JPH0732069B2 - Induction heating cooker - Google Patents

Description

TECHNICAL FIELD The present invention relates to an induction heating cooker used in a general household.

2. Description of the Related Art The inventors have already proposed the induction heating cooker shown in FIG. In FIG. 3, the power supply circuit 1 is composed of a DC power supply 2 and a current limiting coil 3, and a midpoint terminal of the heating coil 4 is connected to one terminal of the power supply circuit 1. A resonance capacitor 5 is connected to both ends of the heating coil 4, and switching elements 6 and 7 each composed of a transistor and a reverse conducting diode are connected in series. The other end of the power supply circuit 1 is connected to the switching elements 6 and 7. The control circuit 8 compares the detection signal of the input power detection means 10 provided between the power supply circuit 1 and the switching elements 6 and 7 with the set value of the input power setting means 9 to control the oscillation frequency of the oscillation circuit 11 to control the switching element 6 , 7 is on / off controlled. 12 is a load pot.

Next, the operation of the induction heating cooker having the above configuration will be described with reference to FIG. FIG. 4 shows the terminal voltage V ₁ and the terminal current i ₁ of the switching element 6 of the induction heating cooker shown in FIG.
5 is a waveform diagram of a terminal voltage V ₂ and a terminal current i ₂ of the switching element 7. FIG.

When 0 ≦ t <t ₁ , the switching element 6 is off and the switching element 7 is on. During this period, V ₁ is generated by the resonance of the heating coil 4 and the resonance capacitor 5,
= T ₁ , V ₁ = 0 and the capacitor voltage V _c = 0. V _c =
When it becomes O, the reverse conducting diode of the switching element 6 is turned on, and 0> t ₁ . The control circuit 8 turns off the switching element 7 at t ₂ which is Delta] t _a elapsed from t _1. Then, this time a voltage due to resonance of the heating coil 4 and the resonance capacitor 5 is generated in the V _2, after V ₂ = 0 becomes Delta] t _b elapsed in t _3, the control circuit 8 turns off the switching element 6 in t _4.

By repeating the above operation, a high frequency current is supplied to the heating coil 4 and the pot 12 is induction-heated. During the period of Δt _a and Δt _b , both the switching element 6 and the switching element 7 are in the conductive state. Increasing Δt _a and Δt _b increases the input current I _in , increases the heating power, and lowers the operating frequency.

The control circuit 8 controls the oscillating frequency of the oscillating circuit 11 so that the output of the input power detecting means 10 constituted by a resistor or the like becomes equal to the value set by the input power setting means 9, and controls the heating power. .

FIG. 6 is a circuit diagram of another induction heating cooker proposed by the inventors.

In FIG. 6, 21 is a power supply circuit composed of a DC power supply 22 and a current limiting coil 23, 24 is a heating coil in which one terminal of the power supply circuit 21 is connected to a midpoint terminal, 25 is a resonance capacitor, and 26 and 27 are either Is a switching element composed of a transistor and a reverse blocking diode, 28 is a control circuit, and 29 is an input power setting means. The control circuit 28 includes an input power detection means 30 and an oscillation circuit 31.
Have. 32 is a load pot.

Next, the operation of the induction heating cooker shown in FIG. 6 will be described with reference to FIG. FIG. 7 is a waveform diagram of the terminal voltage V ₁ and current i ₁ of the switching element 26 and the terminal voltage V ₂ and current i ₂ of the switching element 27 of the induction heating cooker shown in FIG.

When 0 ≦ t <t ₁ , the switching element 26 is off and the switching element 27 is on. During this period, V ₁ is generated by the resonance of the heating coil 24 and the resonance capacitor 25, and t
= T ₁ , V ₁ = 0 and the capacitor voltage V _c = 0. V _c =
When it becomes O, V ₁ <0 due to the action of the reverse blocking diode of the switching element 26. Here, the control circuit 28 turns on the transistor of the switching element 26 turns off the switching element 27 at t ₂ has elapsed Delta] t _a from t _1.

Then, the switching element 26 is turned on, and the voltage due to the resonance of the heating coil 24 and the resonance capacitor 25 is V ₂
Occurs and V ₂ = 0 at t ₃ . Here the control circuit 28
Turns on the transistor of the switching element 27, and turns off the switching element 26 at t _{4 when} Δt _{b has} elapsed from t ₃ .

By repeating the above operation, a high frequency current is supplied to the heating coil 24 and the pot 32 is induction-heated. Increasing Δt _a and Δt _b increases the input current I _in , increases the heating power, and lowers the operating frequency.

The control circuit 28 controls the oscillating frequency of the oscillating circuit 31 so that the output of the input power detecting means 30 constituted by a resistor or the like becomes equal to the set value from the input power setting means 29, and controls the heating power. is there.

Problems to be Solved by the Invention FIG. 5 shows the relationship between the operating frequency and the input power P _in in the induction heating cooker shown in FIG. In FIG. 5, ₀ is
When operated at this frequency with the resonance frequency of the heating coil 4 and the resonance capacitor 5, Δt _a = 0 and Δt _b = 0. The input power P _in is in the range of < ₀ , that is, Δt _a ≧ 0, Δt _b
Although decreases with increasing in the range of ≧ 0, When to operate in the range _{of> 0,} Δt a> ₀ or Delta] t
_b <0. For example Delta] t a _{<If 0,} V _1> must turn on the switching element 6 is 0, the charge of the resonance capacitor 5, through the transistor of the switching element 6, the reverse conducting diode of the switching element 7 Since a short circuit causes a large current to flow, the power loss of the switching element 7 may increase and the temperature may rise abnormally or be destroyed. Therefore, the operation of < ₀ is difficult, and the input power P _in cannot be reduced to P _{in min} or less shown _in FIG.

Next, FIG. 8 shows the relationship between the operating frequency and the input electric power P _in in the induction heating cooker shown in FIG. In Figure 8
₀ is the resonance frequency of the heating coil 24 and the resonance capacitor 25 as in the case of the previous side. The input power P _in decreases with increasing in the range < ₀ . When operated in the range of> ₀ , the short-circuit current of the resonant capacitor does not flow to the switching element as in the previous example, but P _in increases again with the increase as shown in FIG. ,
After all, there is a problem in use that the control below P _{in min} cannot be performed and cooking with a low heat as in the above example cannot be performed.

In view of the above problems, the present invention provides an induction heating cooker that enables a low heat of P _{in min} or less and has high cooking performance.

Means for Solving the Problems In order to achieve this object, the induction heating cooker of the present invention comprises:
A power supply circuit configured by connecting a direct current power supply and a current limiting coil in series, a heating coil having one terminal or a midpoint terminal connected to one terminal of the power supply circuit, and a resonance connected between both terminals of the heating coil. The control circuit includes a capacitor, two switching elements respectively connected to the other terminal of the power supply circuit from both ends of the heating coil, input power setting means, and a control circuit for driving the switching element. When the set value of the input power setting means is a certain value or more, the drive frequency of the switching element is changed according to the set value, and when the set value is a certain value or less, heating is performed according to the set value. The configuration is such that the ratio of time to stop time is changed.

Action With this configuration, the induction heating cooker of the present invention can be made to have a lower heat than when operating at the resonance frequency. Therefore, an induction heating cooker with high cooking performance can be provided.

Example An example of the present invention will be described below with reference to the drawings. FIG. 1 is a circuit diagram of an induction heating cooker according to an embodiment of the present invention. In FIG. 1, 41 is a power supply circuit composed of a DC power supply 42 and a current limiting coil 43, 44 is a heating coil in which one terminal of the power supply circuit 41 is connected to a midpoint terminal, 45 is a resonance capacitor, and 46 and 47 are either Is a switching element composed of a transistor and a reverse conducting diode, 48 is a control circuit, 49
Is an input power setting means. The control circuit 48 is composed of an input power detection means 50, an oscillation circuit 51, a duty control means 52, a relay 53, a DC power supply 54 that outputs a voltage V _Z , and a comparator 55. The input power setting means 49 is composed of a DC power supply 56 and a variable resistor 57. 60 is a load pot.

The oscillating circuit 51 has two input terminals A and B. When the B terminal is high, it stops oscillating, and only when it is low, it oscillates. In addition, Δt _a depends on the voltage V _A applied to the A terminal.
And Δt _b are changed. That Delta] t _a = 0 in the _V A = 0, Delta] t _b = 0, a _{= 0,} an operation of increasing Delta] t _a, Delta] t _b in accordance with _{V A} increases.

The duty control means 52 is an oscillator that oscillates at a predetermined frequency, and the time average value of the output V ₁ of the input power detection means 50.
And _I, the operation of controlling the time ratio of the output of the high and row in accordance with the difference between the output V _R of the input power setting unit 49 performs. That is, when _I > V _R , the output of the duty control means 52 shortens the low time, and when _I <V _{1 R} , the low time is lengthened.

The operation of the above configuration will be described. The power supply circuit 41, the heating coil 44, the resonance capacitor 45, the switching element 46, and the switching element 47 operate in the same manner as the technique of FIG.

V _R> in the case of V _Z is next coil voltage is 0 output is the row relay 53 of the comparator 55, the input terminal of the oscillation circuit 51
A and B are connected to A ₁ and B ₁ , respectively. Since the B terminal is low, the oscillation circuit 51 is always in an oscillating state and the operating frequency is controlled so that V _R = V _I.

In the case of V R _{<V Z} is the output of the comparator 55 is a voltage applied to the coil of the relay 53 becomes high, A, B are connected to A _2, B _2, respectively. Since the A terminal is low, the oscillation frequency becomes ₀ , and the operation of the duty control means 52 controls the ratio of the heating time to the stop time so that V _R = _I.

Therefore, by setting the value of V _Z to V _I when operated at ₀ , the operating frequency and the average input power with respect to the input power set value are set. The relationship is as shown in FIGS. As is clear from FIG. 2b, the induction heating cooker in this embodiment is
It is possible to obtain an average input power that is even lower than the input power at _zero .

In the present embodiment, the switching between the duty control and the control based on the operating frequency is performed by the DC power supply 54, the comparator 55, and the relay 53. For example, it is detected that the voltage at the A terminal is below a certain value. It is also possible to switch to duty control. In that case, even if the load pot changes, the average input power Can be controlled as in FIG. 2b.

Further, although the switching element of the reverse conduction type is used in the present embodiment, the average input power is also used when the switching element of the reverse blocking type as in the technique of FIG. 6 is used. Can be controlled below the input power at _zero .

Also, the same effect can be obtained when the present invention is applied to a heating coil which has no middle point terminal and one terminal of the heating coil is connected to one terminal of the power supply circuit.

EFFECTS OF THE INVENTION As is clear from the above embodiments, in the induction heating cooker of the present invention, in particular, when the set value of the input power setting means is a certain value or more, the two switching elements are operated according to the set value. When the drive frequency is changed and the set value is equal to or less than a certain value, the ratio of the heating time and the stop time is changed according to the set value, so that the average input power is input at the resonance frequency of the heating coil and the resonance capacitor. Since it can be made smaller than the electric power, there is an effect that a low heat is possible and cooking performance is improved.

[Brief description of drawings]

FIG. 1 is a circuit diagram of an induction heating cooker according to an embodiment of the present invention, FIG. 2a is a diagram showing a relationship between an input power set value and an operating frequency of the induction heating cooker of FIG. 1, and FIG. 2b. Is a diagram showing the relationship between the input power set value and the average input power, FIG. 3 is a circuit diagram of an induction heating cooker proposed by the inventors, and FIG. 4 is an operation waveform diagram of the technique in FIG. FIG. 5 is a diagram showing the relationship between the operating frequency and the input power of the technique in FIG. 3, FIG. 6 is a circuit diagram of another induction heating cooker proposed by the inventors, and FIG. 7 is a diagram in FIG. FIG. 8 is a diagram showing the operation waveform of the technique, and FIG. 8 is a diagram showing the relationship between the operating frequency and the input power of the technique in FIG. 42 …… DC power supply, 43 …… Current limiting coil, 41 …… Power supply circuit,
44 ... Heating coil, 45 ... Resonant capacitor, 46 ... Switching element, 47 ... Switching element, 49 ... Input power setting means, 48 ... Control circuit.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Hideyuki Konan 1006 Kadoma, Kadoma City, Osaka Prefecture Matsushita Electric Industrial Co., Ltd. (56) References JP-A-61-193395 (JP, A)

Claims (1)

[Claims] 1. A power supply circuit configured by connecting a direct current power supply and a current limiting coil in series, a heating coil having one terminal or a midpoint terminal connected to one terminal of the power supply circuit, and both terminals of the heating coil. A resonance capacitor connected in between, two switching elements respectively connected to the other terminal of the power supply circuit from both ends of the heating coil, input power setting means, and a control circuit for driving the switching element,
The control circuit changes the drive frequency of the switching element according to the set value when the set value of the input power setting means is a certain value or more, and the setting when the set value is a certain value or less. An induction heating cooker that changes the ratio of heating time to stop time according to the value.