JPS62232890A - Output controller of electromagnetic cooker - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION (a) Industrial Application Field The present invention relates to an electromagnetic cooker, and more specifically to output control that stably changes the output from a low output range to a high output range during heating output adjustment operation. Regarding circuits.

(B) Conventional technology Conventionally, this type of cooking device has two methods of adjusting its output: a frequency control method in which the oscillation frequency of the inverter circuit is varied to change the heating output, and a frequency control method in which the oscillation frequency of the inverter circuit is fixed and the heating output is changed. There is an on-off duty control method in which the overall heating output is changed by varying the ratio of the driving time to the non-driving time. The former, that is, those that take the position of frequency control, are
There is a publication No. 4558. This control method has the disadvantage that there is a lower limit in the low output range, and it is difficult to adjust the output below about 200 W due to storage time and switching speed of the switching elements in the inverter circuit. was. On the other hand, the latter, that is, the one that takes the position of on-off duty control,
There is a publication No. 1-3079. In this method, it is possible to control the output to approximately zero W, but there is a drawback that heating of the load is uneven, especially in a high output range, and the load is burnt.

(c) Problems to be Solved by the Invention In the above-mentioned conventional techniques, either frequency control or on/off duty control has been adopted to control the heating output, but the former Problems remained in both the low output range, the latter and the high output range.

Therefore, an object of the present invention is to provide a cooking device that can perform stable heating over a wide range.

(D) Means for Solving the Problems The present invention provides an output of an electromagnetic cooker equipped with an inverter circuit that allows a switching element to operate and performs self-excited oscillation to generate a high-frequency alternating magnetic field in a heating coil to perform induction heating. The control circuit includes an output setting section capable of varying a setting signal for setting a heating output, and outputting a signal according to the setting signal when the setting signal is a predetermined signal or more, and the setting signal is less than the predetermined signal. a reference voltage circuit that outputs a signal at a constant level when a signal generating circuit that periodically and continuously sends out comparison signals divided into two types; a signal generation circuit that continuously oscillates the inverter circuit when the setting signal is equal to or higher than a predetermined signal; and when the setting signal is less than the predetermined signal, the comparison signal and the setting signal; and a duty ratio setting section that controls the oscillation/non-oscillation ratio of the inverter circuit based on the oscillation/non-oscillation ratio.

(f) The operation reference voltage circuit (20) determines the magnitude of the setting signal from the output setting section (19) and the predetermined signal, and based on the result, a signal corresponding to the magnitude of the setting signal is used for frequency control. Further, the peak point of the sawtooth wave is determined so that duty ratio control by the duty ratio setting section (22) is started when the setting signal becomes less than a predetermined signal.

Example) An example of the present invention will be described below with reference to FIGS. 1 to 7.

(1) is a box-shaped cooker body made of synthetic resin such as plastic or metal, and a top plate (2) made of a non-magnetic heat-resistant insulating material such as ceramic glass is disposed on the top surface. There is. (3) is an operation unit provided on the front side or top front of the main body (1), and has multiple cooking modes such as power switch (4), 1 output adjustment operation, 1 temperature adjustment operation, etc., and can switch the cooking mode. Changeover switch (
5) and an operation switch (6).

(10) is a power supply circuit that operates the electromechanical parts inside the cooker when the power switch (4) is turned on, and (11) operates a switching element based on a signal from the drive circuit (15), which will be described later, to generate self-oscillation. This is an inverter circuit that generates a high-frequency alternating magnetic field in a heating coil to inductively heat a load (12) such as a metal pot placed on a top plate (2). (13) is an inverter circuit. (11) is an oscillation circuit that generates a timing pulse for self-excited oscillation; (14) is a circuit that conducts switching elements based on the timing pulse from the oscillation circuit (13) and the output of a control circuit (16), which will be described later. The on-pulse width determining circuit (15) that determines the time is a drive circuit that amplifies the output signal of the on-pulse width determining circuit (14) and operates the switching element.

Next, the control circuit (16) will be explained in detail. The control circuit (16) in the present invention can be roughly divided into two parts, one being an output setting circuit (17) and the other being a duty circuit.
ratio control circuit<18), and both (17) and (18) control the reference level for determining the output of the pulse width determining circuit (14), that is, the ON pulse width of the switching element.

First, the output setting circuit (17) will be explained. DC voltage ■DD - Resistor (30) - Variable resistor (31> - Resistor (3)
2) - A variable output setting section (19) which is configured with a series circuit connected to the ground and sends out a setting signal for setting the heating output, and a slide terminal section (A) of the variable resistor (31).
A standard that outputs a signal based on the setting signal, that is, a signal corresponding to the setting signal when the setting signal is greater than a predetermined signal, and a signal at a certain level when the setting signal is less than the predetermined signal. It consists of a voltage circuit (20). However, the variable resistor (31) is linked to an operating lever that serves both as a power switch (4) and an operating switch (6). Note that this output setting section (19) is shown for the case where the output is set using the operating lever to simplify the explanation, but the output setting section (19) is shown for the case where the output is set using the touch switch (see Figure 2).
In this case, a stepped waveform that can be created based on the touch switch operation may be used as the signal of the output setting section (19). Further, the reference voltage circuit (20) connects the point (A) to the base of the transistor (34) via the resistor (33), the emitter is grounded via the resistor (35), and the collector is connected to the DC 'ri RV -n. In addition, a Zener diode (36) is connected between the collector and emitter, and the emitter is connected to the on-pulse width determining circuit (described later).
14) Connect to the input end of the comparator (4o) on the ■ side.

On the other hand, the duty ratio control circuit (18) includes a signal generation circuit, for example, a sawtooth wave generation circuit (21), which periodically and continuously sends out a comparison signal whose one period is divided into a rising part and a falling part, and a duty ratio control circuit (21). - ratio setting section (22), the duty ratio setting section (22) inputs the output of the sawtooth wave generation circuit (21) to the O side input terminal of the comparator (37), ) point signal through the resistor (38) ■
input to the side input terminal. The output end of this comparator (37) is connected to the on-pulse width determining circuit (14). The duty ratio setting section (22) is connected to the output setting section (19).
) causes the inverter circuit (11) to continuously oscillate when the setting signal output from the circuit is greater than a predetermined signal, and when the setting signal is less than the predetermined signal, the comparison signal and setting signal are output from the sawtooth wave generation circuit (21). The oscillation/non-oscillation ratio of the inverter circuit (11) is controlled based on both of the following. To be more specific, when a high level signal is output from the comparator (37) (period between when the setting signal is greater than or equal to the predetermined signal and when the comparison signal is less than the setting signal), the on-pulse width determining circuit (14) The inverter circuit (11
) is oscillated by the on-pulse of the on-pulse width determining circuit (14) based on the output signal of the reference voltage circuit (20),
During the period when the comparator (37) can output a low-level signal (corresponding to the period when the comparison signal is equal to or higher than the set signal), the oscillation of the inverter circuit (11) is stopped by preventing the on-pulse width determining circuit (14) from sending out an on-pulse. The output is controlled by on/off duty.

Now, regarding the on-pulse width determining circuit (14), the output of the oscillation circuit (13) is inputted to the - control input terminal of the comparator (40) via the capacitor 39). In addition, the θ side input terminal is connected to VDD via a resistor (41) and a diode (42), respectively.
The input terminal on the ■ side is grounded via the capacitor (43), and also connected to the duty ratio setting section (22) and the reference voltage circuit (20), and the comparator (
40) is the output signal of the reference voltage circuit (20) and the oscillation circuit (
The on-pulse width is determined based on the timing pulse of step 13), and the on-pulse is sent out. However, the transmission of on-pulses is stopped during the period when a low level signal is output from the duty ratio setting section (22). In addition, the on-pulse width determination circuit (1
4) and the control circuit (16) constitute an output control circuit.

The configuration of the present invention is as described above, and its operation will be explained below. First, by turning on the power switch (4), the fan motor (not shown) is driven to start cooling the inside of the cooking device (1), and the DC voltage VD
D is sent out from the power supply circuit (10). Therefore, the top plate (
2) The explanation will continue assuming that an appropriate load (12) is placed on top.

Now, select "Output adjustment" by operating the operation section (3).

Assume that the cooking mode is selected and its output adjustment is set to the maximum (in Figure 1, the variable resistor (31)
(The resistance value at point A is maximized and the potential at point A is maximized.) At this time, the potential at point A is the maximum during the output adjustment operation (see point C in Figure 4), so the duty cycle is
The output of the comparator (37) of the ratio control circuit (18) is always a high level signal and does not affect the on-pulse width determining circuit (14) (that is, the on-off duty ratio is 1). On the other hand, the potential at point A is the maximum within the control range, and if the potential at point A is vA, VA is equal to or higher than a predetermined voltage, that is, VA≧VDD−Vz + 0, 6 [V:
1 (V7 is the Zener voltage of the Zener diode), the transistor (34) becomes conductive, and B
Potential of point v, (hereinafter the potential of this point is referred to as V) force VB
= VA-0, 6 [V) Tonal. In other words, the operation section (
3) The potential VA at point A derived from the output setting unit (19) based on the operation is vA≧Voo Vz+o, s[V
), if it is varied within a range that satisfies
Ao, 6 CV] A potential is output to point B. At this time, V is input to the ■ side of the comparator (40), and this V and the output pulse of the oscillation circuit (13) are combined with the time constant circuit (the capacitor in Fig. 1) of the on-pulse width determining circuit (14). The on-pulse width is determined by comparing (39) with the waveform shaped waveform via the resistor (41). Therefore, since VA is now at its maximum, VB is also at its maximum, and the pulse output from the comparator (40) The width is also the maximum within the control range.This output pulse is
) and drives the switching element of the inverter circuit 11), but the larger the pulse width, the lower the oscillation frequency of the switching element and the greater the heating output by the heating coil. Since the width is the maximum, the heating output will be set to the maximum.

Then, by operating the operation unit (3), the set output is gradually lowered from the maximum and the potential vA at point A is lowered (see from point C to point F in FIG. 4), and the on-pulse width determining circuit The output pulse width of (14) also gradually decreases, the oscillation frequency of the switching element of the inverter circuit (11) gradually increases, and the heating output gradually decreases (however, V A ≥ V oo V z+ 0
, 6 Satisfied t Le WA Box 41: Limited. (See Figure 5). Also, within this range, the output of the comparator (37) of the duty ratio control circuit (18) always becomes a high level signal, and does not affect the on-pulse width determining circuit (14) (i.e., the on-off duty ratio - ratio is 1).

Now, the operation section <3> Output setting section (19) based on the operation
The setting state is V, ≧Vl)EI VZ+ 0-
6. When ヲ is no longer satisfied, that is, when vA is less than the predetermined voltage, in other words, VA < V tro-V z+ 0.
6, the transistor (34) of the reference voltage circuit (20) becomes non-conductive and the potential at point B becomes V,
is fixed at a constant value of V, -VDゎ-v2. (see point F in Figure 4). v,l
is fixed to a constant value, the on-pulse width determining circuit (14
) will also be the minimum within the setting range, and even if you operate the operation section (3) to lower the set output by frequency control, this pulse width will not change, so the lower limit by frequency control will be this pulse. Determined by width. on the other hand,
■ of the comparator (37) of the duty ratio control circuit (18)
vA is input to the input terminal, and this ■4 is VA”V
If it is aligned so that it intersects the peak point of the sawtooth wave output from the sawtooth wave generation circuit (21) when DD-VZ+ reaches 0.6, VA becomes 7 (VA< VDD-v2+
The period during which the output of the comparator <37) is at a low level can be set within the range of 0.0 and 6. That is, as shown in FIG. 7, the ratio of the oscillation period TA during which automatic oscillation of the inverter circuit (11) can be performed and the non-oscillation period T3 during which automatic oscillation is stopped is determined by the operation of the operating section (3). vA is V,
<Vゎ. It is variable only in the range of -V2+0.6, and the heating output is adjusted by duty ratio control. For example, the on/off duty at the output setting point F and point G in FIG. 4 is as shown in FIGS. 7(b) and 7(c). Here, the generation period of the sawtooth wave is from several seconds to 10-odd seconds.

The present invention is as described above, and includes frequency control and duty control.
By adopting both control methods, it is possible to stably control output over a wide range from low output to high output. In addition, since stable heating output can be obtained in the low output range, the range of use can be expanded for cooking such as slow boiling, slow boiling, and simply keeping warm. Furthermore, since the lower limit of frequency control is determined by the reference voltage circuit, the output setting section can be used as is whether it is operated by lever operation or touch switch operation.

(G) Effects of the Invention The present invention is as described above, and includes frequency control and duty control.
Both control methods are adopted, and especially in the low output range, duty control is used, making it possible to stably control output over a wide range from low output to high output. In addition, since the output can be varied particularly stably in the low output range, the range of cooking such as simmering or simply keeping warm can be increased. Furthermore, when the slide lever is used as both the tR switch and the adjustment switch, the low output range is the duty switch.
Since it is controlled, the output can be reduced to approximately zero watts.

[Brief explanation of drawings]

Each figure shows an embodiment of the present invention, FIG. 1 is a main part electric circuit diagram, FIG. 2 is an external perspective view of the cooker, and FIG. 3 is a block diagram.
Figure 4 shows the output voltages at point A and point B corresponding to the setting state,
5 and 6 are operational waveform diagrams of the output setting circuit, and FIG. 7 is an operational waveform diagram of the duty ratio control circuit. (11)... Inverter circuit, (14)... On-pulse width determining circuit, (19>... Output setting section, (2
0)...Reference voltage circuit, (21)...Signal generation circuit, (22)...Duty ratio setting section. Applicant Sanyo Electric Co., Ltd. and one other representative Patent attorney Takuji Nishino

Claims (1)

[Claims] 1. In the output control circuit of an electromagnetic cooker equipped with an inverter circuit that operates a switching element to perform self-excited oscillation and generate a high-frequency alternating magnetic field in a heating coil to perform induction heating, there is a method for setting the heating output. an output setting section that can vary a setting signal; and a reference voltage circuit that outputs a signal according to the setting signal when the setting signal is equal to or higher than a predetermined signal, and outputs a signal at a constant level when the setting signal is less than the predetermined signal. ,
an on-pulse width determining circuit that controls the conduction time of the switching element based on the signal from the reference voltage circuit; and a comparison signal that periodically and continuously sends out a comparison signal in which one cycle is divided into a rising part and a falling part. a signal generation circuit; and when the setting signal is a predetermined signal or more, the inverter circuit is caused to continuously oscillate, and when the setting signal is less than a predetermined signal, the ratio of oscillation/non-oscillation of the inverter circuit is controlled based on the comparison signal and the setting signal. An output control circuit for an electromagnetic cooker, comprising a duty ratio setting section.