JPH02148685A - Electromagnetic cooker - Google Patents

Abstract

PURPOSE:To reduce noise drastically by controlling the heating operation under the condition on which the on-time of a switching means is adjusted to a specified value when an input setting value is below a specified value. CONSTITUTION:A heating means 7 for heating an object to be heated by causing an eddy current in the object to be heated by means of magnetic flux generated by electromagnetic induction heats the object to be heated with a heating output commensurate with the on-time of a switching means 13. Input setting means 31, 33, 35 for setting input for heating an object to be heated are provided. When the values of the input setting are below a specified value, a heating period during which the switching means 13 repeats on-off operations while controlling the on-time of the switching means to a specified constant value, and a resting period are set. The ratio of the length of the heating period to the length of the resting period is controlled according to the input setting value. Thus the oscillation frequency of the switching means 13 is set to a constant value. As a result, noise can be reduced and the power loss can be reduced.

Description

[Detailed description of the invention] [Object of the invention] (Industrial application field) The present invention supplies a high frequency current to a heating coil, generates an eddy current in a heated object by magnetic flux from the heating coil,
Item 5 relates to an electromagnetic cooker that heats an object with Joule heat generated by this eddy current.

(Prior art) An electromagnetic cooker that heats objects by electric induction is highly safe because it does not generate flames, and is clean because the top plate on which the objects are placed can be made of crystallized glass. Various electromagnetic cookers have been developed that have advantages such as high thermal efficiency.

The conventional M magnetic cooker shown in FIG. 5 supplies a predetermined DC voltage from a DC power supply circuit 101 to an inverter circuit 103. By turning on and off the transistor 113 by the drive circuit 115, the heating coil 107 and the resonant capacitor 109 are set in a series-coupled state, and the heating coil 10
Due to the electromagnetic induction effect of the magnetic flux generated from 7, an eddy current is generated in an object to be heated, such as a pan (not shown), thereby heating it.

Pulse width modulation circuit with built-in oscillator (PULSE W
IDT)-I MODtJLATION>119 corrects the oscillation cycle of the oscillation pulse of the oscillator based on the timing pulse from the inverter circuit 103 using the common 171 voltage. Further, the pulse width modulation circuit 119 modulates the pulse width of the excavation pulse based on the signal voltage vOn from the on-time setting circuit 123.

Therefore, when the drive circuit 115 receives a pulse signal from the pulse width modulation circuit 119, it turns on the transistor 113 for a time corresponding to the pulse width of this pulse signal. The on-time setting circuit 123 is connected to a comparison circuit 125, and the comparison circuit 125 is connected to an input current detection circuit 129.

The input current detection circuit 129 detects 1 inch of input current from the AC power supply section based on a detection signal from the current transformer CT provided in the AC power supply section, and detects 1 inch of input current from the AC power supply section.
A signal voltage ■in corresponding to is output to the non-inverting input terminal of the comparison circuit 125 and the load detection circuit 143.

When the input setting operation unit 131 is operated to input settings regarding the heating power for heating the object to be heated, the input setting value vset is changed to the inverse of the comparison circuit 125 via the input power setting circuit 133 and the input current setting circuit 135. given to the input terminal. Therefore, the comparison circuit 125 compares the input set value vset and the signal voltage Vin, and operates the on-time setting circuit 123 according to the comparison result. For example, when the input voltage Vin is large with respect to the input setting value VS6j, the transistor Tr1 is turned on and the value of the signal voltage VOn input to the pulse width modulation circuit 119 is set to a small value.

The load detection circuit 143 monitors the load state by comparing the signal voltage vOn from the on-time setting circuit 123, the signal voltage vin from the input current detection circuit 129, and the signal voltage corresponding to the input current Iin. .

For example, when steel is placed on the heating coil 107, an appropriate input current of 1 inch flows, so it is determined that the load is an appropriate load, and the pulse width modulation circuit 119 continues to operate. Conversely, in a no-load state or when aluminum steel is placed on the heating coil 107, the input current 1i
When n becomes small, it is determined that the load is inappropriate and a stop signal V stp is output to the inverter oscillation stop circuit 145, thereby stopping the operation of the pulse width modulation circuit 119 and prohibiting the heating operation.

The load state monitoring operation by the load detection circuit 143 is performed when a power switch (not shown) is turned on or when the inverter circuit 103 starts a generating operation.

By the way, in the conventional lightning 11 cooker shown in FIG.
If the value of the input power set value set by is less than a predetermined threshold level, for example, IKW,
While controlling the value of input current 1 inch from W to be constant,
The on/off operation of the inverter circuit 103 is controlled according to the input power setting value.

Specifically, when the value of the input power setting value set by the input current setting circuit 133 is less than IKW, the input current setting circuit 135 always sets the predetermined voltage v1.
is output to the inverting input terminal of the comparison circuit 125. As a result, the input current of 1 inch input from the AC power supply section is set to a predetermined constant value, for example, 10A. At this time, the inverter on/off control circuit 153 operates based on the signal @133b from the input power setting circuit 133, and the pulse width modulation circuit 11
9 and the drive circuit 115, the on/off operation of the τ inverter circuit 103 is controlled. That is, there is a heating period in which the transistor 113, which is a switching means, repeats on-off operations, and after this heating period, the transistor 1
Set a pause period for pausing the on/off operation of 13,
The ratio of the length of this heating period to the rest period is controlled according to the signal 133b which is the input power setting value mentioned above.

For example, when the input power setting value set by the input power setting circuit 133 is 500 W, the inverter circuit 103 repeats the on/off operation every 20 msec.

(Problem to be solved by the invention) However, conventional electronics! The ay4 physical equipment controls the inverter circuit 103 on and off when the input power setting value set by the input power setting circuit 133 is less than a predetermined value, and the inverter circuit 103 is turned on and off during the heating period of the inverter circuit 103. There is a problem in that the oscillation frequency of the transistor 113, which is a switching element, changes within a predetermined band width depending on the material of the object to be heated, and noise associated with this changes over a wide band.

To be more specific, FIG. 6 is a characteristic diagram showing the frequency characteristics of the transistor 113 as a switching element with respect to the on time for each material of the heated object.
is the frequency characteristic curve for steel, Figure 6 (B) is the frequency characteristic curve for non-magnetic stainless steel, and Figure 6 (C) is the frequency characteristic curve for steel.
is the frequency characteristic curve for magnetic stainless steel,
FIG. 6(D) is a frequency characteristic curve in the case of a so-called three-layer pot formed by 3R members of stainless steel-iron-stainless steel.

Further, FIG. 7 is a characteristic diagram showing the frequency characteristics of the transistor 113 with respect to the generation period of the inverter circuit 103 for each material of the pot. Figure (B) is a frequency characteristic diagram of non-magnetic stainless steel, Figure 7 (C) is a frequency characteristic diagram of magnetic stainless steel, and Figure 7 (D) is a frequency characteristic diagram of the inverter circuit 10.
FIG. 3 is an explanatory diagram showing the generation cycle of No. 3.

As shown in FIG. 7, when the input power setting value set by the input power setting circuit 133 is, for example, 1 KW or less, the inverter circuit 103 is controlled to turn on and off until the inverter circuit 103 generates a Each time the load detection operation is started, the load detection operation is performed for a predetermined time T1, for example, 101 milliseconds. That is, when the value of the input power setting value set by the input power setting circuit 133 is less than or equal to IKW, the input power setting circuit 13
On-open setting timer 1 based on signal 133a from 3
27 operates to turn on transistors Tr3 and Tr4 for a predetermined time T1, that is, 1011 seconds. As a result, the on-time setting circuit 123 sets the predetermined signal voltage von
is output, and the on-time of the transistor 113 is set to a constant value,
For example, set it to 14 μsec. Therefore, during the fixed period T1 during which such a load condition is detected, the transistor 11
3 oscillates at a frequency corresponding to an on time of 14 μs.

In the case of J steel shown in Figure 6 (A), 266
It oscillates at KHz, and in the case of non-magnetic stainless steel shown in Figure 6 (B), it oscillates at 31 KHz and oscillates at 31 KHz, as shown in Figure 6 (C
) 24KH in the case of stainless steel with magnetism shown in
Oscillates at z.

When such a predetermined period T1 for load detection has elapsed, the inverting input terminal of the comparator circuit 1250 is set to the set value V1 in the next period T2, so that the value of the input current 1 inch from the AC power supply unit PW is a constant value. , for example, is controlled to 10A. Therefore, as shown in FIG. 7, in the case of non-magnetic stainless steel, the oscillation frequency of the transistor 113 is 31 KHz.
changes to 33.4 KHz, and in the case of magnetic stainless steel, the oscillation frequency of the transistor 113 changes from 24 KH2 to 22.7 KH2. As a result, as shown in Figure 7(B), in the case of non-magnetic stainless steel, oscillation occurs with a band width of 2.4 KHz every 20 msec, and in the case of magnetic stainless steel, the oscillation occurs at the 7th frequency.
As shown in Figure (C), it oscillates with a bandwidth of 1.3 KHz every 20a+ seconds.

Depending on the material of the object to be heated, such as a mouth, the transistor 11
The oscillation frequency of No. 3 changes depending on the band width, and the accompanying noise is generated over a wide band.

Furthermore, when cooking with a so-called 3H kabu in a conventional electromagnetic cooker, a new problem has arisen. That is, as shown in FIG. 8, the voltage across the resonant capacitor 109 does not completely fall to OV at the timing when the transistor 113 turns on, so that a short circuit current Is flows through the transistor 113, increasing power loss. This short circuit current 1s differs depending on the object to be heated, and in the case of a three-layer pot as shown in FIG. 9(B), compared with the case of steel as shown in FIG. 9(A),
A larger short-circuit current) S will flow.

Therefore, when the value of the input power setting value set by the input power setting circuit 133 is less than IKW, the on/off operation of the inverter circuit 103 is controlled with the value of 1 inch of input current from the AC power supply section set to 10A. In such a control system, when three subtones are used, the power loss becomes large, and the heat generation m accompanying this increases. Therefore, it is necessary to take measures to dissipate the heat generated by power loss, which poses the problem of increased costs.

The present invention has been made in view of the above problems, and even when the input power setting value is set to a low value, it reduces noise caused by fluctuations in the oscillation frequency of the switching means, and also reduces the amount of heat generated due to power loss. It is an object of the present invention to provide an electromagnetic cooker which reduces costs and further reduces costs.

[Structure of the Invention] (Means for Solving a Problem) In order to achieve the above object, the electromagnetic cooker provided by the present invention includes a switching means that repeats on-off operations, and a heating element that changes depending on the on time of the switching means. heating means for induction heating the object to be heated; input setting means for making input settings for heating the object; and switching means for performing on/off operations when the value of the input setting is below a predetermined value. A return heating period and a rest period for stopping the on/off operation of the switching means after the heating period has elapsed are set, and the ratio of the length of the heating period to the rest period is controlled according to the input setting value. The device has a C configuration including a first control means and a second control means for controlling the on-time of the switching means to a predetermined value when the value of the input setting is equal to or less than a predetermined value.

(Function) The electromagnetic cooker according to the present invention has a heating means that heats the object by generating an eddy current in the object by magnetic flux generated by electromagnetic induction, and this heating means is a switching means. The object to be heated is heated according to the on time.

It also has an input setting means for making input settings for heating the object to be heated, and when the value of the input setting is less than a predetermined value, the on-time of the switching means is controlled to a predetermined constant value. , a heating period in which the switching means repeats on-off operations, and a rest period in which the on-off operation of the switching means is suspended after the heating period has elapsed, and the ratio of the length of this heating period to the rest period is input and set. Control wJ according to the value.

Therefore, when the value of the input setting is below a predetermined value, the heating power of the object to be heated is controlled while the on-time of the switching means is adjusted to a constant value, so that the value of the input setting is set to a lower value. Even in this case, the oscillation frequency of the switching means at this time can be set to a constant value, and noise can be reduced. Furthermore, since the oscillation frequency of the switching means is set to a constant value, power loss can be reduced.

(Example) Examples according to the present invention will be described in detail below with reference to the drawings.

First, the configuration will be described with reference to FIG. 1. A commercial power supply PW, which is an AC power supply, is connected to a DC power supply circuit 1. DC power supply circuit 1 includes four bridge-connected diodes D.
1. D2. D3. D4 and a smoothing capacitor C1, it rectifies and smoothes the AC power from the commercial power supply PW, and converts it into predetermined DC power. This DC power supply circuit 1 is connected to an inverter circuit 3 and supplies predetermined DC power to the inverter circuit 3.

In the inverter circuit 3, a heating coil 7 and a resonance capacitor 9 are connected in series, and a transistor 13 is connected in parallel with the resonance capacitor 9. Furthermore, a freewheeling diode 11 is connected in parallel to the resonance capacitor 9.

The base of the transistor 13 is connected to the drive circuit 15, and the transistor 13 is turned on and off based on the signal from the drive circuit 15, so that the heating coil 7 and the resonance capacitor 9 are set in a series resonance state. The electromagnetic induction effect caused by the magnetic flux generated from the heating coil 7 generates eddy currents in the object to be heated, such as steel (not shown), thereby heating the object.

The pulse width modulation circuit 19 is connected to the drive circuit 15 and also to the voltage setting circuit 23. When the voltage Von for setting the on time from the voltage setting circuit 23 is inputted, the pulse width modulation circuit 19 corresponds to the voltage ■On. A pulse signal with a pulse width is output to the drive circuit 15. When the drive circuit 15 receives a pulse signal from one pulse width modulation circuit, it turns on the transistor 13 for a time corresponding to the pulse width of this pulse signal.

Therefore, the on-time of the transistor 13 changes depending on the value of the voltage Von from the voltage setting circuit 23. When the voltage Von is changed, the pulse width of the pulse signal from the pulse width modulation circuit 19 is changed, and by changing the ON time of the transistor 13, the heating output, that is, the heating power by the inverter circuit 3 is changed. . Further, the connection point between the heating coil 7 and the resonance capacitor 9 is feedback-connected to the feedback input terminal of the pulse width modulation circuit 19, so that the common ff1ffi pressure of the heating coil 7 and the capacitor 9 is applied to the pulse width modulation circuit 19. It will be done.

Next, the internal configuration of the voltage setting circuit 23 will be explained.

Resistors R1 and R2 are connected in series, a predetermined DC voltage VCC is applied to one end of the resistor R1, and one end of the resistor R2 is connected to ground. A capacitor C3 is connected in parallel with this resistor R2. The connection point between the resistors R1 and R2 is connected to the input terminal P1 of the pulse width modulation circuit 19. This input terminal P1 is connected to the collector of the transistor Tr1 via a resistor R3, and the base of the transistor Trl is connected to the output terminal of the comparison circuit 25 via a resistor R4. Therefore, these circuit sections operate based on the comparison output from the comparison circuit 25, and set the lζth voltage Von for adjusting the on-time of the transistor 13, which is a switching means. Further, the terminal P1 of the pulse width modulation circuit 19 is connected to the transistor Tr3 via a resistor R6.
It is also connected to the collector of the transistor Tr4 via a resistor R7. A predetermined DC voltage VCC is applied to the emitter of the transistor Tr3, and the emitter of the transistor Tr4 is connected to ground. Further, the base of the transistor Tr3 is connected to the on-time setting circuit 27 via a resistor R5. Similarly, the base of the transistor Tr4 is connected to the resistor R8.
It is connected to the on-time setting circuit 27 via. Therefore, the voltage setting circuit 23 controls the transistor Tr3 and the transistor Tr4 based on the signal from the on-time setting circuit 27.
is turned on to set the voltage Von to a predetermined value.

Next, the input current detection circuit 29 and its peripheral devices will be explained.

A current transformer CT is provided in the power line between the AC power supply PW and the DC power supply circuit 1, and outputs a detection signal having a value proportional to the input current fin from the AC power supply PW. The current transformer CT has four diodes D11. D12. D
13. It is connected to a rectifier circuit formed by bridge-connecting D14.

A resistor R11 and a capacitor C11 are connected in parallel to this rectifier circuit. Also, diode D12
The anodes of D14 and D14 are connected to a predetermined DC voltage Vcc via a resistor R9, and to the ground via a resistor R10. Furthermore, the diode D11. which is the output side of the input current detection circuit 29. The cathode of D13 is connected to each of the non-inverting input terminal of the comparison circuit 25 and the load detection circuit 43. This input current detection circuit 29 outputs a signal voltage vin corresponding to the input current lin from the AC FAp w to the non-inverting input terminal and negative part detection circuit 43 of the comparison circuit 25 .

Next, an input setting means for making input settings regarding heating power for heating an object to be heated (not shown) will be explained.

This input setting means includes an input power setting operation section 31 and an input power setting operation section 31.
It is composed of a power setting circuit 33 and an input current setting circuit 35. The input power setting operation unit 31 includes operation switches related to heating power for heating the object to be heated, and outputs information regarding the operation of the operation switches to the input power setting circuit 33. When the input power setting operation section 31 is operated, the input power setting circuit 33 outputs a signal 33a for starting load detection to the setting timer 41. In addition, the input current detection circuit 33 sets the heating power of If to C, for example, the input power value IKW, and the input power setting operation section 31
When the input power value operated by is below the reference value, that is, below IKW, and when the load is appropriate, a signal 33b is output to the inverter on/off signal generator 51. Further, the input power setting circuit 33 is configured so that the value of the input power operated by the input power setting operation section 31 is 1 as described above.
If it exceeds KW, a signal corresponding to this input power is output to the input current setting circuit 35. Input current setting circuit 35
compares the input power and the corresponding input setting value ■set to circuit 2
Output to the inverting input terminal of 5.

Therefore, the comparison circuit 25 receives the voltage ■in from the input current detection circuit 29 and the input setting @ set by the input setting means.
V set and operates the voltage setting circuit 23 according to the comparison result.

The setting timer 41 is a predetermined period T for performing load detection.
It is equipped with a timer for setting 1, and when the signal 33a from the input power setting circuit 33 is input, this period T1
The relevant timer information is output to the on-time setting circuit 27. This allows the on-time setting circuit 27 to control the transistor Tr.
3 and transistor Tr4 are operated only for a predetermined period T1 to set the voltage vOn to a predetermined value. The on-time of the transistor 13 is set to, for example, 10 μsec by the voltage VOn at this time. Further, the terminal P1 of the pulse width modulation circuit 19 is connected to the load detection circuit 43, and the voltage vOn that is the output of the voltage setting circuit 23 is applied to the load detection circuit 43. Further, the load detection circuit 43 is given the voltage Vin from the input current detection circuit 29, and the load detection circuit 43 receives the input voltage von and the voltage V.
The load condition is monitored by comparing the input current 1 inch with the corresponding signal voltage. For example, when steel is placed on the heating coil 7, an appropriate input current of 1 inch flows, so it is determined that the load is appropriate. Conversely, when there is no load or when the aluminum steel is exposed to the heating coil 7, the input current Jin becomes smaller.
It determines that the load is inappropriate and outputs a stop signal 43b to the inverter oscillation stop circuit 45. As a result, the inverter generation stop circuit 45 stops the operation of the pulse width modulation circuit 19 and prohibits the heating operation. Such a load detection operation is repeatedly performed based on the signal 43a output from the load detection circuit 43. For example, as shown in FIG. 3(D), when the inverter circuit 3 starts the oscillation operation, the load detection operation is repeated for a predetermined period T1.

Inverter on/off signal generator 1 is input power setting circuit 3
3, and when a signal 33b from this input power setting circuit 33 is input, the oscillation cycle of the inverter circuit 3 as shown in FIG. 3(0) is set. That is, a heating period To is set in which the transistor 13, which is a switching means, repeats on-off operations, and a rest period Toff is set in order to suspend the on-off operation of the transistor 13 after the heating period Ton has elapsed. In addition, the inverter on/off signal generator 51 inputs a signal 33b(7)Iif which is an input setting value of the ratio of the length of the heating period Ton to the rest period ToH.
control according to l. Inverter on/off signal generator 5
1 is an on-time setting circuit 27 and an inverter on-off control υ
The on-time setting circuit 2 is connected to each of the D circuits 53 and transmits a signal 51a related to the oscillation period of the inverter circuit.
7 and the inverter on/off control circuit 53, respectively. The inverter on/off control circuit 53 is connected to the pulse width modulation circuit 19, and when the signal 51a from the inverter on/off signal generator 51 is input, this signal 5
1a, one pulse width modulation circuit is controlled to control the oscillation period of the inverter circuit 3. Further, when the on-time setting circuit 27 receives the signal 51a from the inverter on-off signal generator 51, the transistor Tr3 and the transistor T
Run r4.

That is, as shown in FIG. 3(D), the on-time setting circuit 2
7 sets the voltage Von to a predetermined value for a further predetermined period T2 after the predetermined period T1 has elapsed. As a result, the on-time of the transistor 13 is set to a constant value, for example, 14 μsec, during the heating period Ton.

Next, the action will be explained.

An explanation will be given of the operation when a load such as steel is placed on the heating coil 7, and the input electric power as the heating power for heating the iron chain is set to a value exceeding, for example, IKW.

First, a load detection operation, which will be described later, is performed based on a signal 33a from the input power setting circuit 33, and the input current setting circuit 35 sets an input setting value V se corresponding to the input power.
t is output to the inverting input terminal of the comparison circuit 25. As a result, the comparator circuit 25 operates the voltage setting circuit 23 so that the voltage
Controls the value of On.

The pulse width of the pulse signal from the pulse width modulation circuit 19 changes according to the value of this voltage VOn, and the on-time of the transistor 13 changes. That is, the pulse width modulation circuit 1 in which the drive circuit 15 outputs C according to the input setting value v set
By turning on and off the transistor 13 based on the pulse signal from the heating coil 7 and the co-composition capacitor 9, the heating coil 7 and the co-composition capacitor 9 are set in a series resonant state. In such a resonant state, when the transistor 13 is turned on, the
) flows, and when the transistor 13 is turned off, a collector voltage ■Ce as shown in FIG. 2(B) is applied.

As described above, when the heating coil 7 and the co-forming capacitor 9 are set in a series resonant state, an eddy current is generated in the bottom of the pot (not shown) due to the electromagnetic induction effect due to the magnetic flux generated from the heating coil 7, which heats the steel. .

Next, the operation when the input power setting operation section 31 is operated to set the input power to IKW or less when performing heat retention or the like will be described.

First, the im number 33a output from the input power setting circuit 33
Based on -Ut4 load detection operation is started. Specifically, the setting timer 41 operates the on-time setting circuit 27 only for a predetermined period T1 based on the signal 33a.

As a result, the on-time setting circuit 27 turns on the transistor Tr3.
Then, the transistor Tr4 is turned on to set the voltage von to a predetermined value.

As a result, the on-time of the transistor 13 is set to a predetermined value, for example, 14 μsec. At this time, the load detection circuit 43
Then, compare the value of the voltage On from the voltage setting circuit 23 and the voltage Vin from the input current detection circuit 29 to determine whether the load placed on the heating coil 7 is appropriate or inappropriate. Determine.

On the other hand, the inverter on/off signal generator 51 sets the generation cycle of the inverter circuit 3 as shown in FIG. 3(D) based on the signal 33b from the input power setting circuit 33. If the aforementioned load detection circuit 43 determines that the load is inappropriate, for example, it outputs a signal 43a to the setting timer 41 and a signal 43c to the inverter on/off signal generator 51 after a predetermined period of time has elapsed. As a result, the load detection operation described above is repeatedly executed. Further, when the load detection circuit 43 determines that the load is appropriate, the heating operation is continued. That is, the inverter on/off signal generator 51 transmits the signal 51a to the on-time setting circuit 27.
Output to. As a result, the on-time setting circuit 27 sets the predetermined period T for performing load detection as shown in FIG.
Transistor T only for a predetermined period T2 after 1 has elapsed.
The voltage (on) is set to a predetermined value by operating r3 and the transistor Tr4. As a result, the on-time of the transistor 13 is set to 14 μsec. Therefore, the heating period Ton
During the period , the on-time of the transistor 13 is set to a constant value, that is, 14 microseconds, so the generation frequency of the transistor 13 is set to a constant value.

Such a load detection operation and subsequent heating operation are repeatedly performed at predetermined intervals. In other words, Figure 3 (D)
As shown in , during the heating period Ton, the predetermined load detection period T
In step 1, the load detection operation is performed with the on-time of the transistor 13 set to a predetermined value. Further, during the predetermined period T2 following this load detection period T1, the on-time of the transistor 13 is kept for a predetermined time, that is, 1
Execute the heating operation with the setting set to 4 msec. When such a predetermined heating period Ton has elapsed, a resting period Tor
During the period r, the operation of the inverter circuit 3 is stopped and heating operation is prohibited. Thereafter, the inverter circuit 3 is similarly operated at predetermined intervals to heat the object to be heated. Therefore, as shown in FIG. 3A, during the heating period TOn, the transistor 13 oscillates 1J at a frequency corresponding to an on time of 14 μsec, that is, 26.6 KHz.

Next, a non-magnetic stainless steel is placed on the heating coil 7, and the input power setting operation section 31 is operated to input 1 degree of heating power to IKW to heat the non-magnetic stainless steel. The operation when set to the following values will be explained.

Similarly to the above, the inverter on/off signal generator 51 generates the third signal based on the signal 33b from the input power setting circuit 33.
The oscillation cycle of the inverter circuit 3 as shown in FIG. 3(D) is set. During the heating period 1"on, there is a load detection period T1 followed by a predetermined period T2 as described above.
In the period T1, the on time of the transistor 13 is set to 14 μs, and in the period T2, the on time of the transistor 13 is also set to 14 μs.

As a result, as shown in FIG. 3B, during the heating period Ton, the transistor 13 performs an oscillation operation at a constant frequency corresponding to the on-time of 14 μsec, that is, 31KH2.

Similarly, when stainless steel that requires magnetism is placed on the heating coil 7 and the input power is set to a value less than IKW, the heating period Ton as shown in Fig. 3(C). In this case, the on time of transistor 13 is 14μ
Since it is set to seconds, the Laran jitter 1 performs oscillation operation at a constant frequency of 24KH7'C.

Next, the case of heating using three-layer steel will be explained.

That is, while placing the three-layer steel on the heating coil 7,
When the input power setting operation section 31 is operated to set the input power as a heating power for heating this three-layer steel to IKWk, the transistor 13 is turned on during the heating period Ton as described above. Since the on-time of the transistor 13 is set to 14 μsec, the transistor 13 performs an oscillation operation at a constant frequency.

At this time, the short circuit current flowing through the collector of the transistor is approximately 6
6A, which can be reduced to the same short-circuit current value as in the case of steel. Therefore, power loss due to this short circuit current can be significantly reduced.

Next, another embodiment of the present invention will be described with reference to FIG.

In this embodiment, the heating coil 7 and the capacitor 10 of the inverter circuit 3 are connected in parallel, and the heating coil 7 and the capacitor 10 are set to a parallel resonance state by the on/off operation of the transistor 13, and the heating coil 7 and the capacitor 10 are connected in parallel. It is characterized in that the object to be heated is heated by generating an eddy current through the electromagnetic induction effect of the generated magnetic flux.

In the embodiment shown in FIG. 4, similarly to the embodiment shown in FIG. Since the on-time of the transistor 13 forming the inverter circuit 3 is set to a predetermined constant value, the transistor 13 performs an oscillation operation at a constant frequency. Therefore, even when the input power is set to a low value, the generation of noise accompanying this can be reduced.

[Effects of the Invention] As explained above, according to the present invention, when the value of the input setting for heating the object to be heated is below the predetermined value, the ON time of the switching means is set to the predetermined l(I). Since the heating operation is controlled in a state where the heating operation is adjusted to the desired temperature, the generation of noise can be significantly reduced.

Further, the short I8 current of the switching means can be suppressed to a low level, and the power loss accompanying this can be significantly reduced. Moreover, since the power loss accompanying this can be significantly reduced, the photothermal structure j5 can be simplified and costs can be reduced.

[Brief explanation of the drawing]

Fig. 1 is a circuit diagram showing an embodiment of the present invention, Fig. 2 is a signal waveform diagram of Fig. 1, and Fig. 3 shows the oscillation frequency of the switching means when the embodiment of Fig. 1 is used. Characteristic diagrams shown for each material of the heated object, FIG. 4 is a circuit diagram showing another embodiment of the present invention, FIG. 5 is a circuit diagram showing a conventional example, and FIG.
The figure shows the frequency characteristics of the conventional switching means against the ON time for each material of the heated object. Figure 7 shows the frequency characteristics of the conventional switching means for each material of the heated object. FIG. 8 is an explanatory diagram showing the short-circuit current flowing through the transistor of the conventional example, and FIG. 9 is a characteristic diagram showing the short-circuit current flowing through the collector of the transistor with respect to the input power of the conventional example. 3... Inverter circuit 7... Heating coil 13... Transistor 23... Voltage setting circuit 27... On time setting circuit 31... Input power setting operation section 33... Input power setting circuit 35 ...Input current setting circuit

Claims (1)

[Scope of Claims] Switching means for repeating on-off operations; heating means for inductively heating a heated object according to the ON time of the switching means; and input settings for making input settings for heating the heated object. means; a heating period in which the switching means repeats on-off operations when the input setting value is below a predetermined value;
a first control means that sets a pause period in which the on/off operation of the switching means is paused after the heating period elapses, and controls a ratio of the length of the heating period and the pause period in accordance with an input setting value; An electromagnetic cooking device comprising: second control means for controlling the on-time of the switching means to a predetermined value when the value of the input setting is equal to or less than a predetermined value.