JPH012303A - circuit protection element - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to electronic devices, and more particularly to the property ( PTC characteristics (PosILiveLempe
The present invention relates to a circuit protection element in which layers are biased.

[Conventional technology]

Substances with PTC characteristics (PTC compositions) are used to control overcurrent when short-circuits occur in circuits that include heaters that stop generating heat when the temperature rises to a certain level, positive temperature coefficient thermistors (PTCTIIERMIS'rl:R), thermal sensors, batteries, etc. It can be used as a circuit protection element, etc., which limits the current to a value greater than or equal to the current value, and restores the circuit when the short circuit is removed. P
Currently, various materials have been developed as TC compositions. There is one in which conductive particles such as carbon black are uniformly dispersed in the coalescence.

The method for producing this PTC composition consists of kneading conductive particles such as carbon black with one or more resins used as a polymer and dispersing them in the polymer. Furthermore, conventional circuit protection elements that utilize a PTC composition, for example, in which this material is sandwiched between metal electrode plates, mainly consist of a PTC composition molded body 2, as shown in FIG.
, electrode plates 4a and 4b sandwiching these, and leads 8a and 8b connected to each of the electrode plates.

The relationship between the temperature of the PTC composition of this element and the element resistance is:
For example, as shown in Figure 11, the element electrical resistance at room temperature (room temperature resistance Rr) is small, but when the temperature rises to a certain amount -[-, the resistance increases rapidly and reaches a peak (peak resistance). .

When an overvoltage Vo is applied across the electrodes of this conventional circuit protection element, as shown by the dotted line in FIG. 7, if the room temperature resistance Rr of this circuit protection element is (V).

/Rr) flows and generates heat, and the resistance of this element increases rapidly based on the PTC characteristics, limiting the overcurrent to a value below a certain value.

[Problem that the invention seeks to solve]

However, in conventional circuit protection elements made of PTC compositions, the resistance depends on the temperature of the PTC composition, and at the beginning of overvoltage application, self-heating is small and the resistance is low (
A large current flows depending on the temperature (room temperature). Further, since the resistance of the PTC composition is controlled by temperature, the circuit protection element is affected by the environmental temperature of the element, and there is a risk that the circuit protection element may malfunction due to external heat. As mentioned above, at the beginning of overvoltage application, the temperature is low, so an overcurrent flows according to a small resistance value, and the cutoff time to limit this overcurrent to a predetermined current value is 10-1 to several hundred seconds. Therefore, it is impossible to protect circuits including electronic devices such as ICs that are susceptible to overcurrent.

This invention was made based on the above background,
The purpose of this is to limit the current to below the threshold value from the initial stage when overvoltage is applied, to ensure excellent temperature stability without being affected by external environmental temperature, and to securely control circuits that include electronic devices that are susceptible to overcurrent. An object of the present invention is to provide a circuit protection element that protects the circuit.

[Means for solving problems]

According to the present invention, this problem can be solved by providing a current suppressing layer that does not allow a current exceeding a threshold current to flow, and a P that is electrically and thermally connected to the current suppressing layer.
This is achieved by a circuit protection element characterized by including a PTC layer having TC characteristics and at least two electrodes electrically connected to the outside.

In a preferred embodiment, the PTC layer is a polymer with conductive particles dispersed therein.

This invention will be explained in more detail below.

PTC Composition The circuit protection element in this invention includes at least two electrodes, a current control layer, and a PTC layer made of a PTC composition. This PTC composition is, for example, B a T i
Examples include those in which a monovalent or trivalent metal oxide is added to Oa, and those in which conductive particles and, if necessary, thermally conductive fillers are added to a polymer.

The polymers used in this invention include polyethylene,
Polyethylene oxide, t-4-polybutadiene, polyethylene acrylate, ethylene-ethyl acrylate copolymer, ethylene-acrylic acid co-1F combination, polyester, polyamide, polyether, polycaprolactam, fluorinated ethylene-propylene Jl: iR combination, chlorination Polyethylene, chlorosulfonated ethylene, ethylene-vinyl acetate copolymer, polypropylene, polystyrene, styrene-acrylonitrile copolymer, polyvinyl chloride, polycarbonate, polyacetal, polyalkylene oxide, polyphenylene oxide, polysulfone,
Examples include fluororesins and blend polymers of at least two selected from these. In this invention, the type of polymer, composition ratio, etc. can be appropriately selected depending on desired performance, use, etc.

The conductive particles dispersed in the polymer are made of electrically conductive substances, such as carbon black,
Particles of conductive substances such as silver powder, gold powder, carbon powder, graphite, copper powder, carbon fiber, nickel powder, and silver-plated fine particles can be used. The particle size of this conductive particle,
It is desirable to appropriately select various specific areas and the like depending on the use and desired properties of the PTC composition.

In a preferred embodiment of the invention, the thermally conductive particles that can be dispersed in the polymer are comprised of inorganic or hexa-organic substances with thermal conductivity, such as, for example:
Examples include at least one substance selected from silicon, silicon nitride, silicon carbide, Bed, and alumina, and mixtures thereof. The particle size, specific area, etc. of this thermally conductive particle are P
Various types can be appropriately selected depending on the intended use and desired characteristics of the TC composition.

In preparing the PTC composition, in addition to the above-mentioned polymer, conductive particles, and thermally conductive particles, various additives can be mixed as necessary. Examples of such additives include flame retardants, antioxidants, stabilizers, etc., such as antimony compounds, phosphorus compounds, chlorinated compounds, and brominated compounds.

In the present invention, the PTC composition is prepared by blending and kneading raw materials, polymers, conductive particles, thermally conductive particles, and other additives in predetermined proportions. In the present invention, the polymer may be prepared by blending and kneading conductive particles and then thermally conductive particles, or thermally conductive particles and then conductive particles, or both at the same time. Furthermore, the blending ratio of the polymer and particles depends on the particle content of the target composition, the type of polymer, and the Fu? of the mixer and kneader. It can be selected as appropriate depending on Ji and the like. In this invention, pretreatment such as pulverization, heating, and mixing may be performed before kneading.

Current Suppression Layer The circuit protection element of the present invention has a current suppression layer that is electrically and thermally connected to the PTC layer. The current suppressing layer in this invention means that the current flowing through this layer increases as the applied voltage increases, but even if the applied voltage exceeds a certain value, the flowing current substantially saturates, and the current is below a threshold current of 1 sh. For example, it has an applied voltage V-current characteristic as shown in FIG. 12.

Layers exhibiting such behavior can be obtained using a variety of devices. An example of such a device is a device in which a current path (channel) is formed in a semiconductor, and this channel can be changed by an external electric field. The current suppression layer may also be substituted with field effect transistors (FETs) and related devices. MOS-FET (
Insulated gate FET), junction gate FET, Schottky group! There are FETs, etc.

Circuit Protection Element The circuit protection tooth T of the present invention consists of the above-mentioned PTC layer, a current suppression layer, and at least two electrodes electrically connected to the outside. The types of electrode materials that can be used here include metals that can be used as ordinary electrodes, such as nickel, cobalt,
These include aluminum, chromium, tin, copper, silver, iron (including iron alloys such as stainless steel), zinc, gold, lead, and platinum.

It is desirable that the shape, dimensions, etc. of the electrode be appropriately selected depending on the intended use of the circuit protection element. In this invention, the electrode material may be a rolled metal foil or an annealed metal.

In the circuit protection element of this invention, the PTC layer and the current suppression layer are electrically and thermally connected. Here, "thermal connection" means that when there is a difference between the temperature of the PTC layer and the temperature of the current suppression layer, that is, when there is a temperature gradient, thermal energy is supplied from the high temperature side to the low temperature side. means.

The members of this invention may be combined arbitrarily as long as it does not contradict the purpose of this invention. Next, aspects of its configuration and its manufacturing method will be explained with reference to the accompanying drawings.

FIG. 1 shows one embodiment of a circuit protection element according to the present invention.

In the circuit protection element 1 of this embodiment, a PTC layer 2 and a current suppression layer 3 are laminated, and electrodes 4a and 4b are connected to the outside thereof, and further electrical connection is made to the outside from these electrodes.

FIG. 2 shows another embodiment of the invention. In this aspect, 2
A current suppression layer 3 is laminated so as to be sandwiched between the two PTC layers 2a and 2b, and electrodes 4a and 4b are further layered on the PTC layer.
is connected. This circuit protection element 1 is, for example, p
A conductor plate of type St'''1' is prepared, a through hole 5 is made perpendicular to the surface of this plate, and an impurity is doped into this to form a current path (n channel). niP
It is obtained by placing the TC composition and electrode respectively and hot pressing.

Next, the embodiment using FET is shown in Fig. 3 (A) and (B).
). In the circuit protection cable 1 of this embodiment, the current suppression layer 3 constitutes a junction FET, the drain electrode is the electric current of this element), and the source electrode S and gate electrode G of the FET are the PTC electrode P on the back surface of the FET. is followed by an electrical I, and the PTC layer 2 is sandwiched between the electrode P and the electrode 4b,
The current suppression layer 3 and the PTC layer 2 are thermally connected via the electrode P. A circuit configuration diagram of this embodiment is shown in FIG. 3(B).

FIG. 4 shows another embodiment according to the invention. This current suppression layer 3 is composed of a junction FET, and the FET and source S are connected to PT.
C layer 2a is connected, and on the other hand, PT is connected to the drain D of the FET.
C layer 2b is connected, and electrodes 4a and 4b are laminated on each PTC layer.

FIG. 5 shows yet another embodiment. In this example, a DE mode MOS-FET is used as the current suppression layer 3, and the FET
The PTC layer 2a is connected to the source S, and the other nodes j,, FE
A PTC layer 2b is connected to the drain D of T, and electrodes 4a and 4b are stacked on each PTC layer.

FIG. 6 shows another embodiment of the circuit protection element. In this embodiment, two Schottky barrier FETs are used, and the two FE
The PTC layer 2 is sandwiched between T3a and T3b and bonded with silicone resin for thermal connection. In this element 1,
The source electrode S and gate electrode G of the FET are connected to a common conductive layer 7, this common conductive layer 7 is connected to the electrode Pa on the back surface of the FET, and the electrode pb between the PTC layer 2 and the FET Bb is connected to the common conductive layer 7.
constitutes the external electrode 4b of the element, and the drain electrode of the FET is connected to the conductive layer 8 to constitute the electrode 4a of the element.

This invention is not limited to the above-mentioned embodiments, and various modifications are possible.

For example, although the example is an n-channel, there is also a p-type embodiment in which all of the n-type and p-type structures of the embodiments described in - are reversed, and the polarity is also reversed.

Resin Covering In the present invention, a resin film can be formed on the surface of the circuit protection element if necessary. Examples of such resins include epoxy resins, phenolic resins, polyethylene, polypropylene, polystyrene, polyvinyl chloride, polyvinyl acetate, polyvinyl alcohol, acrylic resins, fluororesins, polyamide resins, polycarbonate resins, polyacetal resins, and polyalkylene resins. Renoxide, saturated polyester resin, polyphenylene oxide, polysulfone, poly-p-xylene, polyimide, polyamideimide, polyesterimide, polybenzimidacyl, polyphenylene sulfide, silicon resin, urea resin, melamine resin, furan resin, alkyd resin, Examples include unsaturated polyester resins, diallyl phthalate resins, polyurethane resins, blend polymers thereof, and L resins modified by reaction with chemical reagents, radiation crosslinking, copolymerization, and the like. Preferred resins among these resins are epoxy resins and phenol resins. These resins contain various additives such as plasticizers, curing agents, crosslinking agents, oxidation preventive agents,
Fillers, antistatic II-agents, flame retardants, etc. may be added. The resin used in this invention has at least a white insulation property, and has good adhesion to the surface of the circuit protection Jk element. The resin coating method is not particularly limited, and can be carried out by, for example, pouring, painting, dipping, etc. Further, curing after coating the resin can be performed by chemical treatment, heating, radiation irradiation, etc. depending on the type of resin.

[For production]

The operation of the device of the present invention having the above configuration will be explained.

The embodiment shown in FIG. 3 will be explained as an example.

In this configuration, a depletion layer is formed at the pn junction at the interface between the n-channel and the p-type semiconductor surrounding it, making the n-channel somewhat narrower. When a normal voltage is applied, current flows through this n-channel.

When an overvoltage is applied to the circuit due to an accident, etc., if overvoltage is also applied between SD and D of this current suppression layer, the depletion layer protrudes from the p-region of the gate and the depletion layer protrudes from the p-region of the substrate. When they touch, a pinch-off condition occurs. Even if the voltage across SD increases, the potential difference between the contact point of this depletion layer and the source does not change, so the current flowing through the depletion layer remains constant and saturates. That is, this current suppressing layer does not allow current exceeding the threshold current to flow. Energy corresponding to the bond between the saturation current and overvoltage is generated from this current suppression layer, raising the temperature of the PTC layer that is thermally connected to it, and due to this PTC characteristic, electricity suddenly increases at a predetermined temperature. Increase resistance. This high resistance limits the current flowing through this circuit protection element to a predetermined value to protect the circuit from overvoltage and overcurrent.

The solid line in FIG. 7 shows the current I-time characteristic when an overvoltage is applied to the circuit protection element of the present invention.

As shown in this figure, in the initial stage, the threshold current is 1 s due to the current suppression layer.
h, and then the PTC layer further limits the current to a predetermined value.

〔Effect of the invention〕

The circuit protection element according to the present invention configured and operated as described above has the following effects.

To more reliably protect a circuit by limiting the current flowing through an element to a current equal to or higher than a threshold value from the initial stage when an overvoltage is applied to a circuit. In the conventional circuit protection element with only PTC layer,
Although it tripped after the PTC layer generated heat and the cut-off time was long, since the overvoltage is limited to the threshold current F from the initial stage when it is applied to the circuit, it is possible to effectively protect ICs and the like that are susceptible to overcurrent.

〔Example〕

Two n-channel Schottky barrier gate type FETs (25 and 279 (MGF-18O-1) manufactured by Wang Ling Electric) were prepared, and the following components were separately kneaded for 60 minutes to prepare a PTC composition.

High density polyethylene 62Wt',,
6 (Mirason 27 manufactured by Mitsui Petrochemicals) Carbon black 38 wt% Using these materials, a circuit protection element was obtained by constructing it as shown in FIG. Note that the conductive layer connected to the source S and the drain D
Ω is connected to a protective resistor 850 between the conductive layer and the conductive layer connected to the protective resistor 850. The resistance between the drain D and source S of the FET is 2.0Ω.The resistance between Pa and Pb between the PTC layers is 2.0Ω.
It was 8Ω. The static characteristics of the device of this example are shown in FIG.

Here, IDSS is the current flowing through the element, and vSE is P
VDS represents the voltage across the TC layer, and VDS represents the voltage across the FET. When VDR (-VSE+VDS) exceeds 1.2 m, IDSS saturates to about 170 mA, and at voltages beyond that, the current actually decreases. Therefore, the trip current in the circuit protection element in this example is set to about 170 mA.

Next, in order to measure the dynamic characteristics of this element, an overvoltage was applied to this element all at once, and the current flowing at that time was measured. The results are shown by the solid line in FIG. The element in this example has 3
V was applied. The resistance of the element is approximately 5Ω, so 600m
A current of A was supposed to flow, but it was limited to about 400 mA due to the operation of the current suppression layer.

For comparison, only between the PTC layers of this device, that is, S
A voltage of 1.8V was applied between E. The results are shown by the dotted line in FIG. As shown in this figure, the initial current is approximately 6
00mA current, Ohm's law holds 17. voltage between SE (1,8V)/resistance between SE and 8 ohm)
- It almost agrees with the calculated value of about 0.64 A, and from this it can be said that the current depends on the applied voltage.

[Brief explanation of the drawing]

FIG. 1 is a sectional view of an element showing one embodiment of the present invention, FIG. 2 is a sectional view of another embodiment of the invention, FIG. 3A is a sectional view of an element showing one embodiment of the invention, and FIG. Figure B is a circuit configuration diagram of the element shown in Figure 3A, Figures 4 and 5 are cross-sectional views showing other aspects of the invention, Figure 6A is a cross-sectional view showing other aspects of the invention; Figure B is a circuit configuration diagram of cable r shown in Figure 6A, Figure 7 is a graph showing the relationship between current and elapsed time for the element of the present invention and the conventional element, and Figure 8 is the static characteristic of the element of the example. FIG. 9 is a graph showing the dynamic characteristics of the element of the example, FIG. 10 is a cross-sectional view of a conventional circuit protection element, FIG. 11 is a temperature-resistance related graph showing PTC characteristics, and FIG. 12 is a graph showing the dynamic characteristics of the element of the example. is a graph showing applied voltage-current characteristics of a current suppression layer. DESCRIPTION OF SYMBOLS 1... Circuit protection element, 2... PTC layer, 3... Current suppression 1□11 layer, 4... Electrode, 5... Through hole, 7...
...Common conductive layer, 8... Conductive layer applicant's agent Sato-O Pb (E) DE Figure 8 Figure 10 Temperature Figure 11 Applied voltage (V)

Claims (2)

[Claims] 1. A current suppressing layer that does not allow a current exceeding a threshold current to flow; and a PTC having PTC characteristics that is electrically and thermally connected to the current suppressing layer.
A circuit protection element comprising a layer and at least two electrodes electrically connected to the outside. 2. The circuit protection element according to claim 1, wherein the PTC layer is a polymer in which conductive particles are dispersed.