JPH0341953B2 - - Google Patents

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to an electromagnetic cooker in which a high-frequency current is passed through a heating coil, and an object to be heated, such as a pot, is heated by induction using the magnetic flux generated by the coil. It is.

[Prior Art] In this type of electromagnetic cooker, two methods have been used to adjust the heating output: a variable input current method and a duty cycle method.

Among these, the variable input current method changes the current supplied to the heating coil by controlling a switching transistor installed in the middle of the heating coil's energizing path.
The heating output is adjusted by controlling the output level of the heating coil itself. On the other hand, the duty cycle method is configured to adjust the heating output over a wide range by keeping the output level of the heating coil constant and intermittent output with a variable duty cycle. There is.

[Problem to be solved by the invention]

However, with the conventional variable input current type electromagnetic cooker mentioned above, there is a limit to how low the output level of the heating coil can be lowered due to limitations in the conduction characteristics of the switching transistor, and it is said that it is not possible to obtain a very small heating output. It has drawbacks. Also,
Although the duty cycle type induction cooker can adjust the heating output over a wide range, it constantly changes the large input current intermittently in order to intermittent the output of the heating coil, which causes lights to flicker and other devices to adjust. It has the disadvantage of having a negative impact on

The present invention has been made in consideration of the above-mentioned circumstances, and provides an electromagnetic cooker that does not have any adverse effects on other devices such as flickering of electric lights, and is capable of adjusting heating output over a wide range. The purpose is to

[Means to solve the problem]

In order to solve the above-mentioned problems, the electromagnetic cooker of the present invention includes a switching means for turning on and off electricity to the heating coil, a heating output setting means for variably setting the heating output of the heating coil, and a heating output setting means for variably setting the heating output of the heating coil. an output level control means that controls the output level of the heating coil by controlling the switching means on and off at a duty cycle according to a set value of the output level control means; and a minimum output level within a controllable range by the output level control means. The lower limit value, which is the lower limit of the set value, is compared with the set value set by the heating output setting means, and when the set value falls below the lower limit value, the above-mentioned duty cycle is set according to the difference. and control limiting means that intermittently limits the control by the output level control means, and the output level of the heating coil is controlled even when the control limiting period of the control limiting means is equal to or less than the lower limit value. It is characterized in that it is set longer than the control cycle of the output level control means.

[Effect]

In the above configuration, the controllable range of the switching means by the output level control means is determined by the delay characteristics of the switching element such as a transistor used as the switching means. Therefore, if the set value of the heating output setting means is a value that causes the output level control means to perform control within the above controllable range, the output level control means will set the duty according to the set value at that time. The switching means is turned on and off in cycles. The output level of the heating coil is controlled by energizing the heating coil on and off by this switching means, and the heating output is adjusted according to the set value.

On the other hand, when the setting value of the heating output setting means is lowered below the lower limit value corresponding to the lowest output level within the controllable range by the output level control means, the output level of the heating coil follows the above setting value due to the delay characteristic of the switching means. I won't. In this case, the control limiting means compares the set value of the heating output setting means with the lower limit value and determines that the set value has fallen below the lower limit value, and sets the duty cycle according to the difference between the two. The control by the output level control means is intermittently limited.

At this time, the control restriction period of this control restriction means is
Since the output level of the heating coil is set to be longer than the control cycle of the output level control means so that the output level of the heating coil is controlled even by the set value below the lower limit value, the output level of the heating coil is controlled by the output level control means. This makes it possible to easily control even low output level ranges that cannot be controlled by

Furthermore, since the control limiting means operates while the output level of the heating coil is maintained at the above-mentioned minimum output level, the input current supplied to the heating coil is
Intermittent in a small and suppressed state. therefore,
By intermittent output from the heating coil, it is possible to eliminate the effects on other equipment, such as flickering lights.

〔Example〕

Embodiments of the present invention will be described in detail below with reference to FIGS. 1 to 3.

Figure 1 shows the circuit configuration of the electromagnetic cooker of this embodiment.
A rectifying and smoothing circuit 2 is provided at the input stage that receives the commercial power supply 1, thereby converting the commercial power supply 1 into direct current.
A heating coil 3 that generates magnetic flux for induction heating and a resonant capacitor 4 that forms a resonant circuit together with the heating coil 3 are connected to the next stage of the rectifying and smoothing circuit 2, and further, between both terminals of the resonant capacitor 4, A switching circuit (switching means) consisting of a diode 5 and a transistor 6 is connected to constitute an inverter circuit which causes a resonant current to flow through the heating coil 3 by its switching operation.

A current transformer 7 is coupled to the input line of the inverter circuit, and the current transformer 7 detects the input current to the inverter circuit. A conversion circuit 8 that converts the detection signal from the current transformer 7 into a voltage according to the signal level is connected to the secondary side of the current transformer 7, and its output voltage e is connected to the input terminal of the next stage OP amplifier 9. connected to input. On the other hand, the above
A variable resistor 10 separately provided as heating output setting means for variably setting the heating output of the heating coil 3 is connected to the input terminal of the OP amplifier 9.
The set voltage e _v is always inputted as a set value for setting the heating output. As a result, in the OP amplifier 9, the output voltage e from the conversion circuit 8 corresponding to the input current is compared with the set voltage e _v of the variable resistor 10, and the output voltage e of the conversion circuit 8 is always A control operation is performed to output an output voltage with a feedback amount equal to the set voltage e _v . In other words, here, when the voltage e is smaller than the set voltage e _v , the difference is
When the output voltage f of the OP amplifier 9 increases and, conversely, the voltage e is larger than the set voltage e _v , the output voltage f of the OP amplifier 9 decreases by an amount corresponding to the difference.

The output terminal of the OP amplifier 9 is connected to the input terminal of the next stage comparator 11, and this comparator 11 is connected to the triangular wave oscillator 1 connected to the input terminal.
2's output voltage g and the above OP amplifier 9's output voltage f
People are starting to compare the two. The output a of the comparator 11 becomes H (high level voltage) and L (low level voltage) signals as shown by a ₁ and a ₂ in Fig. 2b, and the width of the H signal is f as shown in Fig. 2a. As shown by ₁ ·f ₂ , it increases as the level of the output voltage f of the OP amplifier 9 increases.

The comparator 11 is connected so that its output a is input to the base of the transistor 6 of the above-mentioned inverter circuit via the next-stage AND gate 13, and switching control of the transistor 6 is performed by the output a. The output level of the heating coil 3 increases as the on-time of the transistor 6 increases. This constitutes an output level control means for adjusting the level.

As mentioned above, the output level of the heating coil 3 decreases as the H signal width of the output a of the comparator 11 becomes narrower. In other words, the lower the setting voltage e _v of the variable resistor 10 is, the lower the output level becomes. However, once the voltage drops to a certain level (the set voltage at this time is e _vn ), the output level will not drop following the set voltage e _v due to the delay characteristics of the transistor 6. Therefore, the output level at this time becomes the lowest output level within the controllable range by the output level control means.

On the other hand, the output terminal of another comparator 14 is connected to the other input terminal of the AND gate 13,
This comparator 14 compares the set voltage e _v of the variable resistor 10 connected to the input terminal with the output voltage h of the triangular wave oscillator 15 connected to the input terminal.

The peak value of the output voltage h of the triangular wave oscillator 15 is preset to a lower limit value e _vn corresponding to the minimum output level at the set voltage e _v . Therefore, when the set voltage e _v is larger than the lower limit value e _vn as shown by k in FIG. 3a, the H signal is always input to one input terminal of the AND gate 13, and the The output level of the heating coil 3 is controlled by the output level control means. On the other hand, when the set voltage e _v falls below the lower limit value e _vn as shown by k' in Fig. 3a, the output b of the comparator 14 becomes H and L signals as shown in Fig. 3b; Comparator 1 via AND gate 13 for the time width of the signal
1 output a is input to the base of transistor 6. As a result, the operating time of the switching circuit is intermittently controlled by the output b of the comparator 14 while the output level of the heating coil 3 is maintained at the lowest output level.

As mentioned above, the triangular wave oscillator 15, the comparator 14 and the AND gate 13 are connected to the variable resistor 10.
The set voltage e _v and the lower limit value e _vn are compared, and when the set voltage e _v falls below the lower limit value e _vn , the output level control means controls the transistor 6 at a duty cycle according to the difference. This constitutes a control limiting means that intermittently limits the control of.

By the way, the cycle of the output waveform of the triangular wave oscillator 15, which is the control limit cycle of the control limit means, is set as described above so that the output level of the heating coil 3 is controlled even by the set voltage e _v below the lower limit value e _vn . The period is set to be sufficiently long (for example, one minute) compared to the period of the output waveform of the triangular wave oscillator 12, that is, the control period of the output level control means. As a result, the switching circuit operates for the remaining 40 seconds after stopping for 20 seconds out of one minute, depending on the level of the set voltage e _v , and if the level of the set voltage e _v is further decreased, the switching circuit operates for the remaining 40 seconds. It will be driven intermittently in long cycles, such as stopping and operating for 30 seconds.
In other words, the number of H and L signals at the output a of the comparator 11 is controlled by the duty cycle of the output b of the comparator 14 within the control limit period, so that the output level of the heating coil 3 is set to the minimum output level. This makes it possible to control even below the level.

According to the above configuration, for example, at a rated value of 1200 W (input voltage 100 V), the output level is lowered by the output level control means to its control limit of about 200 W, and below that, the output level control means controls the transistor 6. By intermittently controlling the operation using the control and restriction means described above, it is possible to obtain a low output of 20W. Therefore, in the configuration of this embodiment, the lower limit of the output level of the heating coil 3 by the conventional variable input current method is
Compared to about 200W, the lower limit can be significantly lowered, and it can be easily obtained even with a small heating output.

Also, to obtain a low output power such as 50W,
In the conventional duty cycle method, the current (12A) was intermittent while maintaining the output level at 1200W, which had an adverse effect on other devices such as flickering lights in ordinary homes. In the example, the lower limit of the output level is kept at around 200W,
When obtaining an output lower than that level, the current of 2 A is intermittent at that level, so that troubles such as flickering of the electric light as seen in the above-mentioned conventional example do not occur. Moreover, with the configuration of this embodiment, even if the control of the output level of the heating coil 3 is switched from the output level control means to the control limiting means, the settings can be set using the variable resistor 10 without requiring a corresponding switching operation. The heating output of the heating coil 3 can be variably adjusted steplessly by the voltage e _v , which also has the advantage of being extremely easy to use.

〔Effect of the invention〕

As described above, the electromagnetic cooker of the present invention includes a switching means for intermittent energization of the heating coil;
A heating output setting means for variably setting the heating output of the heating coil, and an on/off control of the switching means according to a duty cycle according to a set value of the heating output setting means to control the output level of the heating coil. The output level control means compares a lower limit value corresponding to the lowest output level of the controllable range by the output level control means and is the lower limit of the set value with the set value set by the heating output setting means, and sets the set value. and control limiting means that intermittently limits the control by the output level control means at a duty cycle corresponding to the difference when the value falls below the lower limit value, and the control limiting cycle of the control limiting means is provided. However, the heating coil output level is set to be longer than the control cycle of the output level control means so that the output level of the heating coil is controlled even with the set value below the lower limit value.

According to this, even if the output level of the heating coil cannot be controlled due to the delay characteristic of the switching element constituting the switching means, the control limiting means intermittently limits the control by the output level controlling means, so that the output level is small. Heating output can be easily obtained.

Further, the control limiting means is configured to operate when the set value of the heating output setting means becomes equal to or less than the lower limit value corresponding to the lowest output level in the controllable range by the output level control means, so that the control limit means is configured to operate when the set value of the heating output setting means becomes equal to or less than the lower limit value corresponding to the lowest output level of the controllable range by the output level control means. This means that the current flowing through the device is kept at a low level and is intermittent, which prevents disturbances such as flickering of lights.

Therefore, if the present invention is adopted, it is possible to provide an electromagnetic cooker that does not adversely affect other devices and whose heating output can be adjusted over a wide range.

[Brief explanation of drawings]

1 to 3 show one embodiment of the present invention. FIG. 1 is a circuit diagram showing the main parts of the electromagnetic cooker. FIGS. 2a and 2b are waveform diagrams showing the operation of the comparator in the output level control means, respectively. FIGS. 3a and 3b are waveform diagrams showing the operation of the comparator in the control limiting means, respectively. 3 is a heating coil, 5 is a diode, 6 is a transistor, 7 is a current transformer, 8 is a conversion circuit, 9 is an OP amplifier, 10 is a variable resistor (heating output setting means),
11 is a comparator, 12 is a triangular wave oscillator, 13 is a
14 is a comparator, and 15 is a triangular wave oscillator.

Claims (1)

[Scope of Claims] 1. Switching means for intermittent energization of the heating coil, heating output setting means for variably setting the heating output of the heating coil, and a duty cycle according to the set value of the heating output setting means. output level control means for controlling the output level of the heating coil by turning on and off the switching means; and a lower limit value corresponding to the lowest output level in a controllable range by the output level control means and serving as the lower limit of the set value. , the set value set by the heating output setting means is compared, and when the set value falls below the lower limit value, the control by the output level control means is intermittently performed at a duty cycle according to the difference. and a control limiting means for limiting the output level of the heating coil such that the control limiting period of the control limiting means controls the output level of the heating coil even with the set value below the lower limit value. An electromagnetic cooker characterized in that the control cycle is set longer than the control cycle of