JP2876912B2 - Induction heating cooker - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention comprises switching means connected in series between DC power supplies and alternately conducting at a constant frequency, and an inverter circuit for controlling the output by varying the driving time ratio of the switching element. The present invention relates to an induction heating cooker.

[0002]

2. Description of the Related Art In recent years, an induction heating cooker for inducing an eddy current in the bottom of a load pan by using a high-frequency magnetic field to heat has attracted attention as a clean, safe and highly heat-efficient cooking means. , High output, and multiple heating units.

Conventionally, as an inverter used in an induction heating cooker, for example, as disclosed in Japanese Patent Application Laid-Open No. 188888/1986, in a single quasi-E class voltage resonance type inverter, the conduction time of a switching means is known. The output of the switching element is controlled by a so-called frequency-variable output level control means for controlling the output level and controlling the output level control means at a low output. A method has been proposed in which the adjustment range at the time of low output is not limited by characteristics, and in a multi-port induction heating cooker, generation of an audible frequency interference sound due to a frequency shift between adjacent heating coils is prevented. For example, Japanese Utility Model Laid-Open No. 57-179
No. 296, a method of setting the oscillation frequency range of each inverter so that the difference between the oscillation frequencies of adjacent high-frequency inverters is equal to or higher than the audible frequency, or disclosed in Japanese Patent Application Laid-Open No. 58-48386. As described above, the difference between the driving frequencies of the respective variable frequency oscillation circuits is detected, and when the difference exceeds a predetermined value, the frequency variable output control is switched to the duty variable output control based on the on / off time ratio of the variable frequency oscillation circuit. Methods have been proposed. Furthermore, a push-pull inverter that oscillates at a constant frequency has been proposed as disclosed in Japanese Patent Application Laid-Open No. 1-260785, for example, which has a configuration as shown in FIG.

That is, in FIG. 6, a commercial power supply 1 is rectified by a rectifier 2, and an output low-frequency DC voltage is supplied to an inverter 5 via a choke coil 3 and a power supply capacitor 4. In the inverter 5, a series circuit of the transistor 6 and the transistor 7 is connected to the input DC, a diode 8 is connected to the transistor 6 in anti-parallel, and a diode 9 is connected to the transistor 7 in anti-parallel. The heating coil 10 and the resonance capacitor 1 are connected between the connection point of the transistor 7 and the negative potential of the DC input.
One series circuit is connected. The base-emitter of each of the transistors 6 and 7 is connected to the control circuit 12.

In the above configuration, the transistors 6 and 7 are turned on alternately at a constant frequency, and a voltage and a current are applied as shown in FIG. 7A is a collector-emitter voltage waveform of the transistor 6, FIG. 7B is a collector current waveform of the transistor 6, FIG. 7C is a collector-emitter voltage waveform of the transistor 7, and FIG. Is the collector current waveform of the transistor 7 and the diode 9
5 is a current waveform of FIG.

First, at time t0, the transistor 6 conducts, and the resonance current indicated by the hatched portion shown in FIG. 7A flows through the circuit loop shown by the broken line (a) in FIG. Time point t0 shown in FIG.
Transistor 6 is turned off at time t1 after a lapse of T1 from
I do. When the transistor 6 is turned off, an electromotive force is generated in the heating coil 10 by the energy stored in the heating coil 10, and the hatched portion in FIG. 7D in the circuit loop indicated by the dashed line (b) and the broken line (c) in FIG. The resonance currents shown in (b) and (c) flow. When a current flows through the circuit loop (c), the control circuit 12 supplies a drive signal to the transistor 7 so that the transistor 7 conducts. Then, at time t2 after a lapse of T2 from time t1, the transistor 6 is turned on again and the above operation is repeated. Repetition period T
0 = T1 + T2 is controlled to be constant.

Next, when the conduction time of the conduction time T1 of the transistor 6 is increased to be substantially equal to the conduction time T2 of the transistor 7, the heating coil current increases and the heating output increases. At this time, the waveform of the current flowing through the transistor 6 is as shown in FIG. 7E, and the waveform of the current flowing through the transistor 7 is as shown in FIG. However, the repetition frequency T0
= T1 + T2 does not change. 7 (E) and 7 (F) are different from the waveforms of FIGS. 7 (B) and 7 (D) in that FIG.
At time t4, a mode occurs in which the transistor is turned off when current is flowing through the transistor 7,
Accordingly, a current flows through the circuit loop (d) of FIG.
A current indicated by a hatched portion (d) in FIG.

[0008]

However, in the inverter configuration disclosed in Japanese Patent Application Laid-Open No. 61-188787, the frequency is variable, so that when a plurality of heating coils are arranged close to each other, the difference in load material and the output setting can be reduced. There is a problem that interference noise is generated due to the difference between the respective oscillation frequencies due to the difference.

In the configuration disclosed in Japanese Utility Model Laid-Open No. 57-179296, it is necessary to make the difference between the oscillation frequencies of the inverters driving the adjacent heating coils equal to or more than a predetermined value. Considering the variation of the oscillation frequency due to the difference of the load material and the variation of the frequency due to the output adjustment even if it is set, the difference of the oscillation frequency of the adjacent inverter is reduced by the combination of the different load materials and the different output settings, and an interference sound is generated. There is a fear that there is a problem. To avoid such a problem, there is a problem that the oscillation frequency of one of the inverters becomes high, for example, 20 kHz and 50 kHz, and the switching loss of the switching element used in the inverter becomes high.

In the configuration disclosed in Japanese Patent Application Laid-Open No. 58-48386, the correlation between the output and the oscillating frequency differs depending on the load material. If there is a difference between the two, there is a problem in cooking performance that the output level when switching from the frequency variable output control to the duty control is not constant.

In the configuration disclosed in Japanese Patent Application Laid-Open No. 1-260785, when the output of the inverter is low, that is, FIG.
At time t0 or time t2 in (B), a mode occurs in which the transistor 6 starts conducting when a forward voltage substantially equal to the DC power supply voltage value is applied between the collector and the emitter of the transistor 6, and a large turn-on occurs. Loss occurs in the transistor 6, and a steep change in current and voltage at turn-on may cause high-frequency noise. Also, at the time of high output of the inverter, as shown in FIG. 7E, a turn-off mode occurs in the transistor 7 at the time t4. Or the amount of generated high-frequency noise may increase. For example, the snubber resistor 13 and the snubber capacitor 1 shown in FIG.
It is necessary to suppress the rising slope of the collector voltage of the transistor 7 by a circuit such as 4.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and provides an inverter capable of controlling the output at a constant frequency with a small switching loss occurring in the switching means, a small amount of high frequency noise, and an induction heating cooker. The first object is to reduce the size and cost of the device.

A second object of the present invention is to provide an induction heating cooker according to the first aspect, wherein a reverse voltage applied to the first bypass means is suppressed, and the first bypass means is destroyed by a reverse voltage exceeding its withstand voltage. Is to prevent that.

A third object of the present invention is to provide the induction heating cooker according to the first aspect, wherein a semiconductor rectifier is used as the reverse current blocking means of the first switching means, and a reverse recovery current is applied when a reverse voltage is applied to the semiconductor rectifier. At the moment, a reverse voltage is applied to the first switching means to prevent the first switching means from being destroyed.

A fourth object of the present invention is to provide the induction heating cooker according to the first aspect, wherein the driving time ratio between the first switching means and the second switching means is not within a predetermined range.
The object of the present invention is to increase the turn-on current of the switching means, increase the switching loss, and eliminate the possibility of overheating and destruction.

A fifth object is that in an induction heating cooker having a plurality of inverters and a heating coil, even if a plurality of heating coils are driven simultaneously, the frequency difference is caused by a mutual frequency difference in any load state or output setting state. An object of the present invention is to suppress the influence of a leakage electromagnetic field generated from a device on surrounding electronic devices without generating interference noise.

A sixth object of the present invention is to provide an induction heating cooker according to the first aspect in which the oscillation accuracy of the oscillation frequency is increased and the configuration of the output control unit is simplified.

[0018]

Means for Solving the Problems In order to achieve the first object, a first means of the present invention is a first means connected in series between DC power supplies and connected to a positive electrode of the DC power supply.
A second switching means connected to the negative side of the DC power supply; a reverse current blocking means of the first switching means connected in series to the first switching means; A first bypass unit that bypasses a reverse current that is about to flow into the switching unit; a heating coil that resonates by changing a resonance circuit loop by turning on or off the first switching unit or the second switching unit; A resonance circuit comprising: a resonance capacitor; a second bypass means for bypassing a current flowing into the first resonance capacitor when a predetermined voltage is applied to the first resonance capacitor; and a second switching circuit. A second resonance capacitor for resonating with the heating coil and applying a resonance voltage to the second switching means when the means is off. And capacitors, is provided with a driving time ratio control means for varying the driving time ratio to drive the said first switching means and said second switching means alternately at a constant frequency.

In order to achieve a second object, a second means of the present invention has the same structure as the first means, and further includes a reverse current blocking means of the first switching means.
And the first bypass means is connected between the high potential side terminal of the reverse current blocking means and the low potential side terminal of the second switching means. is there.

Further, in order to achieve a third object, a third means of the present invention has the structure of the first means,
Further, a reverse voltage limiting means for suppressing a reverse voltage applied to the first switching means is provided in parallel with the first switching means.

In order to achieve a fourth object, a fourth means of the present invention has the structure of the first means,
An output for outputting a signal corresponding to the instantaneous output power to the drive time ratio control means, fixing the instantaneous output power to a predetermined value, and intermittently driving the duty ratio control means for operating the drive time ratio control means. Setting means; and soft start means for gradually changing a drive time ratio controlled by the drive time ratio control means from an initial value to a value corresponding to a predetermined value of the instantaneous output power.

In order to achieve a fifth object, a fifth means of the present invention comprises: a plurality of heating coils; and a plurality of inverter circuits each including the plurality of heating coils and converting a direct current into a high-frequency current, The plurality of inverter circuits are respectively connected in series between DC power supplies, a first switching means connected to a positive electrode side of the DC power supply, and a second switching means connected to a negative electrode side of the DC power supply. A reverse current blocking means of the first switching means;
A first bypass unit that bypasses a reverse current of the second switching unit; a heating coil that resonates by changing a resonance circuit loop by turning on or off the first switching unit or the second switching unit; and a first resonance unit. A resonance circuit composed of a capacitor, a second bypass unit that bypasses a current flowing into the first resonance capacitor when a predetermined voltage is applied to the first resonance capacitor, and a second switching unit. When turned off, a second resonance capacitor that resonates with the heating coil and applies a resonance voltage to the second switching means, and alternately drives the first switching means and the second switching means at a constant frequency. Together with a drive time ratio control means for changing the drive time ratio and the frequency switching means. That.

In order to achieve the sixth object, a sixth means of the present invention comprises a clock oscillating means for generating a high frequency clock pulse, and a heating output which operates digitally by an output signal of the clock oscillating means. An output control unit that outputs a signal corresponding to the clock signal; and a frequency dividing unit that digitally divides the frequency of the clock pulse to generate a signal having a predetermined frequency. A driving time ratio control means for alternately driving the first switching element and the second switching element at a predetermined oscillation frequency in accordance with an output signal of the means and changing a driving time ratio is provided.

[0024]

According to the induction heating cooker of the present invention, when the first switching means provided on the positive potential side of the DC power supply becomes conductive by the configuration of the first means, the second switching means on the negative potential side becomes conductive. Since it is off, a resonance current flows through the first switching means to the resonance circuit of the heating coil and the first resonance capacitor.

When the first switching means is turned off while the resonance current is flowing, an electromotive force is generated in a direction for maintaining the heating coil current by the energy stored in the heating coil. Due to the electromotive force generated in the heating coil, a resonance current is generated in a circuit loop including the heating coil, the first resonance capacitor, and the second bypass unit.
While this resonance current is flowing through the second bypass means,
When the second switching means is driven in advance and the direction of flow of the resonance current changes, the second bypass means blocks the current, so that the resonance current flows smoothly into the second switching means.

When a time elapses after the resonance current starts flowing through the second switching means and the current di / dt becomes zero and starts to decrease, the voltage applied to the heating coil is inverted. When the voltage applied to the heating coil is inverted, the voltage applied to the first resonance capacitor is inverted, and a predetermined voltage is applied.
Does not flow to the second resonance means. That is, since the first resonance capacitor is bypassed by the second bypass means, the energy stored in the heating coil causes the heating coil, the second switching means, and the second bypass means (in some cases, the internal impedance to be small). A circulating current in a fixed direction without vibration flows through a closed circuit constituted by a DC power supply.

Therefore, when the second switching means is turned off after a predetermined time, a voltage having a polarity such that the high potential side of the second switching means has a positive potential is generated in the heating coil. This voltage charges or discharges the second resonance capacitor to generate a resonance voltage between the second resonance capacitor and the heating coil. At this time, the applied voltage of the second switching means also rises due to the resonance voltage applied to the second resonance capacitor and exceeds the DC power supply voltage, but since the reverse current blocking means of the first switching means is provided, After the voltage rises and reaches the peak voltage, it returns to the DC voltage again. Therefore, it is possible to provide a predetermined time from when the voltage applied to the second switching means exceeds the DC power supply voltage to when it returns to the voltage again. During this time,
When the first switching element is driven, a first switching means turn-on loss (a spike-like current that turns on when a forward voltage is applied to the first switching means and charges or discharges the second resonance capacitor). No loss due to the product of the applied voltage) and the occurrence of high-frequency noise at turn-on can be prevented.

When the second switching means is turned off as described above, the voltage applied to this element becomes a resonance voltage, so that the rate of rise of the voltage dv / dt is relatively small, and the switching loss at the time of off is reduced. Thus, the product of the applied current and the applied voltage can be suppressed, and naturally, the high-frequency noise can be reduced by the effect of suppressing dv / dt.

Further, the driving time of the first switching means, the driving time of the second switching means, and the slight time width provided together so that the first switching means and the second switching means do not conduct simultaneously. The driving time of the first switching element and the driving time of the second switching element are varied while keeping the sum of the constants constant, in other words, the driving time of the first switching means and the second driving time at a constant repetition frequency. Since the driving time ratio control means for varying the driving time ratio of the switching means (hereinafter referred to as driving time ratio) is provided, it is possible to change the magnitude of the heating coil current at a constant oscillation frequency. Can be continuously and variably controlled.

According to the configuration of the second means, the reverse current blocking means of the first switching means is connected in series to the low potential side of the first switching means, and the reverse current blocking means is connected to the low potential side of the first switching means. Since the first bypass means is connected between the potential side terminal and the low potential side terminal of the second switching means, the resonance current bypassed by the first bypass means is connected to the heating coil via the reverse current blocking means. It flows to the first resonance capacitor. Then, the direction and inclination of the resonance current change, and the above-described circulating current flows to the second switching means. When the second switching means is turned off, a resonance voltage is applied to the second switching means, and the high potential of the DC power supply is applied. Is applied. This voltage is
For example, when the first bypass means is directly connected in anti-parallel to the second switching means, the voltage is applied to the first bypass means as it is, so that it is necessary to increase the withstand voltage. Is applied to a series circuit of the reverse current blocking means and the first bypass means.
Therefore, since there is a reverse voltage blocking means, a high voltage higher than the DC power supply voltage is not applied to the first bypass means, and it is possible to use a first bypass means having a low reverse voltage tolerance.

Further, according to the configuration of the third means, the second
When the switching means is turned off, the voltage due to the resonance of the heating coil and the second resonance capacitor is applied to the second switching means as described above, and a voltage is applied to the series circuit of the first switching means and the reverse current blocking means. Although a voltage is applied, a reverse voltage limiting means for suppressing a reverse voltage applied by the first switching means is provided in parallel with the first switching means, so that a reverse current blocking means of the first switching means is provided. Even when a reverse rectifying current is applied in a stepwise manner from the forward direction, such as a semiconductor rectifying element, a reverse recovery current flows and an instantaneously conductive state is used. The reverse voltage applied to the first switching means can be suppressed to prevent the first switching means from being destroyed.

Further, according to the configuration of the fourth means, the instantaneous output power controlled by the drive time ratio control means is fixed to a predetermined value, and the duty ratio control means for operating the drive time ratio control means intermittently. Because it has
When the drive time ratio of the first switching means becomes smaller than a predetermined value or becomes larger than a predetermined value, a turn-on current flowing at the time of turning on the first switching means increases to increase a loss of the first switching means.
Alternatively, the output adjustment range can be expanded without increasing the high-frequency noise caused by the turn-on current.

That is, if the drive time ratio of the first switching means is too small or too large and the heating coil current value when the first switching means is off is small, the first switching The energy stored in the heating coil when the means is turned off decreases, and the resonance current value by the heating coil and the first resonance capacitor decreases. Therefore, the value of the circulating current flowing through the second switching means, which subsequently occurs as described above, becomes small, and after the second switching means is turned off, the peak value of the resonance voltage by the heating coil and the second resonance capacitor becomes small. Therefore, the potential of the high potential side terminal of the second switching means does not reach the DC positive potential,
Will be turned on with the forward potential applied to the switching means. Therefore, a spike-like current that charges or discharges the second resonance capacitor flows through the second switching means, which may cause a large turn-on loss and high-frequency noise due to the turn-on current. Since the instant output power controlled by the time ratio control means is fixed to a predetermined value and output setting means is provided for driving the duty ratio control means for intermittently operating the drive time ratio control means, the turn-on current is regulated. The instantaneous output power can be fixed so as not to exceed the value, and the average output power can be varied by the duty ratio control means, so that the output adjustment range can be widened. Also, the turn-on current increases when the current when the first switching means is off is small, and the current supplied to the heating coil is small, that is, when the power consumed by the load is small, the induction heating cooker is operated. Even if the power supply is operated intermittently, power supply fluctuation applied to the power supply can be reduced. Also, the soft start means for gradually changing the drive time ratio controlled by the drive time ratio control means at a constant oscillation frequency from an initial value to a value corresponding to the predetermined value of the instantaneous output power is provided. Even when a plurality of induction heating cookers are operated in close contact with each other, no harsh interference noise due to the mutual frequency difference is generated.

According to the configuration of the fifth means, a plurality of heating coils and a plurality of inverters for driving the heating coils are provided. Each of the inverters has the same configuration as that of the first means. Switching loss and high-frequency noise can be suppressed to a low level. In addition, it is possible to cook at a predetermined frequency regardless of the size of the pot bottom diameter of the load pan, the material of the pot, or the size of the output. The start operation can also be performed at a constant frequency without changing the frequency, and there is no possibility of generating an interference sound with an adjacent heating coil.

Further, there is provided switching means for switching the oscillation frequency of the output signal of the driving time ratio switching means, so that it is easy to make a difference between the frequencies of adjacent heating coils. It is constant in any load state or cooking state. Therefore,
When a plurality of heating coils are operated at the same time, in any combination of operation modes, it is necessary to eliminate the overlap of the spectrum of the high-frequency noise generated from the mutual heating coils or the inverter circuit, that is, the fundamental oscillation frequency component and the harmonic component superimposed thereon. In addition, it is possible to suppress the influence on other electronic devices, and conversely, it is possible to prevent the generation of a mutual interference sound that becomes an unpleasant audible sound due to an excessively large frequency difference. Therefore, it is not necessary to adjust the oscillation frequency range by changing the inductance of the heating coil and the capacitance value or output value of the resonance capacitor to prevent interference noise as in the past, and it is not necessary to adjust the number of adjacent heating coils or inverter components. This facilitates sharing.

Further, according to the configuration of the sixth means, a frequency dividing means for digitally dividing a high-frequency clock pulse by a counter or the like to reduce the frequency to a predetermined frequency is provided. The driving time ratio control means can alternately conduct the first switching means and the second switching means at this accurate repetition frequency. Therefore, the oscillation frequency can be accurately and constantly controlled at a desired frequency. Further, a clock pulse for operating an output control unit for transmitting a signal corresponding to an output is supplied to the driving time ratio setting means for setting a driving time ratio between the first switching means and the second switching means. Since it is shared with a clock pulse, it can be constituted by the same microcomputer, for example, and the oscillation frequency of the induction heating cooker can be easily switched by processing a program or by switching an oscillator for generating a clock pulse. Can be simplified.

[0037]

【Example】

(Embodiment 1) An embodiment of the present invention will be described below with reference to the drawings.

In FIG. 1, a commercial power supply 13 is rectified by a full-wave rectifier 14, and the output low-frequency DC voltage is supplied to an inverter circuit 17 via a choke coil 15 and a power supply capacitor 16. In the inverter circuit 17, a series connection of an NPN transistor (hereinafter simply referred to as a transistor) 18 and a diode 19 and an NPN transistor (hereinafter simply referred to as a transistor) 20 are connected in series between a positive electrode and a negative electrode of the input direct current. ing. A diode 21 is connected in anti-parallel to the transistor 18, a cathode of a diode 22 is connected to an anode of the diode 19, and an anode of the diode 22 is connected to the transistor 2.
0 emitter. The heating coil 23 having an inductance of about 50 to 60 μH has a capacity of about 0.2 μF.
Is connected in parallel. A parallel circuit and a series circuit of a resonance capacitor 24 having a capacitance of about 2.7 μF are connected between the collector of the transistor 20 and a negative DC terminal. The cathode is connected to a connection point between the heating coil 23 and the resonance capacitor 24. The control circuit 27 includes a microcomputer, receives an output signal of the current transformer 28 and a collector-emitter voltage of the transistor 20, and outputs a drive pulse between the transistor 18 and the base-emitter of the transistor 20 as an output signal.

The operation of the induction heating cooker configured as described above will be described with reference to FIG. The choke coil 15 and the power supply capacitor 16 separate the high frequency generated by the inverter circuit 17 from the commercial power supply. The power supply capacitor 16 has a capacitance of about 10 μF, has a very small impedance in terms of high frequency, A high-frequency large current generated by the inverter circuit flows as a power supply.

FIG. 2A is a waveform showing the collector-emitter voltage of the transistor 18, FIG. 2B is the collector current waveform of the transistor 18, and FIG. 2C is the collector-emitter voltage of the transistor 20. FIG. 2D shows the waveform of the collector current of the transistor 20 and the current flowing through the diode 22, and FIG. 2E shows the current waveform of the resonance capacitor 26.

In FIG. 2B, at time t1, the transistor 18 is turned on, and the collector current indicated by the hatched portion (a) flows through the circuit loop indicated by the broken line (a) in FIG. At time T1 after time t1, that is, at time t2, the transistor 18 is turned off (accurately, the drive signal is turned off). Then, due to the energy stored in the heating coil 23, an electromotive force is generated at both ends of the heating coil 23 where the connection point between the heating coil 23 and the resonance capacitor 24 is positive and the connection point between the heating coil 23 and the cathode of the diode 19 is negative. I do. Due to this electromotive force, resonance currents indicated by oblique lines (b) and (c) in FIG. 2 flow through circuit loops indicated by dashed lines (b) and (c) in FIG.

Since the transistor 20 is driven after a slight delay time Td1 from the time point t2 when a forward current flows through the diode 22, that is, before the direction of the resonance current changes, the circuit loop (FIG. 1) of FIG. When the circuit loop in which the current flows from b) to the circuit loop (c) is switched, current flows continuously, and no voltage is generated between the emitter and the collector of the transistor 20. This delay time Td
1 is also set by the control circuit 27 so that the transistor 18 and transistor 20 do not conduct simultaneously because they become too short.

As shown in FIG. 2D, at time t3, the resonance current flowing through the circuit loop (c) reaches a peak, di / dt becomes zero near the peak of the waveform, and the sign of di / dt reverses thereafter. Since the polarity of the voltage induced in the heating coil 23 is inverted and the diode 25 is biased in the forward direction,
The resonance capacitor 24 is bypassed by the diode 25, and a current flows through a circuit loop (d) indicated by a broken line in FIG.
This circuit loop comprises the heating coil 23 and the transistor 20
And a diode 25, which does not include a capacitor and does not resonate, so that a circulating current in a fixed direction with a small change in amplitude flows due to the energy stored in the heating coil 23. In other words, the collector current of the transistor 20 is maintained with some decay.

Then, the transistor 20 is turned off after Td1 + T2 time from the time point t2, that is, at the time point t4. Then, the energy stored in the heating coil 23 causes the heating coil 23
An electromotive force is generated in the heating coil 23 where the connection point between the heating coil 23 and the collector of the transistor 20 is positive, and the connection point between the heating coil 23 and the collector of the transistor 20 is positive, charges the resonance capacitor 26 and is shown in FIG. Such a current flows through the circuit loop of FIG. Accordingly, a resonance voltage as shown in FIG. 2 (c) is applied between the collector and the emitter of the transistor 20, and the collector potential rises, reaches a peak value Vcp at time t6, and then falls. It reaches the positive electrode potential Ve.

On the other hand, the delay time Td2 from the time when the transistor 20 is turned off (more precisely, the time when the drive signal is turned off)
Later, the transistor 18 is driven by the control circuit 27. At this point, the reverse current is applied to the diode 19, so that the collector current of the transistor 18 does not flow.
As described above, at time t7, the collector potential of the transistor 20 drops below the DC positive electrode potential Ve, so a forward voltage is applied between the diode 19 and the collector and emitter of the transistor 18, and the transistor 19 conducts and the collector current flows. ,
At the same time, the current flowing through the resonance capacitor 26 becomes zero. This collector current excites the series resonance circuit of the heating coil 23 and the resonance capacitor 24 again, and the above operation is repeated.

The delay time Td2 is set so that the transistor 18 starts driving near time t6 when the collector voltage of the transistor 18 reaches a peak so that the diode 19 and the transistor 18 conduct while a reverse voltage is applied to the series circuit. Is set.

When the transistor 20 is turned off at time t4, the collector voltage rises, and when the voltage exceeds the DC positive electrode potential Ve, the diode 19 applies a reverse voltage stepwise from the forward bias state. At this time, the diode 19
However, since the recovery current flows through the diode 21, there is no danger that a reverse voltage will be applied to the transistor 18 during the period in which the recovery current is flowing and the transistor 18 will be destroyed. Since a small recovery current flows through the diode 21 without a resonance current, a small diode having a relatively small current capacity may be used as long as the diode 21 has a necessary withstand voltage performance.

The control circuit 27 uses a microcomputer to control the time from time t1 to time t7 in FIG. 2, that is, T0 = T1 + Td1 + T2 + Td2 to be constant, and to control the input current by the output voltage of the current transformer 28. Or the collector-emitter voltage of the transistor 20 is monitored, the driving time T1 of the transistor 18 and the driving time T2 of the transistor 20 are simultaneously changed, and the high-frequency current value of the heating coil 23 is varied to obtain a desired output. So that excessive voltage and current are not applied to the semiconductor component.

As described above, according to the present embodiment, the transistor 18 connected to the high potential side of the power supply capacitor 16 serving as the DC power supply and the transistor 2 connected to the low potential side
0, a diode 19 connected in series with the transistor 18 to block the reverse current, a diode 22 to bypass the reverse current flowing into the transistor 20, and a loop through which current flows by turning on and off the transistor 18 and the transistor 20. A resonance circuit of a heating coil 23 and a resonance capacitor 24 that resonate, a diode 25 connected in parallel to the resonance capacitor 24 and an anode connected to the negative electrode side of the DC power supply, and a resonance capacitor 26 connected in parallel to the heating coil 23 And a control circuit 27 for alternately driving the transistors 18 and 20 at a constant repetition frequency to vary the drive time ratio, so that the heating coil 23 is driven at a constant frequency to perform induction heating and the heating output. Can be varied. Also diode 2
5 allows the circulating current to flow through the transistor 20 and maintain the current of the transistor 20 until the driving pulse thereof is turned off. Therefore, when the driving pulse of the transistor 20 is turned off, the rising slope of the voltage between the collector and the emitter of the transistor 20 is generated. A small (dv / dt) resonance voltage can be generated. As a result, switching loss when the transistor 20 is turned off can be suppressed, and the occurrence of high-frequency noise when the voltage increases can be prevented. Further, a diode 19 for blocking a reverse current of the transistor 18 is inserted, and the transistor 20
Can be made higher than the DC power supply voltage, and if the transistor 18 is driven in this state, the subsequent transistor 1
When the transistor 8 is driven, it is possible to prevent a mode in which the transistor 18 is turned on when a forward voltage is applied between its collector and emitter, thereby preventing a turn-on loss of the transistor 18 and generation of high-frequency noise due to a turn-on current.

Further, a diode 19 for blocking a reverse current of the transistor 18 is connected in series to the low potential side of the transistor 18, and a diode 22 is connected between the anode of the diode 19 and the emitter of the transistor 20. The resonance current due to the heating coil 23 and the resonance capacitor 24 which is about to flow flows through the diode 22 and the diode 19. The direction in which the resonance current flows changes, and a current flows through the transistor 20 to turn off the transistor 20.
The collector voltage of the heating coil 23 and the resonance capacitor 26 is applied between the collector and the emitter to cause the collector potential of the transistor 20 to exceed the positive potential of the DC power supply, but the diode 19 is inserted in the resonance current bypass route of the diode 22. Therefore, application of a reverse voltage to the transistor 18 can be prevented, and at the same time, a voltage higher than the DC power supply voltage can be prevented from being applied to the diode 22. Even if the diode 22 is directly connected in anti-parallel between the collector and the emitter of the transistor 20, the same operation as described above is performed.
At this time, since the above-described resonance voltage is applied directly to the diode, a voltage exceeding the DC power supply voltage is applied. Therefore, a diode having a high withstand voltage must be used. However, in the configuration of the present embodiment, the resonance voltage is applied to the transistor 20. Even so, the diode 19 is provided with the function of not applying a voltage higher than the DC power supply voltage, so that an inexpensive device having a low withstand voltage can be used.

Since the diode 21 is connected to the transistor 18 in anti-parallel, a reverse recovery current (recovery current) is generated in the diode 19 even if a diode having a long reverse recovery time is used as the diode 19. During this period, the reverse voltage applied to the transistor 21 is suppressed to a low level, so that the transistor 18 can be prevented from being broken. As described above, the diode may have a small withstand current, and the withstand voltage in the reverse direction may be any as long as it can withstand the DC power supply voltage. Therefore, an inexpensive and small diode can be used.

(Embodiment 2) A second embodiment of the present invention will be described below with reference to the drawings.

In FIG. 3, a commercial power supply 13, a full-wave rectifier 14, a choke coil 15, a filter capacitor 16,
Transistor 18, Diode 19, Transistor 2
0, diode 22, heating coil 23, diode 25
Are given the same reference numerals as in FIG. 1 and have the same functions. In FIG. 1, a resonance capacitor 24 is connected between the negative terminal of a power supply capacitor serving as a DC power supply and the heating coil 23, and a resonance capacitor 26 is connected in parallel with the heating coil 23. In FIG. A resonance capacitor 29 is connected between the side and the heating coil 23, a resonance capacitor 30 is connected in parallel with a series circuit of the transistor 18 and the diode 19, and a current transformer 31 for monitoring a current of the heating coil 23 is added. In the configuration of the control circuit 32, a duty ratio control means 32e is added. Further, in FIG. 1, the cathode of the diode 22 is connected to the anode of the diode 19, but in the present embodiment, it is connected to the collector of the transistor 20.

The control circuit 32 is composed of a digital circuit including a microcomputer and an analog circuit, and has four input switches 32h, 32i, 32j, 32k for allowing the user to adjust the output to a desired output. The output setting means 32g outputs a signal to the duty ratio control means 32e, the activation means 32f, and the drive time ratio control means 32c, and the duty ratio control means 32e outputs an output signal to the activation means 32f. ing. Further, the heating switch 32m is connected to the starting means 32f, and the signal of the starting means 32f is supplied to the soft start means 32f.
The signal of the soft start means 32d is output to the drive time ratio control means 32c. Driving time ratio control means 3
The output signal 2c is sent to a drive circuit 32a that drives between the base and the emitter of the transistor 18 and a drive circuit 32b that drives between the base and the emitter of the transistor 20.

The operation of the induction cooking device configured as described above will be described below. Resonant capacitor 29
1 constitutes a series resonance circuit with the heating coil 23, and changes the resonance loop by alternately conducting the transistors 18 and 20. This is the same as the operation of the resonance capacitor 24 in FIG. Also, the resonance capacitor 30
When the transistor 20 is turned on when a circulating current is flowing through the circuit loop of the diode 25, the heating coil 23, and the transistor 20, the transistor 20 resonates with the heating coil 23 to apply a resonance voltage between the collector and the emitter of the transistor 20. This is the same as the operation of the resonance capacitor 24 in FIG. Although the connection position of the cathode of the diode 22 is different from that of FIG. 1, the operation of bypassing the resonance current that is about to flow into the transistor 20 from the emitter side of the transistor 20 and flowing to the heating coil 23 is the same as that of the diode 22 of FIG. The same is true.

A commercial power supply 13 is connected and a heating switch 32 m
Is turned on, the activation means 32f accepts and outputs an activation signal to the soft start means 32d. The soft start means 32d receives this and sends a signal to the drive time ratio setting section of the drive time ratio control means 32c to control the transistors 18 and 20 to alternately conduct at a constant frequency, thereby minimizing the drive time of the transistor 18. The value is gradually set to a predetermined value, and the output is started from a low output and stabilized at a predetermined output value. This predetermined output value is obtained by a signal output from the output setting means 32g to the drive time ratio control means 32c.
If the output is set and the user does not set the output immediately after startup, the maximum output is set to, for example, 2000 W.

When the user presses the "middle" switch 32j in the state of the maximum output, the output setting means 32g sends a signal to the drive time ratio control means 32c, and the drive time ratio control means 32c.
c shortens the driving time of the transistor 18 in response to this, reduces the output to 1500 W, and corrects the driving time of the transistor 20 to make the oscillation frequency constant. Next, when the "weak" switch is pressed, the output setting means 32g similarly reduces the output to 800W.

Further, when the "weak" switch 32h is pressed, the output setting means 32g sends a signal to the conduction ratio control means 32c to keep the driving time of the transistors 18 and 20 in the "weak" state, A signal is sent to the ratio control means 32e. The duty ratio control means 32e outputs an intermittent pulse for 0.5 seconds on and 4.5 seconds off to the starting means 32f. In response to this, the activation means 32f sends a signal to the soft start means 32d to intermittently perform the oscillating operation of the inverter 33 and reduce the heating output to 1/1.
Set to 0 to 80 W.

The transistor 2 of the transistor 18
If the drive time ratio with respect to 0 is too small, the resonance current by the heating coil 13 and the resonance capacitor 29 becomes small, and the energy stored in the heating coil 33 becomes small.
The circulating current flowing through the circuit loop of No. 5 becomes small. Therefore, the resonance voltage when the transistor 20 is turned off decreases, so that the potential of the collector of the transistor 20 does not reach the positive potential of the DC power supply, and the difference between the resonance voltage value and the positive potential of the DC power supply increases, so that the transistor 18 The forward voltage value applied at the time of driving may become an extremely large value, which may increase the turn-on loss and the occurrence of high-frequency noise. However, such a phenomenon can be suppressed by using the above method. If the lower limit of the drive time ratio of the transistor 18 is set near the permissible limit of the turn-on current as described above, and the instantaneous output power of the inverter is lower, the on-off control operation of the heating operation can be expanded. Therefore, the influence of the duty ratio control, such as flicker, on the power supply can also be suppressed.

Further, in a multi-port induction heating cooker in which a plurality of heating coils are stored in close proximity, when the inverter of FIG. 3 is used to supply a high-frequency current to each heating coil, the output setting is changed from “weak”. In the case of "strong", even if a plurality of inverters are operated at the same time, the frequency becomes the same under any load condition, so that no interference sound is generated due to the frequency difference. In addition, in order to guarantee stable circuit operation at startup, a soft-start operation that gradually changes the oscillation frequency at startup from a high frequency to a low frequency and changes from a low output to a predetermined output like a conventional resonant inverter is used. Rather than performing, a soft-start operation in which the drive time ratio between the transistor 18 and the transistor 20 is varied and the output gradually increases from a low output to a set output at a constant frequency,
Even if one inverter is activated while another inverter is operating, there is no fear that a frequency difference will occur until this inverter reaches a predetermined output and stabilizes, causing interference noise. Similarly, when one inverter is operating at the “strong” setting and the other inverter is set at the “weak” setting, the inverter set at the “weak” setting periodically (5 in this embodiment).
The start-stop operation is repeated (every second), but since both operate at a constant oscillation frequency, there is no fear that unpleasant interference sound will be generated each time one of the inverters performs the soft-start operation.

As described above, the connection positions of the resonance capacitor 29, the resonance capacitor 30, and the diode 22 are different from those in the first embodiment, but the operation is the same, so that the connection is constant under any load condition and output setting. Oscillation can be performed at the oscillation frequency.
Switching loss and high-frequency noise can be suppressed. Further, the drive time ratio control means 32c fixes the drive time ratio between the transistor 18 and the transistor 20, and
Since the drive time ratio between the transistor 18 and the transistor 20 is fixed to a relatively low output state and the output is varied by changing the on / off ratio of the inverter, the output adjustment range is expanded without increasing the switching loss of the transistor. be able to. In addition, since the soft-start operation is performed by changing the drive time ratio of the transistor 18 and the transistor 19 at a constant frequency at the time of startup, when this inverter is incorporated in a multi-port induction heating cooker, adjacent heating during the soft-start operation is performed. No interference sound is generated due to the frequency difference of the magnetic flux generated by the coil.

Embodiment 3 Hereinafter, a third embodiment of the present invention will be described with reference to the drawings.

FIG. 4 is a circuit block diagram of a two-port induction heating cooker incorporating two inverters. Each of the inverters has substantially the same configuration as that of FIG. 3. Components or circuit blocks having substantially the same functions are given the same numbers, and the symbols a and b are added to the numbers to indicate the respective inverters. . 4 is different from the configuration of FIG. 3 in that the number of the resonance capacitors 29 and the number of the resonance capacitors 30 are one in FIG. 3, but in FIG.
It is divided into two resonance capacitors 34a and 35a or two resonance capacitors 34b and 35b, respectively, and connected in series to both ends of power supply capacitors 16a and 16b serving as DC power sources. A heating coil 23a or a heating coil 23b Are connected, the drive time ratio control means 40a and 40b, and the output setting means 41a and 41b
Oscillation frequency setting means 42a and 42b, output / frequency switching means 43a, changeover switches 44a and 44
b, the changeover switch 44a is off and the changeover switch 44b is on.

The operation of the induction cooking device configured as described above will be described below. First, the resonance capacitors 34a, 35a or the resonance capacitors 34b, 35
b are respectively divided, the resonance capacitors 34a
1 or FIG.
1 and 3, the operation is almost the same as that of the circuit configuration shown in FIG. 1 or FIG. 3 only by shunting the resonance current to these two resonance capacitors. Switch 44
Since a is off, the output / frequency switching means 43a sends a signal to the output setting means 41a and the frequency setting means 42a in response to this. The output setting means 41a sets the maximum output of the inverter to 2000 W, sends a signal to the drive time ratio control means 40a, monitors the output of the current transformer 28a, varies the drive time ratio between the transistor 18a and the transistor 20a, and sets the maximum output. 2000W
Control. At the same time, the frequency setting means 42a sets the oscillation frequency to 21 kHz, and sends a signal to the drive time ratio control means 40a to control the oscillation frequency of the inverter to 21 kHz. Since the changeover switch 44b is on, the output / frequency switching means 43b sends a signal to the output setting means 41b and the frequency setting means 42b in response to this. The output setting means 41b sets the maximum output to 1500W, and makes the drive time ratio control means 40b monitor the output of the current transformer 28b to change the drive time ratio to control the maximum output to 1500W. At the same time, the frequency setting means 42b sets the oscillation frequency to 23 kHz, and sends a signal to the drive time ratio control means 40b to control the oscillation frequency of the inverter to 23 kHz.

As described above, the frequency switching means 44
When the heating coil 23a and the heating coil 23b are driven simultaneously, the difference between the oscillation frequencies is 2 kHz.
Can be In this state, the frequency spectrum distribution (magnetic field intensity distribution for each frequency component) of the radiated noise leaking from each inverter to the surroundings or the conduction noise leaking from the power supply line is analyzed and compared. At 4 kHz, and 2 nkHz at n-times frequency. Therefore,
Since the frequency distributions of the leakage magnetic fields do not overlap, the peak value of the leakage magnetic field does not increase even when they are used simultaneously.
In general, the degree to which an electronic device is affected is proportional to the electromagnetic field strength at each frequency component, and regulations by public institutions are also performed at peak values or quasi-peak values. On the other hand, if adjacent heating coils are operated at different frequencies at the same time, interference noise due to the frequency difference may occur, but a frequency shift of approximately 3 kHz or less is almost heard by human ears as interference noise. In this case, there is no fear. In addition, the oscillation frequency is constant regardless of the load material and output level, so there is no danger that the difference will change significantly. Since the soft-start operation at startup is also performed at a constant frequency, the oscillation frequency matches and the peak value of the leakage electromagnetic field There is no danger that the noise will increase, or conversely, it will spread and generate interference sounds in the audible range.

The two inverter circuits described above have different outputs and different oscillation frequencies. For example, they are all mounted on the same printed wiring board using the same components to form a common unit. Therefore, it is possible to reduce the manufacturing cost.

(Embodiment 4) Hereinafter, a fourth embodiment of the present invention will be described with reference to the drawings.

FIG. 5 shows a circuit block of the control circuit of this embodiment. A microcomputer 45 includes a clock oscillating means 46, an AD converter 47, a frequency dividing means 48, an output setting means 50, and a reference level setting means. 49, and a crystal oscillator 51a or a crystal oscillator 52b and a capacitor 52a or a capacitor 52b
6 is connected. The clock oscillator 46 includes a crystal oscillator 51 a and a crystal oscillator 5
1b is selectively connected. Input / output detection means 5 for detecting the input current of the inverter, the output current / voltage of the high frequency part of the inverter circuit such as the heating coil current / voltage, etc.
7 is input to an AD converter 47 of a microcomputer 45, and the output of the AD converter 47 is output setting means 5
Sent to 0. The output signal of the operation input unit 58 is input to the reference level setting unit 49, and the output setting unit 50
The output signals of the converter 47 and the reference level setting means 49 are compared, and a signal corresponding to the difference is output to the driving time ratio control means 54. The drive time ratio control means 54 includes an output setting means 50
Circuit 55 in accordance with the output of the
And a drive signal to the drive circuit 56.

The operation of the induction heating cooker configured as described above will be described below. Changeover switch 5
3 is connected to the crystal oscillator 51a, the clock oscillation means 46, the crystal oscillator 51a, the capacitor 52a,
A clock pulse of 4 MHz is generated by 52b, and the output pulse of the clock oscillating means 46 operates the microcomputer 45 as a system clock. The frequency dividing means 48 includes a counter, and divides the clock pulse to output a 20 kHz rectangular wave.

When the user operates the output adjustment knob or the output adjustment key of the operation input section 58 to set a desired output, an output signal corresponding to the desired output is output. In response to this signal,
The reference level setting means 49 converts the corresponding reference level into a digital signal and sets it. The reference level setting means 49 digitally processes and stores the maximum output set value and the reference level corresponding to the maximum applied voltage and current value of the components of the inverter.

The AD converter 47 converts the analog signal of the input / output detecting means 47 into a digital signal and outputs the digital signal. The output setting means 50 compares the output signal of the AD converter 47 with the output signal of the reference level setting means 49. Then, an output signal corresponding to the difference is set so that the difference becomes zero.
Output to The drive time ratio control means 54 is the output setting means 5
The digital signal output from 0 is converted into an analog signal,
A pulse corresponding to the on / off timing of the transistor 18 and the transistor 20 is supplied to the drive circuit 55 and the drive circuit 56 by the level signal and the 20 kHz rectangular wave output from the frequency dividing means 48 within a frequency of 20 kHz, that is, a period of 40 μsec as a cycle. Output.

Next, when the switch 53 is switched to connect the crystal oscillator 51b to the clock oscillation means 46,
The frequency of the clock pulse is 4.2 MHz. Since the frequency dividing ratio of the frequency dividing means 48 is the same, the output pulse is 21 kHz. Therefore, the oscillation frequency of the inverter is also 21 kHz.

As described above, since the oscillating frequency of the inverter is switched by the changeover switch 53, for example, two sets of inverter units having the same configuration are prepared, and the heating coils thereof are mounted close to the same housing, and two-port induction heating is performed. Even if a cooker is configured, the difference between the oscillation frequencies can be set to 1 kHz by the changeover switch 53, so that the frequency distribution of the spectrum of the leaked electromagnetic field when used simultaneously overlaps and the peak value of the leaked electromagnetic field at a specific frequency is reduced. It can be prevented from increasing.

The driving frequency ratio control means 54 sets the oscillation frequency to a constant value based on a digitally divided pulse of the frequency of the clock pulse of the microcomputer 45.
The output frequency is variably controlled by changing the ON / OFF ratio of the inverter, so that the oscillation frequency accuracy of the inverter is increased, and the oscillation frequency difference between two adjacent inverters can be accurately kept constant even if the load material or output setting is changed. Therefore, when the two inverters are operated at the same time, it is possible to prevent an increase in the leakage electromagnetic field when the oscillation frequencies match, and conversely, to prevent the occurrence of interference noise due to the frequency difference when the frequency difference is widened.

In the first embodiment, the resonance capacitor 2
4 is connected between the negative electrode of the DC power supply and the heating coil 23, but may be connected between the positive electrode of the DC power supply and the heating coil 23 as shown in FIG. As shown in FIG. 4 of the embodiment, the same effect can be obtained even if the heating coil 23 is connected in series between the DC power sources and the heating coil 23 is connected to the dividing point. In the first embodiment, the resonance capacitor 2
6 is connected in parallel to the heating coil 23, it may be connected between the collector of the transistor 20 and the positive electrode of the DC power supply as shown in FIG.
0 collector and the negative terminal of the DC power supply,
Alternatively, as shown in FIG. 4 of the third embodiment, the collector of the transistor 20 and the positive and negative electrodes of the DC power supply may be connected.

In the first embodiment, the diode 22
Is connected to the anode of the diode 19,
It may be connected to the collector of the transistor 20. However, in this case, since a voltage exceeding the DC power supply voltage may be applied to the diode 22 as described above, a diode having a high reverse voltage tolerance is required. If a diode having a very small reverse recovery current can be used as the diode 19, the diode 21 can be omitted.

Further, as described above, in the first embodiment, a parallel circuit of the heating coil 23 and the resonance capacitor 26 and a parallel circuit of the resonance capacitor 24 and the diode 25 are connected in series. Although the latter is connected to the negative electrode side of the DC power supply, the former may be connected to the negative electrode side of the DC power supply as a matter of course by changing the connection position of the two. Also at this time, the resonance capacitor 2
The same effect can be obtained by connecting the transistor 6 in parallel with the transistor 20.

In the first embodiment, the semiconductor elements such as the transistor 18, the diode 19, the transistor 20, and the diode 21 are described as independent elements in FIG. 1, but a plurality of these semiconductor elements can be arbitrarily combined. Thus, it may be used as a single element, or may be replaced with another type of element having a similar function. For example, the transistor 18 and the diode 21 may be integrally formed on the same semiconductor chip to form a reverse conducting transistor, or the transistor 18 and the diode 19 may be similarly combined to be used as a reverse element diode, or may be used as a reverse element diode. Alternatively, the chips may be arranged and integrally molded with an electric insulating member. Also, a plurality of arbitrary components may be connected in parallel to divide a large current for use.

The diode 21 is connected to the transistor 18
May be configured by another element or circuit having a function of limiting the reverse voltage.

[0080]

As described above, according to the present invention, the first switching means connected to the positive potential side of the DC power supply, and the first switching means connected in series to the first switching means and connected to the negative potential side of the DC power supply. Connected second switching means, first bypass means for bypassing a reverse current flowing into the second switching means, and a resonance circuit loop by turning on / off the first switching means or the second switching means. The heating coil that resonates by changing the
And a drive time ratio control means for alternately driving the first switching means and the second switching means at a constant frequency and changing the drive time ratio. It is possible to operate the inverter at a constant frequency regardless of the output setting. Further, when the second switching means is turned off, the second switching means resonates with the heating coil when the second switching means is turned off. Is provided, the voltage applied to the second switching element can be made into a resonance waveform immediately after the second switching element is cut off, so that the switching loss of the second switching element and the high frequency The amount of noise generated can be significantly reduced. Further, since a second bypass means is provided for bypassing a current flowing into the first resonance capacitor when a predetermined voltage is applied to the first resonance capacitor, the second switching device is provided after the current flowing through the second switching element reaches a peak value. , The amount of attenuation of the current value of the second switching element can be reduced, and the second switching element can always be interrupted while the forward current is flowing. The second switching element can be interrupted by the resonance voltage applied after the interruption. The potential of the high-potential side terminal of the first switching element can be higher than or close to the DC potential of DC, and the second switching at the time of turning on of the first switching element which subsequently becomes conductive is enabled.
This can prevent the occurrence of a spike-like turn-on current for charging the resonance capacitor or prevent the value of the turn-on current from increasing, thereby preventing the occurrence or increase of switching loss at that time.

The present invention also relates to a series connection of a first switching element on the high potential side connected between a DC high potential and a low potential and a first diode for blocking reverse current of the first switching element. A series circuit comprising a second switching element on the low potential side, a second diode connected in anti-parallel to the second switching element, a series connection of the first switching element and the second diode, and a second diode. A series circuit consisting of a first resonance capacitor and a heating coil connected between a connection point with a switching element and a DC high potential or a low potential, and a series connection body consisting of a first switching element and a second diode Alternatively, a second resonance capacitor connected in parallel with the second switching element, and the first switching element and the second switching element are alternately driven. In both cases, the drive time ratio control means for changing the drive time ratio is provided, so that the inverter can be operated at a constant frequency regardless of the load material and the output setting, and the switching loss of the second switching element is reduced. The amount of high frequency noise generated can be suppressed. Further, since the cathode is connected to the connection point between the first resonance capacitor and the heating coil and the third diode is connected to the high potential of DC or the anode of the low potential of DC, the third diode is provided. Second
The generation of a spike-like turn-on current for charging the resonance capacitor can be prevented or the value of the turn-on current can be suppressed from increasing, and the occurrence or increase of switching loss at that time can be suppressed. Further, when the inverter has a low output, the resonance voltage applied to the second switching element is reduced after the second switching element is turned off, and when the first switching element is subsequently turned on, the second switching element is turned off. Although turn-on loss for charging the resonance capacitor occurs in the first switching element, since the inverter is provided with duty ratio control means for intermittently operating at a predetermined output or less,
The loss can be suppressed to a predetermined value or less, and the output adjustment range can be expanded without affecting the commercial power supply such as flicker.

According to the present invention, in the induction heating cooker according to the first aspect, the reverse current blocking means of the first switching means is connected in series to the low potential side of the first switching means, and the reverse current blocking is performed. The high-potential terminal of the means and the second
Since the first bypass means is connected between the low potential side terminals of the switching means, the voltage applied to the first bypass means can be equal to or lower than the DC power supply voltage, and the first bypass means can be manufactured at low cost. It can be made small.

Further, according to the present invention, in the induction heating cooker according to the first aspect, in parallel with the first switching means,
Since the reverse voltage limiting means for suppressing the reverse voltage applied to the first switching means is provided, at the moment when the reverse voltage blocking means of the first switching means is suddenly reverse biased from the forward bias, the reverse current blocking means is provided. During a period in which a small reverse recovery current is generated inside, it is possible to prevent a reverse voltage from being applied to the first switching means to cause breakdown.

Further, the present invention has the configuration of the induction heating cooker according to claim 1 and outputs a signal corresponding to the instantaneous output power to the drive time ratio control means, and fixes the instantaneous output power to a predetermined value. In addition, since the output setting means for driving the duty ratio control means for intermittently operating the drive time ratio control means is provided, the drive time ratio of the first switching means becomes too small or too large. It is possible to prevent an increase in the turn-on current of the first switching means and an increase in the switching loss or an increase in high-frequency noise,
The output adjustment range can be expanded. Further, soft start means for gradually changing the drive time ratio controlled by the drive time ratio control means from an initial value to a value corresponding to the predetermined value of the instantaneous output power while providing a constant oscillation frequency is provided. Even when a plurality of induction heating cookers having a configuration are arranged very close to each other and the intermittent start-up operation is performed by the duty ratio control means as described above, generation of annoying interference sound due to a mutual frequency difference can be prevented. .

According to the present invention, there are provided a plurality of inverters similar to the inverters constituting the induction heating cooker according to claim 1, wherein the switching elements have a small loss and a small amount of high-frequency noise is generated. Alternatively, the cooling configuration can be simplified, and a shield member as a measure against high-frequency noise can be omitted, so that a small and inexpensive multi-port induction heating cooker can be provided. Also, since each inverter oscillates at a constant frequency and is provided with a frequency switching means, a difference can be easily provided between the oscillation frequencies of the individual inverters. Since there are no fluctuations, even if multiple inverters are operated simultaneously, the frequency of the harmonics of each high-frequency noise matches and the magnitude of the electromagnetic field at each frequency increases, or conversely, the frequency difference increases and the interference noise increases. There is no fear of generating. In addition, since a plurality of inverters can be made common except for the switching means, and the components can be shared, the manufacturing cost can be reduced.

In the present invention, since the output control section is digitally controlled, it can be easily integrated with a microcomputer or the like together with other control functions, and digitally divides high-frequency clock pulses for operating them. Frequency dividing means for generating a signal of a predetermined frequency by
This frequency dividing means can be easily realized by a counter or the like, and the accuracy of the oscillation frequency can be improved. Since the duty ratio of the first switching element and the second switching element is varied at a constant frequency in accordance with the output of the frequency dividing means and the output of the output control section, the output is changed. It can be constant, and it can be easily integrated with the output control unit as described above. Further, since the processing is performed digitally, various controls can be performed by changing a program, a general-purpose microcomputer can be used, a special integrated circuit can be avoided, and the initial investment amount can be suppressed. Things.

[Brief description of the drawings]

FIG. 1 is a circuit block diagram of an induction heating cooker according to a first embodiment of the present invention.

FIG. 2 is a diagram illustrating the operation of the induction heating cooker according to the first embodiment of the present invention.

FIG. 3 is a circuit block diagram of an induction heating cooker according to a second embodiment of the present invention.

FIG. 4 is a circuit block diagram of an induction heating cooker according to a third embodiment of the present invention.

FIG. 5 is a circuit block diagram of an induction heating cooker according to a fourth embodiment of the present invention.

FIG. 6 is a circuit block diagram of a conventional induction heating cooker.

FIG. 7 is a diagram illustrating the operation of a conventional induction heating cooker.

[Explanation of symbols]

18, 18a, 18b Transistor (first switching means) 19, 19a, 19b Diode (reverse current blocking means of first switching means) 20, 20a, 20b Transistor (second switching means) 21, 21a, 21b Diode (Reverse voltage limiting means) 22, 22a, 22b Diode (first bypass means) 23, 23a, 23b Heating coil 24 Resonant capacitor (first resonant capacitor) 25, 25a, 25b Diode (third bypass means) 26 Resonant capacitor (second resonant capacitor) 27 Control circuit (drive time ratio control means) 29 Resonant capacitor (first resonant capacitor) 30 Resonant capacitor (second resonant capacitor) 32c Drive time ratio control means 32d Soft start means 32e Duty ratio control means 2g Output setting means 33 Inverters 34a, 34b, 35a, 35b Resonant capacitors (first resonant capacitors) 36a, 36b, 37a, 37b Resonant capacitors (first resonant capacitors) 40a, 40b Drive time ratio control means 43a, 43b Output Frequency switching means 44a, 44b switching switch 46 clock oscillation means 50 output setting means (output control unit) 51a, 51b crystal oscillator 53 switching switch 54 driving time ratio control means

────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Yuji Fujii 1006 Kazuma Kadoma, Kadoma City, Osaka Prefecture Matsushita Electric Industrial Co., Ltd. (56) References JP-A-58-169790 (JP, A) (58) Field (Int.Cl. ⁶ , DB name) H05B 6/12

Claims (6)

(57) [Claims] A first switching means connected in series between the DC power supplies and connected to a positive side of the DC power supply; a second switching means connected to a negative side of the DC power supplies; A reverse current blocking means of the first switching means connected in series to the first switching means, a first bypass means for bypassing a reverse current flowing into the second switching means, A switching circuit or a resonance circuit including a heating coil that resonates by changing a resonance circuit loop by turning on and off the second switching means and a first resonance capacitor; and when a predetermined voltage is applied to the first resonance capacitor, the A second bypass unit for bypassing a current that is going to flow into the first resonance capacitor; A second resonance capacitor that resonates with the second switching means and applies a resonance voltage to the second switching means; and a drive time ratio that alternately drives the first switching means and the second switching means at a constant frequency. The induction heating cooker provided with the drive time ratio control means for changing the temperature. 2. A reverse current blocking means of the first switching means is connected in series to a low potential side of the first switching means, and a high potential side terminal of the reverse current blocking means and a second switching means. The induction heating cooker according to claim 1, wherein the first bypass means is connected between the low-potential-side terminals. 3. The induction heating cooker according to claim 1, further comprising a reverse voltage limiting means for suppressing a reverse voltage applied to said first switching means in parallel with said first switching means. 4. A duty ratio control means for outputting a signal corresponding to the instantaneous output power to the drive time ratio control means, fixing the instantaneous output power to a predetermined value, and intermittently operating the drive time ratio control means. Output setting means for driving
2. A soft start means for gradually changing a drive time ratio controlled by said drive time ratio control means from an initial value to a value corresponding to a predetermined value of said instantaneous output power.
An induction heating cooker as described. 5. A semiconductor device comprising: a plurality of heating coils; and a plurality of inverter circuits each including the plurality of heating coils and converting a direct current to a high-frequency current. A first switching means connected to the positive side of the DC power supply, a second switching means connected to the negative side of the DC power supply,
A reverse current blocking means for the first switching means, a first bypass means for bypassing a reverse current of the second switching means, and a resonance circuit by turning on or off the first switching means or the second switching means; A resonance circuit including a heating coil and a first resonance capacitor which resonate while changing a loop; and a second bypass means for bypassing a current flowing into the first resonance capacitor when a predetermined voltage is applied to the first resonance capacitor. A second resonance capacitor that resonates with the heating coil and applies a resonance voltage to the second switching means when the second switching means is turned off; Driving time ratio control means for alternately driving the means at a constant frequency and changing the driving time ratio, Induction heating cooker having a switching means of the serial frequency. 6. A clock oscillating means for generating a high-frequency clock pulse, an output control unit which operates digitally by an output signal of said clock oscillating means and outputs a signal corresponding to a heating output, Frequency dividing means for digitally dividing the frequency to generate a signal of a predetermined frequency, wherein the driving time ratio control means is configured to control the first time in accordance with an output signal of the output control section and an output signal of the frequency dividing means. The induction heating cooker according to claim 1 or 5, wherein the switching element and the second switching element are alternately driven at a predetermined oscillation frequency and the driving time ratio is changed.