JP2900664B2 - Induction heating device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an induction heating apparatus such as an induction heating type electronic jar rice cooker.

[0002]

2. Description of the Related Art Conventionally, an induction heating device such as an electronic jar rice cooker of the induction heating type uses a power control means for changing a conduction period of a switching element in accordance with a signal output from a microprocessor means to control a power applied to a pot. Is changing.

[0003] Hereinafter, an electronic heating rice cooker of an induction heating system (hereinafter referred to as an induction heating rice cooker), which is one of the conventional induction heating devices, will be described with reference to FIGS.

The AC supplied from the AC power supply 1 is converted into DC by the rectifier circuit 2 and the filter 3,
It is connected to the. The resonance circuit 7 includes a heating coil 5 for generating a high-frequency magnetic field to heat the pan 4 and a resonance capacitor 6. A switching element 8 is connected to the resonance circuit 7 and generates a resonance current. Reference numeral 9 denotes a reverse conducting diode for preventing the switching element 8 from being destroyed. Reference numeral 10 denotes a driving unit that drives the switching element 8. Reference numeral 11 denotes a synchronizing pulse generating means for converting the voltage between both ends of the resonance circuit 7 into a voltage of 5 V or less, which is easy to handle, and outputting a timing signal for turning on the switching element 8. When the user presses a key 12 for cooking or keeping warm, for example, the user determines the pressed key and outputs a power corresponding to the key input as a digital signal.
The microprocessor means has an OUT terminal and a P0WER ON / OFF terminal for outputting a signal for heating or stopping the switching element 8 to the driving means 10. Reference numeral 14 denotes a D / A converter for converting a digital signal of the microprocessor 13 into an analog signal. Further, at 15, the switching element 8 is turned on in accordance with the on timing of the synchronization pulse generating means 11, the time during which the switching element 8 is turned on is determined by the voltage level of the D / A conversion means 14, Power control means for controlling the element 8.

Next, the circuit configuration of the power control means 15 will be described in detail. When the output of the comparator 17 is H, the power control means 15 charges the capacitor 16 via the resistors 18 and 19 until the voltage of the − terminal of the comparator 17 reaches the voltage level of the + terminal. . The ON time of the switching element 8 is determined by the charging time. The longer the ON time is, the smaller the power for heating the pot 4 becomes, the smaller the power becomes. By changing the on-time in this manner, the power applied to the pot 4 changes. The off time of the switching element 8 is determined by the length of time when the output of the synchronization pulse generation means 11 is L. That is, while the output of the synchronization pulse generating means 11 is L, the output of the comparator 17 is L, and the electric charge of the capacitor 16 is discharged via the resistor 18 and the diode 20.

In this conventional example, the voltage at the + terminal of the comparator 17 is set to the forward voltage of the two diodes 21 and 22, and the capacitor is connected while the output of the synchronizing pulse generator 11 is at L. The 16 charges are discharged so as to be lower than the voltage of the + terminal of the comparator 17.

The operation of the induction heating rice cooker constructed as described above will be described below. AC 100 V supplied by the AC power supply 1 is converted into DC by the rectifier circuit 2 and the filter 3 and supplied to the heating coil 5. Here, when the user operates the key 12, for example, to instruct rice cooking, the microprocessor means 13 determines that the key 12 has been operated, turns on the POWER ON / OFF terminal, and starts heating.
In this case, the microprocessor means 13 outputs a digital signal by turning on / off a DATA OUT terminal composed of an open collector in order to set the power for cooking rice to 1200 W. In this case, the DATA
When the OUT terminals are all on, the voltage level of the output of the D / A converter 14 is the lowest, and the heating coil 5
Output is also the lowest. When all the DATA OUT terminals are off, the voltage level of the output of the D / A conversion means 14 is the highest, and the output to the heating coil 5 is also the highest.

The operation of the power control means 15 is as shown in FIG. That is, the output voltage waveform of the collector voltage Vce of the switching element 8 is shown in FIG. 5 (a), the output current waveform of the current Ic flowing through the collector is shown in FIG. 5 (b), and the output voltage Vc2 of the filter 3 and the collector voltage Vce are leveled. The converted voltage after the level conversion is as shown in FIG. 5C, and the voltage waveform of the minus terminal of the comparator 17 is as shown in FIG. 5E. When the level conversion voltage of the voltage Vc2 of the filter 3 becomes larger than the level conversion voltage of the collector voltage Vce at the time t1 in FIG. 5C, as shown in FIG.
At 1, the output of the synchronization pulse generating means 11 becomes H. When the output of the synchronizing pulse generator 11 becomes H, the voltage of the + terminal of the comparator 17 becomes H according to the voltage level according to the power of the D / A converter 14. Therefore, the power control unit 15 starts charging the capacitor 16 connected to the negative terminal of the comparator 17 as shown in FIG. That is, charging is started at the timing of time t1 from the power supply via the resistors 18 and 19. This charging ends at time t2 when the voltage at the negative terminal of the comparator 17 reaches the same level as the voltage at the positive terminal. As a result, the output terminal of the comparator 17 becomes L. Driving means 1 at the same time
The switching element 8 is turned off by 0. Thus, current flows from the + terminal of the comparator 17 to the output terminal of the comparator 17 via the diodes 21 and 22. As a result, the voltage of the + terminal of the comparator 17 becomes equal to the voltage of the diode 21 and the diode 22 as shown between time t1 and time t2 in FIG.
Forward voltage of one diode. On the other hand, at time t2, the switching element 8 is turned off, and the collector current Ic stops flowing as shown at time t2 in FIG. At the same time, as shown in FIG. 5A, the collector voltage Vce increases. When the output voltage Vc2 of the filter 3 and the collector voltage Vce are level-converted, the voltage after the level conversion becomes as shown in FIG. 5C, and the voltage at the + terminal of the comparator 17 becomes L at time t3. On the other hand, the electric charge of the capacitor 16 connected to the minus terminal of the comparator 17 is discharged through the resistor 18 and the diode 20,
For this reason, the collector voltage Vce decreases. FIG.
At the time t4 in (c), the capacitor 16 continues discharging until the output of the synchronization pulse generating means 11 becomes H.
At the time t4, the voltage of the capacitor 16 connected to the negative terminal of the comparator 17 becomes +
It is below the same level as the terminal voltage. When the output of the synchronizing pulse generation means 11 becomes H and the voltage of the negative terminal of the comparator 17 becomes lower than the positive terminal, the comparator 1
The output terminal 7 goes high again. As a result, the capacitor 16
Starts the charging again and repeats the operation from time t1 to time t4.

The power control is performed by raising and lowering the voltage level of the + terminal of the comparator 17 so that the capacitor 1
6, the charging time can be freely changed. If the charging time is long, the power can be increased, and if the charging time is short, the power can be decreased.

A case where the voltage level of the + terminal of the comparator 17 is set higher to increase the power will be described with reference to FIG. The output voltage waveform of the collector voltage Vce of the switching element 8 is shown in FIG. 6A, and the output current waveform of the current Ic flowing through the collector is shown in FIG.
FIG. 6C shows a voltage waveform after level conversion of the output voltage Vc2 of the filter 3 and the collector voltage Vce.
The voltage waveform at the + terminal of the comparator 17 is shown in FIG.
The voltage waveform at the negative terminal of the comparator 17 is shown in FIG.

In this case, the discharge time of the power control means 15 to the capacitor 16 is longer than the on-timing time of the switching element 8 of the synchronizing pulse generation means 11 at time t4 in FIG. As a result, the ON timing of the switching element 8 is delayed by only the time t4 to the time t5. For this reason,
The collector voltage Vce of the switching element 8 changes, and the loss of the switching element 8 increases.

Next, a case where the voltage level of the + terminal of the comparator 17 is set low to reduce the power will be described with reference to FIG. The waveform of the output voltage of the collector voltage Vce of the switching element 8 is shown in FIG. 7A, and the waveform of the output current of the current Ic flowing through the collector is shown in FIG.
FIG. 7C shows a voltage waveform after level conversion of the output voltage Vc2 of the filter 3 and the collector voltage Vce.
The voltage waveform at the + terminal of the comparator 17 is shown in FIG.
The voltage waveform at the negative terminal of the comparator 17 is as shown in FIG.

That is, since the power is small, the output voltage of the collector voltage Vce of the switching element 8 also becomes small, and the level conversion voltage of the collector voltage Vce which is the input of the synchronization pulse generating means 11 shown in FIG. Before crossing the level conversion voltage of the output voltage Vc2 of the filter 3 (time t1), that is, before the synchronous pulse generation circuit 11 issues an off timing signal for turning off the switching element 8, the voltage of the capacitor 16 is + It is the same as the terminal voltage. At this time, the output of the comparator 17 is inverted to H, and charging of the capacitor 16 is started. When the capacitor 16 is charged and the voltage at the minus terminal of the comparator 17 rises and becomes equal to the voltage at the plus terminal of the comparator 17 at time t2, the comparator 1
The output terminal 7 is inverted to L. Therefore capacitor 1
6 starts discharging. Since this discharge time is short, at time t3, the comparator 17 starts charging the capacitor 16 again without the output of the synchronization pulse generating means 11 being inverted. Therefore, in this case, a normal inverter waveform cannot be obtained, and the output power becomes unstable.

The rice cooker requires a large power of 1200 W at the time of cooking rice, a power as small as possible at the time of startup because a slow start is required, and a medium power of about 400 W at the time of heat retention.

[0015]

However, in such a conventional configuration, there is no problem in the induction heating device having a constant power, but the output power is unstable in the induction heating device having a variable power. It has a problem that it becomes something. That is, if the level of the + terminal of the comparator 17 is increased to increase the power, not only the charging time but also the discharging time becomes longer. Therefore, the ON timing of the switching element 8 is delayed, Vce at the time of switching is increased, the turn-on loss of the switching element 8 is increased, and normal operation is not achieved. When the power is reduced, the discharging time is shortened, the off time of the switching element 8 is shortened, and the switching element 8 is turned on before resonance in the resonance circuit starts. Therefore, also in this case, a normal resonance waveform cannot be obtained, and a normal inverter operation cannot be performed.

That is, in the conventional configuration, the applied power, that is, the charging time cannot be largely changed. In other words, the range of the voltage level of the + terminal of the comparator 17 cannot be widened, and high-precision and stable control cannot be performed even with a large power and a small power, and it is difficult to set a small power. Is what it is.

Accordingly, the present invention is to solve the problem of the conventional configuration, and to provide an induction heating device capable of controlling stably from a small power to a large power. It is the purpose.

[0018]

Means for Solving the Problems The present invention to achieve the object, a heating coil for inductively heating an object to be heated, before
A high frequency power supplying means for supplying a high-frequency current to the serial heating coil in the induction heating apparatus provided with a driving means for controlling, based on and off of the switching element used in the high frequency power supplying means to the charging and discharging time of the capacitor, before
Turning on the switching element when charging the capacitor,
Turns off at the time of discharge, the discharge time of the capacitor changes the discharge path to be equal to or less than the predetermined value, on-time
Nevertheless, keep the off-time below the specified value.
It is those that.

[0019]

According to the above arrangement, the charging voltage of the capacitor is different.
Even in such a case, the discharge time can be made substantially constant. In other words, no significant change occurs in the discharge time regardless of whether the charging voltage level of the capacitor is high or low. Therefore , accurate and stable control from low power to high power is possible.

[0020]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, an embodiment of the present invention will be described in detail with reference to FIGS. FIG. 1 shows a circuit configuration of an electronic jar rice cooker which is one of the induction heating apparatuses according to one embodiment of the present invention. The configuration of the present embodiment is obtained by adding a rapid discharge circuit 23 for rapidly discharging the charge of the capacitor 16 to a level of about 1.5 V to the configuration of the conventional induction heating rice cooker described with reference to FIG. The power control means 27 is configured around the comparator 17, and two diodes 21 and 22 are connected between the + terminal and the output terminal of the comparator 17. The negative terminal of the comparator 27 is connected to the capacitor 16, the resistor 18 and the resistor 19, and the capacitor 16 is charged via the resistors 18 and 19. A diode 2 is connected between the connection point of the two resistors 18 and 19 and the output of the comparator 17.
0 is connected. The negative terminal of the comparator 17 is connected to a quick discharge circuit 23 that rapidly reduces the voltage of the capacitor 16 to a constant voltage by rapidly discharging the capacitor 16. In this embodiment, the rapid discharge circuit 23 includes a resistor 24, a resistor 25, and a diode 2 having a smaller resistance value than the resistors 18 and 19.
6. The diode 26 is connected to the resistor 2
4 and the connection point of the resistor 25.

The operation of the power control means 27 of the induction heating rice cooker constructed as described above will be described below. The waveform at the peak of the collector voltage Vce of the switching element 8 is shown in FIG. 2A, and the waveform at the peak of the current Ic flowing through the collector is shown in FIG.
FIG. 2C shows a voltage after level conversion of c2 and the collector voltage Vce, FIG. 2D shows a voltage waveform at the + terminal of the comparator 17, and FIG. (E).

As shown by time t1 in FIG. 2C, the voltage obtained by level-converting the output voltage Vc2 of the filter 3, which is the voltage on one side of the heating coil 5, is the voltage on the other end of the heating coil 5. When the collector voltage Vce becomes higher than the level conversion voltage, the output of the synchronizing pulse generator 11 becomes H. Similarly, when this voltage becomes lower, the output of the synchronizing pulse generator 11 becomes L. On the other hand, the microprocessor means 13 determines the power to output, for example, 1200 W when the rice cooker key is input and 400 W when the heat retention key is input by operating the key 12 by the user, and outputs a signal corresponding to this power to the DATA OUT. Is always output as a digital signal. This digital signal is converted into an analog voltage by the D / A converter 14 and supplied to the + terminal of the comparator 17 together with the output of the synchronous pulse generator 11. As a result, the voltage at the + terminal of the comparator 17 is as shown in FIG. The magnitude of the power applied to the heating coil 5 is connected to the + terminal of the comparator 17 which determines the length of time t1 to t2 when the synchronization pulse generating means 11 is H as shown in FIG. Determined by the applied voltage level. The power applied to the heating coil 5 increases as the voltage level increases. The power control means 27 charges and discharges the capacitor 16 connected to the negative terminal of the comparator 17 and generates a signal for turning the switching element 8 on and off, as shown in FIG. This charging time determines the energizing time of the switching element 8, and the output power changes according to the length of the energizing time. That is, the time t1 is the charging start time, and the power supply supplies the resistor 18 and the resistor 19
And charging through. This charging is continued until the voltage at the negative terminal of the comparator 17 reaches the same level as the voltage at the positive terminal at time t2, and the output of the comparator 17 is inverted to L. As a result, the output of the comparator 17 turns off the switching element 8 at time t2 via the driving means 10, and the collector current Ic of the switching element 8 stops flowing as shown at time t2 in FIG. At the same time, the collector voltage Vce starts increasing as shown in FIG. When the output voltage Vc2 of the filter 3 and the collector voltage Vce at this time are level-converted, the voltage after the level conversion is as shown in FIG. Further, at time t3, the output of the synchronization pulse generating means 11 becomes L, and the + terminal voltage of the comparator 17 also becomes L. As shown in FIG. 2D, time t2 and time t3
During the period, a current flows from the + terminal of the comparator 17 to the output terminal of the comparator 17 via the diodes 21 and 22. The voltage of the + terminal of the comparator 17 is equal to the forward voltage of the two diodes 21 and 22. Become.

On the other hand, when the output of the comparator 17 is L, the discharge circuit 23 generates a reference voltage of 1.5 V in this embodiment by the resistors 24 and 25. Since the output terminal of the comparator 17 is L, the comparator 1
The electric charge of the capacitor 16 connected to the-terminal of 7 is supplied to the 1.5 V through the diode 26 from time t2 to time t3.
Discharge until reaching. As a result of this discharge, the capacitor 16
When the terminal voltage becomes 1.5 V or less, the diode 26 becomes almost open, and the resistor 18 and the diode 20 are newly added.
The discharge is continued as shown from time t3 to time t4 in FIG. In this discharge, the collector voltage Vce shown in FIG. 2A decreases, and the level conversion voltage of the output voltage Vc2 of the filter 3 becomes the collector voltage Vc at time t4 shown in FIG.
e, and continues until the output of the synchronizing pulse generation means 11 becomes H.

At time t4, the charge of the capacitor 16 connected to the minus terminal of the comparator 17 is discharged, and this voltage is lowered. In this state, when the output of the synchronizing pulse generator 11 becomes H, the voltage at the-terminal is lower than the voltage at the + terminal of the comparator 17 specified in advance by the output of the D / A converter 14. , The output terminal of the comparator 17 becomes H. Therefore, the capacitor 16 starts charging again, and the operation described above from the time t1 to the time t4 is repeated.

Next, a case where the output power is small, that is, a case where the voltage level of the + terminal of the comparator 17 is set low will be described with reference to FIG. The output voltage waveform of the collector voltage Vce of the switching element 8 is shown in FIG.
The waveform of the output current Ic flowing through the collector is shown in FIG.
FIG. 3C shows the voltage after level conversion of the output voltage Vc2 of the filter and the collector voltage Vce, and FIG. 3D shows the voltage waveform of the + terminal of the comparator 17, and FIG. The voltage waveform is as shown in FIG.

In this embodiment, as described above, when the voltage of the capacitor 16 becomes lower than the reference voltage 1.5 V of the quick charging circuit 23, the discharging circuit constituted by the resistor 18 and the diode 20 operates to reduce the power. Also capacitor 1
The discharge time of No. 6 can be extended. Therefore, unlike the configuration of the conventional example, the collector voltage Vce and the output voltage Vc2 of the filter do not oscillate without crossing each other.
It works normally.

As described above, the power control in which the output signal of the microprocessor means 13 is converted into an analog voltage by the D / A conversion means 14 and applied to the + terminal of the comparator 17 raises or lowers the voltage level of the + terminal of the comparator 17. Can be changed by Comparator 1
By increasing the voltage level of the positive terminal 7, that is, by increasing the charging time for the capacitor 16, the power applied to the heating coil 5 can be increased. When the voltage level of the + terminal of the comparator 17 is lowered,
When the charging time for the heating coil 6 is reduced, the power applied to the heating coil 5 can be controlled to be small. Further, according to the configuration of the present embodiment, the discharge time of the capacitor 16 does not change much if it is equal to or more than a certain voltage level, for example, 1.5 V or more. Therefore, according to the circuit of the present embodiment, it is possible to stably adjust from large power to small power, and it is possible to freely output large power of 1200 W during rice cooking, small power at startup, and medium power of about 400 W during heat insulation. Things. In addition, the discharge time can be freely set at the time of design irrespective of the charge time, which facilitates the design.

The diodes 21 and 22 are
This is for setting the threshold value of the discharge voltage, and may be constituted by a Zener diode. Further, it may be configured using another power control circuit.

As described above, according to the present embodiment, the voltage level for power adjustment can be freely increased, and accurate control can be performed from a large power to a small power.

[0030]

As described above, according to the present invention, the object to be heated is
Heating coil for induction heating, and high frequency
High frequency power supply means for supplying a current, and the high frequency power
Controls the on / off of the switching element used for the supply means.
Drive means for controlling based on the charge / discharge time of the capacitor.
In the induction heating device equipped, when charging the capacitor
When the switching element is turned on and turned off during discharging,
In addition, the discharge time of the capacitor is less than a predetermined value.
Change the discharge path so that the off-time
By suppressing the voltage to a predetermined value or less, the voltage level for power adjustment can be freely increased, and the power can be accurately controlled from a large power to a small power.
In addition, since the discharge time can be freely set at the time of design, the design becomes easy.

[Brief description of the drawings]

FIG. 1 is a circuit configuration diagram of an electronic jar rice cooker using an induction heating method according to an embodiment of the present invention.

FIG. 2 is a waveform chart showing a voltage waveform of each part of the power control means in the embodiment.

FIG. 3 is a waveform chart showing voltage waveforms at various parts of the power control means at the time of low power.

FIG. 4 is a circuit diagram showing a conventional circuit.

FIG. 5 is a waveform diagram showing a voltage waveform of each part of the power control means.

FIG. 6 is a waveform chart showing voltage waveforms at various parts of the power control means at the time of low power.

FIG. 7 is a waveform chart showing voltage waveforms at various parts of the power control means at the time of low power.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 AC power supply 2 Rectifier circuit 3 Filter 5 Heating coil 6 Resonant circuit 7 Resonant capacitor 8 Switching element 10 Driving means 11 Synchronous pulse generating means 12 Key 13 Microprocessor means 14 D / A converting means 15 Power control means 23 Rapid discharge circuit

Claims (1)

(57) [Claims] 1. A heating coil for inductively heating an object to be heated, a high-frequency power supply means for supplying a high-frequency current to the heating coil, and a switching element used in the high-frequency power supply means for turning on and off a capacitor during charging and discharging of the capacitor. in the induction heating apparatus provided with a driving means is controlled on the basis, before
Turning on the switching element when charging the capacitor,
An induction heating device that is turned off at the time of discharging and changes a discharge path so that the discharging time of the capacitor is equal to or less than a predetermined value, so that the off time is suppressed to a predetermined value or less regardless of the on time.