Power device secondary opening evaluation circuit and evaluation method

Abstract

The invention provides a power device secondary opening evaluation circuit and evaluation method. The evaluation circuit comprises a switch module and a contrast test module. The switch module converts the direct-current electric signal into a switch electric signal through opening and closing of a switch tube; the contrast test module is connected with the switch module, performs contrast test on the to-be-tested power tube and the contrast power tube based on the switch electric signal, and evaluates the secondary opening condition of the to-be-tested power tube by triggering the secondary opening of the to-be-tested power tube; wherein the contrast power tube is kept closed during the contrast test. According to the power device secondary opening evaluation circuit and evaluation method provided by the invention, the problem that there is no effective evaluation scheme for secondary opening of the power device in the prior art is solved.

Description

Technical Field

[0001] The present invention relates to the technical field of electronic circuits, and in particular to a power device secondary start-up evaluation circuit and evaluation method. Background Art

[0002] Compared with traditional silicon-based MOSFET, SiC MOSFET has faster switching speed and lower threshold voltage. Therefore, negative voltage drive is often used to achieve reliable shutdown of the device.

[0003] However, in applications, factors such as crosstalk between the upper and lower tubes in a bridge circuit and oscillation during large current shutdown will form a spike voltage on the gate voltage of the device. When the spike voltage exceeds the threshold voltage, the device may turn on the channel. Reopening the device under this spike voltage is called secondary turn-on.

[0004] Secondary turn-on will lead to reduced system efficiency or even failure, but completely eliminating the spike voltage requires sacrificing cost and efficiency. Therefore, how to ensure that the device will not be turned on again under a certain spike voltage is of guiding significance for the application and improvement of the device. Summary of the invention

[0005] In view of the above-mentioned shortcomings of the prior art, an object of the present invention is to provide a power device secondary start-up evaluation circuit and evaluation method, which are used to solve the problem that there is no effective evaluation scheme for the secondary start-up of the power device in the prior art.

[0006] To achieve the above-mentioned object and other related objects, the present invention provides a power device secondary start-up evaluation circuit, the evaluation circuit comprising a switch module and a control test module, wherein:

[0007] The switch module converts the DC signal into a switch signal by turning on and off the switch tube;

[0008] The control test module is connected to the switch module, and performs a control test on the power tube to be tested and the control power tube based on the switch electrical signal, and evaluates its secondary opening condition by triggering the power tube to be tested to be turned on again; wherein, the control power tube remains turned off during the control test.

[0009] Optionally, the switch module includes: a PWM signal source, a first driving resistor, a switch tube and a load resistor;

[0010] The PWM signal source is used to provide a single pulse signal;

[0011] The control end of the switch tube is connected to the single pulse signal via the first driving resistor, the first end is connected to the DC signal, and the second end is connected to the reference ground via the load resistor to generate the switch electrical signal.

[0012] Optionally, the control test module includes: a power tube to be tested, a control power tube, a second driving resistor and a test unit;

[0013] The control end of the power tube to be tested is connected to the reference ground via the second driving resistor, the first end is connected to the switch electrical signal, and the second end is connected to the reference ground;

[0014] The control end of the reference power tube is short-circuited with its second end and connected to the reference ground, and the first end is connected to the switch electrical signal;

[0015] The testing unit is used to test the terminal current and / or terminal voltage of the power tube to be tested and the control power tube.

[0016] Optionally, the control test module further includes: a first sampling resistor and a second sampling resistor;

[0017] The first sampling resistor is connected between the second end of the power tube to be tested and a reference ground, and the second sampling resistor is connected between the second end of the control power tube and a reference ground.

[0018] Optionally, the evaluation circuit further includes: a power module, configured to provide the DC signal.

[0019] Optionally, the power module includes: a DC power supply and a high-voltage capacitor;

[0020] The upper plate of the high-voltage capacitor is connected to the positive output terminal of the DC power supply and generates the DC signal, and the lower plate is connected to the negative output terminal of the DC power supply and connected to the reference ground.

[0021] The present invention also provides an evaluation method based on the power device secondary start-up evaluation circuit as described in any one of the above items, and the evaluation method comprises:

[0022] When the power tube to be tested and the control power tube are subjected to a control test, the influencing parameter of the power tube to be tested is adjusted, and based on the change of the terminal current and / or terminal voltage of the power tube to be tested, it is determined whether to trigger the secondary start-up of the power tube to be tested, so as to evaluate the secondary start-up condition of the power tube to be tested.

[0023] Optionally, the comparison test is performed by charging the junction capacitance of the power tube to be tested and the comparison power tube based on the switching electrical signal.

[0024] Optionally, the influencing parameter of the power tube to be tested is adjusted by adjusting the resistance value of the first driving resistor and / or the resistance value of the second driving resistor.

[0025] Optionally, the method for determining whether to trigger the secondary start-up of the power tube to be tested includes:

[0026] Comparing the terminal currents of the power tube to be tested and the reference power tube, if the terminal current of the power tube to be tested is greater than the terminal current of the reference power tube, determining that the power tube to be tested triggers a secondary start-up;

[0027] And / or, comparing the terminal voltage increments of the power tube to be tested and the reference power tube, if the terminal voltage increment of the power tube to be tested is smaller than the terminal voltage increment of the reference power tube, determining that the power tube to be tested triggers a second turn-on.

[0028] As described above, the power device secondary start-up evaluation circuit and evaluation method of the present invention, during the control test, evaluates the secondary start-up conditions of the power tube to be tested by adjusting the influencing parameters of the power tube to be tested, so as to ensure that the power device will not trigger secondary start-up by designing the influencing parameters in applications where the peak voltage cannot be completely eliminated; the circuit structure of the present invention is simple, the cost is low, and it is easy to use. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 Shown is a schematic diagram of the structure of the evaluation circuit of the present invention.

[0030] Figure 2 Shown is a schematic diagram of the junction capacitance equivalent model of the corresponding power tube of the present invention.

[0031] Figure 3 It is a schematic diagram showing the current flow direction of the junction capacitance Cgd of the power tube to be tested according to the present invention.

[0032] Figure 4 It shows the waveform diagram of the terminal current and the terminal voltage during actual measurement of the evaluation circuit of the present invention.

[0033] Component number description

[0034] 100 Evaluation Circuit

[0035] 110 Power Module

[0036] 120 switch module

[0037] 121 PWM signal source

[0038] 130 Control Test Module

[0039] 131 Test Units DETAILED DESCRIPTION

[0040] The following describes the embodiments of the present invention through specific examples, and those skilled in the art can easily understand other advantages and effects of the present invention from the contents disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and the details in this specification can also be modified or changed in various ways based on different viewpoints and applications without departing from the spirit of the present invention.

[0041] See also Figures 1 to 4 It should be noted that the illustrations provided in this embodiment are only used to illustrate the basic concept of the present invention in a schematic manner, and the illustrations only show components related to the present invention rather than being drawn according to the number, shape and size of components in actual implementation. In actual implementation, the form, quantity and proportion of each component may be changed arbitrarily, and the component layout may also be more complicated.

[0042] like Figure 1 As shown, this embodiment provides a power device secondary start-up evaluation circuit, the evaluation circuit 100 includes a switch module 120 and a control test module 130, and further includes a power module 110. Among them:

[0043] The power module 110 is used to provide a direct current signal.

[0044] As an example, the power module 110 includes a DC power supply Vbus and a high-voltage capacitor Cbus; the upper plate of the high-voltage capacitor Cbus is connected to the positive output terminal of the DC power supply Vbus and generates a DC signal, and the lower plate is connected to the negative output terminal of the DC power supply Vbus and connected to the reference ground.

[0045] When the evaluation test is performed through the evaluation circuit 100 of this embodiment, high voltage and high current are required during the test. The presence of the high-voltage capacitor Cbus can prevent the switch module 120 from directly drawing power from the DC power supply Vbus, avoid power supply damage, and reduce system costs; and the selection of the high-voltage capacitor Cbus should meet the voltage and capacity requirements to avoid overvoltage and voltage drops during the test.

[0046] In addition, regarding the selection of the DC power supply Vbus, the rated voltage of the DC power supply Vbus is determined by the rated voltage of the power tube MDut to be tested in the control test module 130, which can be 80% of the rated voltage of the power tube MDut to be tested, or determined by the application environment. Taking the rated voltage of the power tube MDut to be tested as 1200V as an example, the rated voltage of the DC power supply Vbus can be set to 960V, or set to 800V according to the application environment.

[0047] The switch module 120 is connected to the power module 110, and converts a DC signal into a switch signal by turning on and off the switch tube MDri.

[0048] As an example, the switch module 120 includes a PWM signal source 121, a first driving resistor RDri, a switch tube MDri and a load resistor RL; the PWM signal source 121 is used to provide a single pulse signal; the control end of the switch tube MDri is connected to the single pulse signal via the first driving resistor RDri, the first end is connected to the DC signal, and the second end is connected to the reference ground via the load resistor RL to generate a switching electrical signal.

[0049] Among them, the PWM signal source 121 can be implemented by any existing pulse generation circuit, and this embodiment does not limit this. Since the switch module 120 is a resistive load circuit, the pulse width of the single pulse signal generated by the PWM signal source 121 should not be too long, otherwise it will cause the circuit to heat up, but it should not be too short, otherwise it cannot ensure that the switch tube MDri is fully turned on; in actual applications, the pulse width of the single pulse signal is generally several microseconds, such as 5μs.

[0050] The switch tube MDri is controlled by a single pulse signal to turn on and off, and its switching speed is determined by the resistance value of the first drive resistor Rdri; by adjusting the resistance value of the first drive resistor Rdri, the switching speed of the switch tube MDri can be adjusted, thereby adjusting the voltage change rate dv / dt of the power tube to be tested MDut, that is, the smaller the resistance value of the first drive resistor Rdri, the faster the switching speed of the switch tube MDri, and the larger the voltage change rate dv / dt of the power tube to be tested MDut; conversely, the larger the resistance value of the first drive resistor Rdri, the slower the switching speed of the switch tube MDri, and the smaller the voltage change rate dv / dt of the power tube to be tested MDut.

[0051] The first driving resistor RDri can be a fixed resistor or an adjustable resistor. In practical applications, an adjustable resistor is generally selected as the first driving resistor RDri. In this way, the influencing parameter of the power tube MDut to be tested is adjusted by gradually increasing the resistance of the first driving resistor RDri, and the secondary opening condition of the power tube MDut to be tested is evaluated by triggering the secondary opening of the power tube MDut to be tested. In addition, the switch tube MDri is generally implemented by N-type MOSFET. The resistance of the load resistor RL is determined by the rated current of the power tube MDut to be tested, and it is usually required to satisfy that the current flowing through the power tube MDut to be tested after opening is 50% of the rated current, that is, the current is equal to the ratio of the rated voltage of the DC power supply Vbus to the load resistor RL.

[0052] The control test module 130 is connected to the switch module 120, and performs a control test on the power tube to be tested MDut and the control power tube MRef based on the switch electrical signal, and evaluates its secondary opening condition by triggering the power tube to be tested MDut to be turned on again; wherein, the control power tube MRef remains turned off during the control test.

[0053] As an example, the control test module 130 includes a power tube to be tested MDut, a control power tube MRef, a second driving resistor RDut and a test unit 131; the control end of the power tube to be tested MDut is connected to the reference ground via the second driving resistor RDut, the first end is connected to the switching electrical signal, and the second end is connected to the reference ground; the control end of the control power tube MRef is short-circuited with its second end and connected to the reference ground, and the first end is connected to the switching electrical signal; the test unit 131 is used to test the terminal current and / or terminal voltage of the power tube to be tested MDut and the control power tube MRef.

[0054] The power tube to be tested MDut and the reference power tube MRef are the same type of switch power tubes, and the device parameters of the two are the same. In practical applications, in order to facilitate selection, the switch tube MDri, the power tube to be tested MDut and the reference power tube MRef are the same type of devices with the same parameters; as an optional solution, the switch tube MDri, the power tube to be tested MDut and the reference power tube MRef are all N-type SiC MOSFETs and the device parameters of the three are the same. In this case, the control end refers to the gate, the first end refers to the drain, and the second end refers to the source.

[0055] The second driving resistor RDut can be a resistor with a fixed resistance or a resistor with an adjustable resistance. In practical applications, a resistor with an adjustable resistance is generally selected as the second driving resistor RDut. In this way, the influencing parameter of the power tube MDut to be tested is adjusted by gradually increasing the resistance of the second driving resistor RDut, and the secondary start-up condition of the power tube MDut to be tested is evaluated by triggering the secondary start-up of the power tube MDut to be tested.

[0056] It should be noted that, since adjusting the resistance values ​​of the first driving resistor RDri and the second driving resistor RDut can affect the secondary start-up of the power tube to be tested MDut, when evaluating the secondary start-up condition of the power tube to be tested MDut, the resistance value of at least one of the first driving resistor RDri and the second driving resistor RDut can be adjusted; in practical applications, the resistance value of one resistor is usually fixed and the resistance value of the other resistor is adjusted.

[0057] The test unit 131 includes an oscilloscope. By connecting a current probe to the second end of the corresponding power tube, the terminal current of the corresponding power tube can be measured. By connecting a voltage probe to the first end and the second end of the corresponding power tube, the terminal voltage of the corresponding power tube can be measured. Taking the corresponding power tube as an N-type SiC MOSFET as an example, the terminal current refers to the drain-source current IDS of the corresponding power tube, and the terminal voltage refers to the drain-source voltage VDS of the corresponding power tube.

[0058] As another example, the control test module 130 includes not only the power tube to be tested MDut, the control power tube MRef, the second driving resistor RDut and the test unit 131, but also a first sampling resistor Rs1 and a second sampling resistor Rs2; the first sampling resistor Rs1 is connected between the second end of the power tube to be tested MDut and the reference ground, and the second sampling resistor Rs2 is connected between the second end of the control power tube MRef and the reference ground, and the terminal current of the corresponding power tube is sampled through the corresponding sampling resistor.

[0059] It should be noted that after adding the corresponding sampling resistor in this example, it has no effect on the terminal voltage test of the corresponding power tube, but it has an effect on the terminal current test of the corresponding power tube; when performing the terminal current test on the corresponding power tube, a voltage probe is used instead of a current probe, and the terminal current of the corresponding power tube can be measured by connecting the voltage probe to both ends of the corresponding sampling resistor.

[0060] Correspondingly, the present embodiment further provides an evaluation method implemented based on the evaluation circuit 100 as described above, the evaluation method comprising: when performing a comparison test on the power tube to be tested MDut and the reference power tube MRef, adjusting the influencing parameter of the power tube to be tested MDut, and judging whether to trigger the secondary start-up of the power tube to be tested MDut based on the change of the terminal current and / or terminal voltage of the power tube to be tested MDut, so as to evaluate the secondary start-up condition of the power tube to be tested MDut.

[0061] It should be noted that when performing a comparison test on the power tube MDut under test and the reference power tube MRef, the power tube MDut under test and the reference power tube MRef may be tested in batches or simultaneously, and this embodiment does not limit this.

[0062] As an example, the comparison test is performed by charging the junction capacitances of the power transistor to be tested MDut and the reference power transistor MRef based on the switch electrical signal.

[0063] The equivalent models of the junction capacitance of the power tube to be tested MDut and the reference power tube MRef are as follows: Figure 2 As shown, Cds is the capacitance between the drain and source of the corresponding power tube, Cgd is the capacitance between the gate and drain of the corresponding power tube, and Cgs is the capacitance between the gate and source of the corresponding power tube.

[0064] The switch tube MDri is regarded as the upper tube, and the power tube to be tested MDut and the reference power tube MRef are regarded as the lower tube; when the upper tube is turned on and off, the voltage across the drain and source of the lower tube will change with the upper tube.

[0065] When the switch tube MDri is turned on, there is current to charge the junction capacitance of the lower tube:

[0066] For the control power tube MRef, since its gate and source are short-circuited, the device channel remains closed during the process of increasing the voltage across the drain and source;

[0067] For the power tube MDut to be tested, during the process of the voltage rising between the drain and the source, due to the existence of the second driving resistor RDut, the charging current of the junction capacitor Cgd will generate a voltage on the second driving resistor RDut. When the voltage is higher than the threshold voltage of the power tube MDut to be tested, the power tube MDut to be tested is triggered to be turned on for the second time, such as Figure 3 As shown;

[0068] Among them, the power tube MDut to be tested must satisfy the formula when it is turned on for the second time Cgd is the capacitance between the gate and drain of the power tube MDut to be tested, dv / dt is the voltage change rate of the power tube MDut to be tested, RDut is the resistance value of the second driving resistor, and Vth is the threshold voltage of the power tube MDut to be tested.

[0069] As an example, the influencing parameter of the power tube MDut to be tested is adjusted by adjusting the resistance value of the first driving resistor RDri and / or the resistance value of the second driving resistor RDut.

[0070] It can be known from the above secondary turn-on satisfying formula that whether the power tube to be tested MDut triggers secondary turn-on is determined by the values ​​of Cgd, dv / dt and RDut; after the power tube to be tested MDut is selected, the corresponding Cgd value is fixed, therefore, the influencing parameter of the power tube to be tested MDut is adjusted by adjusting at least one of dv / dt and RDut, so as to evaluate the secondary turn-on condition of the power tube to be tested MDut, and dv / dt is determined by RDri.

[0071] As an example, whether to trigger the secondary start of the power tube to be tested MDut is determined based on the terminal current. The specific method includes: comparing the terminal current of the power tube to be tested MDut and the terminal current of the reference power tube MRef. If the terminal current of the power tube to be tested MDut is greater than the terminal current of the reference power tube MRef, it is determined that the power tube to be tested MDut is triggered to be turned on twice.

[0072] Since the reference power tube MRef remains closed during the reference test, the terminal current of the reference power tube MRef is used as a reference; when the power tube to be tested MDut is triggered to be turned on for the second time, the device channel is opened, and more current flows through the channel. At this time, the terminal current of the power tube to be tested MDut increases; in this way, the terminal currents of the power tube to be tested MDut and the reference power tube MRef are compared, and when the terminal current of the power tube to be tested MDut is greater than the terminal current of the reference power tube MRef, it is determined that the power tube to be tested MDut is triggered to be turned on for the second time.

[0073] As another example, whether the power tube to be tested MDut is triggered to be turned on for the second time is determined based on the terminal voltage. The specific method includes: comparing the terminal voltage increments of the power tube to be tested MDut and the reference power tube MRef. If the terminal voltage increment of the power tube to be tested MDut is less than the terminal voltage increment of the reference power tube MRef, it is determined that the power tube to be tested MDut has been triggered to be turned on for the second time.

[0074] Since the reference power tube MRef remains closed during the reference test, the terminal voltage of the reference power tube MRef is used as a reference; when the power tube MDut to be tested is triggered to be turned on for the second time, the device channel is opened, more current flows from the channel, the charging current of the junction capacitance Cds is reduced, and the voltage rise across the drain and the source slows down or stops rising, that is, the terminal voltage increment decreases or even becomes zero; in this way, the terminal voltage increments of the power tube MDut to be tested and the reference power tube MRef are compared, and when the terminal voltage increment of the power tube MDut to be tested is less than the terminal voltage increment of the reference power tube MRef, it is determined that the power tube MDut to be tested is triggered to be turned on for the second time.

[0075] Of course, in other examples, it is also possible to determine whether to trigger the second turn-on of the power tube MDut to be tested based on both the terminal current and the terminal voltage. The specific method is the same as above and will not be repeated here.

[0076] Next, please combine Figures 1 to 3 , see Figure 4 , the evaluation circuit 100 and the evaluation method thereof of this embodiment are described in detail; wherein the first driving resistor RDri is a fixed resistor, and the second driving resistor RDut is an adjustable resistor, and the resistance value gradually increases from zero.

[0077] During the control test, since the gate and source of the control power tube MRef are short-circuited, during the change of the voltage across its drain and source, the device channel remains closed, and the terminal current tested by the second sampling resistor Rs2 is the charging current of the junction capacitor Cds; the change speed of the voltage across the drain and source of the power tube to be tested MDut is the same as that of the control power tube MRef, but due to the existence of the second driving resistor RDut, when the voltage across the drain and source of the power tube to be tested MDut increases, the charging current of the junction capacitor Cgd flows through the second driving resistor RDut and generates a voltage, and when the voltage is higher than the threshold voltage of the power tube to be tested MDut, the power tube to be tested MDut triggers a second turn-on;

[0078] During the test, the value of the second driving resistor RDut gradually increases from zero, and the terminal current measured by the first sampling resistor Rs1 is used to determine when the power tube MDut to be tested triggers secondary start-up, thereby evaluating the secondary start-up condition of the power tube MDut to be tested.

[0079] Figure 4The waveforms of the terminal current and terminal voltage corresponding to the power tube to be tested MDut and the reference power tube MRef when RDut is 0Ω and 10Ω are shown. It can be seen from the figure that under the same dv / dt, when RDut is 10Ω, during the process of closing the switch tube MDri, the power tube to be tested MDut will trigger a second opening.

[0080] In summary, the power device secondary start-up evaluation circuit and evaluation method of the present invention, during the control test, evaluates the secondary start-up condition of the power tube to be tested by adjusting the influencing parameters of the power tube to be tested, so that in applications where the spike voltage cannot be completely eliminated, the influencing parameters are designed to ensure that the power device will not trigger the secondary start-up; the circuit structure of the present invention is simple, the cost is low, and it is easy to use. Therefore, the present invention effectively overcomes various shortcomings in the prior art and has a high industrial utilization value.

[0081] The above embodiments are merely illustrative of the principles and effects of the present invention, and are not intended to limit the present invention. Anyone familiar with the art may modify or alter the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or alterations made by a person of ordinary skill in the art without departing from the spirit and technical concept disclosed by the present invention shall still be covered by the claims of the present invention.

Claims

1. A power device secondary start-up evaluation circuit, characterized in that: The evaluation circuit includes a switch module and a control test module, wherein: The switch module converts the DC signal into a switch signal by turning on and off the switch tube; The control test module is connected to the switch module, and performs a control test on the power tube to be tested and the control power tube based on the switch electrical signal, and evaluates its secondary opening condition by triggering the power tube to be tested to be turned on again; wherein, the control power tube remains turned off during the control test.

2. The power device secondary start-up evaluation circuit according to claim 1, characterized in that: The switch module includes: a PWM signal source, a first driving resistor, a switch tube and a load resistor; The PWM signal source is used to provide a single pulse signal; The control end of the switch tube is connected to the single pulse signal via the first driving resistor, the first end is connected to the DC signal, and the second end is connected to the reference ground via the load resistor to generate the switch electrical signal.

3. The power device secondary start-up evaluation circuit according to claim 1, characterized in that: The control test module includes: a power tube to be tested, a control power tube, a second driving resistor and a test unit; The control end of the power tube to be tested is connected to the reference ground via the second driving resistor, the first end is connected to the switch electrical signal, and the second end is connected to the reference ground; The control end of the reference power tube is short-circuited with its second end and connected to the reference ground, and the first end is connected to the switch electrical signal; The test unit is used to test the terminal current and / or terminal voltage of the power tube to be tested and the control power tube.

4. The power device secondary start-up evaluation circuit according to claim 3, characterized in that: The control test module further includes: a first sampling resistor and a second sampling resistor; The first sampling resistor is connected between the second end of the power tube to be tested and a reference ground, and the second sampling resistor is connected between the second end of the control power tube and a reference ground.

5. The power device secondary start-up evaluation circuit according to any one of claims 1 to 4, characterized in that: The evaluation circuit further includes: a power module, configured to provide the DC signal.

6. The power device secondary start-up evaluation circuit according to claim 5, characterized in that: The power module includes: a DC power supply and a high-voltage capacitor; The upper plate of the high-voltage capacitor is connected to the positive output terminal of the DC power supply and generates the DC signal, and the lower plate is connected to the negative output terminal of the DC power supply and connected to the reference ground.

7. An evaluation method based on the power device secondary start-up evaluation circuit according to any one of claims 1 to 6, characterized in that: The evaluation methods include: When the power tube to be tested and the control power tube are subjected to a control test, the influencing parameter of the power tube to be tested is adjusted, and based on the change of the terminal current and / or terminal voltage of the power tube to be tested, it is determined whether to trigger the secondary start-up of the power tube to be tested, so as to evaluate the secondary start-up condition of the power tube to be tested.

8. The evaluation method according to claim 7, characterized in that: The junction capacitances of the power tube to be tested and the control power tube are charged based on the switch electrical signal to perform a control test.

9. The evaluation method according to claim 7, characterized in that: The influencing parameter of the power tube to be tested is adjusted by adjusting the resistance value of the first driving resistor and / or the resistance value of the second driving resistor.

10. The evaluation method according to claim 7, characterized in that: The method for determining whether to trigger the secondary start of the power tube to be tested includes: Comparing the terminal currents of the power tube to be tested and the reference power tube, if the terminal current of the power tube to be tested is greater than the terminal current of the reference power tube, determining that the power tube to be tested triggers a secondary start-up; And / or, comparing the terminal voltage increments of the power tube to be tested and the reference power tube, if the terminal voltage increment of the power tube to be tested is smaller than the terminal voltage increment of the reference power tube, determining that the power tube to be tested triggers a second turn-on.

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