformer is grounded; Power switch device one is connected in series with the primary coil of the transformer to provide the original varying current to the primary coil of the transformer; The second end of the primary coil of the transformer is grounded through power switch device one; The drain of power switch device two is connected to the cathode of diode one, and the source of power switch device two is grounded; A capacitor is connected between the drain and source of power switch device two; Power switch device two is used to discharge the voltage on the capacitor in the soft-switching mode; The capacitor is used to stabilize the drain voltage of power switch device two and the drain voltage of the power switch device under test; The source of the power switch device under test is grounded through resistor two, and a load resistor or an actual load is connected between the drain and source of the power switch device under test; The anode of diode four is connected to the anode of diode three, and the cathode of diode four is connected to the drain of power switch device two.

2. The circuit for measuring the drain-source on-resistance of a power switching device during operation, as claimed in claim 1, is characterized in that Omit diode two.

3. The circuit for measuring the drain-source on-resistance of a power switching device during operation according to claim 1, characterized in that, Omit diode two and diode four.

4. The circuit for measuring the drain-source on-resistance of a power switching device during operation according to claim 1, characterized in that, Omit diode one, diode two and diode four, and at the same time change the second end of the secondary coil of the transformer to be grounded through power switch device one.

5. The circuit for measuring the drain-source on-resistance of a power switching device during operation according to any one of claims 1 to 4, characterized in that, The second end of the primary coil of the transformer and the first end of the secondary coil are the same-name terminals.

6. The circuit for measuring the drain-source on-resistance of a power switching device during operation according to any one of claims 1 to 4, characterized in that, Split the only low-voltage DC source into two low-voltage DC sources; The split low-voltage DC source one is only used to supply power to the primary coil of the transformer, and the split low-voltage DC source two is only used to supply current to the power switch device under test when it is conducting.

7. The circuit for measuring the drain-source on-resistance of a power switching device during operation according to any one of claims 1 to 4, characterized in that, The drain withstand voltage of power switch device two is higher than or equal to the drain withstand voltage of the power switch device under test.

8. The circuit for measuring the drain-source on-resistance of a power switch device during operation according to claim 1, characterized in that, The withstand voltages of the four diodes are all higher than or equal to the drain withstand voltage of the power switch device under test; The rated currents of diode one and diode two are the same as those of power switch device two or the power switch device under test; The rated currents of diode three and diode four are the same as those of the power switch device under test.

9. A method for measuring the drain-source on-resistance of a power switch device during operation using the circuit according to any one of claims 1-6, characterized in that Including the following steps; Step S1: All power switch devices are turned off, then power switch device two is turned on to discharge the energy in the secondary coil of the transformer and the capacitor, and then power switch device two is turned off; Step S2: Power switch device one is turned on to raise the drain voltage of the power switch device under test to the required value; Step S3: Power switch device one is turned off, and the capacitor stabilizes the drain voltages of power switch device two and the power switch device under test; Step S4: Power switch device two is turned on, and the drain voltage of the power switch device under test becomes 0; Step S5: The power switch device under test is turned on. At this time, power switch device two is also turned on, and the drain voltage of the power switch device under test is 0; Step S6: The second power switch device turns off, the third diode starts to work, and the voltage Vcs across both ends of the second resistor connected to the source electrode of the power switch device under test is measured. Step S7: The power switch device under test turns off, and the measurement is completed. Step S8: Calculate the source-drain on-resistance Rdson1 of the power switch device under test when operating in the soft-switching mode according to the formula Rdson1 = (Vdc - Vd - Vcs) ÷ Vcs ÷ Rcs; Vdc represents the voltage value of the low-voltage DC source; if there are two low-voltage DC sources, Vdc represents the voltage value of the second low-voltage DC source that provides current when the power switch device under test is conducting; Vd represents the voltage drop across both ends of the third diode, and the calculation method is: first calculate Vcs ÷ Rcs as the current value flowing through the third diode, and then obtain the voltage drop across both ends of the third diode according to the IV curve of the third diode; Rcs represents the resistance value of the second resistor.

10. A method for measuring the drain-source on-resistance of a power switching device during operation using the circuit according to any one of claims 1-6, characterized in that It includes the following steps; Step S1: All power switch devices are turned off, then the second power switch device is turned on to discharge the energy in the secondary coil of the transformer and the capacitor, and then the second power switch device is turned off. Step S2: The first power switch device is turned on to raise the drain voltage of the power switch device under test to the required value. Step S3: The first power switch device is turned off, and the capacitor stabilizes the drain voltage of the second power switch device and the drain voltage of the power switch device under test. Step S4a: The power switch device under test is turned on, the third diode starts to work, and the voltage Vcs across both ends of the second resistor connected to the source electrode of the power switch device under test is measured. Step S5a: The power switch device under test is turned off, then the second power switch device is turned on for a period of time and then turned off, and the measurement is completed. Step S6a: Calculate the source-drain on-resistance Rdson2 of the power switch device under test when operating in the hard-switching mode according to the formula Rdson2 = (Vdc - Vd - Vcs) ÷ Vcs ÷ Rcs; Vdc represents the voltage value of the low-voltage DC source; if there are two low-voltage DC sources, Vdc represents the voltage value of the second low-voltage DC source that provides current when the power switch device under test is conducting; Vd represents the voltage drop across both ends of the third diode, and the calculation method is: first calculate Vcs ÷ Rcs as the current value flowing through the third diode, and then obtain the voltage drop across both ends of the third diode according to the IV curve of the third diode; Rcs represents the resistance value of the second resistor.

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