JPS6133683Y2 - - Google Patents

Description

[Detailed description of the invention] The present invention relates to an isolator used as an element in a circuit such as a microwave, and in particular, a positive temperature coefficient thermistor is connected to the input terminal, and the positive temperature coefficient thermistor is installed in close contact with a resistor to prevent abnormal input. This invention relates to an isolator that protects the isolator and subsequent equipment when this occurs.

If you place a rod-shaped piece of ferrite material in the center of the waveguide of a microwave circuit and apply a DC magnetic field,
Faraday rotation occurs. A circulator is an element that utilizes this phenomenon to rotate signals input from multiple terminals in one direction and sends them to the next terminal. An example is shown in Figure 1. That is, it is a three-terminal circulator and is called a Y-type circulator. In the figure, input signals input from three terminals 2A, 2B, and 2C of the Y-shaped circulator 1 are rotated clockwise by the action of the ferrite rods. That is, the signal input from 2A is sent to 2B, 2B is sent to 2C, and 2C is sent to 2A. If one of these terminals is grounded via a resistor R, an isolator as shown in FIG. 2 can be obtained. That is, in the figure, the isolator 11 has two terminals 12A, 12B and a ground terminal 12C, and the ground terminal 12C is grounded via a resistor R. In this isolator, the signal input from terminal 12A is input to terminal 12B.
However, the signal input from terminal 12B is attenuated by resistor R. Therefore, the input signal is transmitted only in one direction and not in the opposite direction. Also, when a signal input from the terminal 12A is sent to the terminal 12B, a reflected wave is generated, and the reflected wave is also resisted by the resistor R.
It is attenuated by

Conventionally, when this isolator receives an abnormal input signal from its previous stage, there is a risk that the isolator itself will be damaged, and that the subsequent stage equipment and elements will also be damaged.

The purpose of this invention is to improve the above-mentioned drawbacks of conventional isolators, and to provide an isolator that does not damage itself even if an abnormal input signal is sent from the previous stage, and also prevents damage to equipment and elements in the subsequent stage. There is.

The present invention achieves the above object by providing a positive temperature coefficient thermistor in close contact with the resistor of the isolator, and by connecting the positive coefficient thermistor between the front-stage equipment of the isolator and the input terminal.

Embodiments of the present invention will be described below based on the drawings. FIG. 3 is a diagram illustrating the isolator according to the present invention, and FIG. 4 is a perspective view thereof.
In both figures, the input terminal 12 of the isolator 11
A positive temperature coefficient thermistor T is connected between A and the preceding equipment (Figure 3), and the positive coefficient thermistor is installed in close contact with a resistor R attached to the isolator body with bolts, etc. (4th
figure).

FIG. 5 is a graph showing the relationship between electrical resistance and temperature of various thermistors having a certain shape. A normal thermistor has a so-called negative characteristic where the resistance decreases as the temperature rises, as shown in the curve, but a Si positive characteristic thermistor (curve)
A BaTiO ₃ -based positive temperature coefficient thermistor (curve) has a so-called positive characteristic in which the resistance increases as the temperature rises. Since the scale on the second vertical axis is a logarithmic scale and the horizontal axis is a normal scale, the amount of increase in resistance of this positive temperature coefficient thermistor against temperature rise is extremely large.

When an abnormal input signal is sent to the input terminal 12 of the isolator 11 according to the present invention described above,
The reflected wave is transmitted from the ground terminal 12C to the resistor R, and the resistor R generates heat. When the resistor R generates heat, the temperature of the PTC thermistor T installed in close proximity also rises, and its resistance rapidly increases, so the abnormal input signal rapidly decreases, causing damage to the isolator 11 itself and the devices in its subsequent stages. and elements can be protected.

According to the present invention, as described above, it is possible to prevent failures due to abnormal inputs in communication equipment using microwaves, etc., and it has a great effect on improving the performance of communication equipment and preventing failures.

[Brief explanation of drawings]

Figure 1 is a diagrammatic representation of a Y-type circulator, Figure 2 is a diagrammatic representation of an isolator, Figure 3 is a diagrammatic representation of an isolator according to the present invention, and Figure 4 is a diagrammatic representation of an isolator according to the present invention.
The figure is a perspective view thereof, and FIG. 5 is a graph showing the relationship between resistance and temperature of various thermistors. 1...Y type circulator, 2A, 2B, 2C
...Terminal, 11...Isolator, 12A, 12
B...terminal, 12C...ground terminal, R...resistance,
T...Positive characteristic thermistor.

Claims (1)

[Scope of utility model claims] In an isolator, a ferrite material is placed in the center of the waveguide, and one terminal of a three-terminal circulator to which a DC magnetic field is applied is grounded via a resistor.
An isolator characterized in that a positive temperature coefficient thermistor is connected to an input terminal, and the positive coefficient thermistor is arranged closely to the resistor.