JPS623447B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a temperature control device for an electric cooker using a pair of heat-sensitive resistance elements.

Conventionally, as a temperature control device, a heat-sensitive resistance element such as a thermistor is provided at or near a heating element to detect the temperature of the heating element and control energization/de-energization of the heating element.
Alternatively, a device is known in which a thermistor is provided near a heated body heated by a heating element, and the temperature of the heated body is detected to control energization/de-energization of the heating element.

However, in the former case, the temperature ripple can be reduced, as shown in Figure 1, where the temperature change graph of the heater is shown as a dotted line and the temperature change graph of the heated object is shown as a solid line, but the drawback is that the temperature rise of the heated object is extremely slow. , and in the latter case, the second
As shown in the figure, the temperature change graph of the heater is shown by a dotted line, and the temperature change graph of the heated object is shown by a solid line. Although it is possible to improve the temperature rise of the heated object, there is a drawback that the temperature ripple becomes large.

This invention has been made in view of the above points, and an object of the present invention is to provide a temperature control device for an electric cooker that has small temperature ripples and can improve the rise in temperature of a heated object. .

Embodiments of the present invention will be described below with reference to the drawings. In this embodiment, the present invention will be described as applied to a skylight.

Figure 3 is a schematic diagram of the Tenka, where 1 is the case and 2
is a partition plate that separates the cooking chamber 3 and the heat generating chamber 4 in the case 1. A heater 5 is provided within the heat generating chamber 4. A first negative characteristic thermistor 6 is provided as a first heat-sensitive resistance element in the vicinity of the heater 5 in the heating chamber 4, and a second negative characteristic thermistor 6 is provided as a second heat-sensitive resistance element in the cooking chamber 3. A characteristic thermistor 7 is provided.

The heater 5 is controlled by a temperature control circuit shown in FIG. That is, this temperature control circuit connects the heater 5 to a commercial AC power source 8 via a bidirectional three-terminal thyristor 9. Further, an input terminal of a DC power supply circuit 10 is connected to the AC power supply 8. A heating element control circuit 11 is connected between the output terminals of the DC power supply circuit 10. This heating element control circuit 11 includes the first,
A first bias circuit formed by connecting the second thermistor 6, 7 and variable resistor 12 in series in the above order, a second bias circuit formed by connecting resistors 13, 14 in series, and first and second NPN type bias circuits. It is formed of a differential amplifier 17 made up of transistors 15 and 16, and an output circuit 20 made up of a PNP type third transistor 18 and an NPN type fourth transistor 19. The differential amplifier 17 connects the base of the first transistor 15 to a series circuit of the first thermistor 6 and second thermistor 7 forming one side of the first bias circuit and the series circuit forming the other side of the first bias circuit. The second transistor 16 is connected to the connection point with the variable resistor 12 and its collector is connected to the positive side of the output terminal of the DC power supply circuit 10 via the resistor 21, and the base of the second transistor 16 is connected to the resistor 13 of the second bias circuit. . Commonly connected to the DC power supply circuit 10
Connected to the negative side of the output terminal. The output circuit 20 connects the emitter of the third transistor 18 to the positive side of the output terminal of the DC power supply circuit 10, and connects the collector to the resistor 24, 25.
are connected in series to the negative side of the output terminal of the DC power supply circuit 10. Further, the output circuit 20 connects the base of the fourth transistor 19 to the resistor 2.
4 and 25, its collector is connected to the gate of the thyristor 9 via a resistor 26, and its emitter is connected to the negative side of the output terminal of the DC power supply circuit 10.

Next, the operation of the apparatus according to the embodiment of the present invention constructed as described above will be described.

The first transistor 1 in the differential amplifier 17
When the transistor 5 is off and the second transistor 16 is on, the third transistor 18 and the fourth transistor 19 are turned on and the thyristor 9 is controlled to be conductive. Therefore, in this case, the heater 5 is energized. Further, in the differential amplifier 17, when the first transistor 15 is on and the second transistor 16 is off, the third transistor 18 and the fourth transistor 19 are turned on, and the thyristor 9 is controlled to be non-conductive. Therefore, in this case, power supply to the heater 5 is stopped.

Therefore, when the temperature inside the cooking chamber 3 and the heat generation temperature of the heater 5 are both at a predetermined temperature state, the first transistor 15 of the differential amplifier 17 is turned on depending on the resistance value of each thermistor 6, 7. The resistance value of the variable resistor 12 is adjusted accordingly. That is, when the temperature in the cooking chamber 3 is at a predetermined temperature state, when the heat generation temperature of the heater 5 reaches a predetermined temperature, the bias voltage applied from the first bias circuit to the differential amplifier 17 of the heating element control circuit 11 becomes differential. amplifier 1
The resistance value of the variable resistor 12 is adjusted so as to reach the inversion threshold level of 7.

When the AC power source 8 is turned on with the resistance value of the variable resistor 12 adjusted in this way, the temperature in the cooking chamber 3 is low at this time, and the heater 5 is not generating heat, so each thermistor 6, 7 has a large resistance value, and the bias voltage applied from the first bias circuit to the first transistor 15 of the differential amplifier 17 is lower than the inversion threshold level of the differential amplifier 17. When the AC power supply 8 is turned on, the first transistor 15 of the differential amplifier 17 is turned off and the second transistor 16 is turned on, so that the third and fourth transistors 18 and 19 of the output circuit 20 are turned on. Thyristor 9 becomes conductive. Therefore, first, electricity is started to be applied to the heater 5, and the heater 5 starts to generate heat. Then, the temperature in the vicinity of the heater 5 rapidly increases due to the heat generated by the heater 5. On the other hand, the temperature inside the cooking chamber 3 does not rise rapidly even when the heater 5 generates heat, and the temperature rise is delayed compared to the temperature rise in the vicinity of the heater 5. Therefore, when the temperature near the heater 5 reaches the predetermined temperature, the temperature in the cooking chamber 3 is still lower than the predetermined temperature, and the resistance value of each thermistor 6 and 7 at this time determines the first temperature. The bias voltage applied from the bias circuit to the first transistor 15 of the differential amplifier 17 is below the inversion threshold level of the differential amplifier 17. Therefore, the energization of the heater 5 is further continued, and the temperature near the heater 5 further rises above the predetermined temperature, and the resistance value of the first thermistor 6 further decreases accordingly.
In other words, the temperature at which the energization of the heater 5 is controlled has equivalently become higher. Then, when the total resistance value of the first thermistor 6 and the resistance value of the second thermistor 7 is exactly equal to the total resistance value of both thermistors 6 and 7 at a predetermined temperature, the signal is transferred from the first bias circuit to the differential amplifier 17. The applied bias voltage reaches the inversion threshold level of the differential amplifier 17, and the differential amplifier 17 performs an inversion operation. In this way, the third and fourth transistors 18,1
9 is turned off, the thyristor 9 is controlled to be non-conductive, and the power supply to the heater 5 is stopped. Then, the temperature near the heater 5 drops rapidly. On the other hand, the temperature inside the cooking chamber 3 continues to rise toward a predetermined temperature. That is, the resistance value of the first thermistor 6 increases rapidly, and the resistance value of the second thermistor 7 gradually decreases thereafter. When the bias voltage of the first bias circuit becomes smaller than the inversion threshold level of the differential amplifier 17 due to the power supply to the heater 5 being stopped, the differential amplifier 17 performs an inversion operation and returns to its original state, that is, the first transistor 15 is off, and the second transistor 16 returns to the on state. In this way, power supply to the heater 5 is restarted, and the temperature near the heater 5 rises again. When the total resistance value of the first thermistor 6 and the resistance value of the second thermistor 7 becomes equal to the total resistance value of both thermistors 6 and 7 at a predetermined temperature, the voltage is applied from the first bias circuit to the differential amplifier 17. When the bias voltage reaches the inversion threshold level of the differential amplifier 17, the differential amplifier 17 performs an inversion operation. That is, the power supply to the heater 5 is stopped again. At this time, the change in the resistance value of both thermistors 6 and 7 is defined as the change in the resistance value of both thermistors 6 and 7 when the bias voltage of the first bias circuit reaches the inversion threshold level of the differential amplifier 17. By comparison, the temperature inside the cooking chamber 3 has risen and the resistance value of the second thermistor 7 has become smaller than when it first started, so even if the resistance value of the first thermistor 6 does not become as small as it did at the beginning. The bias voltage of the first bias circuit will reach the inversion threshold level of the differential amplifier 17. In other words, the temperature at which the energization of the heater 5 is controlled has become equivalently lower than that at the beginning. Thereafter, such an operation is repeated, and each time, the temperature for controlling the energization to the heater 5 equivalently gradually lowers and approaches the predetermined temperature. When the temperature in the cooking chamber 3 eventually reaches a predetermined temperature, the temperature at which the energization of the heater 5 is controlled becomes equivalently close to the predetermined temperature. That is, the power supply to the heater 5 is stopped when the temperature near the heater 5 slightly exceeds a predetermined temperature, and the temperature in the cooking chamber 3 is maintained at a substantially constant predetermined temperature.

By the way, looking at the above operation in terms of the degree of change in the resistance value of both thermistors 6 and 7, since the temperature in the cooking chamber 3 is low at first, the degree of change in the resistance value of the second thermistor 7 is small, so the first Unless the degree of change in the resistance value of the thermistor 6 becomes large, the differential amplifier 17 will perform an inversion operation and the current supply to the heater 5 will not be stopped. Thereafter, as the temperature inside the cooking chamber 3 rises, the degree of change in the resistance value of the second thermistor 7 increases, so that the differential amplifier 17
The degree of change in the resistance value of the first thermistor 6 necessary for the inversion operation gradually decreases. In other words, the temperature at which the energization of the heater 5 is controlled gradually decreases equivalently. Then, when the temperature inside the cooking chamber 3 reaches a predetermined temperature, for example, if both thermistors 6 and 7 are used that have approximately the same temperature-resistance characteristics, the degree of change in the resistance value of both thermistors 6 and 7 will change. The differential amplifier 17 is approximately equal.
will perform an inversion operation. This means that when the total resistance value of both thermistors 6 and 7 always reaches a predetermined value, the differential amplifier 17 performs an inversion operation and the power supply to the heater 5 is stopped.

Therefore, the changes in the temperature inside the cooking chamber 3 and the changes in the temperature near the heater 5 during these operations are graphed as shown in FIG. In addition, the graph shown by the dotted line in the figure is a temperature change graph in the vicinity of the heater 5, and the graph shown by the solid line in the figure is a temperature change graph in the cooking chamber 3. As is clear from this graph, the temperature at which the energization to the heater 5 is controlled is higher when the temperature inside the cooking chamber 3 is lower than the predetermined temperature indicated by the dashed-dotted line in the figure, as shown by the dashed-dotted line in the figure. As the temperature inside the cooking chamber 3 gradually rises, it decreases, and when the temperature inside the cooking chamber 3 reaches a predetermined temperature, it becomes approximately equal to the predetermined temperature.

In this way, when the temperature inside the cooking chamber 3 is lower than the target predetermined temperature, the heater 5 is
As the temperature that controls the energization to the heater 5 becomes higher and the temperature in the cooking chamber 3 eventually reaches the target predetermined temperature, the temperature that controls the energization to the heater 5 also reaches approximately the predetermined temperature. The rise in temperature is good, so cooking time is shortened and power consumption can be saved. Moreover, since the power supply to the heater 5 is basically controlled according to the temperature in the vicinity of the heater 5, the temperature ripple can be reduced.

In the embodiment described above, a series circuit of a first negative characteristic thermistor 6 and a second negative characteristic thermistor 7 is provided on one side of the first bias circuit,
A variable resistor 12 is provided on the other side, and a bias voltage to be applied to the differential amplifier 17 is applied to a second negative characteristic thermistor 7 which is a connection point between one side and the other side.
Although the description has been made of a device that is taken out from the connection point between the variable resistor 12 and the variable resistor 12, the present invention is not limited to this. For example, the second negative characteristic thermistor 7
If a positive characteristic thermistor is used instead, the positive characteristic thermistor may be inserted on the other side, and the bias voltage may be taken out from the connection point between the first negative characteristic thermistor and its positive characteristic thermistor.

In this case, the positive temperature coefficient thermistor operates to increase the resistance value as the temperature inside the cooking chamber 3 increases, but when the temperature inside the cooking chamber 3 is low, the change in the resistance value of the positive temperature coefficient thermistor is small and the first As the resistance value of the first thermistor 6 becomes smaller, the change in the resistance value of the first thermistor 6 must increase, and as the temperature inside the cooking chamber 3 approaches the predetermined temperature, the change in the resistance value of the positive temperature coefficient thermistor becomes large. As a result, even if the change in the resistance value of the first thermistor 6 is small, the differential amplifier 17 performs an inverting operation, and the same effects as in the previous embodiment can be obtained.

Although the above embodiment describes the application of the present invention to a ceiling fire with a partition plate, it is needless to say that the present invention is not limited to this, and can also be applied to a ceiling fire without a partition plate and other electric cooking appliances. .

As detailed above, according to the present invention, a first heat-sensitive resistance element detects the temperature of a heating element, and a second heat-sensitive resistance element detects the room temperature of the cooking chamber heated by the heating element.
A semiconductor switching circuit responds to a change in the combined resistance value of both heat-sensitive resistance elements, and the switching operation of the switching circuit operates the switching element to energize the heating element.
Non-conductive control is used to control the temperature of the heating element to be sufficiently higher than the target temperature at the initial stage of heating, and then gradually approach the target temperature.
It is possible to provide a temperature control device for an electric cooker that has a small temperature ripple, can improve the rise in cooking chamber temperature, and can save power by shortening cooking time.

[Brief explanation of the drawing]

1 and 2 are graphs showing the temperature changes of the heater and the temperature of the heated object in the conventional example, FIG. 3 is a schematic configuration diagram of a skylight showing an embodiment of the present invention, and FIG. 4 is the same embodiment. control circuit diagram,
FIG. 5 is a graph showing the temperature change of the heater and the temperature change of the cooking chamber in the same example. 3... Cooking chamber, 5... Heater, 6... First negative characteristic thermistor, 7... Second negative characteristic thermistor, 9... Bidirectional 3-terminal thyristor, 11...
Heating element control circuit, 17...differential amplifier.

Claims (1)

[Claims] 1 A heating element and a first unit that detects the temperature of this heating element.
a heat-sensitive resistance element, a second heat-sensitive resistance element that detects the room temperature of the cooking chamber heated by the heating element, and a bias circuit formed by inserting both of the heat-sensitive resistance elements in series, and from this bias circuit. A semiconductor switching circuit that responds to the output bias voltage, and a switching element that controls energization and de-energization of the heating element in response to the switching operation of the semiconductor switching circuit, and the bias circuit is configured to control the heat-sensitive resistance element. have similar temperature resistance characteristics, a bias voltage is output from the connection point between one side and the other side including the series circuit of both heat-sensitive resistance elements, and when both heat-sensitive resistance elements are at different temperatures. If it has resistance characteristics, a bias voltage is output from the connection point between one side and the other side containing each heat-sensitive resistance element individually, and the temperature of the heating element is made sufficiently higher than the target temperature at the initial stage of heating, and then 1. A temperature control device for an electric cooker, characterized in that the temperature in the cooking chamber is controlled so as to gradually approach a target temperature, and the temperature ripple in the cooking chamber is controlled to be small at the target temperature.