JP3501137B2 - Power supply for magnetron drive - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetron driving power source having a magnetron such as a microwave oven as a load.

[0002]

2. Description of the Related Art A conventional magnetron driving power source will be described with reference to the drawings. FIG. 13 is a circuit diagram of a conventional magnetron driving power supply. The conventional magnetron driving power supply is a commercial power supply 1 that is an alternating current, and a diode bridge 2
Is converted into a DC voltage by the ON / OFF operation of the semiconductor switching elements 3 and 4, the inverter circuit 5 generates a high frequency voltage in the primary winding of the high voltage transformer 6, and the high voltage transformer 6 generates a high frequency voltage in the secondary winding. Exciting voltage. The high frequency high voltage is rectified by the high voltage rectifier circuit 7 into a DC high voltage and applied to the magnetron 8. The magnetron 8 is driven by this DC high voltage and generates a radio wave of 2.45 GHz.

FIG. 14 is a diagram showing operation waveforms of a conventional magnetron driving power source. AC voltage V1 of commercial power supply 1
Is rectified into a DC voltage by the diode bridge 2. Although the inductor 9 and the capacitor 10 form a smoothing circuit, the capacity of the capacitor 10 is such that a DC voltage can be held for the inverter circuit 5 operating at 20 kHz to 50 kHz in order to reduce the size of the inverter circuit 5. The capacity of the commercial power supply 1 (50H
z or 60 Hz) has no smoothing ability. Therefore, the voltage V10 of the capacitor 10 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. The inverter circuit 5 uses the pulsating voltage V10 of the capacitor 10.
Since the envelope waveform of the high frequency voltage generated in the primary winding of the high voltage transformer 6 becomes a waveform as shown by V6 (Lp), only a low voltage can be generated in the period when the voltage V10 of the capacitor 10 is low. Absent.

On the other hand, the operating characteristics of the magnetron 8 are shown in FIG.
As shown in (4), a non-linear voltage-current characteristic is shown in which the anode current does not flow unless a predetermined voltage or more is applied between the anode and cathode. Therefore, when the voltage generated in the primary winding of the high voltage transformer 6 is low, the voltage excited in the secondary winding is also lowered at the same time, so that the waveform of the voltage V8 applied to the magnetron 8 is VAK (TH ) Will occur for some time. During this period, since the magnetron 8 stops oscillating, the load magnetron 8
Since the electric power is not consumed in, the current I1 of the commercial power supply 1 stops flowing. As a result, the waveform of the current I1 of the commercial power source 1 is shown in FIG.
As shown in (1), the waveform has a very distorted waveform having a period in which the current is zero, which causes a reduction in the power factor of the magnetron driving power supply and a harmonic current in the input current.

To solve such a problem, there has been proposed a circuit configuration shown in FIG. 16 in which an active filter circuit 13 is provided in the preceding stage of the inverter circuit 5 to improve the power factor of the input current and suppress harmonics. There is. The active filter circuit 13 has a so-called step-up chopper circuit configuration,
The boosted voltage can be controlled by the on-time ratio of the semiconductor switch element 17.

The operation in this case will be described with reference to FIG. The voltage of the commercial power supply 1 shows an AC voltage waveform as indicated by V1. The active filter circuit 13 generates a boosted voltage in the capacitor 15 by controlling the voltage obtained by full-wave rectifying the AC voltage V1 by the diode bridge 2 by turning on and off the semiconductor switch element 14. Although the pulsation rate of the boosted voltage V15 varies depending on the capacity of the capacitor 15, it can be prevented from completely decreasing to 0 like V10 in the configuration of FIG. Therefore, the voltage V6 (Lp) generated in the primary winding of the high voltage transformer 6 can be generated at a predetermined value or more even when the voltage of the commercial power supply 1 is near zero. As a result, the voltage applied to the magnetron 8 can always be kept higher than the oscillating voltage. As a result, the input current I1 can have a substantially sinusoidal waveform with no period of 0 as shown in the figure, and the input power factor can be improved and the harmonic current can be suppressed.

However, in such a configuration, the active filter circuit 13 is added to the inverter circuit 5, and the process of power conversion is rectification → step-up → high frequency generation (inverter circuit) → high-voltage rectification, so the process of power conversion increases. However, there is a problem in that the conversion efficiency is lowered and the circuit scale is increased.

Therefore, a structure in which the constituent parts and circuit functions are further shared is disclosed in Japanese Patent Laid-Open No. 10-271846. FIG. 18 is a circuit diagram showing the circuit configuration of the present invention. With this circuit configuration, boosting function,
The operation of the inverter function is performed at the same time to improve the input power factor and simplify the circuit configuration. 19 and 20 are diagrams for explaining the circuit operation, and FIGS. 19A to 19D are diagrams for explaining the energization paths by turning on and off the semiconductor switch elements Q1 and Q2, respectively, and FIG. 20 corresponds thereto. It is an operation waveform diagram. The circuit operation will be described with reference to FIGS. For convenience of description, the description begins with the semiconductor switch element Q2 turned on in the direction in which the voltage polarity of the commercial power supply 1 is as shown in the figure. When the semiconductor switch element Q2 is on, as shown in FIG. 19A, the capacitor C2 → the commercial power source 1 → the inductive load circuit 19 → the semiconductor switch element Q2.
A current flows through the path of, and the current IQ2 of the semiconductor switch element Q2 monotonically increases as shown in FIG. When the semiconductor switch element Q2 is turned off within a predetermined time, the current path shifts to the state shown in FIG. 19B, and the capacitor C1 is charged through the path of diode D2 → commercial power supply 1 → inductive load circuit 19 → diode D3 → capacitor C1. . When all of the energy stored in the inductive load circuit 19 is released, the capacitor C1 is used as a power source, and the capacitor C1 → semiconductor switch element Q1 → inductive load circuit 19 → commercial power source 1 → capacitor C2 is formed. An electric current flows in. When the semiconductor switch element Q1 is turned off within a predetermined time, the inductive load circuit 19 tries to flow a current in the same direction. Therefore, the path shown in FIG. 19 (d) (commercial power supply 1 → capacitor C2 → diode D4 → inductive load circuit). At 19), a current flows and the energy stored in the inductive load circuit 19 is charged into the capacitor C1. When all the energy stored in the inductive load circuit 19 is released, a current again flows through the path of FIG. 19A and the circuit operation continues. Japanese Patent Laid-Open No. 10-2718
Although not disclosed in 46, in order to realize this operation, the capacitances of the capacitors C1 and C2 need to have a capacitance relationship as shown in Expression 1.

(Equation 1) C1 >> C2 In order to satisfy such a relationship, it is necessary to use a capacitor such as an electrolytic capacitor that can handle a large capacity as the capacitor C1.

By such an operation, the current from the commercial power source 1 can be made to flow over almost the entire power source cycle, and the power factor of the input current is improved, harmonics are suppressed, and the circuit is simplified.

[0011]

However, the above-mentioned conventional structure has the following problems.

That is, even if the voltage of the commercial power supply fluctuates, the magnetron cannot detect the oscillation, but cannot output a predetermined high-frequency output, even though the magnetron is in a state capable of oscillating. Alternatively, there is a possibility that it is determined that the magnetron has oscillated even though the magnetron is not ready to oscillate, an overvoltage is generated in the high voltage circuit, and an excessive voltage duty is given to parts of the high voltage circuit.

The present invention has been made in view of the above problems, and an object thereof is to provide a power supply for driving a magnetron which can reliably determine the oscillation of the magnetron even if the voltage of the commercial power supply fluctuates. There is.

[0014]

In order to solve the above-mentioned conventional problems, a magnetron driving power source of the present invention comprises a first and a second series-connectable semiconductor switch element connected in series, and a first and a second serial connection element. A series connection body of two diodes is connected in parallel, first and second capacitors are respectively connected in parallel to the first and second diodes, and the first and second semiconductor switch elements capable of reverse conduction The connection point and the first
A commercial power supply and a series circuit of a 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 energizes the magnetron through the high-voltage rectifier circuit. A drive circuit for driving the first and second semiconductor switch elements is provided, the drive circuit complementarily drives the first and second semiconductor switch elements, and the drive circuit detects oscillation of the magnetron. The oscillation detector, and the oscillation detector is a non-magnetron
Difference between oscillation period and input current when oscillation is possible
Oscillation is detected due to the difference, and it is
Determine whether the magnetron has actually transitioned to the oscillation state
As much as possible, the reference value for determining whether or not the magnetron has transited to the oscillation state is changed according to the voltage of the commercial power supply.

This makes it possible to reliably determine the oscillation of the magnetron even if the voltage of the commercial power source fluctuates.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS In the invention described in claim 1, 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 the first and second capacitors are connected.
A series circuit of a commercial power source and a primary winding of a high-voltage transformer is connected between a connection point of the semiconductor switch element capable of reverse conduction and a connection point of the first and second diodes, and a secondary winding of the high-voltage transformer is connected. The output of the wire has a drive circuit for energizing the magnetron via a high voltage rectifier circuit to drive the first and second semiconductor switch elements, the drive circuit including the first circuit.
And the second semiconductor switch element is complementarily driven, and the drive circuit has an oscillation detector for detecting the oscillation of the magnetron. The oscillation detector is a magnetron.
The input current of the non-oscillation period and the state when oscillation is possible
Oscillation is detected due to the difference and even if the voltage of the commercial power supply fluctuates
Determines whether the magnetron has transitioned to the oscillation state
It is possible to change the reference value for determining whether or not the magnetron has transited to the oscillation state according to the voltage of the commercial power source, so that the oscillation determination reference value of the magnetron is the voltage of the commercial power source. Since it is set to an appropriate value against fluctuations, it is possible to reliably determine the oscillation of the magnetron even if the power supply voltage fluctuates, and prevent applying excessive voltage duty to the high voltage circuit of the magnetron driving power supply. it can.

The invention as defined in claim 2 is particularly defined by claim 1.
The reference value for determining the oscillation of the magnetron by the oscillation detection unit described in (2) is maximized when the commercial power supply is at the rated voltage, and by reducing the reference value when the voltage of the commercial power supply increases or decreases with respect to the rated voltage, Since the reference value for oscillation of the magnetron is set to an appropriate value for the voltage fluctuation of the commercial power supply, the oscillation of the magnetron can be reliably judged even if the power supply voltage fluctuates, and there is an excessive voltage in the high voltage circuit of the magnetron drive power supply. It is possible to prevent application of voltage duty.

The invention described in claim 3 is particularly characterized by claim 2.
By configuring the oscillation detection unit described in 1) to set the lower limit value to the reference value for determining the oscillation of the magnetron, it will not perform oscillation determination for excessively low power supply voltage or excessively high power supply voltage, so abnormal It is possible to prevent the magnetron driving power supply from operating with a large power for various power supply voltages, and to prevent excessive voltage and current duty from being applied to the inverter circuit.

The invention described in claim 4 is particularly
4. The magnetron driving power source according to any one of 1 to 3 is provided with a power supply voltage detection unit that detects the voltage of the commercial power supply , and the oscillation detection unit reliably operates even if the voltage of the commercial power supply fluctuates.
It is possible to determine whether Ron has transitioned to the oscillation state
As much as possible, by changing the reference value for judging the oscillation of the magnetron according to the output signal of the power supply voltage detection unit, the oscillation judgment reference value of the magnetron becomes an appropriate value for the voltage fluctuation of the commercial power supply. Since the setting is made, it is possible to surely determine the oscillation of the magnetron even if the power supply voltage changes, and it is possible to prevent an excessive voltage duty from being applied to the high voltage circuit of the power supply for driving the magnetron.

The invention described in claim 5 is particularly characterized by claim 4.
By configuring the power supply voltage detection unit described in 1 above to detect the voltage of the series connection body of the first and second capacitors, it is possible to detect the voltage according to the voltage of the commercial power supply when the magnetron driving power supply is stopped. Since the reference value for oscillation of the magnetron is set to an appropriate value for fluctuations in the voltage of the commercial power supply, the oscillation of the magnetron can be reliably judged even when the power supply voltage fluctuates, and the high voltage circuit of the magnetron drive power supply can be used. It is possible to prevent application of excessive voltage duty.

The invention as defined in claim 6 is particularly characterized by claim 1.
5. The magnetron driving power source according to any one of 1 to 5 above is provided with a clocking means to restart when the oscillation of the magnetron cannot be detected within a predetermined time,
It is possible to prevent continuous application of high voltage to the high voltage circuit.

The invention according to claim 7 is particularly characterized by claim 6.
When the magnetron driving power supply is provided with counting means and the operation is stopped when the magnetron driving power supply tries to repeat restarting a predetermined number of times or more, restarting is limited to a predetermined number of times or less. It is possible to detect an abnormality and an abnormality in the power supply voltage, and it is possible to prevent an abnormally high voltage or large current from being applied to the magnetron driving power supply.

[0023]

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

(Embodiment 1) A first embodiment of the present invention will be described with reference to FIGS. 1 to 5. FIG. 1 shows a first magnetron driving power source of the present invention.
3 is a circuit diagram showing an embodiment of FIG. A series connection body of the first and second semiconductor switching elements 20 and 21 and a series connection body of the first and second diodes 22 and 23 are connected in parallel, and the first and second
The first and second capacitors 24 and 25 are connected in parallel to the diodes 22 and 23, respectively, and the commercial power source 1 and the high voltage transformer 26 are connected between the connection points of the semiconductor switch elements 20 and 21 and the diodes 22 and 23. It is configured to connect a series circuit. The secondary winding output of the high voltage transformer 26 is connected to the high voltage rectifier circuit 7 and applies a high DC voltage to the magnetron 8. The magnetron 8 is energized by this high DC voltage and generates a radio wave of 2.45 GHz. In this embodiment, the first and second semiconductor switching devices are IGBTs (insulated gate bipolar transistors) that conduct in the forward direction.
However, it is needless to say that the present invention is also applicable to the case where an element such as a MOSFET having a diode inside is used. The drive circuit 27 gives a drive signal to the respective semiconductor switching elements so as to complementarily drive the first semiconductor switching element 20 and the second semiconductor switching element 21 with a predetermined dead time.

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 21 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 26-> semiconductor switch element 21
→ A current flows through the path of the diode 23, and the current indicated by I21 in the period of FIG. 3A flows through the semiconductor switch element 21 and the primary winding of the high voltage transformer 26, so that the primary winding of the high voltage transformer 26. Store energy in. When the semiconductor switch element 21 is turned off for a predetermined time, the primary winding current of the high voltage transformer 26 tries to continue flowing in the same direction, and this time, as shown in FIG. 2B, the commercial power source 1 → the primary of the high voltage transformer 26. The energy stored in the primary winding of the high-voltage transformer 26 is charged in the capacitor 24 along the path of winding → parallel diode of the semiconductor switching element 20 → capacitor 24. By this operation, the voltage obtained by boosting the voltage of the commercial power supply 1 is stored in the capacitor 24. When all the energy stored in the primary winding of the high-voltage transformer 26 is released, the path shown in FIG.
The energy charged in No. 4 is taken out through the path of capacitor 24 → semiconductor switch element 20 → primary winding of high-voltage transformer 26 → commercial power supply 1. Then, when the semiconductor switching device 20 is turned off for a predetermined time, the primary winding of the high voltage transformer 26 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 25 → semiconductor switch element 21. When the voltage polarity of the commercial power supply 1 is opposite to that shown in the figure, the semiconductor switch elements 20, 21, the diodes 22, 23, and the capacitors 24, 25 are replaced with each other to perform the same operation.

In the above operation, the capacitors 24 and 25
Can perform both an inverter operation for generating a high frequency current in the primary winding of the high voltage transformer 26 by turning on / off the semiconductor switching elements 20 and 21, and an operation for generating a voltage boosted with respect to the voltage of the commercial power source 1 in the capacitors 24 and 25. The capacitors 24 and 25 are designed to have the same capacitance, and the capacitors 24 and 25 have the same capacitance. As a result, when the voltage polarity of the commercial power supply 1 is shown, the voltage obtained by boosting the voltage of the commercial power supply 1 is stored in the capacitor 24. On the contrary, when the voltage polarity of the commercial power supply 1 is opposite to that shown in the figure, the commercial power supply is stored in the capacitor 25. It operates to store the voltage obtained by boosting the voltage of 1. Therefore, regardless of the voltage polarity of the commercial power source 1, the capacitors 24, 25
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. Then, the voltage waveform of the capacitor 24 and 25 with respect to the period of the commercial power supply 1 by continuing this operation is a commercial power supply 1
Generates a boosted voltage according to the voltage polarity of. Therefore, the envelope waveform of the current flowing through the primary winding of the high voltage transformer 26 has a waveform as shown by V26 (Lp). Since this voltage is boosted by the high voltage transformer 26 and applied to the magnetron 8, the voltage applied to the magnetron 8 has a waveform like V8, and it is possible to always maintain a voltage equal to or higher than the oscillation voltage VAK (TH). As a result, the input current I1 can flow in any period of the commercial power supply 1,
It is possible to improve the power factor and suppress harmonics.

Further, in FIG. 3, periods (a) to (b)
The operation is such that the diode 23 is cut off at the time of shifting to, but since the semiconductor switching element 21 is connected in series as a current path, the current is cut off.
Therefore, the switching speed of the diode 23 is not required. Further, since the voltage applied to the diode 23 at the time of turning off is zero, no switching loss occurs at the time of turning off. Therefore, the diode 22,
As the design of 23, it is possible to design so as to focus on the loss during conduction by designing with emphasis on the forward ON voltage VF, and the diodes 22 and 23 are cooled at the same time as the diodes 22 and 23 are downsized. It is easy to simplify the configuration. In particular, a magnetron driving power source used in a microwave oven handles a high 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 important in designing the diodes 22 and 23. 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 of this embodiment, the diodes 22 and 23 can be designed with the emphasis on the forward ON voltage VF by the circuit operation which is completely different from the circuit shown in the conventional example. The loss of the diodes 22 and 23 is minimized to improve the power conversion efficiency of the magnetron driving power source as a whole. The effect is that the capacitors 24 and 25 are operated by the inverter and the capacitors 24 and 25.
5 is a unique effect in the present invention exhibited by also performing the operation of applying the voltage obtained by boosting the voltage of the commercial power supply 1 to 5, and is disclosed in the conventional example.
It is realized by a circuit function and a circuit operation of a capacitor different from the configuration of.

FIG. 4 is a diagram showing changes with time in the voltage Vak applied to the magnetron and the temperature of the cathode of the magnetron in the period from the start of operation to the time when the magnetron can oscillate in the power source for driving the magnetron of this embodiment. The cathode of the magnetron receives power from the heater winding provided in the step-up transformer and its temperature rises to a temperature at which thermoelectrons can be stably emitted from the cathode. Generally, this temperature is about 1900K to 2100K, and the heater winding is designed to supply electric power corresponding to this temperature to the cathode. Figure 5 shows the difference between the input current when the magnetron is in the non-oscillating period and when it is ready to oscillate when the voltage generated by the primary winding of the step-up transformer is constant when the voltage of the commercial power supply fluctuates. It is the figure shown. As can be seen from this figure, when the commercial power supply voltage is near the rated voltage, the difference in input current between the non-oscillation state and the oscillating state of the magnetron is large, and it is relatively easy to set the reference value to detect oscillation. can do. However, there is not much difference in this input current when the voltage deviates from the rated voltage. Therefore, if it is configured to detect the oscillation of the magnetron with a constant input current regardless of the voltage of the commercial power supply, it is determined that the voltage has deviated from the rated voltage even though the magnetron has not transitioned to a state where it can oscillate. In some cases, it is determined that the magnetron is not oscillating even though it has already transitioned to an oscillating state. However, in the present invention, the reference value for determining that the magnetron has oscillated is changed according to the voltage of the commercial power source, and the appropriate reference value is set for each voltage, so the voltage of the commercial power source fluctuates. It is also possible to reliably determine whether or not the magnetron has transitioned to the oscillation state.

(Second Embodiment) A second embodiment of the present invention will be described with reference to FIGS. 6 to 8. FIG. 6 is a diagram showing a circuit diagram of this embodiment. The constituent elements having the same reference numerals as those in the first embodiment have the same operation, and the detailed operation thereof will be omitted here. Reference numeral 29 is a power supply voltage detection unit, which is configured to detect the output voltage of the series connection body of the first and second capacitors. The power supply voltage detection unit 29 transmits a signal to the oscillation detection unit 28 based on the detected voltage, and the oscillation detection unit 28 determines whether or not the magnetron 8 oscillates based on the signal from the power supply voltage detection unit 29. Works to change the value. Here, the voltage of the commercial power source 1 and the output voltage of the series connection body of the first and second capacitors are always V2 = 2 × V1 V1: when the magnetron driving power source is stopped, as shown in FIG. The maximum value V2 of the voltage of the commercial power source is the output voltage of the series connection body of the first and second capacitors. This is because when the first and second semiconductor switching elements 20 and 21 are off and the inverter circuit is stopped, the first and second capacitors 2 are
4, 25 and the first and second semiconductor switch elements 20,
This is because the diodes 22 and 23 connected in anti-parallel to 21 double-rectify the voltage of the commercial power supply 1. Therefore, the first and second capacitors 24, 25
By detecting the output voltage of the serially connected body, it is possible to faithfully detect the voltage fluctuation of the commercial power supply. Then, the oscillation detection unit 28 changes the reference value for determining that the magnetron 8 has oscillated according to the detection voltage of the power supply voltage detection unit 29, as shown in FIG. As a result, since appropriate reference values are set for the respective voltages, it is possible to reliably determine whether or not the magnetron 8 has transited to the oscillation state even if the voltage of the commercial power supply 1 changes. .

(Embodiment 3) A third embodiment of the present invention will be described with reference to FIGS. 9 to 11. FIG. 9 is a circuit diagram of the magnetron driving power source of this embodiment. The components denoted by the same reference numerals as those in the first and second embodiments described above have the same operation, and the detailed description of the operation will be omitted here. In this embodiment, the power supply voltage detection unit is configured to detect a signal from the connection between the commercial power supply and the primary winding of the step-up transformer. As shown in FIG. 10, the voltage at this connection point outputs the same voltage as the commercial power source when the polarity is one of the positive and negative polarities of the commercial power source. The present embodiment also has a power supply polarity determination means for determining the polarity of the power supply voltage, and the power supply voltage detection portion detects the voltage only during the period when the power supply polarity determination means determines that the polarity of the commercial power supply is positive. However, it is configured to measure the voltage of the commercial power supply. Further, the oscillation detection unit changes the reference value for determining that the magnetron has oscillated according to the detection voltage of the power supply voltage detection unit, as shown in FIG. As a result, since the appropriate reference value is set for each voltage, it is possible to reliably determine whether or not the magnetron has transitioned to the oscillation state even if the voltage of the commercial power supply fluctuates.

(Embodiment 4) A fourth embodiment of the present invention will be described with reference to FIG. FIG. 12 is a circuit diagram of the magnetron driving power source of this embodiment. The components designated by the same reference numerals as those in the first, second, and third embodiments described above have the same operation, and a detailed description thereof will be omitted here. Here, 31 is a time measuring means, which measures the time from when the inverter circuit starts to operate and the gate signal starts to be generated in the semiconductor switch element. Function to stop the inverter circuit once and restart it after a predetermined time unless the signal that the oscillation detection section has determined that the magnetron oscillation has been sent has been sent even after a certain time has passed since the inverter circuit started operating. To do.
Further, the counting means 32 counts the number of times the restarting is commanded by the timing means 31, and when restarting a certain number of times or more, the counting means 32 operates so that the inverter circuit is stopped and the restarting is not excessive. As a result, it is possible to prevent the high voltage from being continuously applied to the high voltage circuit even when the oscillation of the magnetron cannot be detected when the power supply voltage is abnormally higher or lower than the rated voltage.

[0033]

As described above, according to the present invention, even a load having a non-linear characteristic such as a magnetron can pass an input current over substantially the entire area of a commercial power source and has a high level like a microwave oven. Even in equipment that handles converted power, it is possible to suppress the loss generated in the inverter circuit and realize a highly efficient power supply for driving the magnetron, and whether the magnetron transits to the oscillation state even if the voltage of the commercial power supply fluctuates. Whether or not it can be reliably determined, and in particular, continuous application of excessive high voltage to the high voltage circuit can be prevented.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing a magnetron driving power source according to a first embodiment of the present invention.

FIG. 2 is a diagram showing a path through which a current flows in each period of the inverter circuit of the magnetron driving power supply.

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

FIG. 4 is a diagram showing changes in the voltage Vak applied to the magnetron and the cathode temperature when the magnetron driving power source is started.

FIG. 5 is a diagram showing changes in the input current in the non-oscillation state and the oscillation state of the magnetron with respect to the voltage fluctuation of the commercial power source in the magnetron driving power source.

FIG. 6 is a circuit diagram showing a magnetron driving power supply according to a second embodiment of the present invention.

FIG. 7 is a diagram showing a relationship between a voltage of a commercial power source and an output voltage of a series connection body of first and second capacitors in the magnetron driving power source.

FIG. 8 is a diagram showing a change in the input current in the magnetron driving power supply in the non-oscillation state and the oscillation state of the magnetron with respect to the voltage fluctuation of the commercial power supply.

FIG. 9 is a circuit diagram showing a magnetron driving power supply according to a third embodiment of the present invention.

FIG. 10 is a diagram showing a relationship between a commercial power supply and a detection voltage of a power supply voltage detection unit in the magnetron driving power supply.

FIG. 11 is a diagram showing changes in the input current in the magnetron non-oscillating state and the oscillating state with respect to the voltage fluctuation of the commercial power source in the magnetron driving power source.

FIG. 12 is a circuit diagram showing a magnetron driving power source according to a fourth embodiment of the present invention.

FIG. 13 is a circuit diagram showing a conventional magnetron driving power supply.

FIG. 14 is an operation waveform diagram of the magnetron driving power supply.

FIG. 15 is an operating characteristic diagram of the magnetron in the conventional power supply for driving the magnetron.

FIG. 16 is a circuit diagram of a conventional magnetron driving power supply to which an active filter circuit is added.

FIG. 17 is an operation waveform diagram of the magnetron driving power supply.

FIG. 18 is a circuit diagram of a power supply device disclosed in Japanese Unexamined Patent Publication No. 10-271846.

FIG. 19 is a circuit diagram showing a current path in each operation mode of the power supply device.

FIG. 20 is an operation waveform diagram of the power supply device.

[Explanation of symbols]

1 Commercial power supply 7 High voltage rectifier circuit 8 magnetron 20 First semiconductor switch element 21 Second semiconductor switch element 22 First diode 23 Second diode 24 First capacitor 25 Second capacitor 26 high voltage transformer 27 Drive circuit 28 Oscillation judging section 29 Power supply voltage detector 30 Power supply polarity determination means 31 Timekeeping means 32 counting means

─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Haruo Suenaga 1006 Kadoma, Kadoma City, Osaka Prefecture Matsushita Electric Industrial Co., Ltd. (72) Emiko Ishizaki 1006 Kadoma, Kadoma City, Osaka Matsushita Electric Industrial Co., Ltd. (72) Inventor Hideaki Moriya 1006, Kadoma, Kadoma-shi, Osaka Matsushita Electric Industrial Co., Ltd. (56) Reference JP-A-8-280173 (JP, A) JP-A-4-32191 (JP, A) JP-A-7-135076 (JP, A) JP-A-2-268709 (JP, A) JP-A-55-130093 (JP, A) JP-A-2002-110337 (JP, A) JP-A-2002-110338 (JP , A) JP 2002-270361 (JP, A) JP 2002-272100 (JP, A) JP 2002-272118 (JP, A) JP 2002-280161 (JP, A) (58) Fields investigated ( Int.Cl. ⁷ , DB name) H05B 6/66 H02M 3/28 H02 M 7/12 H05B 6/12

Claims (7)

(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 transformer are connected between a connection point of the first and second semiconductor switch elements capable of reverse conduction and a connection point of the first and second diodes. Drive circuit for connecting the series circuit of the primary windings of the above, and the output of the secondary winding of the high-voltage transformer for energizing the magnetron through the high-voltage rectifying circuit to drive the first and second semiconductor switching elements. Have
The drive circuit complementarily drives the first and second semiconductor switch elements, and the drive circuit has an oscillation detector for detecting oscillation of the magnetron, and the oscillation detector has a period during which the magnetron is not oscillated. And oscillation possible state
Is detected by the difference in the input current when
Magnetron oscillates reliably even when the power supply voltage fluctuates
To be able to determine whether the transition to
The magnetron oscillates according to the voltage of the commercial power supply.
A power supply for driving a magnetron configured to change a reference value for determining whether or not the transition has occurred . 2. The reference value for the oscillation detector to judge the oscillation of the magnetron is maximum when the commercial power source is at the rated voltage, and is reduced when the voltage of the commercial power source increases or decreases with respect to the rated voltage. The magnetron driving power source according to item 1. 3. The magnetron drive power source according to claim 2, wherein the oscillation detection unit sets a lower limit value to a reference value for determining the oscillation of the magnetron. 4. A power supply voltage detection unit for detecting the voltage of the commercial power supply is provided, and the oscillation detection unit detects the fluctuation of the voltage of the commercial power supply.
Determine whether the magnetron has actually transitioned to the oscillation state
4. The magnetron drive power source according to claim 1 , wherein a reference value for determining the oscillation of the magnetron is changed in accordance with an output signal of the power source voltage detection unit so as to be capable of being controlled. . 5. The magnetron driving power supply according to claim 4, wherein the power supply voltage detection unit is configured to detect the voltage of the serially connected body of the first and second capacitors. 6. A magnetron drive power supply according If you can not detect the oscillation of the magnetron within a predetermined provided timer means hours claim 1 which is configured to be restarted in any one of 5. 7. The magnetron drive power supply according to claim 6 , wherein the magnetron drive power supply is configured to stop its operation when the magnetron drive power supply is to be restarted a predetermined number of times or more.