JP3501133B2 - High frequency heating power supply - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a field of a high-frequency heating device for performing dielectric heating using a magnetron such as a microwave oven, and more particularly to a control for reducing and stabilizing distortion of an input current of a power supply device for driving the magnetron. It is a thing.

[0002]

2. Description of the Related Art A conventional high-frequency heating power supply device for driving a magnetron of this type has a circuit configuration as shown in FIG. 14, and its operation will be described. A commercial power supply 1 which is an alternating current is once converted into a direct current voltage by a diode bridge 2. This DC voltage is converted, and the inverter circuit 5 is operated by turning on / off the semiconductor switching elements 3 and 4 to generate a high frequency voltage in the primary winding of the high voltage transformer 6, and the high voltage transformer 6 generates a high frequency high voltage in the secondary winding. To excite. This high frequency high voltage is applied to the high voltage rectifier circuit 7
It is rectified into a DC high voltage by and is applied to the magnetron 8. The magnetron 8 is driven by this DC high voltage,
Generates 2.45 GHz radio waves. Inductor 9 here
And the capacitor 10 form a smoothing circuit, the capacity of the capacitor 10 is such that it can hold a DC voltage with respect to the operating frequency (20 KHz to 50 KHz) under the current circumstances where the inverter circuit 5 is becoming smaller. It does not have the ability to smooth the frequency of the commercial power source 1.
Therefore, as shown in FIG.
Shows a waveform obtained by simply full-wave rectifying the commercial power supply 1, and shows a pulsating waveform that varies from almost 0 voltage to the maximum voltage of the commercial power supply 1. Since the inverter circuit 5 operates by the pulsating voltage V10 of the capacitor 10, the envelope waveform of the high frequency voltage generated in the primary winding of the high voltage transformer 6 is V6 (L
The waveform becomes as shown in p) and the voltage V1 of the capacitor 10
Similarly, a low voltage can be generated in the period when 0 is low. That is, there occurs a period in which the threshold VAK (TH) at which the magnetron 8 having the nonlinear characteristic oscillates is not reached. During this period, since the magnetron 8 has stopped oscillating, no power is consumed by the magnetron 8 which is a load, so that the current I1 of the commercial power supply 1 stops flowing, and the waveform has a very distorted waveform having a period in which the current becomes 0, This resulted in a decrease in power factor and generation of harmonic current in the input current.

Therefore, in order to complement the voltage in the vicinity of the valley of the pulsating waveform from the commercial power source, a method using a boosting chopper circuit is used to reduce the number of parts and reduce the size of the component and circuit configuration. A number of methods have been proposed in which the operation of this boosting function and the operation of the previous inverter function are performed at the same time, and a typical one is disclosed in Japanese Patent Laid-Open No. 10-27184.
It is published in 6. FIG. 16 is a circuit diagram showing the circuit configuration of the present invention. However, the load circuit 11 in this patent has a small power consumption such as a discharge lamp, and in a power supply device that handles a large amount of power such as a microwave oven, the semiconductor switch elements Q1 and Q2 that control the boosting operation and the inverter operation are turned on and off. The drive signal does not require a so-called dead dime, which is a period for charging and discharging the boosting capacitor. Furthermore, heating power (power consumption) such as high / medium / weak in the heating setting like a microwave oven.
Therefore, it is not necessary to pay particular attention to the control of the drive signals of the semiconductor switch elements Q1 and Q2 at the moment when the polarity of the commercial power source 1 changes or at the 0 voltage portion and the maximum voltage portion of the commercial power source 1.

[0004]

However, the above-mentioned configuration has the following problems. That is, in the case of actually controlling a device that handles a large amount of power such as a microwave oven, when a circuit configuration that requires switching the on / off timing of the semiconductor switch element depending on the polarity of the power supply voltage is used, the polarity changes at the inflection point. Control of drive signals is very important. This is because charging and discharging of the charge-up capacitor is successful due to the duty ratio and the switching timing when one semiconductor switch element that controls the boost charge-up function and the inverter function and the other semiconductor switch element that controls only the inverter function are switched at the inflection point. If not switched, needle-like distortion will occur in the input current near the inflection point. Conventionally, with this kind of circuit configuration, input current distortion was hardly confirmed because the load circuit consumes less power like a discharge lamp and the current value is minute, and the capacity of the charge-up capacitor is also small. In the case of such a load circuit with large power consumption, the input current waveform is greatly distorted, and there is a concern that the power factor will decrease and the harmonic components will expand.

Furthermore, the configuration shown in the conventional example disclosed in Japanese Patent Laid-Open No. 10-271846 is intended for lighting equipment, and the converted power of these equipments is about 100 W to 200 W at the maximum. Therefore, the current flowing through the circuit naturally flows only a minute current of about several amperes. Therefore, the diode loss should not be so much increased even if the forward ON-state voltage VF is increased in the design with emphasis on the switching speed. Is possible.

On the other hand, a magnetron driving power source used in a microwave oven or the like has a conversion power of 1000 W to 1500 W.
Since it handles a large amount of power, the maximum current that flows in the circuit is 4
A large current of 0 A to 50 A flows. For this reason, if the diode is designed with emphasis on the switching speed, the forward ON voltage VF becomes high, so that the loss (conduction loss) when the diode is conducting becomes large, and the loss is reduced by increasing the switching speed. The effect of doing is diminished. Further, the cooling capacity of the household microwave oven is naturally limited due to the size and cost of the microwave oven, so that the diode must be enlarged or limited in order to increase the switching speed and suppress the rise of the forward ON voltage VF. Large radiating fins for radiating heat under cooling conditions are needed. Therefore, in the magnetron driving power source, it is essential to improve the conversion efficiency and reduce the loss generated in each component of the circuit. Therefore, it is very difficult to apply the configuration shown in the conventional example to a magnetron driving power source from the viewpoint of loss reduction. Therefore, when applied to a magnetron driving power supply, it is necessary to have a circuit configuration that neither increases the switching loss nor the on loss of the diode. Further, if an electrolytic capacitor is used as a power source for driving the magnetron due to the large amount of converted power, an electrolytic capacitor having a high capacity and a high withstand voltage is required to suppress the pulsating current of the electrolytic capacitor. As a result, the size of the power supply itself is increased, which causes an increase in the size of the microwave oven equipped with the power supply for driving the magnetron, and the high frequency switching operation impairs the effect of reducing the size and weight of the power supply for driving the magnetron. Have

[0007]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, the present invention provides a power supply device capable of handling a large amount of electric power, in which a first and a second series-conducting semiconductor switch element are connected in series, and A series connection body of first and second diodes is connected in parallel, first and second capacitors are respectively connected in parallel to the first and second diodes, and a connection point of the first and second diodes and the above A series circuit of a commercial power supply and a high-voltage transformer is connected between the connection point of the first and second semiconductor switches capable of reverse conduction, and the high-voltage output of the high-voltage transformer supplies power to the magnetron through a high-voltage rectifier circuit. It is configured to supply.

As a result, when the voltage polarity of the commercial power source is positive in the previous period due to the complementary turning on and off of the first and second semiconductor switching elements, the voltage obtained by boosting the voltage of the commercial power source is applied to the second capacitor. When the voltage polarity is opposite (negative polarity), the voltage obtained by boosting the commercial power supply is applied to the first capacitor. Since the voltage applied to the primary winding of the high-voltage transformer depends on this boosted voltage, even if the voltage of the commercial power source is low, the voltage higher than that required for the magnetron to oscillate is always higher than the primary voltage of the high-voltage transformer. The input current can be applied to the winding, and the input current can be made to flow over almost the entire area of the commercial power source, so that the input current with less distortion can be obtained. Further, the first and second semiconductor switching elements are one of the high voltage transformers.
Since the operation of applying a high-frequency current to the secondary winding and the operation of applying a boosted voltage to the first and second capacitors can be performed at the same time, the number of inverter components can be minimized and the inverter circuit can be miniaturized. it can. In the circuit operation, the semiconductor switch element turns off the first and second diodes to switch the circuit mode. Therefore, these diodes are not restricted by the switching speed and the forward on-voltage V
It is possible to make the design with emphasis on F, and it is possible to make the loss of this diode extremely small and to improve the efficiency of the inverter circuit.

According to the present invention having the above-described structure, the ON / OFF duty ratios of the first and second semiconductor switching elements are set to 50% near the inflection point where the polarity changes, and the boost charge-up function and the inverter function near the inflection point. One of the semiconductor switching elements that controls the other and the other semiconductor switching element that controls only the inverter function are switched. By such means, one switching element that controls the boosting charge-up function and the inverter function near the inflection point where the polarity changes can be switched at the timing when charging / discharging of the charge-up capacitor is completed, so that a stable high power factor can be obtained. At, the input current with the harmonic components cut off is obtained.

[0010]

The invention according to claim 1 is characterized in that the series connection body of the first and second semiconductor switch elements capable of reverse conduction and the series connection body of the first and second diodes are connected in parallel. First and second capacitors are respectively connected in parallel to the first and second diodes, and a connection point of the first and second semiconductor switch elements capable of reverse conduction;
A commercial power source and a series circuit of the primary winding of the high-voltage transformer are connected between the connection points of the second diode and the second diode, and the output of the secondary winding of the high-voltage transformer drives the magnetron through the high-voltage rectifier circuit. Of the above, the ON / OFF duty ratios of the first and second semiconductor switch elements capable of reverse conduction are each set to 50% near the inflection point where the polarity of the commercial power source changes.

The invention according to claim 2 is the first and second aspects.
And a series connection body of semiconductor switch elements capable of reverse conduction and a series connection body of first and second diodes are connected in parallel,
First and second capacitors are connected in parallel to the first and second diodes, respectively, and a connection point of the first and second semiconductor switch elements capable of reverse conduction, and the first and second diodes. A configuration in which a commercial power source and a series circuit of the primary winding of the high-voltage transformer are connected between the connection points of the two, and the output of the secondary winding of the high-voltage transformer includes a drive circuit for driving the magnetron through a high-voltage rectifier circuit. Among them, the control of the commercial power source in the vicinity of the inflection point is provided with polarity determining means and the inflection point is detected to detect both the boosting charge-up function and the inverter function and the role of only the inverter function at the same time complementarily. The configuration is such that the roles of the first and second semiconductor switch elements capable of performing reverse conduction are switched, and the drive circuit serves as an inflection point of the polarity of the commercial power supply.
After detecting ZVP, the first
And second semiconductor switch element capable of reverse conduction in series connection
Allow the body to turn off at the same time to allow sufficient time to discharge the capacitor.
I tried to do it for a minute .

With the above structure, even in a load circuit with large power consumption such as a microwave oven, the needle-like input current waveform distortion at the inflection point where the polarity of the commercial power source changes can be suppressed, and the power factor can be reduced and the harmonic components can be expanded. It was possible to suppress.

[0013]

Embodiments of the present invention will be described below with reference to the drawings.

(Embodiment 1) FIG. 1 shows a circuit configuration used in a first embodiment of the present invention.
A series connection body of the first and second semiconductor switching elements 12 and 13 and a series connection body of the first and second diodes 14 and 15 are connected in parallel, and the first and second diodes 1 and 2 are connected.
First and second capacitors 1 in parallel with 4 and 15 respectively
6, 17 are connected to each other and the semiconductor switch element 12,
A series circuit of the commercial power supply 1 and the high-voltage transformer 18 is connected between the connection point of 13 and the connection points of the diodes 14 and 15. The secondary winding output of the high voltage transformer 18 is connected to the high voltage rectifier circuit 7 and applies a high DC voltage to the magnetron 8. The magnetron 8 is driven by this DC high voltage and generates a radio wave of 2.45 GHz. In the present embodiment, the first and second semiconductor switch elements are described as an IGBT (insulated gate bipolar transistor) that conducts in the forward direction and a diode that is connected in anti-parallel to the IGBT.
It is needless to say that the present invention can be applied even when an element such as an OSFET having a diode inside is used.

FIG. 2 is a diagram showing a path through which a current flows in each period of the inverter circuit, and FIG. 3 is an operation waveform diagram corresponding thereto. The description starts from the state in which the semiconductor switch element 13 is turned on with the polarity of the commercial power supply 1 being shown. In this state, as shown in FIG.
Primary winding of high-voltage transformer 18 → semiconductor switch element 13
→ A current flows through the path of the diode 15, and the current indicated by I13 in the period of FIG. 3A flows through the semiconductor switch element 13 and the primary winding of the high-voltage transformer 18, whereby the primary winding of the high-voltage transformer 18 Store energy in. When the semiconductor switching device 13 is turned off for a predetermined time, the primary winding current of the high voltage transformer 18 tries to continue flowing in the same direction, and this time, as shown in FIG. The energy stored in the primary winding of the high-voltage transformer 18 is charged in the capacitor 16 along the path of winding → parallel diode of the semiconductor switching element 12 → capacitor 16. By this operation, a voltage obtained by boosting the voltage of the commercial power supply 1 is stored in the capacitor 16. When all the energy stored in the primary winding of the high-voltage transformer 18 is released, the path shown in FIG.
The energy charged in 6 is taken out through the route of capacitor 16 → semiconductor switch element 12 → primary winding of high-voltage transformer 18 → commercial power supply 1. Then, when the semiconductor switching element 12 is turned off for a predetermined time, the primary winding of the high voltage transformer 18 tries to keep the current flowing in the same direction. Therefore, as shown in FIG. A current flows through the parallel diode path of the power supply 1 → capacitor 17 → semiconductor switch element 13. When the voltage polarity of the commercial power supply 1 is opposite to that shown in the figure, the semiconductor switch elements 12 and 13, the diodes 14 and 15, and the capacitors 16 and 17 are replaced with each other, and the same operation is performed.

In the above operation, the capacitors 16 and 17
Can perform both an inverter operation for generating a high-frequency current in the primary winding of the high-voltage transformer 18 by turning on / off the semiconductor switching elements 12, 13 and an operation for generating a voltage boosted with respect to the voltage of the commercial power source 1 in the capacitors 16, 17. The capacitors 16 and 17 are designed to have the same capacitance, and the capacitors 16 and 17 have the same capacitance. As a result, when the voltage polarity of the commercial power source 1 is shown, the voltage obtained by boosting the voltage of the commercial power source 1 is stored in the capacitor 16, and when the voltage polarity of the commercial power source 1 is opposite to that shown in the figure, the commercial power source is stored in the capacitor 17. It operates to store the voltage obtained by boosting the voltage of 1. Therefore, the capacitors 16 and 17 are independent of the voltage polarity of the commercial power source 1.
Since the voltages generated at 1 and 2 can be made equal, the current of the commercial power source 1 can have a positive and negative symmetrical waveform. By continuing such operation, as shown in FIG. 4, the voltage waveforms of the capacitors 16 and 17 with respect to the cycle of the commercial power source 1 generate a boosted voltage according to the voltage polarity of the commercial power source 1. Therefore, the envelope waveform of the current flowing through the primary winding of the high-voltage transformer 18 has a waveform as shown by V18 (Lp). This voltage is boosted by the high-voltage transformer 18 and applied to the magnetron 8. Therefore, the voltage applied to the magnetron 8 has a waveform like V8, and the oscillation voltage VAK (TH) is always present.
It is possible to maintain the above voltage. As a result, the input current I1 can flow in any period of the commercial power supply 1, and the power factor can be improved and harmonics can be suppressed.

Further, in FIG. 3, periods (a) to (b)
When the operation shifts to, the diode 15 is cut off, but since the semiconductor switch element 13 is connected in series as a current path, the semiconductor switch element 13 is cut off.
Therefore, the switching speed of the diode 15 is not required. Further, since the voltage applied to the diode 15 at the time of turning off is zero, no switching loss occurs at the time of turning off. Therefore, the diode 14,
As the design of 15, the forward ON voltage VF can be emphasized so that it can be designed to suppress the loss at the time of conduction, and the diodes 14 and 15 can be downsized and the diodes 14 and 15 can be cooled at the same time. It is easy to simplify the configuration. In particular, a magnetron driving power source used in a microwave oven handles a high electric power of 1000 W or more, so the current of the inverter circuit becomes a very large current level of about 40 A to 50 A, and the forward on-voltage VF is emphasized in the design of the diodes 14 and 15. It is useful to improve the efficiency of the inverter circuit by reducing the conduction loss. Therefore, the total power loss of the inverter circuit can be suppressed to a very low level, and a highly efficient magnetron driving power source can be realized.

As described above, in the magnetron driving power source used in this embodiment, the diodes 14 and 15 are designed with the forward ON voltage VF emphasized by the circuit operation which is completely different from the circuit shown in the conventional example. It becomes possible to minimize the loss of the diodes 14 and 15 and improve the power conversion efficiency of the entire magnetron driving power source. The effect is that capacitors 16 and 17 operate as an inverter and commercial power supply 1
This is a peculiar effect which is exhibited by also performing the operation of applying the voltage obtained by boosting the voltage of No. 1, which is realized by the circuit function and the circuit operation of the capacitor different from the configuration of Japanese Patent Laid-Open No. 10-271846 mentioned in the conventional example. It is something.

FIG. 5 shows a more practical circuit configuration of the magnetron driving power source of this embodiment. By providing a low-pass filter 21 consisting of an inductor 19 and a capacitor 20 at the output of the commercial power source 1, an inverter circuit is provided. It is configured so that the high-frequency current of (4) does not flow to the commercial power supply. In this way, the low-pass filter 21 is inserted between the commercial power source 1 and the inverter circuit so that the high frequency current or voltage of the inverter circuit is prevented from sneaking into the commercial power source side, thereby reducing the terminal noise. It will be possible. Note that the above operation does not change even with this configuration. Semiconductor switch element 1 below
The drive circuit 22 that controls the drive signals 2 and 13 will be mainly described.

The drive circuit 22 is a semiconductor switch element 12,
13 is driven to operate the inverter circuit. Drive signal V sent from the drive circuit 22 to the semiconductor switch elements 12 and 13
As shown in FIG. 6A, g12 and Vg13 have waveforms which have a dead time and complementarily turn on and off. In this way, the semiconductor switch elements 12 and 13 are complementarily turned on and off, whereby the inverter circuit transmits power to the magnetron 8.

FIG. 7 shows the relationship between the ON time ratio Don13 of the semiconductor switch element 13 and the converted power P of the inverter circuit. The curve shown by the solid line in the figure is the commercial power supply 1
Shows the change in the converted power P when the voltage polarity of the commercial power source 1 is the polarity shown in FIG. 5, and the curve shown by the broken line is the reverse of this, and the voltage polarity of the commercial power source 1 is the opposite voltage to that in FIG. The change of the conversion electric power P in the case of polarity is shown. Thus, the relationship between the ON time ratio Don13 of the semiconductor switch element 13 and the converted power P of the inverter circuit varies depending on the voltage polarity of the commercial power supply 1. Therefore, when the ON time ratio Don13 of the semiconductor switch element 13 is approximately 50%, the same power conversion can be performed regardless of the voltage polarity of the commercial power source 1 and the current of the commercial power source 1 is as shown in FIG. As shown in, the waveform can be symmetrical. However, if an attempt is made to make the current of the commercial power source 1 a positive and negative symmetrical sine wave, the converted power will be limited to only this one point. In a microwave oven for home use, various heating powers are selected according to the food when heating in the microwave oven. For example, the heating power needs to be adjusted by setting the range "strong", "medium", "weak", and the like. In order to deal with this, the on-time ratio Do of the semiconductor switching device 13
Although it is necessary to change n13 in accordance with the desired output power, the semiconductor switch shown in FIG. 7 is used when adjusting the desired output power with a constant on-time ratio Don13 regardless of the voltage polarity of the commercial power supply 1. From the relationship between the ON time ratio Don13 of the element 13 and the converted power P, the ON time ratio Don1
3 is out of 50%, and the voltage of the commercial power supply 1 shows different current waveforms in the positive period and the negative period. If the control method is erroneous, a positive and negative current waveform will be unbalanced as shown in FIG. In this case, since the current waveform does not have a symmetrical waveform, even harmonics are generated, and eventually the power factor cannot be improved.

Therefore, in this embodiment, the drive circuit 22 operates so that the drive signals of the semiconductor switch elements 12 and 13 are switched according to the voltage polarity of the commercial power supply 1. That is, as shown in FIG. 9, when the voltage polarity of the voltage waveform V1 (dotted line) of the commercial power supply 1 is positive, the semiconductor switch element 13 that controls the boost charge-up and the inverter operation.
The ON time ratio (solid line) Don13 of the semiconductor switch element 13 is increased and the ON time ratio Don1 of the semiconductor switch element 13 is set to the opposite polarity.
Lower 3 Further, when the commercial power supply voltage V1 is positive, the ON time ratio Don13 is the maximum boost charge-up in the valley portion from 0 voltage to the maximum voltage, and conversely in the vicinity of the maximum voltage (peak portion).
on13 is lowered a little. By changing the ON time ratio Don13 of the semiconductor switch element 13 in this way, it is possible to obtain an input current with less distortion, and it is possible to easily adjust the heating power in the ranges "strong", "medium", "weak", and the like. You can do it. Here, the other semiconductor switch element 12 that controls the boost charge-up function and the inverter function when the polarity is negative is the semiconductor switch element 1 described above.
It goes without saying that a complementary operation is performed by following # 3.

At this time, the on-time ratio Don13 is 5 at the inflection point where the polarities of the commercial power supply voltage V1 in FIG.
It is 0%, and the on-times T1 and T2 of Vg13 and Vg12 are equal as shown in FIG. 10 showing the inflection point part in detail. With this control, it is possible to smoothly switch roles between one semiconductor switch element that controls both the boost charge-up function and the inverter function and the other semiconductor switch element that controls only the inverter function at the inflection point. It is possible to suppress needle-like distortion that has occurred in the vicinity of the inflection point in the current and obtain a stable input current.

In addition, as a whole, the conversion power of the magnetron drive power supply is changed while reducing the loss generated in the circuit of the magnetron drive power supply, and the ON time ratio Don13 of the semiconductor switch element 13 starts from a state of about 50%. Even if the converted power deviates in that direction and the converted power increases or decreases, the current waveform of the commercial power source 1 can always maintain a positive and negative symmetrical sinusoidal waveform. Therefore, even if the conversion power is changed, it is possible to realize an operation with a high power factor and a small current distortion while always maintaining a high power conversion efficiency.

(Second Embodiment) FIG. 11 shows a circuit diagram used in a second embodiment of the present invention.
The power supply polarity determination means 23 shown in FIG. 11 determines the voltage polarity of the commercial power supply 1 and transmits a signal indicating whether the commercial power supply 1 has a positive voltage polarity or a negative voltage polarity to the drive circuit 22. As an example thereof, as shown in FIG. 12, when the commercial power source V1 has a positive polarity, the transmission signal V23 has a LOW level, and when the commercial power source V1 has a negative polarity, V23 is HIG.
Judgment is made in the state of H level. The drive circuit 22 operates so as to switch the ON time ratios of the semiconductor switch elements 12 and 13 based on this determination signal, and at the same time, as shown in FIG.
As shown in, the on-time ratio of each is changed according to the polarity of the commercial power supply 1, and the on-time ratio of the semiconductor switch element that controls the boost charge-up function is increased in the valley part of the commercial power supply, and conversely the peak part. Then, control is performed to lower the input current waveform I1 with less distortion.

At this time, the polarity of the commercial power source is determined by the polarity determining means 2
As shown in FIG. 13, after detecting ZVP, which is the inflection point, the capacitor is sufficiently discharged by providing a pause period of simultaneous off for one cycle of the inverter operation, as shown in FIG. You can switch roles. With this configuration, the on / off duty ratio of each semiconductor switching element at the inflection point can suppress needle-like input current distortion at the inflection point even when the on time of Vg13 and Vg12 is set to T1 ≠ T2 as shown in FIG. Becomes

[0027]

As described above, according to the high-frequency heating power supply device of the present invention, the roles of one semiconductor switch element that controls the boost charge-up function and the inverter function and the other semiconductor switch element that controls only the inverter function. It is possible to suppress the needle-like input current distortion at the inflection point, which has occurred in the circuit configuration in which the alternation is required each time the polarity of the commercial AC power supply is switched, and it is possible to obtain a stable input current.

[Brief description of drawings]

FIG. 1 is a circuit diagram for explaining an operation of a magnetron driving power source according to a first embodiment of the present invention.

FIG. 2 is a current path diagram in each operation mode of the power supply for driving the magnetron.

FIG. 3 is an operation waveform diagram of an inverter circuit of the power supply for driving the magnetron.

FIG. 4 is an operation waveform diagram of the power supply for driving the magnetron.

FIG. 5 is a circuit diagram showing a configuration of a power supply for driving the magnetron.

FIG. 6 is a drive signal waveform diagram of a semiconductor switching device of the power supply for driving the magnetron.

FIG. 7 is a graph of the on-time ratio Don13 and the conversion power P of the semiconductor switching element of the magnetron driving power supply.

FIG. 8 is a diagram showing an example of a commercial power supply current waveform of the magnetron driving power supply.

FIG. 9 is a diagram showing a relationship between a commercial power supply and a semiconductor switching element ON time ratio in the magnetron driving power supply.

FIG. 10 is a drive signal waveform diagram of the semiconductor switch element near the inflection point in the magnetron drive power supply.

FIG. 11 is a circuit diagram of a magnetron driving power supply according to a second embodiment of the present invention.

FIG. 12 is an output waveform diagram of the power supply polarity determining means in the power supply for driving the magnetron.

FIG. 13 is a drive signal waveform diagram of the semiconductor switch element near the inflection point in the magnetron driving power supply.

FIG. 14 is a circuit diagram showing a conventional magnetron driving power supply.

FIG. 15 is an operation waveform diagram of the magnetron driving power supply.

FIG. 16 is a circuit diagram of a power supply device disclosed in Japanese Unexamined Patent Publication No. 10-271846.

[Explanation of symbols]

1 Commercial power supply 7 High voltage rectifier circuit 8 magnetron 12 First semiconductor switch element 13 Second semiconductor switch element 14 First diode 15 Second diode 16 First capacitor 17 Second capacitor 18 High voltage transformer 22 Drive circuit 23 Power supply polarity determination means

─────────────────────────────────────────────────── ─── Continued Front Page (72) Inventor Takeshi Kitazumi 1006 Kadoma, Kadoma City, Osaka Prefecture Matsushita Electric Industrial Co., Ltd. (72) Haruo Suenaga 1006 Kadoma, Kadoma City, Osaka Matsushita Electric Industrial Co., Ltd. (56) References JP-A-2002-110337 (JP, A) JP-A-8-280173 (JP, A) JP-A-2002-110338 (JP, A) JP-A-2002-270361 (JP, A) JP-A-2002 −272100 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) H05B 6/66 H02M 3/28 H02M 7/12 H05B 6/12

Claims (2)

(57) [Claims] 1. A series connection body of first and second semiconductor switch elements capable of reverse conduction and a series connection body of first and second diodes are connected in parallel, and are respectively connected to the first and second diodes. A first and a second capacitors are connected in parallel, and a commercial power source and a high voltage are provided between a connection point of the first and second reverse-conductive semiconductor switch elements and a connection point of the first and second diodes. The primary winding of the transformer is connected to a series circuit, and the output of the secondary winding of the high-voltage transformer drives the magnetron via a high-voltage rectifier circuit.
A high-frequency heating power supply device in which the on-off duty ratios of the first and second semiconductor switch elements capable of reverse conduction are each set to about 50% near the inflection point where the polarity of the commercial power supply changes. 2. A series connection body of first and second semiconductor switch elements capable of reverse conduction and a series connection body of first and second diodes are connected in parallel, and each is connected to the first and second diodes. A first and a second capacitors are connected in parallel, and a commercial power source and a high voltage are provided between a connection point of the first and second reverse-conductive semiconductor switch elements and a connection point of the first and second diodes. A drive circuit is connected to the series circuit of the primary winding of the transformer, and the output of the secondary winding of the high voltage transformer drives the magnetron through a high voltage rectifier circuit.
With the above configuration, by detecting the inflection point while having the polarity discrimination means in the control near the inflection point of the commercial power source, the roles of both the boost charge-up function and the inverter function and the role of the inverter function only are complemented. Of the semiconductor switch elements capable of performing the first and second reverse conductions, which are simultaneously performed, and the drive circuit comprises:
After detecting ZVP, which is the inflection point of the polarity of the commercial power supply,
The first and second reverse conductions in the barter operation are possible.
Simultaneous off pause period of series connection of semiconductor switching devices
A high-frequency heating power supply device that is provided with sufficient capacity to discharge the capacitor .