JPS6341731Y2 - - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to a switch using a positive temperature coefficient thermistor.

Conventional temperature-sensitive switches using bimetals are made by bonding two metal plates with different coefficients of thermal expansion to form a bimetal, which is inserted into a part of the current path. For example, a typical conventional temperature-sensitive switch, as shown in Figure 1, consists of a bronze plate 1 (20 x 10 ^-6 cm/°C) with a large coefficient of thermal expansion and an amber plate 2 (1 x 10 ^-6 cm/°C) with a small coefficient of thermal expansion. ), a contact point 3 is provided on the surface of a bronze plate 1, and the contact point is brought into contact with a conductive material 4, and is inserted between electric circuits 5 and 6.
Since the bimetal warps depending on the ambient temperature, the current path can be interrupted or connected depending on the temperature. Therefore, the bimetal can be used for constant temperature control etc. in combination with a heater etc. However, bimetals cannot always achieve sufficient effects for precise control.

Recently, a positive temperature coefficient thermistor (PTC) has been proposed as a non-contact switch, but when the temperature exceeds a certain critical value, the resistance of the PTC increases rapidly, thereby interrupting the current flow. However, even if the resistance becomes large, it is not possible to completely cut off the current.

The purpose of the present invention is to provide a switch capable of precise temperature control or current control using PTC.

The present invention is characterized in that a suitable metal thin plate and a PTC thin plate are bonded together to form a bimetal-like laminate, and a switch is constructed using this as an operating element. The switch of this invention forms a current path through a thin PTC plate, and when the temperature of the controlled object from an electric heater, burner, etc. rises above a predetermined value,
The resistance value of PTC increases and automatically reduces the current,
This not only automatically reduces the power input to the controlled electric heater, but also heats the laminate consisting of PTC and metal (heating by the temperature of the controlled object rather than by its own heat generation), allowing PTC with a low coefficient of thermal expansion and high By acting as a bimetal with a metal having a coefficient of thermal expansion, a switch is opened, allowing precise temperature control.

Figure 2 shows a cross-sectional view of the switch of the present invention.
0 is an insulating support, and the support 10 has a conductor 1
1 and a bimetal-like laminate 12 are supported. The laminate 12 is made by bonding together a metal thin plate 14 having a contact point 13 near the top end and a PTC thin plate 16 (thickness 200 μm) having ohmic electrodes 15 on both sides. The material of the metal thin plate 14 may be selected from bronze, brass, etc. having a large coefficient of thermal expansion, or may be selected from any suitable metal.
PTC is a ceramic material with a coefficient of thermal expansion of 7~
Since the temperature is about 10×10 ⁻⁶ cm/° C., the thin metal plate 14 can be selected from a wide range of materials.
The material of PTC is well known, and for example, barium titanate (BaTiO ₃ ) with a trace amount of semiconductor elements added and Ba partially replaced with Pb can be used. Also, the thickness may be arbitrary, but from 50μ
Approximately 500μ is preferable. The ohmic electrode 15 can be plated with, for example, nickel or silver. The contact 13 is in constant contact with the surface of the conductor 11 and opens at a set temperature due to the difference in coefficient of thermal expansion between the thin metal plate 14 and the PTC 16 in the bimetal-like laminate 12. Note that the materials for the PTC and the thin metal plate are selected depending on the temperature to be controlled.

The switch configured as described above operates as a switch that controls current and is sensitive to temperature.
As an example of use, it is assumed that the terminals connected to the conductor 11 and the lower ohmic electrode 15 are connected to a power source and an electric heater, and the temperature of the electric heater is detected by the temperature-sensitive switch shown in Fig. 2. shall be taken as a thing. Now, when the power switch is turned on,
Current flows through the PTC thin plate 16, the contacts 13, and the conductor 11. At this time, since the PTC thin plate 16 has a low resistance, a large current flows through this switch to the electric heater, so that the temperature of the electric heater can be quickly raised. When the temperature approaches the set temperature of the laminate 12,
Since the resistance of the PTC increases, the current flowing to the electric heater decreases more than the increasing ohmic resistance of the electric heater alone, allowing the temperature to quickly settle to the set temperature. When the temperature attempts to rise further, the laminated body 12 acts as a bimetal, so the contacts 13 open to completely cut off the current and lower the temperature to a predetermined control temperature. In this way, the switch of the present invention has dual functions and is suitable for precise temperature control. FIG. 3 shows the operation of a conventional non-contact switch using PTC, and FIG. 4 shows the operation of the present invention. As can be seen from Figure 3, the conventional switch is useful for efficient heating because the current can be rapidly applied by turning on the switch (this point is also the same with the present invention). Even if it is desired to interrupt the current, the current still flows, but in the case of the present invention, as can be seen from FIG.
It will be seen that since the temperature can be opened, temperature control becomes more precise. Furthermore, in the case of the bimetal shown in FIG. 1, since there is no current limiting function, temperature control depends only on the on/off of the contact 3, and therefore temperature control cannot be performed accurately.

Another example of the use of the switch shown in FIG. 2 is as a circuit breaker. Assuming that the ambient temperature is room temperature, when a current below the rating is flowing through the circuit including this switch, the contact 13 remains closed because no heat is generated. However, if an overcurrent flows in the circuit due to an abnormality (for example, a short circuit), the PTC of this switch will rise in temperature, and the metal plate 14 will also be heated, causing the metal plate 14 and the PTC to rise.
A bimetallic action occurs between the contact point 13 and the contact point 13.

FIG. 5 shows another embodiment of the invention. This embodiment is not much different from the embodiment shown in FIG.
The second point is that the PTC thin plate 16 is formed short.
It is different from the one in the picture. Although this example has slightly lower temperature sensitivity, it saves PTC material. In addition, above 2
In the two embodiments, the contact 13 may be attached to the conductor 11 side, or the present switch may be configured as a temperature-sensitive closed circuit type instead of a temperature-sensitive open circuit type.

FIG. 6 shows another embodiment of the invention. This embodiment has almost the same configuration as the switch described in connection with FIG.
The only difference is that 5' does not reach the free end of the PTC thin plate 16, but ends in the middle. According to this example, heat generation of the PTC thin plate can be suppressed by arbitrarily selecting the length (or area) of the lower electrode 15'. Therefore, there is an advantage that the reaction of the bimetal can be made variable accordingly.

[Brief explanation of the drawing]

Fig. 1 is a cross-sectional view showing the structure of a conventional bimetal, Fig. 2 is a cross-sectional view of the temperature-sensitive switch of the present invention, Fig. 3 is a graph showing the operation of a conventional non-contact switch, and Fig. 4 is a cross-sectional view of the temperature-sensitive switch of the present invention. 5 is a sectional view showing another embodiment of the present invention, and FIG. 6 is a sectional view showing still another embodiment of the present invention. The main parts in the figure are as follows. 11: conductor, 12: laminate, 13: contact, 1
4: Metal thin plate, 15, 15': Ohmic electrode,
16: PTC thin plate.

Claims (1)

[Scope of utility model registration request] A switch characterized in that a metal thin plate and a PTC thin plate are bonded together and associated with a conductor through a contact point, and an external terminal is provided so as to form a current path passing through the conductor and the PTC thin plate.