Patent Description:
In general, a cooking appliance refers to a device for heating and cooking food using gas or electricity. Various products such as a microwave oven using microwaves, an oven using a heater, a gas stove using gas, an electric stove using electricity, or a cooktop including a gas stove or an electric stove have come into widespread use.

The gas stove directly generates flame using gas as a heating source, while the electric stove heats a container and food placed on a top plate thereof using electricity.

In the gas stove, heat loss caused by flame is large and contaminants are discharged due to incomplete combustion, thereby polluting room air. Therefore, recently, electric stoves are attracting attention.

Electric stoves may be classified into an inductive electric stove which directly heats a container in which a magnetic field is generated by a magnetic induction method, and a resistive electric stove which heats a top surface made of ceramic using a hot wire.

The inductive electric stove has a short cooking time at a high temperature and must use a dedicated magnetic container. The resistive electric stove may use an existing container but has a relatively long cooking time.

Even if an existing resistive electric stove uses a heating element made of a nichrome wire, an electric heater using a plane heating element is being developed in order to reduce the thickness of the heating element.

In addition, in order to shorten the cooking time, a resistive electric stove using an electric heater capable of heating a limited area at a high temperature is being developed.

As an example of such an electric heater, <CIT>) discloses a plane heating element including a substrate including a surface made of an electrically insulating material, a heating element attached to the surface of the substrate and having a predetermined shape, and a power supply for supplying electricity to the heating element.

In the electric heater, the temperature distribution of an object to be heated may be changed according to the shape (that is, the pattern) of the plane heating element, and the plane heating element may be formed in a shape capable of heating the object to be heated as uniformly as possible.

The plane heating element of the electric heater includes a plurality of tracks having a straight-line shape or an arc shape and adjacent tracks of the plurality of tracks may be connected through a bridge (or a track).

As another example of the heater, European Patent Publication No. <CIT>) discloses a temperature sensitive device. Such a device is configured by printing a heater track made of a conductive material and a plurality of electrodes on a ceramic coating layer. As current is supplied through the electrodes, radiant heat is generated in the heater track.

However, the existing plane heating elements include a heating unit in which a single hot wire is formed within a limited area in a predetermined pattern shape, and the heating portion is designed to have a high resistance in order to heat at a high temperature of <NUM> or higher.

Of course, an electrode for supplying current to the pattern is provided, and the electrode must be configured to have a low resistance so as not to heat.

According to the related art, in order to configure the resistance of the electrode to be significantly lower than the resistance of the pattern, the electrode is configured to be much wider than the width of the pattern.

However, the required power required for each size of the cooking appliance differs, and there is a limit in configuring the pattern only by one hot wire in order to heat up to a high temperature step by step according to the user's need.

Therefore, a plane heating heater having a plurality of patterns and a plurality of electrodes can be configured, but it must be provided in a limited area.

However, in order to connect a plurality of electrodes to one power supply, the electrodes must be located close to each other in a limited area in the same direction, and there is a limit to increase the resistance of the electrodes by making the electrodes wider than the width of the pattern. Meanwhile, if a pattern is formed in a limited area and generates heat at a high temperature, there is a problem that local heat is generated according to the shape of the pattern, thereby breaking the heat wire.

In other words, a path difference in which current flows according to the pattern shape is generated, and a larger path difference causes a large deviation of the current density, local heating occurs at a portion having a high current density, and a hot wire breakdown phenomenon occurs.

<CIT> discloses a layer heater having conductive overlays on bend portions and terminal pads. <CIT> discloses two plane heating elements, one of which is positioned to surround another. <CIT> discloses a glass ceramic plate comprising a cooking area subdivided into at least one inner and one outer area which include individual heating elements for each partial area.

The present invention has been made in order to solve the above problems of the related art, and an object of the present invention is to provide an electric heater including a plane heating element capable of significantly reducing the resistance of an electrode in a limited area.

Another object of the present invention is to provide an electric heater including a plane heating element capable of preventing local heating even if a difference in current density inside the pattern portion is large.

The present invention is defined by the appended independent claim. According to the present description, there is provided an electric heater including: a substrate <NUM> (an insulating material capable of forming a conductor pattern on a surface of an insulating substrate); and a plane heating element <NUM> configured to be formed on one surface of the substrate <NUM>, in which the plane heating element <NUM> includes: a pattern portion <NUM> configured to connect a start point and an end point to each other; and an electrode portion <NUM> configured to be connected to the start point and the end point of the pattern portion <NUM>, and the electrode portion <NUM> is formed to be thicker than the thickness of the pattern portion <NUM>. Therefore, the resistance of the electrode can be formed to be remarkably small in a limited area, so that an unheated unit can be constituted.

At this time, the electrode portion <NUM> may include a positive electrode <NUM> located outside the pattern portion <NUM> and connected to the start point of the pattern portion <NUM>, and a negative electrode <NUM> located outside the pattern portion <NUM> so as to be horizontal to the positive electrode <NUM> and connected to the end point of the pattern portion <NUM>.

In addition, the pattern portion <NUM> may include a plurality of tracks <NUM> spaced apart from each other and having an arc shape increasing from the inside to the outside, and a plurality of bridges <NUM> connecting the tracks <NUM> in series.

At this time, the pattern portion <NUM> may be configured with a symmetrical shape with respect to a reference line passing through the center of the pattern portion <NUM>.

In addition, the electrode portion <NUM> may be formed to be thicker than the thickness of the track <NUM>, the thickness of the electrode portion <NUM> may be formed within a range of <NUM> to <NUM> with respect to the thickness of the track <NUM>, and the electrode portion <NUM> may generate heat at <NUM> or less during current flows.

In addition, the bridge <NUM> may be formed to be thicker than the thickness of the track <NUM>, the thickness of the bridge <NUM> may be formed within a range of <NUM> to <NUM> with respect to the thickness of the track <NUM>, and the bridge <NUM> may generate heat at <NUM> or less during current flows.

Therefore, even if the difference in current density flowing along the bridge is large, the resistance of the bridge can be made small so that it is possible to prevent the bridge portion from being subjected to local heating and thereby causing insulation breakdown.

In addition, the plane heating element may include an inner side plane heating element <NUM> formed at the center thereof, and at least one outer plane heating element <NUM> provided to surround the inner plane heating element <NUM>, and the electrode portion may include an inner electrode portion <NUM> for supplying current to the inner plane heating element <NUM>, and an outer electrode portion <NUM> for supplying current to the outer plane heating element <NUM>, that is, the pattern portion can be configured as a multi-pattern, and the heat intensity at various stages can be realized.

According to the following description, there is further provided an electric heater including: a substrate <NUM> (an insulating material capable of forming a conductor pattern on a surface of an insulating substrate); and a plane heating element <NUM> configured to be formed on one surface of the substrate <NUM>, in which the plane heating element <NUM> includes: a pattern portion <NUM> configured to connect a start point and an end point to each other; and an electrode portion <NUM> configured to be connected to the start point and the end point of the pattern portion <NUM>, and the pattern portion <NUM> includes a plurality of tracks <NUM> spaced apart from each other and having an arc shape increasing from the inside to the outside, and the electrode portion <NUM> is formed to be thicker than the thickness of the track <NUM>.

In addition, in the present invention, the thickness of the electrode portion <NUM> may be formed within a range of <NUM> to <NUM> with respect to the thickness of the track <NUM>.

In addition, the pattern portion <NUM> may further include a plurality of bridges <NUM> connecting the tracks <NUM> in series and the bridge <NUM> may be formed to be thicker than the thickness of the track <NUM>.

In addition, the thickness of the bridge <NUM> may be formed in a range of <NUM> to <NUM> with respect to the thickness of the track <NUM>.

The electric heater according to the present invention can be configured to be thicker than the pattern portion even if the electrode portion is formed in a limited area, and the resistance of the electrode portion can be greatly reduced. Therefore, the heating temperature of the electrode portion formed in a limited area can be effectively lowered.

In addition, in the present invention, the bridges having a large difference in current density among the pattern portions are made thicker than the tracks, so that the resistance of the bridges can be configured to be significantly reduced. Therefore, it is possible to prevent the local heating and the hot wire breakage of the bridge portion of the pattern portion, and the entire area on which the pattern portion is formed can be uniformly heated.

In addition, in the present invention, it is possible to constitute a multi-pattern portion on the same plane and to provide heating intensity at various stages. Therefore, the limited area can be gradually heated to a high temperature step by step.

Hereinafter, the present embodiment will be described in detail with reference to the accompanying drawings.

<FIG> is a perspective view illustrating an electric stove, to which an electric heater according to an embodiment of the present invention can be applied, and <FIG> is a control block diagram of an electric stove, to which an electric heater according to an embodiment of the present invention can be applied. The electric heater <NUM> of the present invention may configure a portion of an electric stove such as a cooktop.

The electric stove may include a cabinet <NUM> forming an outer appearance. The electric heater <NUM> may be provided on the cabinet <NUM>. The upper surface of the cabinet <NUM> may be opened and the electric heater <NUM> may be provided on the upper surface of the cabinet <NUM>.

The electric stove may include an input unit <NUM> for manipulating the electric stove and a display <NUM> for displaying a variety of information such as information on the electric stove. In addition, the electric stove may further include a power supply <NUM> connected to the electric heater <NUM> to apply current to the electric heater <NUM>. The electric stove may further include a controller <NUM> for controlling the power supply <NUM> and the display <NUM> according to input of the input unit <NUM>.

The electric heater <NUM> may be provided on the cabinet <NUM> such that the upper surface thereof is exposed to the outside. An object to be heated by the electric stove may be placed on the upper surface of the electric heater <NUM>, and the upper surface of the electric heater <NUM> may be a surface in which the object to be heated is seated.

<FIG> is a cross-sectional view illustrating an electric heater according to an example useful for understanding the present invention.

The electric heater <NUM> may include a substrate <NUM> and a plurality of plane heating elements <NUM> formed on one surface of the substrate <NUM>.

The substrate <NUM> may be an insulating substrate having a conductor pattern formed on a surface thereof. The upper surface of the substrate <NUM> may be a surface <NUM> in which the object to be heated is seated. The lower surface of the substrate <NUM> may be a surface <NUM> in which the plane heating elements <NUM>, <NUM>, and <NUM> are formed.

The substrate <NUM> may include only a base <NUM> formed of an insulating material or may include a base <NUM> formed of an insulating material or a non-insulating material and an insulating layer <NUM> formed on one surface of the base <NUM>.

The base <NUM> may be glass and the insulating layer <NUM> may be formed on the lower surface of the glass using a coating or a printing method.

The plane heating element <NUM> may be directly formed on one surface of the base <NUM> formed of an insulating material or may be formed on the insulating layer <NUM>.

The base <NUM> may be formed in a shape of a plate on which the object to be heated is placed or in a shape of a container in which the object to be heated is received.

The insulating layer <NUM> may be formed on the lower surface of the base <NUM>. The insulating layer <NUM> may be formed on the entire lower surface of the base <NUM> or may be formed on a portion of the lower surface of the base <NUM>. The insulating layer <NUM> may be formed only in a zone in which the plane heating element <NUM> will be formed. The insulating layer <NUM> may configure the entire lower surface of the substrate <NUM> or a portion of the lower surface of the substrate <NUM>.

The plane heating element <NUM> may be formed on the lower surface <NUM> of the insulating layer <NUM>. The plane heating element <NUM> may have a size smaller than the substrate <NUM> and the lower surface of the substrate <NUM> may have a heated zone H, in which the plane heating element <NUM> is formed, and an unheated zone UH located around the heated zone H.

The heater <NUM> may further include a coating layer <NUM> surrounding the plane heating element <NUM>. The coating layer <NUM> may be formed of an electrically insulating material to protect the plane heating element <NUM>. The substrate <NUM> may be formed of a flexible material, such as a flexible insulating film. In this case, the electric heater <NUM> may be a flexible planar heater. Such a flexible planar heater may be attached to a member, on which the object to be heated is placed, to heat the object to be heated, like the upper plate of the electric stove.

<FIG> is a plan view illustrating a single-type plane heating element according to an example useful for understanding the present invention, and <FIG> are cross-sectional views taken along line A-A' and line B-B' in <FIG>.

The single-type plane heating element according to the present invention comprises only a first plane heating element <NUM> composed of one hot wire as illustrated in <FIG>, and includes a pattern portion <NUM> in which hot wires are arranged in a predetermined shape, and an electrode portion <NUM> for supplying current to the pattern portion <NUM>.

The pattern portion <NUM> is configured with a heating unit in which a certain kind of hot wires are closely arranged in a limited area having a circular shape, connects between a start point and an end point, which are located to the outermost side, along various paths, and is configured with a symmetrical shape with respect to the center of the pattern portion <NUM> illustrated in <FIG> in the lateral direction.

According to the example, the pattern portion <NUM> includes a plurality of tracks <NUM> spaced apart from each other and increasing in size from the center toward the outside, and a plurality of bridges <NUM> connecting the tracks <NUM> in series.

At this time, the area where the pattern portion <NUM> is formed and the length of the hot wire which constitutes the pattern portion <NUM> may be set in proportion to the required power.

The electrodes <NUM> are formed of a unheated unit having a relatively lower heating value than the pattern portion <NUM>, the electrodes <NUM> include a positive electrode <NUM> to which current is input and a negative electrode <NUM> to which current is output, and the positive electrode <NUM> and the negative electrode <NUM> may be horizontally located outside the pattern portion <NUM> with a predetermined gap therebetween.

The positive electrode <NUM> is a portion which extends from the start point of the pattern portion <NUM> and is
connected to an external input terminal, and the negative electrode <NUM> is a portion which extends from the end point of the pattern portion <NUM> and is connected to the external output terminal.

When a current is supplied to the single-type plane heating element having such a structure, current flows sequentially along the positive electrode <NUM>, the pattern portion <NUM>, and the negative electrode <NUM>.

At this time, the pattern portion <NUM> acts as a kind of resistance to generate heat at <NUM> or higher, and an object to be heated placed on the pattern portion <NUM> is cooked.

However, it is preferable that the electrode portion <NUM> is configured to generate heat at a temperature of <NUM> or less, or substantially no heat.

Of course, the width of the electrode portion <NUM> may be configured to be larger than the width of the pattern portion <NUM> in order to greatly reduce the resistance of the electrode portion <NUM>.

However, since the area for forming the electrode portion <NUM> is limited, it is preferable that the thickness of the electrode portion <NUM> is thicker than the thickness of the pattern portion <NUM>.

As illustrated in <FIG>, the thickness T<NUM> of the positive electrode <NUM> is configured to be larger than the thickness T<NUM> of the pattern portion-side track <NUM> and can be formed in a range of <NUM> to <NUM> with respect to the thickness T<NUM> of the track <NUM> but it is not limited thereto.

Of course, the negative electrode <NUM> may also be configured to be thicker than the thickness T<NUM> of the track <NUM>.

On the other hand, when current flows along the pattern portion <NUM>, the track <NUM> does not have a gently curved shape, that is, a relatively large radius of curvature is not configured, whereas the bridge <NUM> has a sharply curved shape, that is a relatively small radius of curvature is configured.

At this time, a difference in density of the current flowing between the inside and outside of the bridge <NUM> is large, and the bridge <NUM> excessively generates local heat as compared with the track <NUM>.

Therefore, in order to prevent local heating of the bridge <NUM>, it is preferable that the resistance of the bridge <NUM> is configured to be small.

Of course, like the electrode portion <NUM>, the bridge <NUM> may have a wide width in order to reduce the resistance, but considering the limited area, it is preferable that the bridge <NUM> has a large thickness.

As illustrated in <FIG>, the thickness T3 of the bridge <NUM> is configured to be larger than the thickness T<NUM> of the track <NUM> and may be formed in a range of <NUM> to <NUM> with respect to the thickness T<NUM> of the track <NUM>, but is not limited thereto.

In order to manufacture the single-type plane heating element having the above-described structure, the electric energizing material is printed on the surface of the substrate in a form of tracks, bridges, and electrode portions, is dried, and then the same electric energizing material or different kinds of electric energizing materials is printed on the surface of the substrate once again in the form of a bridge and an electrode portion, and then the single-type plane heating element can be manufactured in the form of firing.

In addition to such a printing process, various processes such as a spray process can be used, but it is not limited thereto.

As described above, it is possible to easily manufacture the plane heating element having the bridges and electrode portions thicker than the tracks, and the electrode portion can be constituted of the unheated unit and the local heating of the bridge can be solved.

<FIG> is a plan view illustrating a dual-type plane heating element according to an embodiment of the present invention, and <FIG> are cross-sectional views taken along lines C-C' and D-D' in <FIG>.

As illustrated in <FIG>, the dual-type plane heating element according to the present invention includes an inner plane heating element <NUM> located at the center of the same plane, and an outer plane heating element <NUM> located to surround the inner plane heating element <NUM>.

The inner plane heating element <NUM> includes an inner pattern portion <NUM> arranged in a predetermined shape, an inner electrode portion <NUM> supplying a current to the inner pattern portion <NUM>, and an inner connector <NUM> connecting between the inner pattern portion <NUM> and the inner electrode portions <NUM>.

The inner pattern portion <NUM> and the inner electrode portion <NUM> are configured in the same manner as the pattern portion and the electrode portion described in the above-described single-type plane heating element, and a detailed description thereof will be omitted.

The inner connector <NUM> is formed of an auxiliary heating unit capable of generating heat at the same temperature as the inner pattern portion <NUM>. The inner connector <NUM> is a portion which extends from the start point and the end point of the inner pattern portion <NUM> to the inner electrode portion <NUM>.

The inner connector <NUM> is located between openings provided at one side of the outer pattern portion <NUM> to be described below, that is, at least one pair of outer bridges <NUM>.

One inner connector <NUM> connects between the start point of the inner pattern portion <NUM> and the inner positive electrode <NUM> and the other inner connector <NUM> connects between the end point of the inner pattern portion <NUM> and the inner negative electrode <NUM> to each other.

Since the inner connectors <NUM> and <NUM> are directly connected to the inner positive electrode <NUM> and the inner negative electrode <NUM> so that a large potential difference is generated between the inner connectors <NUM> and <NUM> during current flow and the inner connectors <NUM> and <NUM> may be shortcircuited.

Therefore, in order to prevent a short circuit between the inner connectors <NUM> and <NUM>, the inner connectors <NUM> and <NUM> must be installed far so as to maintain an insulation gap, and are located parallel to each other so that the gap between the inner connectors <NUM> and <NUM> should be maintained at least <NUM> or more, but they are not limited to these.

The outer plane heating element <NUM> includes an outer pattern portion <NUM> arranged outside the inner pattern portion <NUM> in a predetermined shape and an outer electrode portion <NUM> connected to the outer pattern portion <NUM>.

The outer pattern portion <NUM> is formed by a heating unit closely arranged in a ring-shaped limited area surrounding the outside of the inner pattern portion <NUM>, the inner pattern portion <NUM> connects between the start point and the end point, which are located at the innermost side, along various paths and is configured in a symmetrical shape in the lateral direction.

According to an embodiment, the outer pattern portion <NUM> includes a plurality of outer tracks <NUM> and a plurality of outer bridges <NUM> like the inner pattern portion <NUM>.

In addition, a portion of the inner connectors <NUM> and <NUM> are located between the opening portions provided on one side of the outer pattern portion <NUM>, that is, the outer bridges <NUM>.

The outer electrode portion <NUM> includes an unheated unit extended from a start point and an end point of the outer pattern portion <NUM>, and the outer electrode portion <NUM> includes an outer positive electrode <NUM> and an outer negative electrode <NUM> located horizontally.

Of course, the outer electrode portion <NUM> is located in the same direction as the inner electrode portion <NUM> in order to supply current to the inner/outer plane heating elements <NUM> and <NUM> by one power supply.

When current is supplied to the outer plane heating element <NUM> configured as described above, a current flows sequentially along the outer positive electrode <NUM>, the outer pattern portion <NUM>, and the outer negative electrode <NUM> like the internal plane heating element.

At this time, the outer pattern portion <NUM> is formed of a heating unit which generates heat at <NUM> or more, but the outer electrode portion <NUM> should be formed of an unheated unit which generates heat at <NUM> or less and hardly generates heat.

The outer electrode portion <NUM> is thicker than the outer pattern portion <NUM> when considering the limited area on which the outer electrode portion <NUM> can be formed so that the resistance of the outer electrode portion <NUM> is preferably configured to be substantially small.

As illustrated in <FIG>, the thickness T<NUM> of the outer positive electrode <NUM> is formed to be thicker than the thickness T<NUM> of the outer track <NUM>, and the thickness T<NUM> of the outer track <NUM> may be formed in a range of <NUM> to <NUM> with respect to the thickness T1 of the outer track <NUM>, but it is not limited thereto.

Of course, the outer negative electrode <NUM> may be also formed to be thicker than the thickness T<NUM> of the outer track <NUM>.

In addition, since the outer bridge <NUM> is formed in an excessively curved shape as compared with the outer track <NUM>, the outer bridge <NUM> can be locally heated due to a difference in current density between the inside and the outside. Therefore, it is preferable that the outer bridge <NUM> also have a very small resistance in order to prevent local heating.

As illustrated in <FIG>, the thickness T<NUM> of the outer bridge <NUM> is formed to be thicker than the thickness T<NUM> of the outer track <NUM> and may be formed in a range in a range of <NUM> to <NUM> with respect to the thickness T<NUM> of the outer track <NUM>, but it is not limited thereto.

The outer plane heating element configured as described above can configure the outer bridge and the outer electrode portion to be thicker than the outer tracks by a process of printing at least twice like the single-type plane heating element.

<FIG> is a plan view illustrating a triple-type plane heating element according to another embodiment of the present invention, and <FIG> are cross-sectional views taken along lines E-E' and F-F' in <FIG>.

As illustrated in <FIG>, the triple-type plane heating element according to the present invention includes a first plane heating element <NUM> located at the center of the same plane, a second plane heating element <NUM> located to surround the first plane heating element <NUM>, and a third plane heating element <NUM> located to surround the second plane heating element <NUM>.

Since the first plane heating element <NUM> includes a first pattern portion <NUM>, a first electrode portion <NUM>, and a first connector <NUM> and is configured like the inner pattern portion, the inner electrode portion, and the inner connector described in a dual pattern-type inner plane heating element, a detailed description thereof will be omitted.

Since the second plane heating element <NUM> includes the second pattern portion <NUM>, the second electrode portion <NUM>, and the second connector <NUM> and is configured like the outer pattern portion and the outer electrode portion described in the dual pattern-type outer plane heating element, a detailed description thereof will be omitted.

However, the second connector <NUM> is formed as an auxiliary heating unit capable of generating heat at the same temperature as that of the second pattern portion <NUM>, is a portion extended from the start point and the end point of the
second pattern portion <NUM> to the second electrode portion <NUM>, and is provided outside the first connector <NUM>.

Accordingly, the first and second connectors <NUM> and <NUM> may be located between the opening portions provided at one side of the second and third pattern portions <NUM> and <NUM>, that is, at least a pair of second and third bridges <NUM> and <NUM>.

One second connector <NUM> connects between the start point of the second pattern portion <NUM> and the second positive electrode <NUM> and the other second connector <NUM> connects between the end point of the second pattern portion <NUM> and the second negative electrode <NUM>.

The third plane heating element <NUM> includes a third pattern portion <NUM> arranged in a predetermined shape outside the second pattern portion <NUM> and a third electrode portion <NUM> connected to the third pattern portion <NUM>.

The third pattern portion <NUM> is formed by a heating unit closely arranged in a ring-shaped limited area surrounding outside the second pattern portion <NUM>, connects between the start point and the end point, which are located at the outermost side, along various paths, and is configured in a symmetrical shape in the lateral direction.

According to an embodiment, the third pattern portion <NUM> may include a plurality of third tracks <NUM> and a plurality of third bridges <NUM> like the second pattern portion <NUM>.

The third electrode portion <NUM> includes an unheated unit extending from the start point and the end point of the third pattern portion <NUM> and includes the third positive electrode <NUM> and the third negative electrode <NUM>, which are located horizontally.

Of course, in order to supply current to the first and second plane heating elements <NUM> and <NUM> by one power supply and to supply current to the third plane heating element <NUM> by the other power supply, the third electrode portion <NUM> is located in a direction opposite to those of the first and second electrode portions <NUM> and <NUM>.

Current sequentially flows along the third positive electrode <NUM>, the third pattern portion <NUM>, and the third negative electrode <NUM> when a current is supplied to the third plane heating element <NUM> configured as described above.

Similarly, the third pattern portion <NUM> may include a heating unit which generates heat at a temperature of <NUM> or higher, but the third electrode portion <NUM> should be formed of an unheated unit which generates heat at <NUM> or less, or hardly generates heat.

Therefore, it is preferable that the third electrode portion <NUM> is configured to have a much smaller resistance like the first and second electrode portions <NUM> and <NUM>.

As illustrated in <FIG>, the thickness T<NUM> of the third positive electrode <NUM> is formed to be thicker than the thickness T<NUM> of the third track <NUM>, and can be formed in a range of <NUM> to <NUM> with respect to the thickness T<NUM> of the third track <NUM>, but it is not limited thereto.

Of course, the third negative electrode <NUM> may be also formed to be thicker than the third track <NUM>.

In addition, it is preferable that the third bridge <NUM> is configured to have a very small resistance in order to eliminate the local heating due to the current density difference, like the first and second bridges <NUM> and <NUM>.

As illustrated in <FIG>, the thickness T<NUM> of the third bridge <NUM> is formed to be thicker than the thickness T<NUM> of the third track <NUM> and can be formed in a range of <NUM> to <NUM> with respect to the thickness T<NUM> of the third bridge <NUM>, but it is not limited thereto.

Claim 1:
An electric heater comprising:
a substrate (<NUM>); and
a plane heating element formed on one surface of the substrate (<NUM>),
wherein the plane heating element includes:
an inner plane heating element (<NUM>) formed at the center thereof, and
at least one outer plane heating element (<NUM>) provided to surround the inner plane heating element (<NUM>), and
wherein the inner plane heating element (<NUM>) includes:
an inner pattern portion (<NUM>) arranged in a predetermined shape having a start point and an end point;
an inner electrode portion (<NUM>) connected to the start point and the end point of the inner pattern portion (<NUM>), and
an inner connector (<NUM>) disposed between the inner pattern portion (<NUM>) and the inner electrode portion (<NUM>),
wherein the outer plane heating element (<NUM>) includes:
an outer pattern portion (<NUM>) arranged outside the inner pattern portion (<NUM>); and
an outer electrode portion (<NUM>) connected to the outer pattern portion (<NUM>),
wherein the inner electrode portion (<NUM>) is formed to be thicker than the inner pattern portion (<NUM>), and
wherein the outer electrode portion (<NUM>) is formed to be thicker than the outer pattern portion (<NUM>),
wherein the outer pattern portion (<NUM>) includes a plurality of outer tracks (<NUM>) and a plurality of outer bridges (<NUM>) connect the plurality of outer tracks (<NUM>) in series; and
the inner connector (<NUM>) is located between at least one pair of outer bridges (<NUM>),
characterized in that the inner connection (<NUM>) is an auxiliary heating unit capable of generating heat at the same temperature as the inner pattern portion (<NUM>).