Transient voltage protection circuit

Abstract

To provide a transient voltage protection circuit capable of improving transient voltage protection characteristics.SOLUTION: A transient voltage protection circuit 1 comprises a coil 3 and a varistor 5. The coil 3 and the varistor 5 are connected in parallel between a signal line L1 and a ground line L2.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a transient voltage protection circuit.

Background Art

[0002] In an electronic circuit including a semiconductor or the like, a varistor is used for the purpose of protecting elements from various surges (transient voltages) such as electrostatic discharge (ESD) (see, for example, Patent Document 1).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] One aspect of the present invention aims to provide a transient voltage protection circuit capable of improving transient voltage protection characteristics.

Means for Solving the Problems

[0005] A transient voltage protection circuit according to one aspect of the present invention is a transient voltage protection circuit connected between a signal line and a ground, and includes a coil part and a first transient voltage protection part, and the coil part and the first transient voltage protection part are connected in parallel between the signal line and the ground.

[0006] The transient voltage protection circuit according to one aspect of the present invention includes a coil section. The coil section has a high resistance (impedance) to signals having high frequency components, but magnetic saturation occurs with respect to a large voltage (load) such as ESD. Thus, in the coil section, when magnetic saturation occurs, the resistance becomes low, and current flows. Therefore, in the transient voltage protection circuit, a large voltage such as ESD input to the signal line can be discharged to the ground. As a result, the transient voltage protection circuit can reduce the clamp voltage. Further, since the transient voltage protection circuit includes the coil section and the first transient voltage protection section, the energy due to ESD or the like can be distributed between the coil section and the first transient voltage protection section. Therefore, the transient voltage protection circuit can improve the resistance to transient voltages. As described above, the transient voltage protection circuit can improve the transient voltage protection characteristics.

[0007] In one embodiment, the coil section is configured to be magnetically saturated when a voltage higher than the signal voltage of the signal line is applied, and the magnetic saturation voltage at which the coil section is magnetically saturated may be smaller than the operating voltage at which the first transient voltage protection section operates. In this configuration, magnetic saturation can be caused in the coil section before the first transient voltage protection element section operates.

[0008] In one embodiment, in the current-voltage characteristics, the characteristics may change at a first threshold voltage and may also change at a second threshold voltage smaller than the first threshold voltage.

[0009] In one embodiment, a second transient voltage protection section is provided, and the first transient voltage protection section, the coil section, and the second transient voltage protection section are connected in parallel between the signal line and the ground, and the coil section and the second transient voltage protection section may be connected in series in the order of the second transient voltage protection section and the coil from the signal line side. With this configuration, the resistance to transient voltages can be further improved.

[0010] In one embodiment, the operating voltage at which the second transient voltage protection unit operates may be higher than the signal voltage of the signal line. In this configuration, when a voltage higher than the signal voltage is applied to the second transient voltage protection unit, the second transient voltage protection unit can be operated. Therefore, the device connected to the signal line can be appropriately protected.

[0011] In one embodiment, the magnetic saturation voltage at which the coil portion becomes magnetically saturated may be smaller than the operating voltage at which the first transient voltage protection unit operates. In this configuration, magnetic saturation can be caused in the coil portion before the first transient voltage protection element unit operates.

Advantages of the Invention

[0012] According to one aspect of the present invention, the transient voltage protection characteristics can be improved.

Brief Description of the Drawings

[0013]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Modes for Carrying Out the Invention

[0014] Hereinafter, with reference to the accompanying drawings, preferred embodiments of the present invention will be described in detail. In the description of the drawings, the same or corresponding elements are denoted by the same reference numerals, and duplicate descriptions are omitted.

[0015] [First Embodiment] FIG. 1 is a diagram showing a transient voltage protection circuit 1 according to the first embodiment. As shown in FIG. 1, the transient voltage protection circuit 1 is connected between a signal line L1 and a ground line L2. The transient voltage protection circuit 1 is a circuit for protecting a device to be protected (for example, an IC (Integrated Circuit)) when a large voltage (surge voltage) flows into the signal line L1 due to ESD or the like. The signal line L1 is connected to the device to be protected. The ground line L2 is connected to the ground G. The transient voltage protection circuit 1 includes a coil (coil portion) 3 and a varistor (first transient voltage protection portion) 5.

[0016] In the transient voltage protection circuit 1, the coil 3 and the varistor 5 are electrically connected in parallel between the signal line L1 and the ground line L2.

[0017] The coil 3 is, for example, a chip bead. The coil 3 is composed of, for example, a body, external electrodes, and a coil disposed inside the body. The coil 3 is configured to generate magnetic saturation when a voltage equal to or higher than a predetermined voltage is applied. The predetermined voltage is a magnetic saturation voltage and is higher than the maximum value of the signal voltage flowing through the signal line L1. The signal voltage is the voltage of a control signal or the like flowing through the signal line L1.

[0018] The varistor 5 is, for example, a chip varistor. The varistor 5 is composed of, for example, a body, external electrodes, and internal electrodes disposed inside the body. The varistor 5 is configured to operate when a voltage equal to or higher than a predetermined voltage is applied. The predetermined voltage is a varistor voltage (operating voltage). The varistor voltage can also be said to be a breakdown voltage.

[0019] In the transient voltage protection circuit 1, the magnetic saturation voltage at which the coil 3 becomes magnetically saturated is smaller than the varistor voltage at which the varistor 5 operates. That is, in the transient voltage protection circuit 1, the magnetic saturation of the coil 3 occurs prior to the operation of the varistor 5.

[0020] FIG. 2 is a diagram showing an example of the current-voltage characteristics of the coil 3 and the varistor 5. In FIG. 2, the horizontal axis represents voltage [V], and the vertical axis represents current [A]. In FIG. 2, the characteristics of the coil 3 are shown by a solid line, and the characteristics of the varistor 5 are shown by a dashed line. As shown in FIG. 2, in the coil 3, snap-back operation occurs (the snap-back phenomenon appears) at the magnetic saturation voltage (snap-back voltage), and magnetic saturation occurs. That is, it can be said that the coil 3 has a snap-back operation. In the coil 3, magnetic saturation causes a low resistance, and current flows. In the varistor 5, breakdown occurs when the voltage exceeds the varistor voltage. In the varistor 5, when the voltage exceeds the varistor voltage, the resistance becomes low, and current flows.

[0021] FIG. 3 is a diagram showing the current-voltage characteristics of the transient voltage protection circuit 1. In FIG. 3, the horizontal axis represents voltage [V], and the vertical axis represents current [A]. In FIG. 3, the results measured by TLP (Transmission Line Pulse) measurement are shown.

[0022] As shown in FIG. 3, in the current-voltage characteristic (current-voltage characteristic) of the transient voltage protection circuit 1, there are two portions where the characteristic (impedance) switches (hereinafter referred to as "switching portions"). Starting from the switching portion, a main change occurs in the graph of the current-voltage characteristic. In the transient voltage protection circuit 1, the first switching portion occurs at the first threshold voltage V1, and current flows. After the first switching portion, the current flows more than before. The slope of the graph after the first switching portion is greater than the slope of the graph up to the first switching portion. Subsequently, in the transient voltage protection circuit 1, the second switching portion occurs at the second threshold voltage V2. As a result, the transient voltage protection circuit 1 becomes a low resistance, and more current flows. The slope of the graph after the second switching portion is greater than the slope of the graph from the first switching portion to the second switching portion. Between the first switching portion (first threshold voltage V1) and the second switching portion (second threshold voltage V2), it gradually becomes a low resistance (current gradually flows) with a time width. The first threshold voltage V1 is greater than the second threshold voltage V2. The first threshold voltage V1 is greater than the signal voltage. It can also be said that the first threshold voltage V1 is the magnetic saturation voltage.

[0023] As described above, the transient voltage protection circuit 1 according to the present embodiment includes the coil 3. The coil 3 has a high resistance (impedance) to a signal having a high frequency component, but magnetic saturation occurs with respect to a large voltage (load) such as ESD. Thus, in the coil 3, when magnetic saturation occurs, it becomes a low resistance, and current flows. Therefore, in the transient voltage protection circuit 1, a large voltage such as ESD input to the signal line L1 can be discharged to the ground line L2 (ground G). As a result, the transient voltage protection circuit 1 can reduce the clamp voltage.

[0024] FIG. 4 is a diagram showing the clamp characteristics. In FIG. 4, the horizontal axis represents time [ns], and the vertical axis represents voltage [V]. In FIG. 3, the measurement result of the coil 3 is shown by a dashed-dotted line, the measurement result of the varistor 5 is shown by a broken line, and the measurement result of the transient voltage protection circuit 1 is shown by a solid line. FIG. 3 shows the measurement result (waveform) when a predetermined ESD waveform is applied by an ESD gun.

[0025] As shown in FIG. 4, in coil 3, when a voltage is applied, the peak value of the voltage (for example, about 1800 V) is high immediately after the application, but the voltage decreases immediately after the peak. In coil 3, the average value of the voltage with respect to time is low. In varistor 5, when a voltage is applied, the peak value of the voltage immediately after the application (for example, about 800 V) is lower than that of coil 3, but the voltage is higher than that of coil 3 even after the peak. In varistor 5, the average value of the voltage with respect to time is higher than that of coil 3. In transient voltage protection circuit 1, when a voltage is applied, the peak value of the voltage can be suppressed immediately after the application, and the average value of the voltage with respect to time can be lowered. In transient voltage protection circuit 1, a clamping characteristic is obtained by making use of the good clamping characteristics of coil 3 and varistor 5.

[0026] Also, in transient voltage protection circuit 1, since coil 3 and varistor 5 are provided, energy such as ESD can be distributed to coil 3 and varistor 5. Therefore, in transient voltage protection circuit 1, the resistance to transient voltage can be improved. Accordingly, in transient voltage protection circuit 1, the transient voltage protection characteristic can be improved.

[0027] In transient voltage protection circuit 1 according to the present embodiment, coil 3 magnetically saturates when a voltage higher than the signal voltage of signal line L1 is applied. The magnetic saturation voltage at which coil 3 magnetically saturates is smaller than the varistor voltage of varistor 5. In this configuration, magnetic saturation can be caused in coil 3 before varistor 5 operates.

[0028] In transient voltage protection circuit 1 according to the present embodiment, the S parameter can be controlled by matching the inductance of coil 3 and the capacitance of varistor 5. Therefore, in transient voltage protection circuit 1, by appropriately matching the inductance of coil 3 and the capacitance of varistor 5, it is possible to obtain desired impedance characteristics. Thereby, in transient voltage protection circuit 1, a low capacitance can be achieved.

[0029] In the transient voltage protection circuit 1 according to this embodiment, as shown in FIG. 3, in the current-voltage characteristics, there are switching portions at the first threshold voltage V1 and the second threshold voltage V2. At this time, between the first threshold voltage V1 and the second threshold voltage V2, the waveform is continuous so as to gradually become a low resistance. Therefore, between the first threshold voltage V1 and the second threshold voltage V2, current does not flow instantaneously to the ground G. Thereby, it is possible to suppress the occurrence of a shift in the reference potential of the ground G.

[0030] [Second Embodiment] Subsequently, a second embodiment will be described. FIG. 5 is a diagram showing a transient voltage protection circuit according to the second embodiment. As shown in FIG. 5, the transient voltage protection circuit 10 includes a coil (coil portion) 12, a first varistor (first transient voltage protection portion) 14, and a second varistor (second transient voltage protection portion) 16.

[0031] The coil 12 is, for example, a chip bead. The coil 12 is constituted by, for example, a body, external electrodes, and a coil disposed inside the body. The coil 12 is configured to cause magnetic saturation when a voltage equal to or higher than a predetermined voltage is applied. The predetermined voltage is smaller than the operating voltage (varistor voltage) at which the first varistor 14 operates and the operating voltage (varistor voltage) at which the second varistor 16 operates. The predetermined voltage may be lower than the signal voltage.

[0032] The first varistor 14 is, for example, a chip varistor. The first varistor 14 is constituted by, for example, a body, external electrodes, and internal electrodes disposed inside the body. The first varistor 14 is configured to operate when a voltage equal to or higher than a predetermined voltage is applied. The predetermined voltage is the varistor voltage (operating voltage). The varistor voltage can also be said to be the breakdown voltage.

[0033] The second varistor 16 is, for example, a chip varistor. The second varistor 16 is composed of, for example, a base body, external electrodes, and internal electrodes disposed within the base body. The second varistor 16 is configured to operate when a voltage equal to or higher than a predetermined voltage is applied. The varistor voltage at which the second varistor 16 operates is higher than the signal voltage of the signal line L1. The total voltage of the varistor voltage of the second varistor 16 and the magnetic saturation voltage of the coil 12 is smaller than the varistor voltage of the first varistor 14.

[0034] In the transient voltage protection circuit 10, the first varistor 14, the second varistor 16, and the coil 12 are electrically connected in parallel between the signal line L1 and the ground line L2. The second varistor 16 and the coil 12 are electrically connected in series in the order of the second varistor 16 and the coil 12 between the signal line L1 and the ground line L2.

[0035] FIG. 6 is a diagram showing the current-voltage characteristics of the transient voltage protection circuit 10. In FIG. 6, the horizontal axis represents voltage [V], and the vertical axis represents current [A]. FIG. 6 shows the results measured by TLP (Transmission Line Pulse) measurement. As shown in FIG. 6, in the transient voltage protection circuit 10, the current increases non-linearly with respect to the voltage. In the transient voltage protection circuit 10, since the coil 12 and the second varistor 16 are connected in series, the characteristics of the varistor appear.

[0036] As described above, the transient voltage protection circuit 10 according to the present embodiment includes a coil 12. The coil 12 has a high resistance (impedance) to a signal having a high frequency component, but magnetic saturation occurs with respect to a large voltage (load) such as ESD. Thus, in the coil 12, when magnetic saturation occurs, the resistance becomes low, and thus a current flows. Therefore, in the transient voltage protection circuit 10, a large voltage such as ESD input to the signal line L1 can be discharged to the ground line L2 (ground G). Thereby, in the transient voltage protection circuit 10, the clamp voltage can be reduced.

[0037] Further, in the transient voltage protection circuit 10, since the coil 12, the first varistor 14, and the second varistor 16 are provided, energy such as ESD can be distributed to the coil 12, the first varistor 14, and the second varistor 16. Therefore, in the transient voltage protection circuit 10, the resistance to transient voltage can be improved. Accordingly, in the transient voltage protection circuit 10, the transient voltage protection characteristics can be improved.

[0038] In the above embodiment, the second varistor 16 and the coil 12 are connected in series in the order of the second varistor 16 and the coil 12 from the signal line L1 side. In this configuration, when a voltage higher than the total voltage of the varistor voltage of the second varistor 16 and the magnetic saturation voltage of the coil 12 is applied, it becomes a low resistance and current flows. For example, as shown in FIG. 6, when trying to operate at a voltage of several tens of V, if only the coil 12 is used, it is necessary to provide a coil 12 that can handle several tens of V. In this case, since the coil 12 can be enlarged, it is difficult to miniaturize the transient voltage protection circuit 10. In the transient voltage protection circuit 10, since the second varistor 16 and the coil 12 are connected in series, the magnetic saturation voltage of the coil 12 may be small. Therefore, a small coil 12 can be used, and the circuit can be miniaturized.

[0039] As described above, the embodiments of the present invention have been described. However, the present invention is not necessarily limited to the above-described embodiments, and various modifications are possible without departing from the gist thereof.

[0040] In the above embodiment, the form using the varistor 5, the first varistor 14, and the second varistor 16 as the transient voltage protection unit has been described as an example. However, the transient voltage protection unit may be, for example, a diode.

[0041] In the above embodiment, as shown in FIG. 3, an example of a form in which current flows continuously between the first switching portion (first threshold voltage V1) and the second switching portion (second threshold voltage V2) was described. However, as shown in FIG. 7, in the transient voltage protection circuit, the waveform may be discontinuous between the first switching portion (first threshold voltage V1) and the second switching portion (second threshold voltage V2). In this configuration, immediately after the first switching portion is formed, it becomes a low resistance and current flows. Therefore, the clamp characteristics can be improved.

Description of Symbols

[0042] 1, 10... Transient voltage protection circuit, 3... Coil (coil portion), 5... Varistor (first transient voltage protection portion), 12... Coil (coil portion), 14... First varistor (first transient voltage protection portion), 16... Second varistor (second transient voltage protection portion), G... Ground, L1... Signal line, V1... First threshold voltage, V2... Second threshold voltage.

Claims

1. A transient voltage protection circuit connected between a signal line and a ground, comprising: a coil part; a first transient voltage protection part, wherein the coil part and the first transient voltage protection part are connected in parallel between the signal line and the ground; the coil part is configured to be magnetically saturated when a voltage higher than the signal voltage of the signal line is applied; a transient voltage protection circuit, wherein the magnetic saturation voltage at which the coil part is magnetically saturated is smaller than the operating voltage at which the first transient voltage protection part operates.

2. The transient voltage protection circuit according to claim 1, wherein in the current-voltage characteristic, the characteristic switches at a first threshold voltage and also switches at a second threshold voltage smaller than the first threshold voltage.

3. A transient voltage protection circuit connected between a signal line and a ground, comprising: a coil part; a first transient voltage protection part; a second transient voltage protection part, wherein the first transient voltage protection part, the coil part, and the second transient voltage protection part are connected in parallel between the signal line and the ground; the coil part and the second transient voltage protection part are connected in series in this order, i.e., the second transient voltage protection part and the coil part, from the signal line side; a transient voltage protection circuit, wherein the magnetic saturation voltage at which the coil part is magnetically saturated is smaller than the operating voltage at which the first transient voltage protection part operates.

4. The transient voltage protection circuit according to claim 3, wherein the operating voltage at which the second transient voltage protection part operates is higher than the signal voltage of the signal line.

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