JPH056230A - Electronic control type kotatsu - Google Patents

Abstract

PURPOSE:To provide the electronic control type kotatsu (Japanese foot warmer with a quilt over it) which can shorten rising time and can extremely reduce temperature width around a heat generating body in a stabilized case in executing phase control while using a lamp heater for the heat generating body. CONSTITUTION:At the electronic control type kotatsu equipped with a heat generating body 23, temperature sensing means 8 detecting the change of a surrounding temperature generated by the heat generating body and control means 16 executing the phase control to the electrification of the heat generating body corresponding to the signal of the temperature sensing means, a holding means is provided to hold the electrification of the heat generating object in an almost maximum state until the surrounding temperature is increased to a prescribed temperature, and a changing means 4 is provided to change this prescribed temperature to a low temperature side and to obtain temperature hysteresis when the surrounding temperature is increased to the prescribed temperature.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electronically controlled kotatsu used, for example, in a general household.

[0002]

2. Description of the Related Art Generally, as a temperature control device used for household electric kotatsu or the like, for example, JP-A-58-1 is used.
The inventions described in JP-A-58722 and JP-A-58-165166 are known. In the former, the amount of air blown to the semiconductor heater is controlled by controlling the energization of a motor that drives a fan, which is a blowing means, and the amount of air blown to the semiconductor heater is indirectly controlled by the amount of air blown. .. In the latter case, the power to the heater is turned off.
It is performed by N-OFF control.

Further, the one shown in FIGS. 8 and 9 is also well known. FIG. 8 is a circuit diagram of the electronically controlled kotatsu. For example, when "low" is set in the controller (50), phase control of the triac (24) in the controller (50) is performed, and the duty factor corresponding to the setting is performed. (W number is small)
Controls the heater (51). FIG. 9 is a circuit diagram of a so-called microcomputer-controlled semiconductor warm air kotatsu, which uses a semiconductor heater (52) and a microcomputer (5
3) controls the respective energization rates of the blower motor (54) and the semiconductor heater (52), and controls the temperature inside the kotatsu in combination with the change in the wattage of the semiconductor heater (52) itself. It is a thing. That is, in FIG. 9, the temperature setting variable resistor (55), the resistors (56) (57), and the thermistor (5
8) forms a bridge circuit with 8) and operates as a temperature detecting means, and its output signal is input to the A / D input terminal of the microcomputer (53). Note that (59) is a thermistor for detecting the room temperature and constitutes another bridge circuit. The temperature in the kotatsu is judged by the output signal, that is, the A / D input, and when the temperature in the kotatsu is considerably lower than the set temperature, D of the microcomputer (53)
The two outputs trigger the triac (61) through the transistor (60) to energize the motor (54) 100%, and the D0 output causes the transistor (62) to pass.
The triac (63) is triggered via the switch and the semiconductor heater (52) is also energized 100%. After that, when the temperature inside the kotatsu reaches a predetermined temperature, the duty ratio of the semiconductor heater (52) is reduced to 50%. Further, when the temperature inside the kotatsu reaches the set temperature, the duty ratio of the motor (54) is increased to 50%.
In addition, the temperature is controlled by reducing the electric conductivity of the semiconductor heater (52) to 10%. Therefore, it is possible to control the temperature of kotatsu, which takes a short time until the set temperature is reached (hereinafter referred to as rising) and has an extremely small variation range in the kotatsu after the set temperature is reached (hereinafter referred to as stable).

[0004]

However, the lamp heater cannot be used for those whose temperature is controlled by the air volume, or when the temperature is controlled by turning the heater on and off, the temperature inside the kotatsu becomes stable. When O
A temperature range (differential) occurs between N time and OFF time, and when the heater is a lamp type, the heater O
The FF has a drawback in that the lamp is turned off and the generation of radiant heat is suddenly reduced to lower the sensible temperature.

Further, in the one shown in FIG. 8, since the heater is phase-controlled at the duty ratio corresponding to the setting, it takes time to reach the target temperature (set temperature) at the start-up when the set temperature is low. There was a problem.

Further, in the structure shown in FIG. 9, since the semiconductor heater is used, there is no radiant heat, and the sensation of heating feeling at the initial stage of energization is inferior to that of the lamp heater, and the lamp heater is controlled by this circuit. In this case, since the phase control ratios are 100%, 50%, and 10%, there is a problem that the range of temperature change becomes large at the time of switching.

The present invention has been made in view of the above circumstances, and provides an electronically controlled kotatsu in which when a lamp heater is used as a heating element, the rise time is short and the temperature range around the heating element can be made extremely small when stable. Is what you are trying to do.

[0008]

SUMMARY OF THE INVENTION The present invention comprises a heating element,
In an electronically controlled kotatsu comprising a temperature-sensing means for detecting a change in ambient temperature due to the heating element and a control means for phase-controlling the energization of the heating element in response to a signal from the temperature-sensing means, the control means comprises: A configuration including a holding unit that holds the energization of the heating element in a substantially maximum state until the temperature rises to a predetermined temperature, and a changing unit that changes the predetermined temperature to a low temperature side when the ambient temperature rises to the predetermined temperature. It is what

[0009]

Since the present invention is configured as described above, the energization of the heating element is maintained at a substantially maximum state regardless of the ambient temperature until the ambient temperature of the heating element reaches a predetermined temperature, and the temperature rises to the set temperature. To improve the start-up characteristics. Then, after reaching the predetermined temperature, the phase is controlled according to the ambient temperature to keep the width of the temperature change small. Further, when the ambient temperature reaches a predetermined temperature, the predetermined temperature is changed to a low temperature side to provide a temperature hysteresis to prevent a large change in the duty ratio of the heating element.

[0010]

Embodiments of the present invention will now be described in detail with reference to the drawings, but the present invention is not limited to the following embodiments.

In FIG. 1A, (1) is a zero-cross pulse generation circuit, which outputs a pulse signal (b) when the voltage (a) of the AC power supply (2) becomes OV. (3) is a delay circuit, which is electrically connected to the zero-cross pulse generating means (1), delays the pulse signal (b) for a predetermined time, and then outputs the pulse signal (c). (4) is a changing means, which is connected to the delay circuit (3), and is connected to the timer circuit (4
a) and a capacitor (4b) connected to control the time width of the delay signal (d) of the timer circuit (4a), and a transistor (4c) and a resistor (4d) that control the charging time of the capacitor (4b). (4e). Figure 1
In the circuit shown in B, the timer circuit (4a) has a timer IC 55
5 is used, the charging time of the capacitor (4b) connected to the threshold terminal is set to the transistor (4c).
And the resistance (4e) connected to the collector of the transistor (4c) and the resistance (4d) connected in parallel to the series circuit of the transistor (4c) and the resistance (4e). That is, when the transistor (4c) is turned on, the resistor (4d) and the resistor (4e) are connected in parallel, the charging time is shorter than when the transistor (4c) is turned off, and the output of the timer circuit (4a) is output. The time width of the delay signal (d) becomes short. (5) is a capacitor,
The transistor (6) is connected in parallel. That is, the collector of the transistor (6) is connected to one end of the capacitor (5), the emitter is connected to the other end, and the other end is connected to the ground. A variable resistor (7) is connected to the DC power supply line at one end of the capacitor (5). The variable resistor (7) is for temperature adjustment. Reference numeral (8) is a temperature sensing means, for example, a thermistor having a negative characteristic, which is connected in series with the resistor (9) and constitutes a bridge circuit with the series circuit of the capacitor (5) and the variable resistor (7). (10) is a comparison circuit, the + input end of which is the connection point of the capacitor (5) and the variable resistor (7), and the-input end is the connection point of the temperature sensing means (8) and the resistor (9). It is connected. (11) is a determination means, for example, J
・ K flip-flop, whose J input terminal is a comparison circuit (1
0) and a clock (hereinafter referred to as CLK) input terminal are connected to the output terminal of the changing means (4). Further, a series circuit of a resistor (12) and a light emitting diode (13), a resistor (14), and a light emitting diode (15) are provided at the Q output terminal of the judging means (11) and its inverting output terminal (hereinafter referred to as Q output terminal). Are connected to each of the series circuits. The light emitting diode (13) emits light indicating that the temperature is low, and the light emitting diode (15) emits light indicating that the temperature is appropriate. Reference numeral (16) denotes a duty ratio control means, and two AND circuits (17) and (18), diodes (19) and (20) connected to their respective output terminals, and cathodes of the respective diodes (19) and (20). A semiconductor control means (24) connected in series with a trigger means (22) composed of a transistor (21) connected to the base and a heating element (23) such as a lamp heater.
Composed of and. A triac is suitable as the semiconductor control means (24). A series circuit of the heating element (23) and the semiconductor control means (24) is connected in parallel to the AC power source (2).

Further, one input terminal of the AND circuit (17) is connected to the Q output terminal of the judging means (11), and the other input terminal is connected to the output terminal of the one-shot multivibrator (25). Further, one input end of the AND circuit (18) is connected to the bar Q output side of the judging means (11), and the other input end is connected to the output end of the one-shot multivibrator (26). The one-shot multivibrator (25) is provided with a semiconductor control means (2
4) is connected to the output terminal of the zero-cross pulse generation circuit (1) so as to output the trigger signal (e), and the one-shot multivibrator (26) is connected to the comparison circuit (1).
It is connected to the output terminal of the comparison circuit (10) so as to output the trigger signal (1) of the semiconductor control means (24) when the output of 0) changes from low level to high level.

Next, the operation of this embodiment will be described with reference to FIGS. 2A and 2B.

The capacitor (5) is repeatedly charged and discharged at a constant cycle by the pulse signal (c) output from the delay circuit (3). That is, when the transistor (6) is OFF, charging is performed through the variable resistor (7), and when the transistor (8) is ON, discharge is performed by the pulse signal (c). The charging voltage of the capacitor (5) during this charging / discharging is (g).

Now, it is assumed that the ambient temperature of the heating element (23) is low. The comparison circuit (10) compares the charging voltage (g) with the voltage (f) divided by the temperature sensing means (8) and the resistor (9), and the charging voltage (g) determines the voltage (f). When it exceeds, the high potential level output signal (h) is output. Judgment means (11)
Is the output signal (h) when a predetermined time (t1) has elapsed after the start of charging the capacitor (5), that is, when the output signal (d) of the timer circuit (4a) falls from a high potential to a low potential level. If the output signal (h) is taken in and has a high potential level, it is determined that the ambient temperature has not reached the predetermined temperature, and the output signal (i) is output from the Q output terminal. That is, during the period when the ambient temperature is low and the voltage (f) is low, the charging voltage (g) is equal to the voltage (f) before the predetermined time (t1) has elapsed.
Therefore, the output signal (h) is at a high potential level when the predetermined time (t1) has elapsed, and the determination means (1)
1) holds the output signal (i) until the ambient temperature rises to a predetermined temperature. The output signal (i) causes the light emitting diode (24) to emit light, indicating that the temperature is low.

Further, the output signal (i) is the AND circuit (1
7), the one-shot multivibrator (25) is triggered by the trailing edge of the pulse signal (b) from the zero-cross pulse generation circuit (1) and is output for the pulse width time of the one-shot pulse signal (e). AND circuit (1
It is output as an output signal (j) from 7) and turns on the transistor (21). When the transistor (21) is turned on, the semiconductor control means (24) is triggered to energize the heating element (23). Semiconductor control means (24)
The timing at which is triggered depends on the one-shot pulse signal (e) output immediately after the zero crossing, so as can be seen from FIG. 2A, the heating element (23) has a duty ratio (energization of about 100%). The waveform is m and the energization is shown by a solid line).

Here, the output signal (l) of the one-shot multivibrator (26) which outputs the trigger signal of the semiconductor control means (24) in response to the output of the comparison circuit (10) is the AND circuit (18). Since the output signal (k) from the judging means (11) input to one input terminal is "L", it is cut off by the AND circuit (18). Therefore, during the period when the output signal (i) is held, that is, until the ambient temperature rises to the predetermined temperature, the heating element (23) is energized regardless of the ambient temperature (output of the comparison circuit (10)). The temperature rise time inside the kotatsu can be shortened by keeping it at about 100%.

When the ambient temperature thereafter rises, the output signal (h) of the comparison circuit (10) becomes a high potential level after a lapse of a predetermined time (t1) after the start of charging, as shown in FIG. 2B. That is, as the temperature rises (suitable temperature), the resistance value of the temperature sensing means (8) decreases, and therefore the voltage (f) applied to one input end of the comparison circuit (10) rises, It takes t1 or more until the charging voltages (g) match. Judgment means (11)
Is “L” at the time when the output signal (h) input to the J input end has passed the predetermined time (t1), and therefore the output signal indicating that the ambient temperature has reached the predetermined temperature from the bar Q output end. Output (k). At this time, the output signal (i) becomes "L". Therefore, the gate of the AND circuit (17) is closed and A
Since the gate of the ND circuit (18) is opened, the trigger signal (e) output from the one-shot multivibrator (25) is cut off immediately after the zero cross, and instead the one-shot multi-vibrator is output according to the output of the comparison circuit (10). Trigger signal (l) output from the multivibrator (26)
Is supplied. As a result, the heating element (23) is kept in a 100% energized state until the ambient temperature reaches a predetermined temperature, and when the temperature exceeds the predetermined temperature, it is triggered when the voltage (f) and the charging voltage (g) match. The phase is controlled according to the temperature, and the power is turned on.

When the output signal (i) becomes "L",
The transistor (4c) of the changing means (4) is turned on,
The resistor (4d) and the resistor (4e) are connected in parallel to shorten the charging time for the capacitor (4b) (the charging voltage waveform of the capacitor (4b) is shown as (n) in FIG. 2B). As a result, the time width of the delay signal (d) of the changing means (4) becomes short. Here, the energization of the heating element (23) is 100% until 100% immediately before the time when the energization by the phase control is switched from the above 100% energization to the energization by the intersection angle of the charging voltage (g) and the voltage (f). Since the current has been changed to almost 50% as indicated by (m) in FIG. 2B, the ambient temperature of the heating element (23) is rapidly decreased as indicated by the dotted line α in FIG. 3A. I will end up. Here, if the time width of the delay signal (d) is not shortened, the output of the comparison circuit (10) becomes "H" at the time when t1 elapses due to a decrease in ambient temperature, and the determination means (11) sets a predetermined value. The signal (i) indicating that the temperature has dropped to below the
The state of 0% energization is reached, and thereafter the energized state of 100% and 50% is repeated. However, in this embodiment, even if the voltage (f) decreases due to the temperature decrease and the charging voltage (g) exceeds the voltage (f) earlier, the time width of the delay signal (d) becomes smaller than that time. Since the temperature is changed to a short time (t2), that is, the temperature at which the determination means (11) outputs the signal (k) is changed to a low temperature side to have temperature hysteresis, a predetermined time (t2) has elapsed from the start of charging. ) Has elapsed, the output of the comparison circuit (10) is maintained at "L", so that the energization is controlled by the phase control without switching to 100% energization.

This point will be described in detail with reference to FIG. At the time of reading the level comparison result of the charging voltage (g) of the capacitor (5) and the voltage (f) corresponding to the resistance change of the temperature sensing means (8), a predetermined time ( The time t1) is set (hereinafter referred to as point I). Since the temperature of the temperature sensing means (8) is low at the beginning of energization,
When the level comparison result of the charging voltage (g) and the voltage (f) is read at point I, it is (g)> (f), so in this case, the heating element (23) is energized by about 100% (for example, about 500 W). When the energization of 500 W causes the ambient temperature to rise rapidly, the voltage (f) also rises accordingly, and when it reaches a predetermined temperature near the set temperature, (g) = (f) at point I.
At this point, point I is moved to detection point II in order to have temperature hysteresis. That is, the level comparison result of the charging voltage (g) and the voltage (f) is changed to be read when a time t2 shorter than t1 elapses after the charging of the capacitor (5) is started. As a result, the temperature when (g) = (f) at the detection point II point is changed to a temperature lower than the temperature when (g) = (f) at the detection point II point. Then, once the voltage (f) reaches the charging voltage (g) at the detection point I point, the detection point moves to the point II, so that at the detection point II point, (g) <(f), and the determination means ( 11) outputs a signal (k) indicating a predetermined temperature or higher. The heating voltage is applied to the heating element (23) by charging voltage (g).
The phase control is performed according to the intersection angle (signal 1) between the voltage and the voltage (f). At this time, the ambient temperature temporarily drops, the temperature of the temperature sensing means (8) also drops, and the voltage (f) drops to the voltage (f '). However, even at this time, since the detection point is the II point, the charging voltage (g) is lower than the voltage (f ′) ((g) <(f ′)), and the phase control state is continued. Therefore, 100% energization does not occur, and voltage (f)
The number of W increases in inverse proportion to the decrease from the voltage to the voltage (f '), and about 350 W is energized at the voltage (f'), and the power is linearly supplied in proportion to the temperature. By the way, considering the case where the detection point is fixed to point I, I
In the case where a lamp heater is used for the heating element (23), about 100% energization and about 50% energization alternate with the change of the ambient temperature, that is, the voltage (f) movement, at the point as a boundary. Results in repeated brightening and darkening.

The above operation will be described with reference to FIGS. 1A and 2B. The output signal (k) causes the light emitting diode (1
5) is turned on and an appropriate temperature is displayed, and the output signal (k) is input to one input end of the AND circuit (18) and at the leading edge of the output signal (h) input to the other input end. Triggered one-shot multivibrator (2
6) is ANDed with the one-shot pulse signal (i) output by 6) and the output signal (j) is output from the AND circuit. Then, as in the case of the above low temperature, the transistor (21) is turned on by the output signal (j), and at this timing, the semiconductor control means (24) is phase-controlled to generate the heating element (23).
Energization is controlled.

As described above, when the ambient temperature is low, the energization is maintained at about 100%, and when the temperature reaches the predetermined temperature, the phase control according to the temperature is performed and the energization of the heating element (23) is controlled. However, if a higher temperature is required or if a lower temperature is desired, the variable resistor (7) can be operated to set the desired temperature. That is, the resistance value is changed by operating the variable resistor (7), and thus the way the charging voltage of the capacitor (5) rises is changed to change the set temperature. For example, when the temperature setting is “high”, the resistance value VR of the variable resistor (7) is set to V
If R = 0 and conversely VR = MAX in the case of "low", it rapidly rises in "high" and rises gently in "low". FIG. 3A shows a state in which the ambient temperature of the heating element (23) in this embodiment changes up to the set temperature, and changes with the wattage of the heating element (23) shown in FIG. 3B. , Shows that the temperature is controlled to the set temperature without a sudden temperature change.

Next, another embodiment of the present invention will be described with reference to FIGS.
This will be explained in Section 7. FIG. 5 is a circuit diagram showing the entire electronically controlled kotatsu using the temperature control device of the present invention.
Is a microcomputer. In the other embodiment, a microcomputer (27) is used for the judging means, the changing means and the duty ratio controlling means. FIG. 6 is an excerpt of the characteristic circuit of the present invention for controlling the temperature detection and the trigger signal of the semiconductor control means (24). The operation of this other embodiment will be described in detail below with reference to FIGS.

The waveform diagram shown in FIG. 7 shows the waveforms of the voltages at the input / output terminals and the respective parts of the control circuit shown in FIG.

The microcomputer (27) detects the zero-cross pulse Pz and, as a result, outputs the reset pulse Pr from the terminal R4. When the reset pulse Pr becomes "L" level, the voltage from the terminal R1 starts charging the capacitor (5) through the variable resistor (29) and the resistor (30). Here, the variable resistor (29) is a variable volume for temperature setting, like the variable resistor (7) of the above-mentioned embodiment, and can change the value of the charging resistance to the capacitor (5). The charging voltage at this time is Vc. Next, when the reset pulse Pr becomes "H" level, the transistor (32) is turned on and the charging voltage Vc of the capacitor (5) is discharged.

On the other hand, in order to detect the internal temperature of the kotatsu, a thermistor having a negative characteristic (hereinafter referred to as the thermistor) of the temperature sensing means (8) installed at a predetermined position in the kotatsu is connected in series with the resistor (33). And is connected to one input end of the comparison circuit (10). Therefore, the level of the voltage VTh at the connection point rises as the temperature inside the kotatsu rises.

The operation when the kotatsu temperature is low, that is, when the temperature setting is "high" will be described with reference to the first part of FIG. The charging voltage Vc and the voltage VTh are compared by the comparison circuit (10). The comparison result is input to the terminal K4 of the microcomputer (27) via the transistor (34). Microcomputer (27)
Determines whether the comparison result is the “H” level at every 90 ° of the AC voltage waveform, and at this point the comparison result (terminal K4)
Is at the "L" level, that is, if the charging voltage Vc> the voltage VTh, it is determined that the predetermined temperature has not been reached, and the pulse signal PR2 is output to the terminal R2. This pulse signal P
R2 is output at the timing when the heating element (23) is energized by about 100%. That is, if the pulse signal PR2 is output immediately after the zero-cross pulse Pz is output,
The comparison output from the comparison circuit (10) is connected to the capacitor (35).
This is because it can be applied to the base of the transistor (36) at a timing earlier than the trigger pulse VB obtained via the. The collector of this transistor (36) has a resistor (3
7) is connected to the gate of the semiconductor control means (24), and the semiconductor control means (24) is triggered at the timing of the pulse signal PR2 to energize the heating element (23).

Next, when the temperature inside the kotatsu approaches the set temperature at the temperature setting "high", the second portion and the third portion in FIG.
As shown in the portion, the charging voltage Vc <the voltage VTh at the time when the AC voltage waveform is 90 °, so that the “H” level signal is input to the terminal K4 of the microcomputer (27). Therefore, the microcomputer (27) determines that the charging voltage Vc has not reached the voltage VTh and has reached the predetermined temperature or higher, and does not output the pulse signal PR2 from the terminal R2. That is, the retention of 100% energization is released.
However, instead, the charging voltage Vc and the voltage VTh
When the two coincide with each other, the comparing means (10) outputs a high potential level signal, and the voltage of the terminal R1 is differentiated by the capacitor (35) and the resistor (38) to obtain the trigger pulse VB. This trigger pulse VB causes the transistor (3
6) is turned on, a gate signal flows to the semiconductor control means (24) at the intersection angle of Vc = VTh, and the heating element (23) is turned on to perform phase control. At this time, the microcomputer (27) shifts the time point for judging the comparison result from every 90 ° of the AC voltage waveform, for example, every 60 °.
That is, the predetermined time is shortened, and the temperature at the time of switching to the phase control is lowered to have the temperature hysteresis. Therefore, similarly to the above-described embodiment, it is possible to minimize the temperature change due to the change from 100% energization to 50% energization when the phase control is replaced. Then, after the temperature has once dropped, the determination time is shifted forward, so that the phase control corresponding to the temperature is continued. Since the energization rate (W number) at this time is larger than the W number for maintaining and stabilizing the temperature in the kotatsu, the temperature in the kotatsu keeps increasing and therefore the voltage VTh also keeps increasing. As a result, the charging voltage Vc
The intersection (coincidence point) between the voltage VTh and the voltage VTh shifts to the right side, as shown in the second and third parts of FIG. The third part of FIG. 7 shows the case where the temperature inside the kotatsu reaches the set temperature when the temperature is set to "high", and the duty ratio (W number)
When the temperature decreases to a W number at which the temperature in the kotatsu can be maintained, the increase in the temperature in the kotatsu stops.

Further, when the temperature setting is changed to "low", as shown in FIG.
As shown in the third portion, the peak of the charging voltage Vc decreases, the intersection with the voltage VTh, that is, the coincidence point disappears, and the heating element (23) is not energized. That is, the heating element (2
When 3) is the lamp heater, the lamp heater is turned off. In this case, since the kotatsu user wanted to lower the temperature, the temperature setting was changed to the "low" side, so turning off the lamp heater gives the user the feeling that the kotatsu temperature has dropped (actually It goes down), so it is better to turn it off. Then, since the lamp heater is turned off, the temperature inside the kotatsu gradually decreases, and when the temperature approaches the "low" set temperature, the charging voltage Vc and the voltage VTh match (cross), but this crossing angle is equal to the duty ratio of 0. %, The temperature inside the kotatsu keeps dropping. As the temperature inside the kotatsu decreases, the intersection of the charging voltage Vc and the voltage VTh is shown in FIG.
In, the current rate increases as it shifts to the left side, and eventually stabilizes at the wattage required to maintain the "low" setting setting. In the other embodiment, the input of the terminal K4 is 90
The temperature is detected at 60 ° and 60 °, but since it is processed by a microcomputer, the size of the kotatsu and the heating element (23)
By changing the detection angle according to the number of W, it is possible to easily set the energization range of about 100% to a range suitable for using kotatsu.

[0030]

According to the present invention, the energization of the heating element is maintained at a substantially maximum state regardless of the ambient temperature until the ambient temperature of the heating element reaches a predetermined temperature, and the time until the temperature rises to the set temperature is shortened. Therefore, the rising characteristics can be improved. Then, after reaching the predetermined temperature, the phase is controlled according to the ambient temperature to keep the width of the temperature change small. Further, when the ambient temperature reaches a predetermined temperature, the predetermined temperature can be changed to a low temperature side to provide a temperature hysteresis and prevent a large change in the duty ratio of the heating element.

[Brief description of drawings]

FIG. 1 is a circuit diagram of an embodiment of the present invention, in which A is a whole circuit diagram,
B is a circuit diagram of a main part.

FIG. 2 is a waveform diagram for explaining the operation of the embodiment, showing A
3B is a waveform diagram when the ambient temperature is low, and B is a waveform diagram when the ambient temperature is high.

FIG. 3 is a graph for explaining the operation of the embodiment, in which A
Is a graph showing a change in ambient temperature of the heating element, and B is a graph showing a change in wattage of the heating element.

FIG. 4 is a graph for explaining the operation of the embodiment with the transition of a predetermined time.

FIG. 5 is an overall circuit diagram of another embodiment.

FIG. 6 is a main part circuit of another embodiment.

FIG. 7 is a waveform diagram for explaining another embodiment.

FIG. 8 is a circuit diagram of a conventional example.

FIG. 9 is a circuit diagram of a conventional example.

[Explanation of symbols]

 4 Change Means 8 Temperature Sensing Means 11 Judging Means 16 Duty Rate Control Means 23 Heating Element

Claims (1)

Claim: What is claimed is: 1. A heating element, a temperature sensing means for detecting a change in ambient temperature due to the heating element, and phase control of energization of the heating element in response to a signal from the temperature sensing means. In the electronically controlled kotatsu having a control means, the control means holds the energization of the heating element in a substantially maximum state until the ambient temperature rises to a predetermined temperature, and when the ambient temperature rises to the predetermined temperature, An electronically controlled kotatsu comprising a changing means for changing the predetermined temperature to a low temperature side.