JPS6336116B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a temperature control device for a heating element.

As shown in FIG. 1, a surface heating element usually includes a heating element 1 in which a heating electrode 1a is covered with an insulating film 1b.
A thermosensitive element 2 made by sandwiching a plastic film 2a made of nylon or the like having resistance-temperature characteristics between two aluminum electrodes 2b and 2c is attached so that the temperature of the heating element 1 can be directly detected by the thermosensitive element 2.

A conventional temperature control device for a surface heating element that controls the temperature of such a surface heating element is shown in FIG. In the figure, TR is a power transformer. C ₁ and C ₂ are constant impedance elements each consisting of a capacitor, R ₁ and R ₂ are resistors, respectively, and TC ₁ and
TC ₂ is a thermal element whose impedance changes depending on the temperature of the heating element, D ₁ and D ₂
are diodes, and these are the signal detection stage 3.
It consists of R _a , R _b , R _c and R _d are each a resistor, Q ₄ is a transistor, and these constitute an emitter follower stage 4 for impedance conversion. _C4 is a capacitor that smoothes the output of the emitter follower stage 4. SW is a switching circuit, RY ₁ is a relay for supplying power to the load, S ₁ and S ₂ are relay contacts of relay RY ₁ for power supply, and D ₃ is a diode, which constitute switching circuit stage 5. ing. R ₁₅ and R ₁₆ are each a resistor, Q ₃ is a transistor, RY ₂ is a protection relay, S ₃ is a relay contact of protection relay RY ₂ , D ₄ is a diode, these are capacitors C ₄
This constitutes an over-rise prevention circuit stage 6 that operates in response to a failure that abnormally increases the voltage across the terminal. 7 is a heater of a surface heating element. TF is a temperature fuse, R is a heating resistor, and these constitute the cut-off means 8. When the overheat prevention circuit stage 6 operates, the resistor R generates heat and blows out the temperature fuse TF, thereby stopping power supply to the heater 7. Cut off.

The temperature control device of this surface heating element is a power transformer.
The AC applied voltage on the secondary side of the TR is divided between constant impedance elements C ₁ and C ₂ and heat-sensitive elements TC ₁ and TC ₂ , respectively. However, since the impedance of the heat-sensitive elements TC ₁ and TC ₂ at this time changes depending on the temperature, the divided voltage changes depending on the temperature.

This divided voltage is rectified by diodes D ₁ and D ₂ and received by the emitter follower stage 4 having high input impedance and low output impedance. Here, the emitter follower stage 4 has a function of reducing the influence of large impedance fluctuations in the signal division system composed of constant impedance elements C ₁ and C ₂ and thermal elements TC ₁ and TC ₂ , and also The influence on the switching circuit stage 5 is also reduced.

The signal received by emitter follower stage 4 is smoothed by capacitor _C4 and applied to switching circuit SW. This switching circuit SW relays the AC100V power supply to the heater 7 according to the signal.
The temperature of the heater 7 is maintained constant by controlling the relay contacts S ₁ and S ₂ of RY ₁ .

In addition, the overheat prevention circuit stage 6 detects that due to some reason (for example, welding of relay contacts S ₁ and S ₂ ), the temperature of the surface heating element rises abnormally and the voltage across the capacitor C ₄ exceeds a certain voltage. A temperature fuse inserted in the middle of the AC100V power supply operates when the temperature rises to supply power to the heat generating resistor R, and the temperature of the heat generating resistor R rises.
The TF is fused to stop the power supply to the heater 7, thereby protecting the heated object.

However, such a conventional temperature control device for a surface heating element has a drawback that the overheat prevention circuit stage 6 does not operate unless the input signal significantly increases due to an abnormality compared to a normal state. That is, even if the input signal, that is, the voltage across the capacitor _C4 becomes extremely low due to an abnormality, the overheat prevention circuit stage 6 will not operate, nor will the switching circuit stage 5 perform control, and the heater 7 will be continuously energized. That's what it means.

Therefore, a temperature control device for a surface heating element has been proposed which can reliably prevent the temperature of the heating element from rising excessively and protect the heated object.

As shown in FIG. 3, this surface heating element temperature control device includes a protection circuit stage 9 that operates in response to a failure that causes the voltage across the capacitor _C4 to drop abnormally and forcibly activates the overrise prevention circuit stage 6. In addition to the circuit of FIG. 2, an emitter follower stage 4' is used in place of the emitter follower stage 4. The protection circuit stage 9 is
It consists of resistors R _e , R _j , R _g , _Rh and transistor Q ₅ . In addition, the emitter follower stage 4' removes the resistor R _a of the emitter follower stage 4, and connects a resistor R _k between the cathodes of diodes D ₁ and D ₂ and the positive side of the capacitor C ₄ , that is, the resistor R _c side. There is. However, the heater 7 in FIG.
A, 7B and heater 7A, 7B switching means switch
They are replaced by S ₄ , S′ ₄ , S ₅ , and S′ ₅ . A power switch _S6 is also provided on the primary side of the power transformer TR.

Next, the temperature control device for this surface heating element will be explained in detail. Similar to the conventional example, this surface heating element temperature control device divides the AC applied voltage on the secondary side of the power transformer TR between constant impedance elements C ₁ and C ₂ consisting of capacitors and heat sensitive elements TC ₁ and TC ₂ . are doing. At this time, the heat-sensitive elements TC ₁ and TC ₂ can be increased or decreased according to the number of heaters 7A and 7B of the surface heating elements.
Furthermore, since the impedance changes depending on the temperature, the divided voltage changes depending on the temperature.

Since the constant impedance elements C ₁ and C ₂ are selected to have the same value, the divided voltage is determined by the impedance of the heat-sensitive elements TC ₁ and TC ₂ .
If the characteristics of TC ₁ and TC ₂ have approximately the same value, the output voltages V ₁ and V ₂ corresponding to temperature will have the same value. This divided voltage is then rectified by diodes D ₁ and D ₂ and received by the emitter follower stage 4' having high input impedance and low output impedance.
This emitter follower stage 4' has a heat sensitive element TC ₁ ,
One of the thermosensitive elements TC ₂ , for example the thermosensitive element TC ₁ , remains at a constant room temperature (for example, when switches S ₄ and S' ₄ of the heater 7A that raise the temperature of the thermosensitive element TC ₁ are turned off), and the other Even if the temperature of heat-sensitive element TC ₂ increases, the divided output voltage can be received with high input impedance, so both heat-sensitive elements TC ₁ and TC ₂
Since the output voltage is almost the same as that obtained when the output voltage is at the same temperature, and the output impedance is low, the influence on the next stage is also reduced. In addition, the resistor R _k constituting the emitter follower stage 4' is replaced by the capacitor C ₄
By connecting to the positive side of transistor Q, it is possible to prevent overvoltage from being applied to transistor _Q4 in the event that heat sensitive elements _TC1 and _TC2 are short-circuited or open, without impairing the high input impedance/low output impedance characteristics. Prevent the destruction of ₄ .

The signal received by emitter follower stage 4' is smoothed by capacitor _C4 . The voltage across the capacitor _C4 is applied to the base side of the transistor _Q5 of the protection circuit stage 9 via the resistor _Re , and is also applied to the overheat prevention circuit stage 6 and the switching circuit SW in the same manner as in the conventional case.

Under normal conditions, depending on the voltage across capacitor _C4 ,
Switching circuit SW supplies AC100V power to heaters 7A and 7B to relay contact S ₁ of relay RY ₁ ,
Control with S ₂ to keep the temperature of the surface heating element constant.

Next, when an abnormal condition occurs in which the output voltage of capacitor C ₄ increases (for example, welding of relay contacts S ₁ and S ₂ ), if the voltage exceeds a certain voltage, overrise prevention circuit stage 6 operates to close relay contact _S3 , supply AC100V power to the heating resistor R, raise the temperature of the heating resistor R, and depending on the temperature
Temperature fuse TF connected in series to AC100V power supply
is fused to stop power supply to heaters 7A and 7B.

Next, when an abnormal condition occurs in which the voltage across the capacitor _C4 drops (for example, a short circuit of the capacitor _C4 ), if the voltage falls below a certain voltage, the transistor _Q5 of the protection circuit stage 9 is activated. Transitioning from the on state to the off state, the voltage V _DD is applied to the base of the transistor Q ₃ of the overheat prevention circuit stage 6 through the resistors R _g , _Rh ,
A voltage divided by _R16 is applied (the resistance value of this voltage is determined so as to turn on transistor _Q3 sufficiently), and as a result, overheat prevention circuit stage 6 is forced to operate, and relay RY is immediately turned on. ₂ to blow out the temperature fuse TF and stop the power supply to the heaters 7A and 7B. In this case, the abnormal failure of the temperature control device of the surface heating element is limited to the rise or fall of the voltage across the capacitor _C4 , so by adding the protection circuit stage 9, it is possible to cover all abnormal failure modes. .

In this way, in this proposed example, since the protection circuit stage 9 is added, the capacitor caused by abnormal failure
Continuous energization to heaters 7A and 7B of the surface heating element can be stopped in a sufficiently safe manner against the phenomenon of increase or drop in the voltage across _C4 , and therefore, an excessive rise in temperature of the surface heating element can be reliably prevented. The object to be heated can be protected. In addition, because the resistor R _k that makes up the emitter follower stage 4' is connected to the positive side of the capacitor _C4 instead of the negative side of the capacitor _C4 like the conventional resistor R _a , the emitter follower stage 4' has a high input impedance and low output. Without impairing impedance characteristics, it is possible to prevent overvoltage from being applied to transistor Q ₄ in the event that heat sensitive elements TC ₁ and TC ₂ are short-circuited or open, thereby preventing destruction of transistor Q ₄ .

An example of such a proposal is that due to an abnormal drop in the voltage across capacitor C ₄ , transistor Q ₅ is shut off, and the voltage across transistor Q ₅ increases, causing the transistor to shut off.
Transistor Q ₅ not only conducts through Q ₃ but also by causing transistor Q ₅ to transition from the conducting state to the active state during extreme drops in the supply voltage V _DD
The voltage across the transistor Q3 increases, causing the transistor _Q3 to conduct and blowing the temperature fuse TF.

However, a drop in the power supply voltage V _DD is not dangerous, and in this case, it will unnecessarily blow out the temperature fuse TF (malfunction).

Therefore, an object of the present invention is to prevent malfunction of the cut-off means when the power supply voltage drops;
Moreover, it is an object of the present invention to provide a temperature control device for a heating element that can reliably prevent an excessive rise in temperature of the heating element.

An embodiment of this invention is shown in FIG. That is, this temperature control device for a surface heating element has a resistor R _i connected in parallel between the collector and emitter of the transistor Q ₅ of the protection circuit stage 9, and the other configuration is the same as that shown in FIG.

During normal operation, this surface heating element temperature control device responds to the voltage across the capacitor _C4 as in the proposed example.
Switching circuit SW supplies AC100V power to heaters 7A and 7B to relay contact S ₁ of relay RY ₁ ,
The temperature of the surface heating element is kept constant by controlling S ₂ , and in this case, transistor Q ₅ is completely conductive and resistor R _i is short-circuited by transistor Q ₅ , even though there is no resistor R _i . equal. In addition, for an extreme drop in the power supply voltage V _DD that is not abnormal, transistor Q ₅ shifts from the normal fully conductive state to the active state, and the collector voltage V _Q5 of transistor Q ₅ changes to
Increases from 0V. Along with this, the resistance R _i becomes the resistance
It is connected in series with R _g and works to limit the rise in collector voltage V _Q5 , suppressing the value of collector voltage V _Q5 and not making transistor Q ₃ conductive until a certain drop in power supply voltage V _DD is reached. Note that the resistance value of the resistor R _i is set so as to perform the above operation.

Other operations are similar to the proposed example.

In addition to the effects of the proposed example, the surface heating element temperature control device of this embodiment has the effect of preventing malfunction of the protection circuit stage 9 in response to an extreme drop in the power supply voltage V _DD , which does not require blowing out the temperature fuse TF. have

As described above, the temperature control device for a heating element according to the present invention uses the heat-sensitive elements TC ₁ and TC ₂ whose impedances change depending on the temperature of the heating element and the constant impedance elements C ₁ and C ₂ to control the AC voltage. A signal detection stage 3 that divides the voltage and rectifies the divided voltage obtained.
A capacitor _C4 smoothes the output voltage of the signal detection stage 3, and the temperature of the heat generating element is controlled to be constant by intermittent energization to the heat generating element depending on the level of the voltage across the capacitor _C4 . a switching circuit stage 5 to conduct the switching circuit, a cutoff means 8 inserted in series with the switching circuit stage 5 in the current conduction path to the heating element, and a voltage obtained by dividing the voltage across the capacitor _C4 between the base and emitter. A collector-emitter is connected between the base and emitter of the first transistor _Q3 and the first transistor _Q3 , which activates the cutoff means 8 by becoming conductive in response to an abnormal increase in the applied voltage across the capacitor _C4 . are connected in parallel through the first resistor _Rh , and the voltage obtained by dividing the voltage across the capacitor _C4 is the base voltage.
A voltage obtained by dividing the power supply voltage _VDD is applied between the collector and emitter of the second transistor _Q5 and the second transistor _Q5 , which is applied between the emitter and shuts off in response to an abnormal drop in the voltage across the capacitor _C4 . A second resistor R _g is connected in parallel to the second transistor Q ₅ and is connected in parallel to the second transistor Q 5 to cause the second transistor Q ₅ to change from a conductive state to an active state due to a drop in the power supply voltage V _DD . 2 transistors
Since it is provided with the third resistor R _i that limits the rise in the voltage across _Q5 , the following effects are achieved. That is, the cutoff means 8 is activated in response to an abnormal rise or fall in the voltage across the capacitor _C4 , and it is possible to reliably prevent an excessive rise in temperature of the heating element and protect the heated object. Moreover,
A third resistor R _i is connected in parallel to the second transistor Q ₅ and both ends of the second transistor Q 5 are connected as the second transistor Q ₅ transitions from a _conductive state to an active state due to a drop in the power supply voltage _V DD. Since the voltage rise is limited, even if the power supply voltage V _DD drops, the voltage between the base and emitter of the first transistor Q ₃ can be prevented from reaching the conduction voltage. Malfunction of the cutoff means 8 when the voltage V _DD drops can be prevented.

[Brief explanation of the drawing]

Fig. 1 is a sectional view of a surface heating element, Fig. 2 is a circuit diagram of a conventional temperature control device for a surface heating element, Fig. 3 is a circuit diagram of a proposed example, and Fig. 4 is a circuit diagram of an embodiment of the present invention. It is a diagram. 3...Signal detection stage, 5...Switching circuit stage, 7
A, 7B...Heater, 8...Shutoff means, _C1 , _C2 ...Constant impedance element, _C4 ...Capacitor, _TC1 ,
TC ₂ ...thermal element, Q ₃ , Q ₅ ...transistor, R _g ...
Resistance, R _h ...resistance, R _i ...resistance.

Claims (1)

[Claims] 1. A signal detection stage that divides the AC voltage between heat-sensitive elements TC ₁ and TC ₂ and constant impedance elements C ₁ and C ₂ that change impedance according to the temperature of the heating element and rectifies the obtained divided voltage. 3 and
A capacitor C ₄ smooths the output voltage of the signal detection stage 3, and the temperature of the heating element is controlled to be constant by intermittent energization to the heating element depending on the high bottom of the voltage across the capacitor C ₄ . a switching circuit stage 5; and a cutoff means 8 inserted in series with the switching circuit stage 5 in the energizing path to the heating element.
and a voltage obtained by dividing the voltage across the capacitor _C4 is applied between the base and the emitter, and conduction occurs in response to an abnormal increase in the voltage across the capacitor _C4 , thereby operating the cutoff means 8. The collector and emitter of the transistor Q ₃ and the base and emitter of the first transistor Q ₃ are connected in parallel through a first resistor R _h , and a voltage obtained by dividing the voltage across the capacitor C ₄ is generated. base·
A voltage obtained by dividing the power supply voltage _VDD is applied between the collector and emitter of the second transistor _Q5 and the second transistor _Q5 , which is applied between the emitter and shuts off in response to an abnormal drop in the voltage across the capacitor _C4 . A second resistor R _g is connected in parallel to the second transistor Q ₅ and is connected in parallel to the second transistor Q 5 to cause the second transistor Q ₅ to change from a conductive state to an active state due to a drop in the power supply voltage V _DD . 2 transistors
A temperature control device for a heating element, comprising a third resistor R _i that limits the rise in voltage across _Q5 .