JPS6044793B2 - induction heating device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an induction heating device used, for example, in a cooking appliance.

In general, an induction heating device has a basic circuit configuration as shown in FIG.

That is, an inverter circuit 1 is provided, and an output coil 2 for induction heating and a capacitor 3 are connected to the output terminal of the inverter circuit 1.
A series circuit is connected with the output coil 2 to cause a heat-generating object 4 such as a magnetic pot to generate heat. The inverter circuit 1 has a smoothing capacitor 7 connected to an AC power source 5 via a full-wave rectifier bridge circuit 6, and a pair of power transistors 8,
9 are connected in series, and a high frequency oscillation circuit 10 is provided on the other hand, and the oscillation output of the oscillation circuit 10 is transmitted to the drive circuit 1.
1 to each of the transistors 8 and 9, and the transistors 8 and 9 are alternately operated at high frequency. By the way, in the circuit described above, the output coil 2 and the heating element 4 can be considered as a type of transformer, in which case the output coil 2 corresponds to the primary coil, and the heating element 4 corresponds to the iron core and the secondary coil. Therefore, the load circuit of the above-mentioned circuit is represented as shown in FIG.

In the figure, 2a is the leakage reactance of the output coil 2, and 4a is the leakage reactance of the output coil 2.
is the leakage reactance of the heating element 4, 4b is the equivalent resistance of the heating element 4, VO is the output voltage of the inverter circuit 1, and IL is the load current. Further, if the circuit shown in FIG. 2 described above is shown as an equivalent circuit, it becomes as shown in FIG. 3. In the figure, x is the equivalent inductive reactance of the entire circuit including the excitation impedance of the output coil 2, Xc is the capacitive reactance of the capacitor 3, and R is the equivalent resistance of the entire circuit. So, in this equivalent circuit, if we set X=XO, we get a rectangular wave voltage. , load current 1L and voltage across the terminals of capacitor 3. The relationship is as shown in Figure 4, where the load current 1L is a rectangular wave voltage.
It becomes a nearly sinusoidal wave that is in phase with . Therefore, at the moment when each transistor 8, 9 in FIG. 1 performs a switching operation, that is, at time Tl, t3 in FIG. 4, IL becomes approximately zero, so that the collector-emitter voltage VcE (= VO) and collector current 1c (=IL
) is as shown in FIG. 5, and there is almost no loss during the switching operation of each transistor 8, 9. That is, the maximum. Efficiency will be gained. Also, in this circuit, if XL half Xc, for example
If the circuit is an inductive load as XO.

．． Due to the phase shift of 151L (the phase of IL is delayed), a loss occurs during the switching operation of the transistor. In addition to this, a spike voltage induced by the sudden change in current is applied to the transistor. For example, X
If O〉X and the circuit is a capacitive load. (51L
Due to the phase shift (the phase of IL advances), the current at the time when each transistor 8, 9 is turned on increases rapidly, causing a large loss during the switching operation of the transistor. By the way, in the above-mentioned FIG. 3, the capacitance of the capacitor 3 is expressed as the inductance of the equivalent reactance of C1 as L, . If the frequency of VO is f, then Xc and XL can be expressed by the following formula.

Therefore, when XO = x, f = stutter → te, and it is possible to tune to the fundamental wave of o.

Therefore, if the equivalent reactance changes due to a difference in the material or size of the heating element 4 or a shift in the relative position between the heating element 4 and the output coil 2, it is necessary to adjust the frequency of o so that it can be tuned. If the frequency is controlled to be optimal, the heating element 4 can be operated to generate heat with good efficiency at all times. In this way, V for the equivalent reactance change of the circuit. Conventionally, an auto-tuning circuit has been known as a circuit that controls the frequency of the motor so that it can be synchronized, and this auto-tuning circuit is attached to an induction heating device. However, in addition to the above-mentioned problems, the induction heating apparatus has the following problems.

In other words, when a magnetic material with an area much smaller than the area of the output coil 2, such as a spoon or a knife, is provided as a heat generating object, or when the heat generating object is removed, the equivalent resistance R becomes small and the inverter There is a problem that the input to the circuit increases and the load current 1L becomes excessive. In addition, if a heating element made of copper or aluminum, a plywood of copper or thermi and a magnetic material, or a material with a thick plating applied to the magnetic material is mistakenly used, the equivalent resistance R will be small. The input of the inverter circuit increases and the load current becomes 1L.
There is a problem that the amount of For this reason, for example, it is possible to install a current detection circuit to detect the load current, but in general, induction heating equipment loses synchronization and generates current spikes during the transition period when the inverter circuit starts oscillating. However, if the current detection circuit operates, the device becomes completely unusable.On the other hand, if the operating level of the current detection circuit is increased, the purpose of providing the current detection circuit is completely lost. be.

Furthermore, as mentioned above, during the transition period when the inverter circuit starts oscillating, current spikes and voltage spikes caused by out-of-synchronization are applied to the power transistors of the inverter circuit, which shortens the life of the inverter circuit. There is. Furthermore, during the transition period when the inverter circuit starts oscillating, the magnetic flux of the output coil increases rapidly, so there is a problem in that abnormal noise is generated due to the magnetic attraction force acting from the output coil on the heating element. This invention was devised to solve these problems, and its purpose is to minimize current and voltage spikes when the inverter circuit starts oscillating, thereby extending the life of the inverter circuit. It is an object of the present invention to provide an induction heating device that can increase the length of time and is free from the possibility of generating abnormal noise when an inverter circuit starts oscillating.

Another object of the present invention is to provide an induction heating device that can detect a change in impedance of an inverter circuit when the inverter circuit starts oscillating.

Another object of the present invention is to provide an induction heating device that can detect a load current flowing through an output coil circuit for induction heating. DESCRIPTION OF THE PREFERRED EMBODIMENTS A high frequency induction heating range according to an embodiment of the present invention will be described below with reference to the drawings.

First, the schematic structure of the apparatus will be described with reference to FIG.

Inside the device main body 101 is a pair of induction heating output coils 10.
2, 103 are arranged at a predetermined interval, and a magnetic pot 104 is placed on each output coil 102, 103 as a heating element.
, 105 are placed respectively. Magnetic pots 104 and 1 are provided at the center of each of the output coils 102 and 103, respectively.
First and second load detectors 106 and 107, such as proximity switches, are attached to detect whether or not 05 is placed. Next, the circuit configuration of the device will be described with reference to FIG.

This device drives two output coils in a time-sharing manner using one inverter circuit, and is provided with an inverter circuit 108, and a capacitor 109 and a normally open contact 110a of a first relay 110 are connected to the output terminal of the inverter circuit 108. The output coil 102 is connected in series, and the output coil 103 is connected in series with the capacitor 109 and the normally closed contact 110b of the first relay 110. The inverter circuit 108 has an AC current of 1
11, the first contact switch 112 of the second relay 112
The input side of a full-wave rectifier bridge circuit 113 is connected through the normally closed side of a, the smoothing capacitor 114 is connected to the output side of the bridge circuit 113, and the smoothing capacitor 1
14, a pair of NPN power transistors 115, 11
6 parallel circuits and a pair of NPN power transistors 11
A series circuit with 7,118 parallel circuits is connected. Note that each of the above transistors 115, 116, 117, 11
The emitter circuit of No. 8 has resistors 119, 120, and 120, respectively.
121 and 122 are inserted in series. A high frequency oscillation circuit 123 is provided, and a high frequency oscillation output generated by the oscillation circuit 123 is alternately supplied to the pair of transistors 115, 116 and the pair of transistors 117, 118 by an inverter drive circuit 124. . This inverter circuit 108 connects the aforementioned output coil circuit to a parallel circuit of a pair of transistors 117 and 118. Note that the inverter circuit 108 includes a pair of transistors 115, 116 and 117, 11.
Diodes 125 and 126 are connected in parallel to each of the 8 parallel circuits. A low voltage drive circuit 127 is interposed in the power supply side circuit of the inverter circuit 108.

This low voltage drive circuit 127 includes a pair of resistors 128 and 129.
The resistor 128 is connected to the second relay 1.
The resistor 129 is connected in parallel to the normally closed side of the 12 first contact switches 112a, and the resistor 129 is connected to the normally closed side of the 12 first contact switches 112a.
13 through the normally open side of the second contact switch 112b of the second relay 112. An auto-tuning circuit 130 is connected between the output section of the inverter circuit 108 and the high-frequency oscillation circuit 123.

This auto-tuning circuit 130 is connected to the output coil 1.
02, 103, the high frequency oscillation circuit 12 according to the reactance change of the output coil circuit so that the output coil circuit formed by the capacitor 109 can be tuned.
For example, a pair of transistors 117 and 11 in the inverter circuit 108
a phase difference detection circuit 131 that detects the phase difference between the voltage 9 across the parallel circuit of 8 and the voltage across the capacitor 109 of the output coil circuit; and the output of this detection circuit is amplified and supplied to the high frequency oscillation circuit 123. A differential amplifier circuit 132 is formed. In other words, the output frequency of the inverter circuit 108 is variably controlled according to the load condition to maintain the resonant state of the output coil circuit. On the other hand, regarding the control circuit such as the inverter circuit, 1 in the figure
33 is a low frequency oscillation circuit, and this oscillation circuit 133 has a reference period T.

A low frequency signal ((FIG. 8a)) with a pulse width Tp generated at The device sends out an output of "1" for the required time in response to the drop ((b in Figure 8). The output sending time (period in charge of the first coil) of "1" can be arbitrarily set using a variable resistor 135. It is a type of monostable multivibrator.This first timer circuit 13
The 46r2 output of No. 4 is input to one input terminal of the first AND gate circuit 137 for two inputs.
Further, the "r" output of the first timer circuit 134 is input to a first relay drive circuit 136.
This relay drive circuit 136 is connected to the first timer circuit 13.
When the output from 4 to 1 is input, the first relay 11
0 coil 110c is energized. The output of the first load detector 106 (c in FIG. 8) is input to the other input terminal of the first AND gate circuit 137. Therefore, the output of the first AND gate circuit 137 is such that when the output of the first timer circuit 134 is ゜゜1゛ and the output of the first load detector 106 is ゛1゛, the output is ``゜1゛.'' (d in Figure 8), this "1" output is the second ζ-AND gate circuit 1 for two inputs.
38 and the first monostable multivibrator 139 . The first monostable multivibrator 139 normally has an output of ゜゜1゛, and responds to the rise of the output of the first timer circuit 134 for a short period of time (first relay 110 and Enough time for the contacts of relay 112 of No. 2 to switch.)
It causes the output to fall to the “0” state ((8th
e in the figure, its output is the second AND gate circuit 13
8 is input to the other input terminal of 4. The second AND gate circuit 138 is configured such that the output of the first AND gate circuit 137 is “゜1゛” and the first monostable multivibrator 1
39 When the output is ゜゜1゛, the output becomes ゜゜1゛ ((8th
f)) in the figure, its "゜1" output is inputted to one input terminal of the third AND gate circuit 141 for two inputs via one input terminal of the first OR gate circuit 140 for two inputs. The third AND gate circuit 141 is configured such that a memory circuit output, which will be described later, is input to the other input terminal.Furthermore, the output of the first timer circuit 134 is input to the second timer circuit 142. I'm letting you do it.

This second timer circuit 142 is connected to the first timer circuit 1.
3) It sends out ゜゜1゛ output for the required time in response to the fall of the 4 outputs ((g in Figure 8)), and the ``゜1゛ output sending time (the period in charge of the second coil) is variable. resistance 143
It is a type of monostable multivibrator, and can be set arbitrarily. - The ゜゜1゛ output of the second timer circuit 142 is input to one input terminal of a fourth AND gate circuit 144 for two inputs. The other input terminal of this fourth AND gate circuit 144 is connected to the output of the second load detector 107 ((h in FIG. 8).
] is now entered. Therefore, the output of the fourth AND gate circuit 144 is transmitted to the second timer circuit 142.
When the output is ゜゜1゛ and the output of the second load detector 107 is ゜゜1゛, the output is ゜゜1゛ ((h in Fig. 8), this ゜゜1゛ output has two inputs. The second monostable multivibrator 146 is inputted to one input terminal of the fifth AND gate circuit 145 for the second monostable multivibrator 146.The second monostable multivibrator 146 is similar to the first monostable multivibrator 139 described above. Usually the output is ゛゜1
In response to the rise of the output of the second timer circuit 142, the output is activated for a required short period of time (sufficient time for the contacts of the first relay 110 and the second relay 112 to switch). The output is input to the other input terminal of the fifth AND gate circuit 145.The fifth AND gate circuit 145 Fourth AND gate circuit 14
4 output is "゜1゛" and the second monostable multivibrator 146 output is "1", the output becomes ゜゜1゛ ((
k in FIG. 8, its "1" output is inputted to one input terminal of the third AND gate circuit 141 via the other input terminal of the first OR gate circuit 140. The output of the first OR gate circuit 140 is the logical sum of the outputs of the second and fifth AND gate circuits 138 and 145.
Figure 1)). Further, the output of the first AND gate circuit 137 is input to a third monostable multivibrator 147, and the output of the fourth AND gate circuit 144 is input to a fourth monostable multivibrator 148. The third monostable multivibrator 147 responds to the rise of the output of the first AND gate circuit 137 and causes its output to rise to the "1" state for a required period of time (m in FIG. 8). The fourth monostable multivibrator 148 responds to the rise of the output of the second AND gate circuit 144 and causes its output to rise to the "1" state for a required period of time (n in FIG. 8). Said third
, the fourth monostable multivibrator 147, 148 outputs are input to a second OR gate circuit 149. This second
The output of the output circuit 149 (o in FIG. 8) is input to the second relay drive circuit 150. This second relay drive circuit 150 receives the ゜゜1゛ output from the second OR gate circuit 149 and energizes the coil 112c of the second relay 112. Further, the output of the second OR gate circuit 149 is input to a reset trigger circuit 151. This reset trigger circuit 15
Reference numeral 1 is a differential circuit which generates a trigger pulse in response to the rise of the output of the second OR gate circuit 149 (p in FIG. 8). On the other hand, an impedance detection circuit 152 detects a change in impedance of the output coil circuit of the inverter circuit 108.

This impedance detection circuit 152 detects the voltage across the smoothing capacitor 114 of the inverter circuit 108 by resistor 1.
53 and a capacitor 154, and is detected by a voltage detection circuit 156 (q in FIG. 8), and as long as the detected voltage level exceeds a preset voltage level V, the output is ゜" 1, and when the above-mentioned detection voltage level falls below the level, the output falls to "O". Further, the amount of current ((r in FIG. 8)) flowing through the output coil circuit of the inverter circuit 108 is detected by a load current detection circuit 158.
The amount of current flowing through the emitter resistors 121 and 122 of 7 and 118, respectively, is detected by the current detection circuit 163 through a filter circuit 162 consisting of resistors 159 and 160 and a capacitor 161, and the voltage drop across both resistors 121 and 122. As long as the detected current amount is below the preset current amount ILS, the output is in the state of "゜1゛," and when the detected current amount exceeds IL, the output is 66.
It is starting to fall to 0゛. and the output of the impedance detection circuit 152 and the load current detection circuit 15.
Eight outputs are input to each input terminal of a sixth AND gate circuit 164 for two inputs, and the output of the sixth AND gate circuit 164 is input to a memory circuit 157. The memory circuit 157 is composed of, for example, an R-S flip-flop, and the output of the sixth AND gate circuit 164 is input to its set input terminal, and the output of the reset trigger circuit 151 is inputted to its set input terminal via an inverter circuit 165. It is configured to be input to the input terminal. The memory circuit 157 is normally operated in a resetting state and the output is in a state of ゜1゛.
When the output is "0", it is set and the output becomes "0", and then it is set by the output of the reset trigger circuit 151 and the output becomes "r" again (see s in Fig. 8). 》. Therefore, the memory circuit 157 is set when either the output of the impedance detection circuit 152 or the output of the load current detection circuit 158 becomes "0", and its output becomes "0".The output of the memory circuit 157 is The third AND gate circuit 141 described above
The output of the third AND gate circuit 141 is "゜゛" when the output of the first OR gate circuit 140 is "゜1゛" and the output of the memory circuit 157 is "゜"1゛. 1'', and its output ゜゜1゛ energizes the inverter drive circuit 124 to drive the inverter circuit 108.
The sum of the output transmission times of the second timer circuits 134 and 142 (the sum of the period in which the first coil is in charge and the time in which the second coil is in charge) is a reference for the low frequency signal generated from the low frequency oscillation circuit 133. Period T. The degree of variation of variable resistors 135 and 143 is mechanically limited so that it becomes smaller than . Next, the operation of the apparatus according to the present invention constructed as described above will be explained based on the time chart shown in FIG.

The low frequency oscillator circuit 133 generates a low frequency signal with a pulse width Tp at a reference period TO, and now the low frequency signal is as shown in a of FIG.
At time T as shown in .

- TiO~Tll, T2O-T2l,..., time t1~Tll is the first reference period, time Tll~T2l is the second reference period, time T2
Hereinafter, l~ will be described as the third reference period. In addition, time T. Previously, the output coil 102, 1 for induction heating
Appropriate magnetic pots 104 and 105 are placed normally on 03, so the outputs of the first and second load detectors 106 and 107 are both in the state of "゜1゛5". First, a case will be described in which both output coils 102 and 103 are operating normally during the first reference period of time (~Tll).

When the low frequency signal of the low frequency oscillation circuit 133 falls at the start of the first reference period, that is, at time t1, the output of the first timer circuit 134 rises to "°1" as shown in FIG. 8b. This is the period in which coil No. 1 is in charge.

Then, the first relay drive circuit 136 is energized, and the coil 110c of the first relay 110 is energized. On the other hand, the first
As shown in Fig. 8c, the output of the load detector 106 of
1'', so when the output of the first timer circuit 134 becomes "1", the output of the first AND gate circuit 137 becomes "1" as shown in d of FIG. As a result, the output of the first monostable multivibrator 139 becomes 0° for a short period of time T2, as shown in FIG. 8e. So it's time!
Since the output of the first AND gate circuit 137 is "゜1゛" and the output of the first monostable multivibrator 139 returns to "゜゜1゛," the second AND gate circuit 13
8, the output is ゜" at the time as shown in Fig. 8 f.
It becomes 1゛. This second AND gate circuit 138 output is the first OR. The signal is supplied to one input terminal of a third AND gate circuit 141 via a gate circuit 140 . The output of the memory circuit 151 is supplied to the other input terminal of the third AND gate circuit 141, but since the device is currently operating normally, the memory circuit 157 is in the reset state and the output is ゜゜1゛. is in a state of When the output of the second AND gate circuit 138 becomes ``1'', the third AND gate circuit 141 responds to the output as shown at t in FIG.
The output becomes ゜゛1゛, and the inverter drive circuit 124 operates. On the other hand, when the output of the first AND gate circuit 137 reaches ゜゜1゛, the output of the third monostable multivibrator 147 changes to ゜゜1゛ as shown in Fig. 8.
The output is kept in the ゜゜1゛ state for the required time of 3, and the ``゜1'' output is supplied to the second relay drive circuit 150 via the second OR gate 149. Coil 1 of second relay 112 by
12c is energized a. Therefore, when the low frequency signal falls at time t1, first the normally closed contact 110b of the first relay 110 is opened, and its normally open contact 110a is closed, as shown at u in FIG. is connected to the output terminal of the inverter circuit 108 via a capacitor 109.

At the same time, as shown in v in FIG. 8, the normally closed sides of the contact switches 112a and 112b of the second relay 112 are opened and the normally open sides are closed, so that the low voltage drive circuit 127 is connected to the power supply side circuit of the inverter circuit 108. Connected. That is, a resistor 128 is connected in series between one end of the AC power supply 111 and one end of the input end of the full-wave rectifier bridge circuit 113, and a resistor 129 is connected between the output ends of the full-wave rectifier bridge circuit 113. Then, at time T2, the inverter circuit 108 is driven by the inverter drive circuit 124. Therefore, the inverter circuit 108 starts energizing the output coil 102 at time T2 during the period in which the first coil is in charge. The amount of energization to the output coil 102 at the start of this energization, that is, the amount of output coil circuit current is the low voltage drive circuit 1
27, it is suppressed to a small amount as shown by r in FIG. Then, at time T3, the output of the third monostable multivibrator 147 becomes '40'', and the coil 11 of the second relay 112 by the second relay drive circuit 150
2c is stopped, the normally open side of each contact switch 112a, 112b of the relay 112 is opened, and the normally closed side is closed. That is, the low voltage drive circuit 127 is separated from the power supply side circuit. Therefore, the power supply side circuit of the inverter circuit 108 becomes the normal voltage level, and the output coil 10
The amount of current supplied to the magnetic pot 2 increases as shown at r in FIG. Then, at time ζ, when the output of the first timer circuit 134 falls to "0", the first AND gate circuit 137
The output also becomes "0".

On the other hand, in response to the fall of the output of the first timer circuit 134, the output of the second timer circuit 142 rises to ``1'' as shown in g in FIG. 8, and the second coil is in charge. Then, the first relay drive circuit 136 is deenergized and the first relay drive circuit 136 is deenergized.
The coil 110c of the relay 110 is deenergized. on the other hand,
Since the output of the second load detector 107 is ゛1゛, which is the same as the output of the first load detector 106 as shown in h of Fig. 8, the fourth AND gate circuit is connected as shown in i of Fig. 8. 144
The output becomes ゜゜1゛. Therefore, the output of the second monostable multipipulator 146 reaches the time T as shown in j of FIG.
4 to T5 for a short period of time. Therefore, at time 4, the output of the fourth AND gate circuit 144 is "4r',
And since the output of the second monostable multivibrator 146 returns to ゛゜1゛, the output of the fifth AND gate circuit 145 becomes ゛゜1゛ at time T5 as shown in k in Fig. 8.
It becomes ゛. The output of this fifth AND gate circuit 145 is supplied to one input terminal of the third AND gate circuit 141 via the first OR gate circuit 140. Since the other input terminal of the third AND gate circuit 141 is supplied with the "1" output from the memory circuit 157 in the same manner as during the period in charge of the first coil, the fifth AND gate circuit 14
When the output of the third AND gate circuit 141 becomes "1", the output of the third AND gate circuit 141 becomes "1" and the inverter drive circuit 124 operates as shown at t in FIG. On the other hand, when the output of the fourth AND gate circuit 144 becomes ゛1゛, the output of the fourth monostable multipipulator 148 responds to it as shown in n of FIG. is brought into the "r" state, and its 46r output is sent to the second relay drive circuit 150 via the second OR gate 149.
supplied to However, during the period in which the second coil is in charge, as well as in the period in which the first coil is in charge, at the beginning, the second relay drive circuit 150
The coil 112c of the relay 112 is energized. Therefore, when the output of the first timer circuit 134 falls at time T4, first the first relay 1 is activated as shown in u in FIG.
10 normally open contacts 110a are opened and the normally closed contacts 110
b is closed, and the output coil 103 is connected to the output end of the inverter circuit 108 via the capacitor 109.

At the same time, as shown in v in FIG. 8, the normally closed sides of the contact switches 112a and 112b of the second relay 112 are opened and the normally open sides are closed, so that the low voltage drive circuit 127 is connected to the power supply side circuit of the inverter circuit 108. Connected. In other words, the resistance 128 is the same as at the beginning of the period in which the first coil is in charge.
is one end of the AC power supply 111 and the full-wave rectifier bridge circuit 113
and one end of the input terminal of the resistor 12.
9 and the output terminals of the full-wave rectifier bridge circuit 113. Then, at time 3, the inverter circuit 108 is driven by the inverter drive circuit 124. Therefore, the inverter circuit 108 starts energizing the output coil 103 at the time of the period in which the second coil is in charge. The amount of current applied to the output coil 103 at the start of this energization, that is, the amount of output coil circuit current, is suppressed to a small level as shown in r in FIG. 8 by the action of the low voltage drive circuit 127. Then, at time t, the fourth monostable multivibrator 1
48 output becomes ゜゜0゛, and the second relay drive circuit 15
0 stops the energization of the coil 112c of the second relay 112, and each contact switch 112a of that relay 112
, 112b are opened and their normally closed sides are closed. That is, the low voltage drive circuit 127 is separated from the power supply side circuit. As a result, the voltage level of the power supply side circuit of the inverter circuit 108 becomes normal, and the amount of current flowing to the output coil 102 increases as shown in r in FIG. Let's do it. Then, at the time point, the output of the second timer circuit 142 becomes ゜'0.
When ' falls, the output of the fourth AND gate circuit 144 also becomes '0'.
The output becomes ゛0゛, and the drive of the inverter circuit 108 by the inverter drive circuit 124 is stopped.Then, from this time until the time Tll when the first reference cycle ends, the coil is inactive, and both outputs are Coil 102,1
03 are not energized. Therefore, even if the magnetic pot 105 is removed from the output coil 103 at time TBl during this pause period, the output power of the second load detection circuit 107 remains 0, as shown in h of FIG. It does not affect the operation of the device. As described above, during normal operation, the output coil 102 is energized during the period in which the first coil is responsible, and the output coil 103 is energized during the period in which the second coil is in charge.

Therefore, if this operation is repeated over a plurality of reference periods, each magnetic pot 104, 105 will be connected to the output coil 1.
Normal heat generation operation is performed with an average power of 02,103.
The amount of current applied to both output coils 102 and 103 is kept small by operating the low voltage drive circuit 127 for a short period of time immediately after the start of the period in which the two coils are in charge, so that when the inverter circuit starts oscillating, What happens when the output coil circuit is not in a resonant state can be suppressed to a very small level, and each transistor 1 of the inverter circuit 108
15, 116, 117, 118, etc. can be prevented. Additionally, if a large current suddenly flows through the output coil when the inverter circuit starts oscillating, there is a risk that the magnetic pan will be attracted to the output coil and generate abnormal noise, but this can also prevent such abnormal noise from occurring. . Next time Tl
The cases where various states occur in the second reference period from l to T2l will be described.

When the low frequency signal of the low frequency oscillation circuit 133 falls at the start of the second reference period, that is, at time Tll, the output of the first timer circuit 134 rises to ``R5'', which is in charge of the first coil, as described above. A period is started.

Immediately after the start of the period in which the first coil is in charge, the amount of current applied to the output coil 102 is kept small by the required short-time low voltage drive circuit 127, as described above. Then, at time TB2 during the period in which this first coil is in charge, a steel knife is fired. A small magnetic material is placed on the output coil 103. Now, the device is in the period in which the first coil is in charge, the output coil 102 is energized, and the output coil 103 is energized.
Since the knife is not energized, the output coil 1
Even if it is placed on 03, the abnormal state J of the circuit will not occur.
Then, at time TAl in the period in which the first coil is in charge, an operation for removing the magnetic pot 104 from above the output coil 102 is started. Then, the magnetic pot 104 becomes the output coil 102.
As the distance from the output coil 102 increases, the amount of current flowing through the output coil 102 gradually increases as shown by r in FIG. Then, at time TA2, when the current amount exceeds IL, the output of the current detection circuit 163 becomes ``0''.The output of the sixth AND gate circuit 164 becomes ``40'', and the memory circuit 157 is set. The output falls to "0" as shown at s in FIG. 8. Then, the output of the third AND gate circuit 141 becomes "0" as shown at t in FIG. The operation of the inverter drive circuit 124 is thus stopped, and the inverter circuit 108 stops its oscillation operation.
That is, during the period in which the first coil is in charge, the magnetic pot 104
is removed from the output coil 102, the accompanying increase in the amount of current is detected by the current detection circuit 163, and when the amount of current exceeds ILS, the inverter circuit 1
The oscillation operation of 08 is stopped. Therefore, when the inverter circuit 10 is not placed on the output coil,
There is no possibility that 8 will perform an oscillation operation. Then magnetic pot 104
is completely separated from the top of the output coil 102, and at time TA3, the output of the first load detection circuit 106 becomes ゜゜0゛ as shown in e of Fig. 8.

Thereafter, at time Tl4 in the second reference period, the first
When the output of the second timer circuit 134 falls to 4°0', the output of the second timer circuit 142 becomes "1" as shown in the eighth g.
The period in which the second coil is in charge begins. At the same time, the first relay 1 by the first relay drive circuit 136
The energizing operation of the No. 10 coil 110c is stopped. Thus, between times Tl4 and Tl5, the normally closed contact 110b of the first relay 110 is closed, and the second output coil 103 is connected to the output end of the inverter circuit 108 instead of the first output coil 102. On the other hand, the output of the fourth monostable multivibrator 148 becomes "1" for a required short time, the second relay drive circuit 150 energizes the coil 112c of the second relay 112, and the low voltage drive circuit 127 drives the inverter circuit 108. Furthermore, when the output of the fourth monostable multivibrator 148 rises to "1", the reset trigger circuit 151 outputs a trigger signal as shown in p of FIG. occurs, causing the memory circuit 157 to perform a reset operation. At time Tl4, the output of the memory circuit 157 returns to the "°1" state.
Similarly to the above, the output coil 103 starts to be energized after the output of the second monostable multivibrator 146 rises to "1", that is, from time Tl5. At the beginning of energization, it is driven by the low voltage drive circuit 127.
Since the knife is now placed on the output coil 103, the impedance of the output coil circuit is considerably low. Therefore, the voltage generated across the smoothing capacitor 114 becomes considerably low, and the impedance detection circuit 15
The output of the smoothing circuit 155 at 0 suddenly drops as shown at q in FIG. And when the time loss is 15, the smoothing circuit 15
5 output level becomes below s, the output of the voltage detection circuit 156 becomes ゜"0゛. Therefore, the sixth AND gate circuit 1
The output 64 becomes 0° as in the case where the amount of current increases abnormally, and the memory circuit 157 is set again and its output falls to 0° as shown at s in FIG. Therefore, the output of the third AND gate circuit 141 is
As shown in f in the figure, it becomes "0", the operation of the inverter drive circuit 124 is stopped, and the inverter circuit 108 stops its oscillation operation.In other words, a suitable magnetic pot like an iron knife is placed on the output coil 103. When the period in which the second coil is in charge starts in a state where a magnetic material smaller than the magnetic material is placed, the voltage detection circuit 156 detects an abnormal state of the circuit as a voltage drop, and the oscillation operation of the inverter circuit 108 is stopped.Therefore, an appropriate magnetic pot is not placed on the output coil, and a small magnetic material such as an iron knife is placed on the output coil. If the magnetic pot is placed on the output coil, an abnormal state of the circuit is detected immediately after the output coil starts energizing, and the oscillation operation of the inverter circuit 108 is stopped. Therefore, an appropriate magnetic pot is not placed on the output coil. There is no risk that the output coil will continue to be energized in this state.
Furthermore, when the output coil starts to be energized, the amount of current flowing through the output coil is kept small, and a drop in circuit impedance is detected in this state. No regular voltage is applied. Therefore, in a state where the impedance of the circuit is reduced, the inverter circuit 1
There is no risk that a normal voltage will be applied to the inverter circuit 08 and a large current will flow through each transistor of the inverter circuit and the output coil, causing damage to the elements. Note that the output of the second timer circuit 142 then falls to 0.0° at time Tl7, and the period in charge of the second coil ends. As mentioned above, if the magnetic pot placed on the output coil is removed while the output coil is energized, or if an iron knife is placed on the output coil instead of a suitable magnetic pot. If an abnormal state occurs in the circuit due to a mistake such as energizing the output coil when a small magnetic material is placed on the inverter, immediately stop the oscillation operation of the inverter circuit. I can do it.

Moreover, if the circuit is in an abnormal state from the start of energization of the output coil, this can be detected while the inverter circuit is being driven at a low voltage by the low voltage drive circuit 127, and the oscillation operation of the inverter circuit can be stopped. I can do it. Furthermore, a case will be described in which the appropriate magnetic pot 104 is again placed on the output coil 102 at time TA4 in the period in which the first coil is in charge in the third reference cycle from time T2l.

At the start of the third reference period, that is, at time T2l, when the low frequency signal of the low frequency oscillation circuit 133 falls, the output of the first timer circuit 134 rises to ゜1゜, and the first coil The period in charge of is started, and the coil 110c of the first relay 110 is energized by the first relay drive circuit 136 as described above, and the output coil 102 is connected to the output terminal of the inverter circuit 108. However, at this point, the output Since there is no magnetic pot 104 or other magnetic material placed on the coil 102, the output of the first load detector 106 is in the 0' state.Therefore, the output of the first AND gate circuit 137 is “It has become 0゛. On the other hand, since the memory circuit 157 is set and operated during the period in which the second coil is in charge in the second reference period described above, its output is 0". Therefore, the first timer circuit 134 Even if the output reaches ゜゛1゛, the inverter circuit 108 does not start the oscillation operation at this point.Thereafter, at time TA 7 during the period in which the first coil is in charge.
4, when a suitable magnetic pot 104 is placed on the output coil 102, the first load detector 106 detects it and "
1゛Send output. As a result, the output of the first AND gate circuit 137 becomes ゜゜1゛, and the output of the third monostable multivibrator 147 becomes ゜゜1゜ for a required short period of time, as in the normal operation described above, and the second relay drive circuit 150 The coil 112c of the second relay 112 is energized by the output, and the low voltage drive circuit 127 is connected to the power supply circuit of the inverter circuit 108.At the same time, the output of the third monostable multivibrator 147 rises to 1. By rising, a trigger signal is output from the reset trigger circuit 151,
The memory circuit 157 is reset and its output is set to 6'r'.
Make it. Therefore, the output of the first AND gate circuit 137 becomes "1", and the first monostable multivibrator 139
As shown in e of FIG.
energization starts. At the beginning of this energization, the amount of energization to the output coil 102 is kept small by the low voltage drive circuit 127 as described above. Therefore, after time TA4, the same operation as in the period in which the first coil is in charge during the normal operation described above is performed. In the above embodiments, the low voltage drive circuit for the inverter circuit and the output coil for the output terminal of the inverter circuit are connected to and separated from each other by using a relay, but the invention is not limited to this. As shown in FIG. 9, bidirectional three-terminal thyristors 170, 171 are used in place of the first relay, a unidirectional three-terminal thyristor 172 is used in place of the contact switch 112a of the second relay, and A transistor 173 may be used instead of the contact switch 112b of the second relay.

In the figure, 174 and 175 are inverters for signal inversion. Furthermore, it goes without saying that the configurations of the impedance detection circuit and the load current detection circuit are not necessarily limited to those of the embodiments described above. As detailed above, according to the present invention, current and voltage spikes at the start of oscillation of the inverter circuit can be suppressed to a very small level, thereby extending the life of the inverter circuit, and moreover, when the inverter circuit starts oscillation, abnormality occurs. It is possible to provide an induction heating device that is free from the possibility of generating noise.

Furthermore, it is possible to detect changes in the impedance of the inverter circuit in the low voltage drive state when the inverter circuit starts oscillating, and it is also possible to detect the load current flowing through the induction heating output coil circuit during operation, making it possible to constantly respond to abnormal conditions in the circuit. It is possible to provide an induction heating device that can perform the following steps.

[Brief explanation of the drawing]

Figures 1 to 3 are circuit diagrams for explaining the operating principle of the induction heating device, Figure 4 is a waveform diagram of each part in Figure 1, and Figure 5 is a collector of the output transistor of the inverter circuit in Figure 1. A resurge waveform diagram of current and collector voltage, FIG. 6 is a sectional view showing an embodiment of the present invention, FIG. 7 is a circuit diagram of the embodiment, and FIG. 8 is an output waveform and operation of each part in the embodiment. FIG. 9, which is a diagram showing timing, is a circuit diagram showing another embodiment of the inverter circuit section. 102, 103... Output coil for induction heating, 1
04,105...Magnetic pot, 108...
Inverter circuit, 110...First relay, 1
12...Second relay, 127'-...
Low voltage drive circuit, 128, 129... Resistor, 1
52... Impedance detection circuit, 156...
...Voltage detection circuit, 157... Memory circuit,
158... Load current detection circuit, 163... Current detection circuit.

Claims (1)

[Claims] 1. An inverter circuit that energizes an output coil circuit for induction heating, and a frequency that variably controls the output frequency of this inverter circuit according to the load condition to maintain the resonant state of the output coil circuit. a control means; a low voltage drive circuit for driving the inverter circuit at a low voltage by selectively connecting an impedance element to a power supply circuit of the inverter circuit; and a low voltage drive circuit that operates for a required time when the inverter circuit starts oscillating. An induction heating device characterized by comprising a control means for controlling the temperature. 2. An inverter circuit that energizes an output coil circuit for induction heating, a frequency control means that variably controls the output frequency of this inverter circuit according to a load condition and maintains a resonance state of the output coil circuit, and an inverter circuit that energizes an output coil circuit for induction heating. a low voltage drive circuit that drives the circuit at a low voltage; an impedance detection circuit that detects the impedance of the output coil circuit by detecting the input voltage in the inverter circuit; and a low voltage drive circuit that detects the impedance of the output coil circuit by detecting the input voltage in the inverter circuit; An induction heating apparatus comprising: a control means for controlling the operation of the inverter circuit; and a control means for operating the low voltage drive circuit and the impedance detection circuit for a required time when the inverter circuit starts oscillating. 3. An inverter circuit that energizes an output coil circuit for induction heating, a frequency control means that variably controls the output frequency of this inverter circuit according to a load condition and maintains a resonance state of the output coil circuit, and an inverter circuit that energizes an output coil circuit for induction heating; a low voltage drive circuit that drives the circuit at low voltage; an impedance detection circuit that detects the impedance of the output coil circuit;
a load current detection circuit that detects the load current flowing through the output coil circuit; a control means that controls the operation of the inverter circuit according to the detection results of these impedance detection circuits and the load current detection circuit; and the low voltage An induction heating apparatus comprising: a control means for operating a drive circuit and an impedance detection circuit for a required period of time when the inverter circuit starts oscillating.