Protection circuit

Abstract

The present invention uses a low-cost and simple structure to protect an electronic component.　In the present invention, a protection circuit has a varistor connected in parallel to a to-be-protected component between a positive electrode side and a negative electrode side of a power source, and is such that a resistor is disposed between the varistor and the positive electrode side of the power source and / or between the varistor and the negative electrode side of the power source.

Description

Technical Field

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

Background Art

[0002] In order to protect electronic components from surge voltages, varistors are used. A varistor is an element that allows a current to flow rapidly when the applied voltage exceeds a predetermined value (the limiting voltage of the varistor), and the applied voltage is limited to be below the predetermined value. Therefore, by connecting a varistor in parallel with the electronic component to be protected, the voltage applied to the electronic component can also be limited to be below the predetermined value, and the electronic component can be protected from surge voltages.

[0003] At this time, in order to protect the power supply from a short-circuit failure of the varistor, a fuse has conventionally been used (for example, Patent Document 1). The fuse is arranged between the varistor and the power supply so that the positive and negative electrodes of the power supply do not short-circuit during a short-circuit failure of the varistor.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] Thus, when a fuse is used to protect the power supply from a short-circuit failure of the varistor, the fuse also blows during a short-circuit failure of the varistor. Therefore, in addition to replacing the varistor, it is also necessary to replace the fuse.

[0006] Also, as shown in FIG. 3, the fuse may be arranged in series with the varistor and in parallel with the electronic component to be protected. Even if arranged in this way, since the fuse is arranged between the varistor and the power supply, the power supply can be protected from a short-circuit failure of the varistor.

[0007] However, if the fuse is positioned as shown in Figure 3, even after the varistor short-circuits and the fuse blows, current will continue to be supplied from the power supply to the electronic components. In other words, after a varistor short-circuit failure, the electronic components will continue to be supplied with current from the power supply without being protected from surge voltage. Therefore, there is a possibility that the electronic components may be damaged by surge voltage without the user realizing that the varistor has short-circuited.

[0008] Therefore, the present invention aims to protect electronic components with a low cost and simple structure. [Means for solving the problem]

[0009] To solve the above problems, the protection circuit in the present invention has a varistor connected in parallel with the component to be protected between the positive and negative terminals of the power supply, and a resistor is placed between the varistor and the positive terminal of the power supply, and / or between the varistor and the negative terminal of the power supply.

[0010] The component to be protected is an LED, and the resistor may be part of the current-limiting resistor for the LED.

[0011] The aforementioned LED may be a safety component for a railway vehicle. [Effects of the Invention]

[0012] This invention makes it possible to protect electronic components with a low cost and a simple structure. [Brief explanation of the drawing]

[0013] [Figure 1] This figure shows a protection circuit according to one embodiment of the present invention. [Figure 2] This figure shows an example of a protection circuit when multiple protected components C are connected in parallel. [Figure 3] This diagram shows a conventional protection circuit. [Modes for carrying out the invention]

[0014] Figure 1 shows a protection circuit according to one embodiment of the present invention. The protection circuit has a varistor V connected in parallel with the component to be protected C between the positive and negative terminals of the power supply B.

[0015] Therefore, in this embodiment, the voltage applied to the protected component is limited to below the limiting voltage of the varistor V, making it possible to protect the electronic component from surge voltages.

[0016] Furthermore, in the protection circuit according to this embodiment, resistor R1 is placed between varistor V and the positive terminal side of power supply B, and resistor R4 is placed between varistor V and the negative terminal side of power supply B.

[0017] Therefore, in this embodiment, even if the varistor V short-circuits, the positive and negative terminals of the power supply B will not short-circuit. In other words, in this embodiment, it is possible to protect the power supply from a varistor short-circuit failure without using a fuse. Thus, in this embodiment, it is possible to protect the LED with a low-cost and simple configuration.

[0018] The component to be protected C is, for example, an LED, as shown in Figure 1. In this case, resistors R1 to R4 are current-limiting resistors that limit the current supplied to the LED. In other words, resistors R1 and R4 are part of the LED's current-limiting resistors R1 to R4, and in this embodiment, there are no electronic components that are solely for the purpose of preventing short-circuit failure of the varistor V.

[0019] Furthermore, in this embodiment, when the varistor V short-circuits, most of the current supplied from power supply B flows to the varistor V side, and almost no current is supplied to the LED side. Therefore, when the varistor short-circuits, the LED hardly lights up. For this reason, in this embodiment, it is possible to know that the varistor V has short-circuited by checking the illumination of the LED.

[0020] To protect the circuit, a protection device such as an NFB (No Fuse Breaker) may be installed. In this embodiment, even in such a case, it is possible to protect the protected component C without operating this protection device when a short-circuit fault occurs in the varistor.

[0021] The protection circuit according to this embodiment may be used, for example, to protect the LED of a safety component of a railway vehicle such as a side lamp of a vehicle. In a railway vehicle, the housing in which the safety component is housed and the housing in which the power source is housed may be separated. For example, the housing in which the side lamp is housed is installed on the side of the vehicle, and the housing in which the power source for supplying current to the side lamp is housed is installed under the vehicle. In this embodiment, it is possible to install the varistor in the housing in which the safety component is housed, and the installation and replacement of the varistor are easy.

[0022] Even when a plurality of protected components C are connected in parallel, for example, as shown in FIG. 2, the varistor V is connected in parallel with all the protected components C between the positive electrode side and the negative electrode side of the power source B, and resistors R are arranged between the varistor V and the positive electrode side of the power source B and between the varistor V and the negative electrode side of the power source B.

[0023] In the examples shown in FIGS. 1 and 2, resistors are arranged on both sides between the varistor V and the positive electrode side of the power source B and between the varistor V and the negative electrode side of the power source B. However, the resistor may be arranged on only one of the sides between the varistor V and the positive electrode side of the power source B and between the varistor V and the negative electrode side of the power source B.

[0024] The present invention has been described above according to the preferred embodiments thereof. Here, the present invention has been described by showing specific specific examples, but various modifications and changes can be made to these specific examples without departing from the spirit and scope of the present invention described in the claims.

Explanation of Reference Numerals

[0025] V Varistor B Power source C Protected component R1~R4 Resistance

Claims

[Claim 1] The power supply has a varistor connected in parallel with the component to be protected between the positive and negative terminals. A resistor is connected between the varistor and the positive terminal of the power supply, and / or between the varistor and the negative terminal of the power supply. The component to be protected is an LED, a safety component of a railway vehicle. The resistor is part of the current-limiting resistor for the LED, forming a protection circuit.

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