JP3681895B2 - High frequency power supply for magnetron - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a magnetron high-frequency power supply device that drives, for example, a magnetron of a microwave oven.
[0002]
[Prior art]
Inverter power sources capable of continuously and variably controlling microwaves are frequently used in magnetron high frequency power supply devices such as microwave ovens. The inverter power supply converts the DC power obtained from the commercial AC power into high frequency power higher than the commercial frequency, supplies it to the primary winding of the high frequency transformer, and doubles the high frequency voltage generated in the secondary winding. The rectified voltage is applied as an anode voltage between the anode and cathode of the magnetron. Among such inverter power supplies, a half-bridge type has been used to cope with the recent increase in capacity of microwave ovens and increase the output. The half-bridge type inverter power supply can adopt existing switching elements in terms of withstand voltage even when the output is increased, and the DC current component does not remain in the primary winding of the high-frequency transformer, so that the partial excitation phenomenon does not occur. Have advantages.
[0003]
By the way, the output of the magnetron is proportional to the average value of the anode current, but on the other hand, abnormal operation called “moding” (abnormal operation generated in the magnetron due to insufficient heater current, excessive anode current, poor load impedance, etc.). In order to avoid operation in a mode other than the normal oscillation mode, a maximum value is provided for the peak value of the anode current. The magnetron is an electron tube, and if the filament does not reach the required temperature at the start, electron emission does not occur and the oscillation operation does not occur. At this time, the constant voltage characteristic between the anode and cathode of the magnetron does not appear and is almost the same as the release. For this reason, until the filament reaches the required temperature at the start, a high voltage circuit such as a secondary winding of the high-frequency transformer, a voltage doubler rectifier circuit or the like tends to generate overvoltage.
[0004]
On the other hand, as a conventional technique that suppresses the voltage applied to the magnetron at the time of starting, there is a microwave high-frequency power supply device disclosed in, for example, Japanese Patent Laid-Open No. 5-242962. In this prior art, it is determined by a half-bridge circuit, current detection means for detecting the current flowing in the primary winding of the high-frequency transformer, the voltage obtained by the current detected by the current detection means, and the output setting of the magnetron. An error voltage output means for outputting an error voltage corresponding to a difference from the reference voltage, and a switching signal generation means for generating a switching signal for alternately turning on both switching elements at a frequency proportional to the error voltage. Since the detection current of the current detection means becomes almost zero, a switching signal having the maximum frequency in the switching frequency range of both switching elements is generated from the switching signal generation means so as to suppress the voltage applied to the magnetron. As described above, only the technique for suppressing the voltage applied to the magnetron at the time of starting is disclosed in the above-described conventional technique.
[0005]
[Problems to be solved by the invention]
The output of the magnetron is proportional to the average value of the anode current, while a maximum value is provided for the peak value of the anode current in order to avoid abnormal operation called “moding”. For this reason, if the ratio between the peak value and the average value of the anode current is large, there is a problem that the operation with the output value inherent to the magnetron cannot be performed due to the limitation of the maximum value with respect to the peak value of the anode current. The magnetron is an electron tube, and if the filament does not reach the required temperature at the start, electron emission does not occur and the oscillation operation does not occur. At this time, the constant voltage characteristic between the anode and cathode (filament) of the magnetron does not appear and is almost the same as the release. For this reason, it is necessary to heat the filament by operating in the range where the voltage of the high voltage circuit does not exceed the withstand voltage of the circuit until the filament reaches the required temperature at the start of the magnetron.
[0006]
The present invention has been made in view of the above, and until the magnetron heats up, it operates in a range where the voltage of the high voltage circuit does not exceed the withstand voltage of the circuit and detects the phase difference between the inductance current and the inverter output voltage. After detecting heat-up with easy and simple operation, immediately shift to normal output operation, and control the ratio of the peak value and the average value of the anode current of the magnetron to make it operate at high output within the rated range. An object of the present invention is to provide a magnetron high-frequency power supply device.
[0007]
[Means for Solving the Problems]
In order to solve the above-described problem, the invention according to claim 1 is configured such that a series circuit of two switching elements and a series circuit of two resonant capacitors are connected in parallel, and a connection point of the two switching elements is A magnetron comprising a half-bridge type inverter having an inductance formed by a primary winding of a high-frequency transformer generating a supply voltage to the magnetron on the secondary side between the connection points of the two resonance capacitors. In the high-frequency power supply device for an inverter, the inductance current flowing through the inductance is detected, the peak value of the inductance current is controlled based on the detected value, and the phase difference between the inductance current and the output voltage of the inverter is detected, and this detection is performed. The gist is to determine the heat-up state of the magnetron from the result . With this configuration, when starting the magnetron, it is necessary to operate in a range where the voltage of the high voltage circuit does not exceed the withstand voltage of the circuit until the filament heats up. By detecting that the phase difference between the inductance current and the gate control voltage of the switching element having the same phase relationship as that of the inverter output voltage is equal to or less than a predetermined value, it is possible to determine the heat-up of the magnetron .
[0010]
According to a second aspect of the invention, the magnetron high-frequency power supply device according to the first aspect, to be led to the heat-up condition is detected by the detection result of the phase difference, the voltage generated in the resonance capacitor The gist is to control the value below a certain value. With this configuration, until the magnetron heats up, the voltage applied to the primary winding of the high-frequency transformer can be set to a certain value or less, and the high-voltage circuit can be operated in a range that does not exceed the withstand voltage of the circuit.
[0011]
According to a third aspect of the present invention, a series circuit of two switching elements and a series circuit of two resonant capacitors are connected in parallel, and the connection point between the two switching elements and the connection of the two resonant capacitors. A half-bridge type inverter connected with an inductance formed by a primary winding of a high-frequency transformer that generates a supply voltage to the magnetron on the secondary side between the points, and detecting an inductance current flowing through the inductance; In the magnetron high-frequency power supply device that controls the peak value of the inductance current based on the detected value, the detection of the inductance current is sufficiently smaller than the impedance value of the detection capacitor and the detection capacitor in parallel with the resonant capacitor. Connect a series circuit with a resistor of resistance value, as a voltage generated at both ends of the resistor The gist is to do. With this configuration, by detecting the inductance current with the approximate capacitance ratio of the resonant capacitor and the detection capacitor, the response frequency range is wider than that detected by the current transformer, and the peak value of the inductance current is accurately controlled. It becomes possible.
[0012]
According to a fourth aspect of the present invention, there is provided the magnetron high-frequency power supply device according to the third aspect , wherein the voltage generated in the resistor is detected by a peak value rectifier circuit. With this configuration, the peak value of the inductance current can be detected easily and accurately.
[0013]
The gist of a fifth aspect of the present invention is the magnetron high-frequency power supply device according to the third aspect , wherein a voltage generated in the resistor is detected by a comparator. With this configuration, similarly to the above, the peak value of the inductance current is easily and accurately detected.
[0014]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
[0015]
FIG. 1 is a diagram showing a first embodiment of the present invention. First, the configuration of the magnetron high-frequency power supply device will be described. The AC power from the commercial AC power supply 1 is full-wave rectified by the diode bridge rectifier circuit 2 and then smoothed by a filter formed by the choke coil 3 and the smoothing capacitor 4. The DC voltage thus obtained is supplied to a half-bridge type inverter. In the half-bridge type inverter, a series circuit of two switching elements 5a and 5b and a series circuit of two resonant capacitors 7a and 7b are connected in parallel, and a connection point between the two switching elements 5a and 5b An inductance formed by the primary winding 8 of the high-frequency transformer 10 is connected between the connection points of the two resonance capacitors 7a and 7b. A series resonance circuit is formed by the inductance of the primary winding 8 and the resonance capacitor 7a or 7b. 6a and 6b are feedback diodes. The secondary winding 9 of the high-frequency transformer 10 is connected to a voltage doubler rectifier circuit including diodes 12 and 13 and capacitors 14 and 15 for supplying a DC high voltage to the magnetron 16. On the side, a heater winding 11 for supplying current to the filament of the magnetron 16 is provided. Reference numeral 17 denotes a current transformer that detects an inductance current flowing in the inductance formed by the primary winding 8. The detected inductance current is full-wave rectified by the diode bridge 18 and then converted into a voltage value by the resistor 19. The signal is input to the non-inverting input terminal of the first comparator 20. The inverting input terminal of the first comparator 20 is set to + V ₂ voltage. Reference numeral 22 denotes a voltage-controlled oscillator that outputs a frequency signal whose frequency decreases as the input voltage increases. The + _Vp voltage is set to the input terminal of the voltage controlled oscillator 22 via the resistor 25. An output frequency signal from the voltage controlled oscillator 22 is input to the control circuit 23. The output terminal of the control circuit 23 is connected to the drivers 24a and 24b. A switching signal for alternately turning on and off the switching elements 5a and 5b is supplied from the drivers 24a and 24b to the gates of the switching elements 5a and 5b.
[0016]
Next, the operation of the magnetron high-frequency power supply device configured as described above will be described. The + _Vp voltage is input to the voltage controlled oscillator 22, and the voltage controlled oscillator 22 and the control circuit 23 are switched at a frequency (inductive range) equal to or higher than the resonant frequency of the series resonant circuit formed by the inductance and the resonant capacitor 7a or 7b. , 5b are alternately turned on and off. Here, when the switching frequency increases, the inverter input power decreases and the anode current of the magnetron 16 decreases. Conversely, when the switching frequency decreases, the inverter input power increases and the anode current of the magnetron 16 increases. When the voltage V ₁ proportional to the inductance current value (resonance current value) detected by the current transformer 17 exceeds the set voltage V ₂ , the diode 21 connected to the output unit of the first comparator 20 becomes conductive, and voltage control is performed. The input voltage V _{3 of the} oscillator 22 is lowered. As a result, the output frequency of the voltage controlled oscillator 22 increases, the inverter input power decreases, and the anode current of the magnetron 16 decreases. This operation makes it possible to control the peak value of the anode current of the magnetron 16 to be low when the inductance current exceeds a predetermined value. The peak of the inductance current can be controlled by setting the voltage V _2. The output of the magnetron is proportional to the average of its anode current, while a maximum value is provided for the peak value of the anode current in order to avoid abnormal operation called “moding”. For this reason, if the ratio between the peak value and the average value of the anode current is large, the maximum value with respect to the peak value of the anode current is limited, so that the operation with the output value inherent to the magnetron cannot be performed. The peak value of the anode current can be lowered to reduce the ratio between the peak value and the average value of the anode current, and the magnetron 16 can be operated at a higher output within the rated range.
[0017]
2 to 4 show a second embodiment of the present invention. A magnetron is an electron tube. If the filament does not reach the required temperature, no electron emission occurs and no oscillation operation occurs. At this time, the constant voltage characteristic between the anode and cathode of the magnetron does not appear and is almost the same as the release. For this reason, until the filament reaches the required temperature at the start of the magnetron, the voltage applied to the primary winding of the high-frequency transformer is kept below a certain value and the high-voltage circuit is operated within the range that does not exceed the withstand voltage of the circuit. After the upgrade, as described in the first embodiment, it is necessary to reduce the ratio between the peak value and the average value of the anode current and shift to a large output operation within the rated range. The present embodiment realizes these functions. First, a second comparator 26 is provided as means for controlling the voltage applied to the primary winding 8 of the high-frequency transformer 10 to a predetermined value or less during startup. A voltage obtained by dividing the voltage generated in the resonant capacitor 7b by the two resistors 27 and 28 is input to the inverting input terminal of the second comparator 26, and a constant voltage is set to the non-inverting input terminal. . The output terminal of the second comparator 26 is connected to the input terminal of the voltage controlled oscillator 22 via a diode 29 connected in the reverse direction. Further, as means for detecting the heat-up of the magnetron 16, an EXOR gate 30, a CR filter 31, and a third comparator 32 are provided, a detection capacitor 34 for detecting an inductance current, and an impedance value of the detection capacitor 34 A series circuit with a resistor 35 having a sufficiently smaller resistance value is connected in parallel to the resonant capacitor 7b. The inductance current is detected as a voltage generated at both ends of the resistor 35. By making the value of the resistor 35 sufficiently smaller than the impedance value of the detection capacitor 34, the inductance current is an abbreviation of the resonance capacitor 7b and the detection capacitor 34. It is detected by the capacitance ratio, and the response frequency range becomes wider than that detected by the current transformer. The EXOR gate 30 detects the heat-up of the magnetron 16 by detecting the phase difference between the inductance current and the inverter output voltage. A series circuit of a detection capacitor 34 and a resistor 35 is provided at both input terminals thereof. And the gate control voltage of the switching element having the same phase relationship as that of the inverter output voltage. The phase difference output of the EXOR gate 30 is converted into a voltage by the CR filter 31, and the converted voltage is input to the inverting input terminal of the third comparator 32. A constant voltage is set to the non-inverting input terminal of the third comparator 32, and the output terminal is input to the inverting input terminal of the second comparator 26 via the diode 33 connected in the reverse direction. The inductance current detected as a voltage in the series circuit of the detection capacitor 34 and the resistor 35 is also input to the non-inverting input terminal of the first comparator 20. The first comparator 20 functions as a comparator that detects whether or not the inductance current exceeds a predetermined value in a normal operation state to be described later. As this detection means, a known peak value rectifier circuit may be used instead of the comparator.
[0018]
Next, the operation of the magnetron high-frequency power supply device configured as described above will be described with reference to FIGS. 3 and 4. Until the filament reaches the required temperature at the start of the magnetron 16, the voltage generated in the resonant capacitor 7b is divided, and the divided voltage is compared with a constant voltage by the second comparator 26. The input voltage of the voltage controlled oscillator 22 changes so that does not exceed a constant voltage. As a result, the voltage applied to the primary winding 8 of the high-frequency transformer 10 becomes a certain value or less, and the voltage of the secondary winding 9 that is proportional to the voltage of the primary winding 8 also becomes a certain value or less. Is operated in a range where the voltage of the circuit does not exceed the withstand voltage of the circuit. Further, until the magnetron 16 reaches heat up, current does not flow through the secondary winding 9 of the high-frequency transformer 10, and inductance current flows through only the primary winding 8. At this time, as shown in FIG. 3, there is a phase difference of about 90 degrees between the inductance current and the inverter output voltage, and the output of the EXOR gate 30 has a duty of about 50%. Generates about half the power supply voltage. On the other hand, when the filament of the magnetron 16 reaches the required temperature and the magnetron 16 starts oscillating, a current flows through the secondary winding 9 of the high-frequency transformer 10, and as shown in FIG. 4, the inductance current and the inverter output voltage , The output of the EXOR gate 30 has a duty of nearly 100%, and the output of the CR filter 31 becomes high. As a result, the output of the third comparator 32 is inverted, the diode 33 is turned on, and the operation of the second comparator 26 is stopped. As a result, the magnetron 16 shifts to a normal operation state and can perform a large output operation within the rated range.
[0021]
【The invention's effect】
According to the first aspect of the present invention, the phase difference between the inductance current and the output voltage of the inverter is detected, and the heat-up state of the magnetron is determined from the detection result. By detecting that the phase difference from the gate control voltage of the switching element concerned is below a certain value, the heat-up of the magnetron can be detected easily and simply on the primary circuit side of the high-frequency transformer.
[0022]
According to the second aspect of the present invention, since the voltage generated in the resonant capacitor is controlled to a predetermined value or less until it is detected that the heat-up state is reached based on the detection result of the phase difference, the magnetron is heated. Until the voltage is increased, the high-voltage circuit operates within a range that does not exceed the withstand voltage of the circuit, and thereafter, the magnetron can immediately operate at a high output within the rated range.
[0023]
According to the third aspect of the present invention, the inductance current is detected by connecting a series circuit of a detection capacitor and a resistor having a resistance value sufficiently smaller than the impedance value of the detection capacitor in parallel with the resonance capacitor. Since the voltage generated at both ends is used, the response frequency range is wider than that detected by the current transformer, and the peak value of the magnetron anode current can be reliably controlled to be low.
[0024]
According to the fourth aspect of the invention, since the voltage generated in the resistor is detected by the peak value rectifier circuit, the peak value of the inductance current can be detected easily and accurately.
[0025]
According to the fifth aspect of the present invention, since the voltage generated in the resistor is detected by the comparator, the peak value of the inductance current can be detected easily and accurately as described above.
[Brief description of the drawings]
FIG. 1 is a circuit diagram showing a first embodiment of a high frequency power supply for magnetron according to the present invention.
FIG. 2 is a circuit diagram showing a second embodiment of the present invention.
FIG. 3 is a waveform diagram for explaining detection of a phase difference between an inductance current and an inverter output voltage when starting a magnetron in the second embodiment.
FIG. 4 is a waveform diagram for explaining phase difference detection between an inductance current and an inverter output voltage during normal operation in the second embodiment.
[Explanation of symbols]
5a, 5b Switching elements 7a, 7b Resonant capacitor 8 Primary winding (inductance)
9 Secondary winding 10 High frequency transformer 16 Magnetron 17 Current transformer 20 First comparator 22 Voltage controlled oscillator 26 Second comparator 30 EXOR gate 31 CR filter 32 Third comparator 34 Detection capacitor 35 Resistance

Claims (5)

A series circuit of two switching elements and a series circuit of two resonance capacitors are connected in parallel, and a secondary side is connected between the connection point of the two switching elements and the connection point of the two resonance capacitors. A magnetron high-frequency power supply apparatus comprising a half-bridge type inverter connected to an inductance formed by a primary winding of a high-frequency transformer that generates a supply voltage to the magnetron.
An inductance current flowing through the inductance is detected, and a peak value of the inductance current is controlled based on the detected value ,
A high frequency power supply device for magnetron, wherein a phase difference between the inductance current and the output voltage of the inverter is detected, and a heat-up state of the magnetron is determined from the detection result . Until it reaches the heat-up state by a detection result of the phase difference is detected, magnetron high-frequency power source according to claim 1, wherein the controlling the voltage generated in the resonance capacitor below a certain value apparatus. A series circuit of two switching elements and a series circuit of two resonance capacitors are connected in parallel, and a secondary side is connected between the connection point of the two switching elements and the connection point of the two resonance capacitors. Is provided with a half-bridge inverter connected to an inductance formed by a primary winding of a high-frequency transformer that generates a supply voltage to the magnetron, and an inductance current flowing through the inductance is detected, and the inductance is based on the detected value. In the high frequency power supply for magnetron that controls the peak value of current,
The inductance current is detected in parallel with the resonant capacitor by connecting a series circuit of a detection capacitor and a resistor having a resistance value sufficiently smaller than the impedance value of the detection capacitor as a voltage generated at both ends of the resistor. A high-frequency power supply for magnetrons . 4. The magnetron high frequency power supply device according to claim 3, wherein a voltage generated in the resistor is detected by a peak value rectifier circuit. 4. The magnetron high frequency power supply device according to claim 3, wherein a voltage generated in the resistor is detected by a comparator.

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