JPH019069Y2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a switch, particularly a cut-off type switch that is sensitive to overcurrent.

Conventionally, PTC (positive characteristic thermistor) has been proposed as a non-contact switch. In this case, when the temperature exceeds a certain critical value, the resistance of the PTC increases rapidly, thereby interrupting the current flow. However, even with increased resistance, it was not possible to completely cut off the current.

Therefore, an object of the present invention is to provide a switch capable of interrupting current using PTC.

Briefly, the present invention combines a PTC thin plate and a ceramic plate (including PTC) to create a bimetal-like structure, associates the contact provided on the PTC thin plate with a conductor, and creates an electrical path between the conductor and the contact.
This is a switch with external terminals formed to pass through a PTC thin plate. When a large current flows through the PTC thin plate during use, the PTC thin plate generates heat and thermally expands (7 to 10
x10 ^-6 cm/°C). The ceramic plate maintains its original shape because the temperature does not rise, and the contact opens due to the difference in thermal expansion between the PTC thin plate and the ceramic plate.

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows a switch according to the present invention, and 1 is an insulating support made of ceramic or the like. An electrical conductor 2 projects in a cantilevered manner from the carrier 1, and parallel to this a bimetal-like actuating element 3 likewise projects in a cantilevered manner from the carrier 1. According to the invention, the actuating element 3 includes a first PTC thin plate 4 (thickness is about 200μ),
Ohmic electrodes 5 and 8 attached to both sides of the
and the first via the lower ohmic electrode 8.
It consists of a second PTC thin plate 6 (thickness approximately 200μ) bonded to a PTC thin plate. The thickness of this PTC thin plate may be arbitrary, but preferably about 50μ to 500μ. A contact 7 is fixed to the upper ohmic electrode 5. However, the contact 7 may be fixed to the conductor 2 side. Ohmic electrode 8 is external terminal 9
The conductor 2 is connected to an external terminal 10. Typical coefficient of thermal expansion of PTC is 7~
10×10 ⁻⁶ cm/° C., the first PTC laminate 4 in the illustrated embodiment can expand significantly as the temperature increases. That is, when current is applied from the external terminal 10 to the conductor 2, the contact 7, the ohmic electrode 5, the PTC thin plate 4, the ohmic electrode 8, and the external terminal 9, a current flows through the PTC thin plate 4, thereby generating heat.

The first PTC thin plate material is BaTiO ₃ −SrTiO ₃ −
CaTiO ₃ −Y ₂ O ₃ −SiO ₂ −MnO system, and the second PTC sheet material is BaTiO ₃ −PbTiO ₃ −
It is SrTiO ₃ −Y ₂ O ₃ −SiO ₂ −MnO system. All of these are known materials. On the other hand, the material of the ceramic plate is porcelain such as BaTiO ₃ or Al ₂ O ₃ .

The operation of the switch of the present invention having the above configuration is as follows. First, it is assumed that the external terminals 9 and 10 of the switch of the present invention are inserted into a circuit to be protected from overcurrent. If only a current below the rated current is flowing in the circuit, only a small current flows through the PTC thin plate 4, so the heat generated by this PTC thin plate 4 is small, and its temperature rise (preheating) is small. At this time, since the ohmic electrode 5 is made of metal, it has a heat dissipation effect and suppresses temperature rise. However, if an overcurrent flows in the circuit for some reason, the PTC thin plate 4
As a result, the temperature rapidly rises and thermal expansion occurs. On the other hand, the second PTC thin plate 6
Since no current flows through , no temperature rise occurs, and both
A large difference in thermal expansion occurs between PTC thin plates 4 and 6,
The actuating element 3 will be deflected downward and the contacts 7 will open. Note that the overcurrent is also limited by the behavior of the PTC thin plate 4 near the Curie point (resistance increases rapidly above the Curie point), so safety measures have been taken in a double sense.

To explain this with reference to Figure 2, the current
If an overcurrent I _M flows when I ₀ is flowing,
PTC rapidly generates heat, and when the Curie temperature is exceeded, the resistance increases rapidly and the current is limited. The dotted curve in the figure shows the current interruption operation by the non-contact PTC, but the current never reaches zero. On the other hand, in the case of the present invention, complete current interruption occurs due to thermal expansion of the first PTC thin plate 4, as shown by the solid line.

As described above, the present invention has provided a switch that has an excellent blocking effect against overcurrent. Note that since the second PTC thin plate 6 is not heated (it is only preheated), there is substantially no expansion action.
That is, if compared to a bimetal, it is equivalent to a material with a low coefficient of thermal expansion, so any ceramic material can be used without using PTC. The advantage of using the PTC sheet 6 is that the manufacturing process of the actuating element 3 can be simplified.

It will be apparent to those skilled in the art that many variations are possible within the scope of the invention. For example, in the embodiment shown in FIG. 1, by applying a metal layer to the back surface of the second PTC thin plate 6 (only the exposed portion is sufficient), the heat dissipation effect is increased and the metal layer is applied to the back surface of the second PTC thin plate 6.
Preheating of the PTC thin plate 6 can also be suppressed as much as possible.

[Brief explanation of the drawing]

Figure 1 is a sectional view of the switch of the present invention, and
The figure is a graph showing the operating characteristics of the switch of the present invention. In the figure, the main members are as follows. 1: Support, 2: Conductor, 4: First PTC thin plate, 5, 8: Ohmic electrode, 6: Second PTC
Thin plate.

Claims (1)

[Scope of utility model registration request] A PTC thin plate and a PTC or other ceramic thin plate are bonded together and connected to a conductor through contacts, and an external terminal is provided so that a current path is formed through the conductor and the PTC thin plate. A switch to do.