JPH0340904B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Technical Field) The present invention relates to a heater disconnection detection circuit for a heating element in an electric carpet or the like.

(Background Art) Figure 2 is a sectional view showing the configuration of a planar heating element having two systems of heaters H ₁ and H ₂ . Heater H ₁ on one side of variable element T,
A H ₂ heater pattern is formed by printed wiring or the like, and a temperature detection electrode S is formed on the other side. FIG. 3 shows a part of the heating element in a plan view, and the two heaters H ₁ and H ₂ are wired in parallel so that no current flows between the heater patterns.

Therefore, since the impedance of the temperature change element T disposed between the heaters H ₁ and H ₂ and the temperature detection electrode S changes according to the temperature of the heating element, a temperature detection signal is obtained from this impedance change, and temperature control is performed. The power supply to the heater is controlled by the operation of the circuit so that the desired temperature is achieved. Further, by disconnecting either heater H ₁ or H ₂ from the circuit using a changeover switch or the like, the overall capacity of the heating element can be changed.

By the way, in the configuration of the heating element as described above, the two heaters H ₁ and H ₂ are strongly electrically coupled via the temperature change element T, and during normal use, the heaters H 1 and H 2 are connected as described above. Since the patterns are wired in parallel, no current will flow between the two heaters, but if one heater is disconnected, the potential balance between the two heater patterns will be disrupted, and current will flow between the two heaters, creating a dangerous situation. Something happened.

In other words, although Fig. 4 shows a case where a disconnection occurs at terminal part a of heater _H1 , a normal heater
_H2 has a distribution of 100 to 0V when viewed from the ground point, while the disconnected heater _H1 has a uniform voltage of 100V, so a potential difference occurs between adjacent heater patterns, and the current i according to this potential difference It will flow. Here, the point where the current value is the largest is the part of the heater pattern near the disconnected terminal part a,
Therefore, if the area is locally insulated by a cushion, etc., the temperature of that area will rise, and the temperature rise will further reduce the impedance of the temperature change element T, which has negative impedance characteristics, which will further increase the current. This could lead to a dangerous situation due to so-called thermal runaway.

In addition, the system is not limited to the two systems as described above, but even systems with a larger number of systems have similar drawbacks.

(Object of the Invention) The present invention has been proposed in view of the above points, and its purpose is to provide a heating system using a heating element having two or more heater systems in order to switch power. An object of the present invention is to provide a safe heater disconnection detection circuit that can quickly stop energization in the event of a disconnection.

(Disclosure of the Invention) The present invention will be described in detail below with reference to the drawings showing embodiments.

FIG. 1 shows the overall configuration of a heating device to which the heater disconnection detection circuit of the present invention is applied.

In the figure, H ₁ and H ₂ are the heaters of the heating elements shown in Figures 2 and 3, and in this example, the heaters
_H1 can be separated from the circuit by double-switching switches _SW1 and _SW2 , allowing switching between high-power heating by heaters _H1 and _H2 and low-power heating by heater _H2 alone. In other words, the heater
H ₂ is relay contact ry ₁ , ry ₂ and main switch
It is directly connected to a commercial power source (AC100V) via SW and temperature fuse TF, and heater _H1 is connected to both ends of heater _H2 via double-cut switches _SW1 , _SW2 and microresistance _R1 . Here, it is difficult to construct the microresistance _R1 as a single component, but it can be constructed using a printed circuit board foil resistor, a part of the heater pattern, or a jumper resistor with a microresistance value. Can be done. Further, the temperature control circuit 1 is connected to a commercial power source via a main switch SW and a temperature fuse TF.

Next, both ends of the microresistance R ₁ are connected to the non-inverting input terminal and the inverting input terminal of the operational amplifier A ₁ through the resistors R ₂ and R ₃ , respectively, and the output terminal of the operational amplifier A ₁ is connected to its own through the resistor R ₄ . It is connected to the inverting input terminal and to the base of transistor _Q1 via resistor _R5 . Also, transistor
Transistor in parallel with collector-emitter of _Q1
The collector and emitter of Q ₂ are connected, the emitter is connected to the connection point (circuit ground) of heater H ₂ and relay contact ry ₂ , and the base of transistor Q ₂ is connected to changeover switch SW ₁ and other terminals via resistor R ₆ . connected to the fixed contacts of

On the other hand, between the heater side terminals of relay contacts ry ₁ and ry ₂ , there is a series circuit of resistors R ₇ , R ₈ , and R ₉ , and a heating resistor that is thermally coupled to the temperature fuse TF.
R ₁₀ is connected to the series circuit of thyristor SCR,
The gate of the thyristor SCR is connected to the connection point between the resistors ₈ and R ₉ , and the connection point between the resistors ₇ and R ₈ is connected to the collectors of the transistors Q ₁ and Q ₂ via the diode D ₂ . Furthermore, diodes D ₁ and D ₃ are connected with their bases as cathodes so that no reverse voltage is applied between _the bases and emitters of transistors Q 1 and Q ₂ .

In normal temperature control, the temperature of the heating element is compared with the set temperature in the temperature control circuit 1, and if the temperature of the heating element is lower than the set temperature, the temperature control circuit 1 operates to connect the relay contact ry. ₁ ,ry ₂
turns on to energize the heater, and conversely, when the temperature is higher than the set temperature, relay contacts ry ₁ and ry ₂ are turned off to stop energizing. Through these operations, the heating element is maintained at a desired temperature. Further, by operating the changeover switches SW ₁ and SW ₂ , it is possible to switch the amount of heat generated depending on the ambient temperature and the like.

Next, the operation when a heater disconnection occurs will be explained. In this case, the operating state can be divided into the following three types. In other words, the heater is normal when the changeover switches SW ₁ and _{SW 2} are on (during high power heating). The heater _H1 is disconnected when the changeover switches SW _{1 and SW 2 are on (during high power heating). The changeover switches SW 1 and} SW ₂ are turned on. The heater is normal when it is off (during low power heating). Note that in this example, it is not possible to detect a disconnection in heater _H2 , but normally when switching power, there is a size relationship between the power capacities of each heater, and main heater _H2 is selected to have a larger power capacity. Therefore, when heater H ₂ is disconnected and only heater H ₁ is energized, or when heater H ₁ is disconnected from the circuit, the risk of abnormal heating is considered to be low due to the amount of heat generated. It is from.

However, in the above case (normal state), heater _H1 is energized, so a voltage is generated across microresistance _R1 , and this voltage is amplified by operational amplifier _A1 . transistor
Q ₁ is turned on, and the connection point between resistors R ₇ and R ₈ is pulled down to the ground level, so that no gate signal is applied to the gate of thyristor SCR, keeping it off.

In the next case (a state where a wire breakage occurs), the current flowing into heater H ₁ disappears, so the voltage generated across the microresistance also disappears, so transistor Q ₁ turns off, and the resistance The connection point of R ₇ and R ₈ is released from the earth level,
The thyristor SCR turns on in response to a gate signal, energizes the heating resistor _R10 , blows out the temperature fuse TF that is thermally coupled to it, and stops energizing the heater.

The following case is originally a normal state, but due to the heater _H1 being artificially disconnected, there is a slight resistance.
Since no voltage is generated in _R1 , this is prevented from being mistakenly detected as a disconnection. That is, a fixed contact that operates complementary to the fixed contact on the heater H ₁ side of the changeover switch SW ₁ is connected to the base of the transistor Q ₂ via the resistor R ₆ , and the transistor Q ₂ is turned on during low-power heating. Thus, the thyristor SCR is kept off regardless of the detection voltage of the microresistance _R1 .

(Effects of the Invention) As described above, in the present invention, in a heating element having at least two heater patterns arranged in parallel to each other, a double-switch switch connects the main heater in parallel. A microresistance is connected in series with the heater to be used, and a switch element is provided that turns on when no voltage is generated across the microresistance and the selector switch selects the heater. Since the temperature fuse is blown by series-connected heating resistors and the transition to safety mode is made, it is possible to immediately stop the power supply in the event of a heater burnout, creating a highly reliable and safe burnout detection circuit. It has the advantage of being able to provide

[Brief explanation of the drawing]

FIG. 1 is a circuit configuration diagram showing an embodiment of the present invention;
Fig. 2 is a cross-sectional view showing the configuration of a heating element to which the present invention is applied, Fig. 3 is a plan view showing a heater pattern of the above heating element, and Fig. 4 shows the current between the patterns that occurs when the heater is disconnected. It is a conceptual diagram. H ₁ , H ₂ ... Heater, T ... Temperature change element, S
...Temperature detection electrode, 1 ...Temperature control circuit, SW...
...Main switch, SW ₁ , SW ₂ ...Double-way changeover switch, ry ₁ , ry ₂ ...Relay contact, A ₁ ...Operation amplifier, Q ₁ , Q ₂ ...Transistor, SCR ...Thyristor, R ₁ ... Micro resistance, R ₂ ~ _{R 9} ... resistance,
R ₁₀ ...Heating resistance, TF...Temperature fuse, D ₁ ...
_D3 ...Diode.

Claims (1)

[Scope of Claims] 1. In a heating element having at least two heater patterns arranged in parallel to each other, a microresistance is connected in series with the heater connected in parallel to the main heater by a double-switch switch. However, a switch element is provided that turns on when no voltage is generated across this microresistance and the selector switch selects the heater in question, and a heat generating resistor connected in series with this switch element is used to generate a temperature fuse. A heater disconnection detection circuit characterized by transitioning to a safety mode when the fuse is closed. 2. The heater breakage detection circuit according to claim 1, wherein the minute resistance is constituted by a printed circuit board pattern foil resistance, a part of the heater pattern, or a jumper resistance.