TECHNICAL FIELD

The present invention relates to a minisize circuit breaker to be built into a secondary battery pack or the like of an electrical equipment.

BACKGROUND ART

Conventionally, a breaker has been used as a protection device (safety circuit) for a secondary battery, a motor and the like of various electrical equipments.

when an abnormality occurs, e.g. when the temperature of a secondary battery during charging/discharging rises excessively, or when an overcurrent flows through a motor or the like installed in an equipment of an automobile, a home appliance or the like, the breaker cuts off the current to protect the secondary battery, motor and the like.
The breaker used as such a protection device is required to operate accurately (to have good temperature characteristics) in accordance with temperature changes in order to ensure the safety of the equipment as well as to have a stable resistance value when the current flows through.

The breaker is provided with a thermally-actuated element which, according to the temperature change, operates to turn on or turn off the current.

Patent Document 1 discloses a breaker using a bimetal as a thermally-actuated element. A bimetal is an element, which is formed by laminating two types of plate-like metal materials having different coefficients of thermal expansion, and which changes its shape according to the temperature change to control the conduction state of the contacts.

The breaker disclosed in this document is formed by housing in its case, a fixed piece, a terminal piece, a movable piece, a thermally-actuated element, a PTC thermistor and the like. And terminals of the fixed piece and terminal piece protrude from the case to be connected to an electric circuit of an equipment in order to use the breaker.

PRIOR ART DOCUMENT

Patent Document

Patent Document 1: Japanese Patent Application Publication No. 2016-62729

SUMMARY OF THE INVENTION

Problem to be Solved by the Invention

On the other hand, when a breaker is used as a protection device for a secondary battery provided in an electrical equipment, e.g. a notebook size personal computer, a tablet type portable information terminal device, a thin multifunctional mobile phone called smartphone and the like, miniaturization is required for the breaker in addition to the safety as described above.

In recent years, users have a strong desire for miniaturization (thinness) of portable information terminal devices, therefore, devices newly launched on the market by various manufacturers have a pronounced tendency to be designed to be small in order to ensure superiority in the design. Against this background, a breaker which is mounted together with a secondary battery as a component of a portable information terminal device is also strongly required to be further miniaturized.

FIG. 8shows a breaker100having a structure equivalent to that of the breaker disclosed in Patent Document 1.

In this figure, (a) is a sectional view of the breaker100when exposed to a high temperature environment, and (b) is a cross-sectional view of the breaker100thereafter cooled under a thermally neutral environment.

As shown inFIG. 8 (a), by the heat of the high-temperature environment, a thermally-actuated element5is deformed and reversely warps to press the PTC thermistor6toward a bottom of a resin case main body7, and thereby, a support part26of the fixed piece2and a bottom wall75of the case main body7are expanded outwardly. At this time, the bottom wall75of the case main body7has been softened by the increased temperature, and thus makes plastic deformation.

As shown inFIG. 8 (b), such bottom wall75maintains its expanded shape even after being cooled down. Thereby, the thickness dimension of the circuit breaker100is increased, which hinders the thinning of an electrical equipment.

Further, in recent years, aiming to improve production efficiency, it has been considered to directly mount a breaker on a circuit board, and also to use soldering reflow for connecting terminals of the breaker with leads of the circuit board.

In such a reflow process, since the breaker100is exposed to a high temperature environment, the above described expansion of the bottom wall75becomes remarkable.

In particular, the above described expansion of the bottom wall75easily occurs when the thickness of the bottom wall75of the breaker100is small, therefore, it is difficult to achieve further thinning of the electric equipment.

In order to solve the above problems, the present invention was made, and it is an object of the present invention to provide a breaker which can be easily miniaturized by suppressing the expansion of its case caused by the temperature rise.

Means of Solving the Problems

According to the present invention, in order to achieve the above object,

a breaker which comprises

a fixed piece having a fixed contact,

a movable piece having a movable contact and pressing the movable contact against the fixed contact to contact therewith,

a thermally-actuated element deforming with a change in the temperature so as to shift the movable piece

from a conduction state in which the movable contact contacts with the fixed contact

to a turn-off state in which the movable contact is separated from the fixed contact,

a positive temperature coefficient thermistor providing an electrical conduction between the movable piece and the fixed piece when the movable piece is in the above-said turn-off state, and

a resin case accommodating the fixed piece, the movable piece, the thermally-actuated element, and the positive temperature coefficient thermistor,

is characterized in that

the fixed piece has a contacting portion contacting with the positive temperature coefficient thermistor,

the resin case has its bottom surface and a concave portion which is recessed from the bottom surface toward the positive temperature coefficient thermistor across the fixed piece, and

in a planar view when the fixed piece is viewed from the positive temperature coefficient thermistor, the above-said contacting portion is disposed within the concave portion.

In the breaker according to the present invention, it is desirable that, in the above-said planar view, the whole of the positive temperature coefficient thermistor is disposed within the concave portion.

In the breaker according to the present invention, it is desirable that the fixed piece is exposed from the concave portion.

In the breaker according to the present invention, it is desirable that the fixed piece has a terminal which is exposed from the bottom surface to be connected to an external circuit.

In the breaker according to the present invention, it is desirable that the concave portion is formed in a rectangular shape which has a corner portion positioned in a region facing the above-said terminal, and the corner portion is formed in an arc shape which is convex toward the terminal.

A safety circuit for an electrical equipment according to the present invention is characterized by having the breaker.

Effects of the Invention

In the breaker according to the present invention, the fixed piece has the contacting portion which contacts with the PTC thermistor, and

the resin case has the bottom surface, and the concave portion which is recessed from the bottom surface toward the PTC thermistor across the fixed piece.

Then, the contact portion is disposed within the concave portion in the planar view when the fixed piece is viewed from PTC thermistor.

Therefore, even when the breaker according to the present invention is exposed to a high temperature environment, and the positive temperature coefficient thermistor is pressed toward the bottom of the resin case by the reversely-warped thermally actuated element, the fixed pieces and the resin case expand outwardly in a portion where the contact portion is provided, namely, in the concave portion which is recessed in advance. Thus, the increase in the thickness of the resin case thus that of the breaker as a whole can be suppressed, and it becomes possible to easily achieve the miniaturization.

Moreover, the effect to suppress the expansion of the case is remarkably effectual in a reflow process by which the breaker is exposed to high temperatures. Thereby, in the reflow process, the posture of the breaker relative to the circuit board becomes stable, and the contact state between terminals of the breaker and lands of a circuit board becomes stable, therefore, easily good soldering is possible.

