Direct current bias inductor inductance value test circuit

Abstract

The utility model provides a DC bias inductor inductance value test circuit, which is used for measuring the inductance value of an inductor to be measured under the DC bias condition, and is characterized by comprising a DC source, a first switch tube, the inductor to be measured, a hollow coil, a current-limiting resistor and a fly-wheel diode, the hollow coil and the inductor to be measured are electrically connected to form an inductance branch, and the inductance branch, the freewheeling diode and the current-limiting resistor are connected in series to form a freewheeling loop; the inductance branch is connected in series with the direct current source and the first switch tube to form a first loop; according to the direct current bias inductor inductance value test circuit, when a first loop works, the inductance value of an inductor to be tested is obtained according to the inductance value of a hollow coil, the voltage of the hollow coil and the voltage of the inductor to be tested, or according to the inductance value of the hollow coil, the current of the hollow coil and the current of the inductor to be tested; the inductance value test circuit can balance the defects of a pulse method and a direct current method, can effectively obtain inductance values under different currents, overcomes the defect that the direct current method cannot test the inductance values under large currents or is difficult to test the inductance values under large currents, can avoid the defect that the eddy current loss of the pulse method is too large, and is simple in circuit, low in cost and high in precision.

Description

Technical Field

[0001] The utility model relates to the technical field of electronic circuits, and particularly relates to a DC bias inductance value testing circuit. Background Art

[0002] An inductor is an electronic component that has the property of hindering the change of current. An inductor is composed of a coil or a combination of coils. When current passes through the coil, a magnetic field is generated and electrical energy is stored.

[0003] There are two existing methods for testing inductors:

[0004] One is the pulse method. The pulse method generates a large pulse current in the inductor to be tested. The inductance value can be calculated according to the pulse current curve and the inductor voltage. The disadvantage is that there is a large deviation due to eddy current loss.

[0005] The other is the DC method. The DC source provides a large continuous DC flowing through the inductor; then a small pulse current is generated in the inductor to be tested. The inductance value can be calculated according to the pulse current curve and the inductor voltage. The disadvantage is that for different DC currents, different DC sources need to be matched, which is difficult, large in volume and high in cost. Summary of the Utility Model

[0006] The purpose of the utility model is to provide a DC bias inductance value testing circuit to solve the problems of large difficulty and low accuracy in the existing calculation methods of inductor inductance values.

[0007] The utility model provides a DC bias inductance value testing circuit for measuring the inductance value of an inductor to be tested under DC bias. It is characterized in that it includes a DC source, a first switching tube, the inductor to be tested, a hollow coil, a current-limiting resistor and a freewheeling diode; the hollow coil and the inductor to be tested are electrically connected to form an inductor branch, and the inductor branch, the freewheeling diode and the current-limiting resistor are connected in series to form a freewheeling circuit; the inductor branch is connected in series with the DC source and the first switching tube to form a first loop;

[0008] In the DC bias inductance value testing circuit of the utility model, when the first loop works, the inductance value of the inductor to be tested is obtained according to the inductance value of the hollow coil, the voltage of the hollow coil and the voltage of the inductor to be tested, or according to the inductance value of the hollow coil, the current of the hollow coil and the current of the inductor to be tested.

[0009] Further, the inductor branch is a series inductor branch, that is, the hollow coil and the inductor to be tested are connected in series.

[0010] Further, the inductor branch is a parallel inductor branch, that is, the hollow coil and the inductor to be tested are connected in parallel.

[0011] Further, it further includes a first voltage tester and a second voltage tester, which are respectively used to test the voltage of the inductor to be measured and the voltage of the air-core coil.

[0012] Further, it further includes a first current tester and a second current tester, which are respectively used to measure the current of the inductor to be measured and the current of the air-core coil.

[0013] Further, the calculation formula for obtaining the inductance value of the inductor to be measured is: L_test = V_1 * L_a / V_2;

[0014] Wherein, L_test is the inductance value of the inductor to be measured, V_1 is the voltage of the inductor to be measured, V_2 is the voltage of the air-core coil, and L_a is the inductance value of the air-core coil.

[0015] Further, the calculation formula for obtaining the inductance value of the inductor to be measured is: L_test = I_2 * L_a / I_1;

[0016] Wherein, L_test is the inductance value of the inductor to be measured, I_1 is the current of the inductor to be measured, I_2 is the current of the air-core coil, and L_a is the inductance value of the air-core coil.

[0017] Further, it further includes a third current tester, and the third current tester is used to test the current of the inductor branch in the first loop. At this time, considering the equivalent series resistance of the inductor, the calculation formula for obtaining the inductance value of the inductor to be measured is: L_test = (V_1 - R_test * I) * L_a / (V_2 - R_a * I);

[0018] Wherein, L_test is the inductance value of the inductor to be measured, V_1 is the voltage of the inductor to be measured, V_2 is the voltage of the air-core coil, L_a is the inductance value of the air-core coil, I is the current of the inductor branch, R_test is the resistance value of the equivalent series resistance of the inductor to be measured, and R_a is the resistance value of the equivalent series resistance of the air-core coil.

[0019] Further, it further includes a third voltage tester, and the third voltage tester is used to test the voltage of the inductor branch in the first loop. At this time, considering the equivalent series resistance of the inductor, the calculation formula for obtaining the inductance value of the inductor to be measured is: L_test = (V - R_test * I_1) * L_a * I_2 / [(V - R_a * I_2) * I_1];

[0020] Among them, L_test is the inductance value of the inductor to be measured, I_1 is the current of the inductor to be measured, I_2 is the current of the air-core coil, and L_a is the inductance value of the air-core coil. V is the voltage of the inductor branch, R_test is the equivalent series resistance of the inductor to be measured, and R_a is the equivalent series resistance of the air-core coil.

[0021] Further, the DC power source is a battery or an AC-DC power source.

[0022] The above DC-biased inductor inductance value test circuit can conveniently calculate the inductance value of the inductor to be measured by utilizing the stable inductance value of the air-core coil, with simple calculation and high precision. Description of the Drawings

[0023] Figure 1 It is the circuit diagram of the DC-biased inductor inductance value test circuit in the first embodiment of the present invention;

[0024] Figure 1-1 is Figure 1 、 Figure 3 the voltage waveform across the inductor to be measured, the voltage waveform across the air-core coil, and the current waveforms through the inductor to be measured and the air-core coil in the embodiment;

[0025] Figure 2 It is the circuit diagram of the DC-biased inductor inductance value test circuit in the second embodiment of the present invention;

[0026] Figure 2-1 is Figure 2 the current waveform through the inductor to be measured, the current waveform through the air-core coil 40 in the embodiment;

[0027] Figure 3 It is the circuit diagram of the DC-biased inductor inductance value test circuit in the third embodiment of the present invention;

[0028] Figure 4 It is the circuit diagram of the DC-biased inductor inductance value test circuit in the fourth embodiment of the present invention;

[0029] Figure 4-1 is Figure 4 the current waveform through the inductor to be measured 30, the current waveform I_2 through the air-core coil, and the voltage waveform of the inductor branch in the embodiment;

[0030] Figure 5 It is a schematic diagram of an AC-DC power source in the embodiment of the present invention;

[0031] Figure 6 It is the DC bias curve of the inductor.

[0032] Description of the Main Component Symbols:

[0033] DC power source 10 Freewheeling diode 60 Third current tester 101 First switching transistor 20 First voltage tester 70 Third voltage tester 102 Inductor under test 30 Second voltage tester 80 Air-core coil 40 First current tester 90 Current-limiting resistor 50 Second current tester 100

[0034] The following specific embodiments will further illustrate the present utility model in conjunction with the above-mentioned drawings. Specific embodiments

[0035] For the convenience of understanding the present utility model, the present utility model will be described more comprehensively below with reference to the relevant drawings. Several embodiments of the present utility model are given in the drawings. However, the present utility model can be implemented in many different forms and is not limited to the embodiments described herein. On the contrary, the purpose of providing these embodiments is to make the disclosure of the present utility model more thorough and comprehensive.

[0036] It should be noted that when an element is referred to as being "fixedly provided on" another element, it can be directly on the other element or there may also be an intermediate element. When an element is considered to be "connected" to another element, it can be directly connected to the other element or there may be an intermediate element at the same time. The terms "vertical", "horizontal", "left", "right" and similar expressions used herein are only for the purpose of illustration.

[0037] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those of ordinary skill in the technical field to which the present utility model belongs. The terms used herein in the specification of the present utility model are only for the purpose of describing specific embodiments and are not intended to limit the present utility model. The term "and / or" used herein includes any and all combinations of one or more of the related listed items.

[0038] Please refer to Figure 1 , a DC bias inductance value test circuit provided by the first embodiment of the present utility model, which is used to measure the inductance value of the to-be-tested inductor 30 under DC bias conditions, and includes a DC power source 10, a first switch tube 20, the to-be-tested inductor 30, an air-core coil 40, a current-limiting resistor 50 and a freewheeling diode 60; the air-core coil 40 and the to-be-tested inductor 30 are connected in series to form a series inductance branch, and the series inductance branch, the freewheeling diode 60 and the current-limiting resistor 50 are connected in series to form a freewheeling circuit; the series inductance branch is connected in series with the DC power source 10 and the first switch tube 20 to form a first loop; when the first switch tube 20 is turned on, the DC power source 10 discharges after passing through the first switch tube 20, and the first loop works; after the first switch tube 20 is turned off, the first loop does not work, and the freewheeling circuit works, and the freewheeling circuit is used to discharge energy. When the first loop works, the inductance value of the to-be-tested inductor 30 is obtained according to the inductance value of the air-core coil 40, the voltage of the air-core coil 40 and the voltage of the to-be-tested inductor 30.

[0039] Figure 1In an embodiment, in a case, the first voltage tester 70 is connected in parallel across both ends of the inductor under test 30; the second voltage tester 80 is connected in parallel across both ends of the air-core coil 40; when the first loop operates (the first switching tube 20 is turned on), the voltages V_1 of the inductor under test 30 and V_2 of the air-core coil 40 are respectively measured through the first voltage tester 70 and the second voltage tester 80; according to the voltage V_1 of the inductor under test 30, the voltage V_2 of the air-core coil 40, and the inductance value L_a of the air-core coil 40, the calculation formula for obtaining the inductance value L_test of the inductor under test 30 is: L_test = V_1 * L_a / V_2.

[0040] Specifically, Figure 1 In the embodiment, the derivation of L_test = V_1 * L_a / V_2 is as follows: Since the air-core coil 40 has no magnetic core, the inductance value L_a of the air-core coil 40 is known and is a fixed and unchanging value (because there is no magnetic core inside the air-core coil 40 and its magnetic permeability is constant, so the inductance value of the air-core coil 40 is constant). Since the inductor under test 30 and the air-core coil 40 are in series, when the first loop operates, the current I passing through the inductor under test 30 and the air-core coil 40 (i.e., the first loop current, the inductor branch current) is the same. According to Ohm's law, the formula (1) is obtained, that is, I = V1 / ω * L_test = V2 / ω * L_a, where ω is the angular frequency. From formula (1), L_test = V_1 * L_a / V_2 can be deduced. Since V_1, L_a, and V_2 have all been obtained or are known, the inductance value L_test of the inductor under test 30 can be obtained.

[0041] Figure 1 In the embodiment, in a case, the current I of the first loop (i.e., the inductor branch current) can be measured through the third current tester 101, so as to obtain the moment Tpeak when the current of the inductor under test 30 reaches the pulse current peak Ipk. Specifically, the first switching tube 20 is turned on and the first loop operates. The DC source 10 discharges after passing through the first switching tube 20, providing a large pulse current I for the inductor under test 30. Before the current of the inductor under test 30 reaches the pulse current peak Ipk, the voltage V_1 across the inductor under test 30 decreases, the voltage V_2 across the air-core coil 40 increases, and the current I passing through the inductor under test 30 and the air-core coil 40 increases; when the current of the inductor under test 30 reaches the pulse current peak Ipk, the first switching tube 20 is turned off and the first loop is disconnected, or rather, the first loop does not operate, and the freewheeling loop for discharging the inductor energy starts to operate, and the current I passing through the inductor under test 30 and the air-core coil 40 decreases over time. Figure 1-1 Shows Figure 1 In the embodiment, the waveform of the voltage V_1 across the inductor under test 30, the waveform of the voltage V_2 across the air-core coil 40, and the waveform of the current I passing through the inductor under test 30 and the air-core coil 40.

[0042] Please refer to Figure 2 , a DC bias inductor inductance test circuit provided by the second embodiment of the present utility model, compared with Figure 1 the first embodiment shown in Figure 2 in the embodiment, the inductor branch is a parallel inductor branch, and the parallel inductor branch is formed by parallel connection of an air-core coil 40 and the inductor 30 to be measured; the parallel inductor branch, the freewheeling diode 60, and the current-limiting resistor 50 are connected in series to form a freewheeling circuit; the parallel inductor branch, the DC source 10, and the first switching transistor 20 are connected in series to form a first loop; when the first switching transistor 20 is turned on, the DC source 10 discharges after passing through the first switching transistor 20, and the first loop operates; after the first switching transistor 20 is turned off, the freewheeling circuit operates to discharge energy; when the first loop operates, according to the inductance value of the air-core coil 40, the current of the air-core coil 40, and the current of the inductor 30 to be measured, the inductance value of the inductor 30 to be measured is obtained.

[0043] In one case, Figure 2 the embodiment further includes a first current tester 90 and a second current tester 100; when the first loop operates, the current I_1 of the inductor 30 to be measured and the current I_2 of the air-core coil 40 are respectively measured by the first current tester 90 and the second current tester 100, and according to the current I_1 of the inductor 30 to be measured, the current I_2 of the air-core coil 40, and the inductance value L_a of the air-core coil 40, the calculation formula for the inductance value L_test of the inductor 30 to be measured is: L_test = I_2 * L_a / I_1.

[0044] Specifically, Figure 2 in the embodiment, the derivation of L_test = I_2 * L_a / I_1 is as follows. Since the air-core coil 40 has no magnetic core, the inductance value L_a of the air-core coil 40 is known and is a fixed value. Since the inductor 30 to be measured and the air-core coil 40 are connected in parallel, when the first loop operates, the voltages V (i.e., the inductor branch voltage) of the inductor 30 to be measured and the air-core coil 40 are the same. According to Ohm's law, formula (2) is obtained, i.e., V = I_1 * ω * L_test = I_2 * ω * L_a, where ω is the angular frequency. From formula (2), L_test = I_2 * L_a / I_1 can be deduced. Since I_1, L_a, and I_2 are all obtained or known, the inductance value L_test of the inductor 30 to be measured can be obtained.

[0045] Figure 2In an embodiment, in one case, the current I_1 of the inductor 30 to be measured can be tested by the first current tester 90 to obtain the time Tpeak1 when the current of the inductor 30 to be measured reaches the pulse current peak value Ipk1; alternatively / and, the current I_2 of the air-core coil 40 can be tested by the second current tester 100 to obtain the time Tpeak1 when the current of the air-core coil 40 reaches the pulse current peak value Ipk2. Before the current of the inductor 30 to be measured or / and the current of the air-core coil 40 reaches the pulse current peak value Ipk1, the first switching tube 20 is turned on, the first loop operates, the DC source 10 discharges after passing through the first switching tube 20, and the current passing through the inductor 30 to be measured and the air-core coil 40 rises; when the current of the inductor 30 to be measured or / and the current of the air-core coil 40 reaches the pulse current peak value, the first switching tube 20 is turned off, the first loop is disconnected, the first loop does not operate, and the freewheeling loop for discharging the inductor energy starts to operate, and the current passing through the inductor 30 to be measured and the air-core coil 40 decreases. Figure 2-1 shows Figure 2 the waveform of the current I_1 passing through the inductor 30 to be measured and the waveform of the current I_2 passing through the air-core coil 40 in the embodiment.

[0046] In the above description of Figure 1 the embodiment, the case of the equivalent series resistance of the inductor is not considered; in order to obtain a more accurate inductance value of the inductor 30 to be measured, the present invention Figure 3 the DC bias inductor inductance value test circuit in the third embodiment shown, compared with Figure 1 the embodiment, considers the equivalent series resistance of the inductor (the equivalent series resistance R300 of the inductor 30 to be measured and the equivalent series resistance 400 of the air-core coil 40). At this time, the calculation formula for the inductance value of the inductor 30 to be measured is L_test = (V_1 - R_test * I) * L_a / (V_2 - R_a * I).

[0047] Specifically, Figure 3In the embodiment, the derivation of L_test = (V_1 - R_test * I) * L_a / (V_2 - R_a * I) is as follows. Since the air-core coil 40 has no magnetic core, the inductance value L_a of the air-core coil 40 is known and is a fixed value. Since the inductor under test 30 and the air-core coil 40 are in series, when the first loop operates, the current I passing through the inductor under test 30 and the air-core coil 40 (i.e., the first-loop current and the inductor-branch current) is the same. According to Ohm's law, Equation (3) is obtained as (ω * L_test + R_test) * I = V_1, and Equation (4) is (ω * L_a + R_a) * I = V_2. From Equation (3) and Equation (4), L_test = (V_1 - R_test * I) * L_a / (V_2 - R_a * I) can be deduced. Since V_1, L_a, R_test, R_a, V_2, and I are all obtained or known (R_test and R_a can be measured by a resistance tester or given in the inductor specification, etc.), the inductance value L_test of the inductor under test 30 can be obtained.

[0048] Figure 3 In the embodiment, the waveforms of the voltage V_1 across the inductor under test 30, the voltage V_2 across the air-core coil 40, and the current I of the inductor branch can be seen Figure 1-1 .

[0049] Please refer to Figure 4 , a DC bias inductor inductance value test circuit provided by the fourth embodiment of the present invention. Compared with Figure 2 the second embodiment shown in Figure 4 in the embodiment, the equivalent series resistance of the inductor (the equivalent series resistance R300 of the inductor under test 30 and the equivalent series resistance 400 of the air-core coil 40) is considered. When the first loop operates, the voltage test of the inductor branch in the first loop is increased. For example, a voltage tester is further included in the first loop. Specifically, the voltage tester can be connected in parallel across the inductor branch, or across the inductor under test 30, or across the air-core coil 40, and then connected in series with the DC source 10 and the first switching tube 20 to form the first loop, and the voltage V of the inductor branch is measured by the voltage tester.

[0050] At this time Figure 4 in the embodiment, the calculation formula for the inductance value of the inductor under test 30 is L_test = (V - R_test * I_1) * L_a * I_2 / [(V - R_a * I_2) * I_1].

[0051] Specifically, Figure 4In the embodiment, the derivation of L_test = (V - R_test * I_1) * L_a * I_2 / [(V - R_a * I_2) * I_1] is as follows. Since the air-core coil 40 has no magnetic core, the inductance value of the air-core coil 40 is known and is a fixed and unchanging value. Since the inductor under test 30 and the air-core coil 40 are in parallel, when the first loop is working, the voltage V across the inductor under test 30 and the air-core coil 40 is the same. According to Ohm's law, Equation (5) is obtained as (ω * L_test + R_test) * I_1 = V, and Equation (6) is (ω * L_a + R_a) * I = V. From Equation (5) and Equation (6), L_test = (V - R_test * I_1) * L_a * I_2 / [(V - R_a * I_2) * I_1] can be deduced. Since I_1, L_a, R_test, R_a, I_2, and V have all been obtained or are known (R_test and R_a can be measured by a resistance tester or given in the inductor specification sheet, etc.), the inductance value L_test of the inductor under test 30 can be obtained.

[0052] Figure 4-1 shows Figure 4 In the embodiment, the waveform of the current I_1 passing through the inductor under test 30, the waveform of the current I_2 passing through the air-core coil 40, and the waveform of the voltage V of the inductor branch.

[0053] In the above Figures 1-4 In the embodiment, the DC power source 10 can be a battery or an AC-DC power source.

[0054] The AC-DC power source can be isolated or non-isolated. In one embodiment, the AC-DC power source is isolated. For example, it can be Figure 5 the circuit shown, that is, composed of an AC input terminal 1, a transformer 2, a rectifier bridge 3, a DC-DC conversion circuit 4, and a capacitor 5. The AC input terminal 1 connects the alternating current to the primary side of the transformer 2. The secondary side of the transformer 2 is connected to the input terminal of the DC-DC conversion circuit 4. The output terminal of the DC-DC conversion circuit 4 is connected to the capacitor 5. Both ends of the capacitor 5 are the two ends of the DC power source 10. Among them, the DC-DC conversion circuit 4 can be a boost circuit (such as Figure 5 the circuit within the dotted line in), a buck circuit, or a buck-boost circuit. In other embodiments, the DC-DC conversion circuit 4 can be omitted, and the output terminal of the rectifier bridge 3 is directly connected to both ends of the capacitor 4. When the AC-DC power source is isolated, since the primary and secondary sides are electrically isolated, electric shock to the human body can be avoided during the test, improving the safety during the test.

[0055] In the above Figures 1-4In the embodiment, the current tester (the first current tester / the second current tester / the third current tester) is a Hall sensor, a CT, etc., that is, any one of the first current tester / the second current tester / the third current tester can be a Hall sensor or a CT or other types of current testers.

[0056] In the above Figures 1-4 embodiment, the first switching tube can be a controllable switch such as an IGBT, a MOSFET, a triode, a relay, a contactor, etc.

[0057] In the above Figures 1-4 embodiment, when the current in the first loop is small during operation, the number of the first switching tubes is 1; if the current in the first loop is large during operation, the first switching tube can be formed by two or more switching tubes in parallel; that is, the number of the first switching tubes can be adaptively adjusted according to the magnitude of the current when the first loop is operating.

[0058] In the above Figures 1-4 embodiment, the output voltage of the DC source 10 can be 50V - 1000V, or other voltage ranges can be selected according to actual needs.

[0059] In addition, Figure 6 is a graph of the DC bias of the inductor, where the horizontal axis current represents the DC bias current, Figure 6 showing the corresponding relationship of the inductance values under different DC bias currents. It can be seen that before the DC bias current reaches the peak current, the inductance (inductance value) of the inductor changes with the change of the current. More specifically, before the DC bias current reaches the peak current, the inductance (inductance value) of the inductor decreases with the increase of the current; after the DC bias current reaches the peak current, the inductance value of the inductor no longer changes; through the above description of the present invention, it can be known that the present invention can obtain the inductance value of the inductor to be measured under different current conditions (within the range from 0 to the current peak) by connecting the air-core coil in parallel or in series with the inductor to be measured, according to the inductance value of the air-core coil, the voltage of the air-core coil and the voltage of the inductor to be measured, or according to the inductance value of the air-core coil, the current of the air-core coil and the current of the inductor to be measured.

[0060] Through the above circuit, the defects of the pulse method and the DC method can be balanced, the inductance values at different currents can be effectively obtained, the defect that the DC method cannot or is difficult to measure the inductance value at a large current can be overcome, and at the same time, the defect of excessive eddy current loss of the pulse method can be avoided; the circuit is simple, the cost is low, and the accuracy is high.

[0061] The above-described embodiments merely represent several implementation manners of the present utility model. The description thereof is relatively specific and detailed, but it should not be construed as a limitation to the scope of the patent of the present utility model. It should be noted that for those of ordinary skill in the art, without departing from the concept of the present utility model, several modifications and improvements can still be made, and these all fall within the protection scope of the present utility model. Therefore, the protection scope of the patent of the present utility model shall be subject to the appended claims.

Claims

1. A DC bias inductor inductance test circuit, used to measure the inductance of an inductor under DC bias conditions, characterized in that, It includes a DC power source, a first switching tube, an inductor under test, an air-core coil, a current-limiting resistor, and a freewheeling diode; After the air-core coil and the inductor under test are electrically connected, an inductor branch is formed. The inductor branch, the freewheeling diode, and the current-limiting resistor are connected in series to form a freewheeling circuit; The inductor branch, the DC power source, and the first switching tube are connected in series to form a first circuit.

2. The DC bias inductance value test circuit according to claim 1, wherein The inductor branch is a series inductor branch, that is, the air-core coil and the inductor under test are connected in series.

3. The DC bias inductance value test circuit according to claim 1, wherein The inductor branch is a parallel inductor branch, that is, the air-core coil and the inductor under test are connected in parallel.

4. The DC bias inductance value test circuit according to claim 2, wherein It further includes a first voltage tester and a second voltage tester, which are respectively used to test the voltage of the inductor under test and the voltage of the air-core coil.

5. The DC bias inductance value test circuit according to claim 3, characterized in that, It further includes a first current tester and a second current tester, which are respectively used to measure the current of the inductor under test and the current of the air-core coil.

6. The DC bias inductance value test circuit according to claim 5, wherein The first current tester and the second current tester are Hall sensors or CTs.

7. The DC bias inductance value test circuit according to claim 1, wherein, The first switching tube is any one of IGBT, MOSFET, triode, relay, and contactor.

8. The DC bias inductance value test circuit according to claim 4, wherein It further includes a third current tester, and the third current tester is used to test the current of the inductor branch in the first circuit.

9. The DC bias inductance value test circuit according to claim 5, characterized in that, It further includes a third voltage tester, and the third voltage tester is used to test the voltage of the inductor branch in the first circuit.

10. The DC bias inductance value test circuit according to any one of claims 1, wherein The DC power source is a battery or an AC-to-DC power source.

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