JP2001185340A - Power supply circuit for driving magnetron - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a power supply circuit for driving magnetron which prevents the occurrence of moding and enables oscillation of high-quality microwave with little noise. SOLUTION: A full-bridge inverter circuit 6 is controlled on driving by an inverter control part 10. Alternate current with variable pulse width is supplied to a high-voltage transformer 7 and high voltage is applied to an electrode of a magnetron 3 through full-wave double-voltage rectifying circuit 9, and, alternate current with all-time constant pulse width is supplied to a transformer 8 for heating cathode. Thus, always constant power is supplied to cathode of the magnetron 3, and the moding is prevented from occurring, since the temperature of the cathode is made stable.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetron drive power supply circuit for driving a magnetron by converting low-voltage DC power generated by a DC power supply such as a solar cell into high-voltage DC power.

[0002]

2. Description of the Related Art Conventionally, a magnetron drive power supply circuit has been used in a high-frequency heating device such as a microwave oven for performing induction heating using microwaves. As this type of magnetron driving power supply circuit, there is one disclosed in Japanese Patent Application Laid-Open No. 9-115454. As shown in FIG. 11, the magnetron drive power supply circuit includes a rectifier circuit 22 for rectifying AC from a commercial power supply 32 and an inverter circuit 2 for converting DC from the rectifier circuit 22 to AC of a predetermined frequency.
3, a control circuit 24 for driving and controlling the inverter circuit 23, a transformer 25 for boosting the AC output from the inverter circuit 23, and a high-voltage rectifier circuit 26 for rectifying the high-voltage AC obtained from the secondary side of the transformer 25. The microwave is oscillated from the magnetron 3 with the high-voltage DC power supplied by the high-voltage rectifier circuit 26. The secondary winding of the transformer 25 includes a high-voltage winding 27 for generating a high voltage applied between the anode and the cathode of the magnetron 3, and a cathode heating winding 28 for heating the cathode of the magnetron 3. And one transformer 25 has two roles of applying a high voltage to the anode and supplying power to the cathode filament of the magnetron 3. Further, the operating frequency of the inverter circuit 23 is increased to about 20 to 50 kHz, which contributes to the weight and size reduction of the transformer 25. As the high-voltage rectifier circuit 26, a high-voltage rectifier circuit is used because it is necessary to apply a high DC voltage to the anode of the magnetron 3. The control circuit 24 controls ON (ON) and OFF (OFF) of a switching element in the inverter circuit 23 to adjust an ON period in which power is substantially transmitted from the rectifier circuit 22 to the transformer 25. Thus, the voltage applied to the magnetron 3 is controlled to change the microwave output.

[0003]

However, in the above-mentioned conventional magnetron drive power supply circuit, one transformer 2 is provided.
5 has two roles, that is, the application of a high voltage to the anode of the magnetron 3 and the supply of power to the cathode filament of the magnetron 3, there are the following problems. That is, when the voltage applied to the anode of the magnetron 3 is reduced to reduce the microwave output,
It is necessary to shorten the ON period of the switching element in the inverter circuit 23. However, if this ON period is shortened, the high-frequency power supplied to the cathode heating winding 28 side also decreases, and the temperature of the cathode filament of the magnetron 3 decreases. Will decrease. When the temperature of the cathode filament falls below the temperature required for normal oscillation of the magnetron 3, moding (abnormal oscillation state) occurs, which causes a reduction in oscillation efficiency and a reduction in the degree of vacuum, thereby shortening the life of the magnetron. On the other hand, if the voltage applied to the anode of the magnetron 3 is increased by increasing the ON period of the switching element in the inverter circuit 23 to increase the microwave output, the high-frequency power supplied to the cathode heating winding 28 also increases. As a result, the temperature of the cathode filament rises above the temperature required for normal oscillation of the magnetron 3, which not only shortens the life of the cathode filament but also broadens the spectrum of the oscillating microwave.

SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide a magnetron drive power supply circuit which can suppress the occurrence of moding, has a narrow band of oscillating microwaves, and has little noise.

[0005]

To solve the above-mentioned problems, a magnetron drive power supply circuit according to the present invention includes a high-voltage transformer for applying a high voltage between an anode and a cathode of a magnetron via a rectifier circuit; A cathode heating transformer for heating the cathode of the magnetron, a full-bridge inverter circuit for supplying power to the high-voltage transformer and the cathode heating transformer, and supplying a constant AC power to the cathode heating transformer, An inverter control unit that controls the full-bridge inverter circuit so as to supply variable AC power to the high-voltage transformer.

The magnetron drive power supply circuit of the present invention is connected to a DC power supply and includes a full-bridge inverter circuit having four switching elements, a high-voltage transformer, a cathode heating transformer, and a rectifier circuit to drive the magnetron. A magnetron drive power supply circuit, comprising a voltage dividing circuit provided at a stage preceding the full bridge inverter circuit and having at least a first and a second voltage dividing capacitor, and a stage preceding the four switching elements of the full bridge inverter circuit. Alternatively, the midpoint between one of the two switching elements in the latter stage is connected to one end of the primary winding of the high-voltage transformer and one end of the primary winding of the cathode heating transformer, and the other of the former stage or the latter stage is connected. To the other end of the primary winding of the high-voltage transformer Then, the other end of the primary winding of the cathode heating transformer is connected to a midpoint between the first voltage dividing capacitor and the second voltage dividing capacitor, and the primary winding of the high voltage transformer is connected. The on-time of one of the two switching elements of the preceding stage or the subsequent stage connected to one end and one end of the primary winding of the cathode heating transformer is always kept constant, and the two switching elements are alternately kept for a fixed time. While the other one of the preceding or succeeding stage connected to the other end of the primary winding of the high-voltage transformer.
By making the on-time of the two switching elements variable,
The present invention is characterized by including an inverter control unit that alternately conducts the two switching elements by the ON time.

According to the above configuration, the voltage dividing circuit having the first and second voltage dividing capacitors suppresses the fluctuation of the DC power output from the DC power supply and divides the output voltage of the DC power supply. Supply it to the cathode heating transformer. On the other hand, the output voltage of the DC power supply is applied to the full-bridge inverter circuit, and the full-bridge inverter circuit is driven and controlled by an inverter control unit, and variable AC power is supplied from the full-bridge inverter circuit to the high-voltage transformer. While being supplied, constant AC power is always supplied to the cathode heating transformer. Therefore, constant power is always supplied to the cathode of the magnetron, and the temperature of the cathode is stabilized. Therefore, occurrence of moding is suppressed.

In one embodiment, the inverter control section includes a gate drive signal generation section for generating a signal for driving the full bridge inverter circuit, and a control amount for sending on-time data to the gate drive signal generation section. An operation unit, and a command signal monitoring unit that controls the variable on-time data given to the gate drive signal generation unit so as not to exceed a set value during a period until a predetermined time elapses after the start of the full bridge inverter circuit. Is provided.

In one embodiment, the command signal monitoring section includes:
During the period from the activation of the full bridge inverter circuit to the elapse of the predetermined time, the variable on-time data is compared with a predetermined set value, and the variable on-time data or the set value is compared. The smaller value is output to the gate drive signal generator.

According to the above configuration, after the full-bridge inverter circuit is activated, a period until a predetermined time elapses,
The command signal monitoring unit controls the variable on-time data given to the gate drive signal generation unit so as not to exceed a set value. Therefore, immediately after the start of the full-bridge inverter circuit, the on-time of the switching element having a variable conduction time becomes equal to or less than a predetermined time, and the AC power supplied to the high-voltage transformer side is suppressed to a small value. A low output operating state where the anode current is small is maintained. In this way, the anode current of the magnetron is limited until the temperature of the cathode of the magnetron rises, so that the occurrence of moding is prevented.

In one embodiment, a smoothing capacitor is provided between the voltage dividing circuit having the first and second voltage dividing capacitors and the full bridge inverter circuit.

According to the above configuration, the fluctuation of the current flowing into the full-bridge inverter circuit is suppressed by the smoothing capacitor, and the destruction of the switching element due to the inflow of the surge current is prevented.

In one embodiment, switch means is connected to one end or the other end of the primary winding of the cathode heating transformer.

According to the above configuration, it is possible to stop energizing the primary winding of the cathode heating transformer by the switching means.

In one embodiment, current detecting means is provided between the rectifier circuit and the anode of the magnetron.

According to the above configuration, it is possible to perform control according to the current of the anode of the magnetron based on the output of the current detecting means.

In one embodiment, a control amount monitoring unit is provided for turning off the switch means when the output from the current detecting means is equal to or more than a predetermined value while the switch means is conductive.

According to the above configuration, the control amount monitoring unit includes:
When it is detected that the output from the current detecting means is equal to or greater than a predetermined value while the switch means is in the conductive state, the switch means is turned off. In this way,
When the anode current of the magnetron flows over a predetermined value, the switch means is turned off to cut off the power supply to the cathode of the magnetron, so that the magnetron shifts to a self-excited oscillation state, and The anodic current is more stable. Therefore, the oscillation spectrum characteristics of the microwave can be improved.

[0019] In one embodiment, the control amount monitoring unit sends the gate drive signal to the gate drive signal generation unit when the switch means is non-conductive and the output from the current detection means is equal to or less than a predetermined value. A stop signal for stopping driving of the full-bridge inverter circuit is output.

According to the above configuration, the control amount monitoring unit includes:
When the output from the current detecting means is equal to or less than a predetermined value when the switch means is in a non-conductive state, the gate drive signal generating unit stops driving the full-bridge inverter circuit. As described above, when the anode current of the magnetron decreases to a predetermined value or less while the switch means is in the non-conducting state, the driving of the full-bridge impeller circuit is stopped, so that the magnetron maintains the self-excited oscillation state. It is possible to prevent the occurrence of moding due to the inability to do so.

[0021]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a magnetron drive power supply circuit according to the present invention will be described in detail with reference to the illustrated embodiments. The magnetron drive power supply circuit of this embodiment is used for a wireless power transmission system that wirelessly and efficiently transmits power obtained by a solar cell to a load system.

(Embodiment 1) FIG. 2 is a diagram showing a wireless power transmission system using microwaves using the magnetron drive power supply circuit 1 of Embodiment 1. This wireless power transmission system comprises a magnetron drive power supply circuit 1, a solar cell 2
And the module composed of the magnetron 3 converts light energy into microwave power, receives the microwave power transmitted in the space by the rectenna (rectifying antenna) 14 and reconverts it into DC power, thereby wirelessly. For long-distance power transmission. In order to realize high-efficiency power transmission in the above-mentioned wireless power transmission system, the microwave serving as a medium for transmission has a low side lobe level in the oscillation frequency spectrum, that is, a low noise and a wide frequency band of the oscillation spectrum. It must be narrow. In order to satisfy such requirements, the magnetron drive power supply circuit 1 has the following configuration.

FIG. 1 shows a circuit configuration of the magnetron drive power supply circuit 1. This magnetron drive power supply circuit 1
A voltage dividing circuit including first and second voltage dividing capacitors 4 and 5, a full-bridge inverter circuit 6, a high-voltage transformer 7, a cathode heating transformer 8, a full-wave voltage doubler rectifier circuit 9, and an inverter controller 10 is provided. The first and second voltage dividing capacitors 4 and 5 suppress the fluctuation of the DC power output from the solar cell 2, divide the output voltage of the solar cell 2 in half and supply it to the cathode heating transformer 8. are doing. The full-bridge inverter circuit 6 converts DC power input from the solar cell 2 into high-frequency AC (several tens to 100 kHz). Switching element Q constituting the full-bridge inverter circuit 6
As 1 to Q4, for example, IGBT (insulated gate bipolar transistor) or the like is used. The high-voltage transformer 7 boosts (1 to 3 kV) the low-voltage high-frequency AC (100 to 300 V) output from the full-bridge inverter circuit 6 and supplies the boosted (1 to 3 kV) to the full-wave voltage doubler rectifier circuit 9.
It plays a role of insulating the side (primary side) from the magnetron 3 side (secondary side). The cathode heating transformer 8 steps down (3-9) a low-voltage high-frequency alternating current (50-150 V) output from the voltage dividing circuit composed of the first and second voltage dividing capacitors 4 and 5 and the full-bridge inverter circuit 6.
V) to supply the cathode filament 11 of the magnetron 3. The full-wave voltage doubler rectifier 9 includes a high-voltage transformer 7.
Rectifies and doubles the high-frequency AC output from the DC power supply, and supplies high-voltage DC power (2 to 6 kV) to the magnetron 3.

On the other hand, the full bridge inverter circuit 6
The inverter control unit 10 for controlling the driving of the control unit includes a control amount calculation unit 12 and a gate drive signal generation unit 13. The gate drive signal generator 13 switches the switching elements Q1 to Q2 of the full-bridge inverter circuit 6 according to the ON time data t _on sent from the control amount calculator 12.
4 is generated.

Next, the operation of the magnetron drive power supply circuit 1 having the above configuration will be described with reference to FIGS. 3, 4 and 5.

The gate drive signal generator 13 reads the value of the ON time data t _on sent from the control amount calculator 12 for each switching cycle (T seconds), and configures the full bridge inverter circuit 6. A drive signal for each of the four switching elements Q1 to Q4 is generated. FIG. 3 shows the driving signal, that is, the switching element Q1.
The switching timing of each of Q4 to Q4 is shown. The switching elements Q1 and Q2 are ON / OFF controlled by the gate drive signal generation unit 13 so as to be alternately turned ON every half the time T / 2 of the switching cycle. The same applies to switching elements Q3 and Q4. Periods C and F indicated by hatching in FIG. 3 are dead times provided to prevent the switching elements Q1 and Q2 and the switching elements Q3 and Q4 from being simultaneously turned on. All the switching elements Q1 to Q4 are turned off. Suppose switching elements Q1 and Q2 or switching element Q
3 and Q4 are simultaneously turned on, the solar cell 2 is short-circuited in the full-bridge inverter circuit 6, and the switching element Q
Since a short-circuit current flows through 1 and Q2 or Q3 and Q4, the switching elements Q1 to Q4 are destroyed by an overcurrent.

First, switching elements Q1 and Q4 are turned on.
Then (period A in FIG. 3), as shown in FIG.
A current flows through a path from the positive side of the solar cell 2 → the switching element Q1 → the primary winding of the high voltage transformer 7 → the switching element Q4 → the negative side of the solar cell 2. That is, power is supplied from the solar cell 2 to the high-voltage transformer 7 via the full-bridge inverter circuit 6. At this time, a voltage is induced on the secondary winding side of the high-voltage transformer 7 in the direction of the arrow in FIG. 4A, and the high-voltage capacitor 15 is charged as indicated by the plus sign in FIG. Is done. Therefore, the voltage of the sum of the voltage of the high-voltage capacitor 15 and the voltage of the high-voltage capacitor 14 charged in the cycle preceding a half cycle (T / 2 seconds) is applied to the magnetron 3. Then, the switching element Q1
Is turned off (period B in FIG. 3), the state shifts to the state in FIG. 4B, and power is not supplied from the solar cell 2 to the high-voltage transformer 7. Therefore, power is supplied from the solar cell 2 to the high-voltage transformer 7 substantially only during the period of the pulse width t _on .

On the other hand, over both periods A and B in FIG. 3, as shown in FIGS. 4 (a) and 4 (b), the solar cell 2 positive side → first
The current flows through the voltage dividing capacitor 4 → the primary winding of the cathode heating transformer 8 → the switching element Q4 → the negative side of the solar cell 2; (The voltage across the second voltage dividing capacitor 5). After that, the switching element Q4
FF is performed, and all the switching elements Q1 to Q4 are turned off (period C in FIG. 3). Therefore, power is supplied from the solar cell 2 to the cathode heating transformer 8 over the period of the pulse width t _max .

Next, the switching elements Q2 and Q3 are turned on.
Then (D period in FIG. 3), as shown in FIG.
A current flows through a path from the positive side of the solar cell 2 → the switching element Q3 → the primary winding of the high-voltage transformer 7 → the switching element Q2 → the negative side of the solar cell 2;
Power is supplied from the solar cell 2 side to the high voltage transformer 7 side via the. At this time, a voltage is induced on the secondary winding side of the high-voltage transformer 7 in the direction of the arrow in FIG. 5A, and the high-voltage capacitor 14 is charged as indicated by a plus sign in FIG. Is done. Therefore, the voltage of the sum of the voltage of the high-voltage capacitor 14 and the voltage of the high-voltage capacitor 15 charged in the cycle half a cycle (T / 2 seconds) is applied to the magnetron 3. Thereafter, the switching element Q2 is turned off (period E in FIG. 3), and the state shifts to the state in FIG.
Power is no longer supplied from the solar cell 2 to the high-voltage transformer 7. Therefore, power is supplied from the solar cell 2 to the high-voltage transformer 7 substantially only during the period of the pulse width t _on .

On the other hand, over both periods D and E in FIG. 3, as shown in FIGS. 5A and 5B, the positive side of the solar cell 2 → the switching element Q3 → the primary winding of the cathode heating transformer 8 →
A current flows in a path on the negative side of the second voltage dividing capacitor 5 → the solar cell 2, and a half voltage of the output voltage of the solar cell 2 (the voltage across the first voltage dividing capacitor 4) is applied to the cathode heating transformer 8. Is applied. After that, the switching element Q3
FF is performed, and all the switching elements Q1 to Q4 are turned off (period F in FIG. 3). Therefore, power is supplied from the solar cell 2 to the cathode heating transformer 8 over the period of the pulse width t _max .

As described above, this magnetron drive power supply circuit 1 repeats switching with six periods from A to F in FIG. 3 as one cycle. The gate drive signal generator 13 shown in FIG. 1 generates a new gate drive signal for each cycle (T seconds) based _{on the} ON time data ton received from the control amount calculator 12. The value of the pulse width t _max used for generating the drive signals for the switching elements Q3 and Q4 is set in the gate drive signal generator 13 and is unchanged.

Here, the ON time data t given from the control amount calculating section 12 to the gate drive signal generating section 13
Consider the operation when the value of _on changes from one cycle before. First, if the value of the ON time data t _on is increased, because the period in which power from the solar battery 2 to the high voltage transformer 7 is supplied becomes longer, the charging period of the high-voltage capacitor 14 and 15 of the full-wave voltage doubler rectifier circuit 12 Becomes longer. Therefore, the voltage applied to the magnetron 3 increases, the anode current increases, and the microwave output also increases. In the same principle, if the value of the ON time data t _on the contrary becomes smaller, the voltage applied to the magnetron 3 decreases,
The anode current decreases and the microwave output also decreases. On the other hand, as described above, switching elements Q3 and Q4
Since the drive signal does not change by the ON time data t _on, power supplied from the solar battery 2 to the cathode heating transformer 8 is always constant. Therefore, a constant power is always supplied to the cathode filament 11 of the magnetron 3, so that the filament temperature is kept constant.

The advantages of the above switching control will be described below.

A first advantage is that when the magnetron 3 is operated at a low output, the occurrence of moding which occurs in the conventional magnetron drive power supply circuit as shown in FIG. 11 can be suppressed. That is, since the temperature of the cathode filament 11 of the magnetron 3 is constant irrespective of the length of the ON time t _on of the switching elements Q1 and Q2 of the full-bridge inverter circuit 6, the low output operation (the ON time data t _on is small) is achieved. Stable normal oscillation is possible at any time. Therefore, occurrence of moding can be suppressed.

Further, immediately after the full-bridge inverter circuit 6 is started, that is, when the temperature of the cathode filament 11 of the magnetron 3 is still low, the control amount calculation unit 12
By setting an upper limit _on the ON time data ton generated by the controller and performing low-power operation until the temperature of the cathode filament 11 rises, the occurrence of moding, which is likely to occur when the magnetron 3 is started, is ensured. Can be suppressed. FIG. 6A shows a configuration of an inverter control unit 31 for performing the above control. This inverter control unit 31 is different from the inverter control unit 10 shown in FIG.
6 is the only difference. The newly provided command signal monitoring unit 16 monitors the ON time data t _on sent from the control amount calculation unit 12 to the gate drive signal generation unit 13. The command signal monitoring unit 16 follows the sequence shown in the flowchart of FIG. 6B and sets the ON time data t _on and the predetermined set value t _lim until the elapse of τ _st seconds after the activation of the full-bridge inverter circuit 6. , And the smaller value is reset as new ON time data t _on , and given to the gate drive signal generator 13. Here, τ _st may be a value larger than the time required from the start of the magnetron until the temperature of the cathode filament 11 becomes constant. By doing this,
The ON time data t _on can be kept below the set value t _lim. The command signal monitoring unit 16 repeats the above-described sequence every switching cycle T.

The second advantage is that the oscillation frequency spectrum characteristic of the magnetron 3 is improved by suppressing the moding and stabilizing the anode current of the magnetron 3. 7 (a) and 7 (b) show a microwave oscillation frequency spectrum in the conventional magnetron drive power supply circuit shown in FIG. 11 and a microwave oscillation frequency spectrum in the magnetron drive power supply circuit 1, respectively. 7 (a) and 7 (b), comparing the microwave frequency bands that fall within the output range from the maximum value (dB) of the microwave output to a value 30 dB lower, the former is 2. From 428 GHz to 2.46
The latter is 14 MHz from 2.437 GHz to 2.451 GHz, whereas the range is 34 MHz up to 2 GHz.
MHz range. Therefore, the latter has a lower side lobe level, which is an extra frequency component, than the former, has a narrower frequency band, and as a microwave oscillation source, the magnetron drive power supply circuit 1 is superior to the conventional magnetron drive power supply circuit. It can be said that.

Incidentally, the magnetron drive power supply circuit 1
In the state shown in FIGS. 4A and 5A, power is supplied to both the high-voltage transformer 7 and the cathode heating transformer 8 via the full-bridge inverter circuit 6.
A current having an amplitude exceeding 10 A may flow between the first and second voltage dividing capacitors 4 and 5 and the full-bridge inverter circuit 6 in some cases. Therefore, as shown in FIG.
By connecting the smoothing capacitor 17 between the voltage dividing circuit composed of the first and second voltage dividing capacitors 4 and 5 and the full bridge inverter circuit 6, fluctuation of the current flowing into the full bridge inverter circuit 6 is suppressed. As a result, the surge current to the switching elements Q1 to Q4 can be reduced to prevent the switching elements Q1 to Q4 from being destroyed.

(Embodiment 2) Generally, in order to emit thermoelectrons from a cathode filament into a vacuum tube of a magnetron, a current for cathode heating is forcibly passed through the magnetron. In the oscillation state where the anode current is flowing, the cathode filament is sufficiently heated only by the collision of electrons with the cathode, so that a heating current is sent from the outside to the cathode filament to heat the cathode filament. Oscillation can be sustained without doing so. Therefore, in the magnetron driving power supply circuit 1 of the first embodiment, a switch means for turning on and off the power supply to the cathode heating transformer 8 is provided, and the power supply to the cathode is cut off at an appropriate time, so that the temperature of the cathode of the magnetron is reduced. , And the frequency characteristics can be further improved.

FIG. 9 is a circuit diagram showing a magnetron drive power supply circuit 19 according to Embodiment 2 of the present invention. This magnetron drive power supply circuit 19 differs from the magnetron drive power supply circuit 1 of the first embodiment only in the following points. That is, the switching means 18 is provided between the connection point between the first voltage dividing capacitor 4 and the second voltage dividing capacitor 5 and the primary winding of the cathode heating transformer 8, and the full-wave voltage rectifying circuit 9 is provided. A current detecting means 20 for detecting an anode current value of the magnetron 3 is provided between the power supply and the anode of the magnetron 3, and a control amount monitoring unit 21 for monitoring a voltage value output from the current detecting means 20 is connected to an inverter control unit. 30.
Here, for example, a relay or the like can be used for the switch unit 18.

In the magnetron drive power supply circuit 19,
Control amount calculation unit 12 reads the value of the voltage value V _an, output from the current detector 20, is the control of the inverter by multiplying a gain to the deviation between the voltage value V _an, an output command value V _{re f} by performing the negative feedback with respect to oN time data t _on, the feedback control is performed so that the voltage value V _an, becomes constant. Therefore, by giving an appropriate output command value _Vref to the control amount calculation unit 12, the operating state of the magnetron 3 can be controlled, and an oscillation state in which a desired anode current flows through the magnetron 3 can be obtained.

Next, the operation of the magnetron drive power supply circuit 19 having the above configuration will be specifically described with reference to the flowchart of FIG.

First, when the switch means 18 is in the conductive state, the control amount monitoring unit 21 checks whether the anode current of the magnetron 3 is equal to or more than a predetermined value. That is, when the switch unit 18 is in the conductive state, it is checked whether the voltage value V _an output by the current detection unit 20 is equal to or _larger than the set value V _h . Voltage value V
_{When an} ≧ set value _Vh is satisfied, magnetron 3
It is determined that oscillation continues even if the current to the cathode filament 11 is cut off, and the switch means 18 is turned off. When the switch 18 is in the non-conductive state, the control amount monitoring unit 21 checks whether the anode current of the magnetron 3 is equal to or less than a predetermined value. That is, it is checked whether the voltage value V _an output by the current detection means 20 is equal to or less than the set value V _l . When the voltage value V _an ≦ set value V ₁ is satisfied, it is determined that the anode current of the magnetron 3 is insufficient and oscillation cannot be continued, and the gate drive signal generation unit 13 is fully bridged. A signal for stopping the inverter circuit 6 is transmitted. The control amount monitoring unit 21 repeats the above-described sequence every switching cycle T.

The effect obtained by bringing the switch means 18 into a non-conductive state during the oscillation as described above will be described below. When the switch means 18 is turned off, no cathodic current flows through the magnetron 3, so that the emission state of thermoelectrons from the cathode filament 11 is stabilized, and the anodic current of the magnetron 3 becomes more stable and constant. . FIG. 7C shows a microwave oscillation frequency spectrum at this time. The microwave frequency band falling within the output range from the maximum value (dB) of the microwave output to 30 dB lower is the range of 8 MHz from 2.440 GHz to 2.448 GHz. Therefore, in the microwave oscillation frequency spectrum of FIG. 7C, the side lobe level, which is an extra frequency component, is suppressed lower than that of the microwave oscillation frequency spectrum of FIG. It can be seen that is improved.

In order to maintain such an oscillation state,
When the anode current of the magnetron 3 is higher than the threshold value and the anode current drops below the threshold value, the temperature of the cathode filament 11 drops below the temperature required for normal oscillation of the magnetron 3, and moding occurs. . As described above, in order to prevent this, the control amount monitoring unit 21 detects that the voltage value V _an output by the current detection unit 20 is equal to or less than the predetermined value when the switch unit 18 is in the non-conduction state. Then, the full bridge inverter circuit 6 is stopped.

As described above, in the magnetron driving power supply circuit 19 of the second embodiment, the spread of the microwave frequency spectrum generated by the magnetron 3 is reduced to about one-fourth as compared with the conventional magnetron driving power supply circuit. hand,
It is possible to improve the quality of microwaves and suppress the occurrence of moding.

In the first and second embodiments, the voltage dividing circuit is the first type.
And the second voltage dividing capacitors 4 and 5,
A voltage dividing circuit may be composed of two or more voltage dividing capacitors. In this case, the voltage dividing capacitors on both sides of the connection point to which the primary winding of the cathode heating transformer is connected become the first and second voltage dividing capacitors.

[0047]

According to the present invention, the following effects can be obtained.

Since the temperature of the cathode filament of the magnetron can be kept constant irrespective of the change in the operating state of the magnetron, the occurrence of moding at the time of start-up or low-power operation is suppressed, and the microwave output with little noise is reduced. Obtainable.

Further, the cathode current can be turned off when the anode current of the magnetron exceeds a certain threshold value, so that the thermoelectron emission state of the cathode filament is stabilized,
By making the anode current of the magnetron more stable and constant,
Furthermore, noise during microwave output can be reduced, and the oscillation frequency spectrum characteristics can be improved.

[Brief description of the drawings]

FIG. 1 is a circuit diagram of a magnetron drive power supply circuit according to a first embodiment of the present invention.

FIG. 2 is a diagram illustrating a wireless power transmission system using microwaves using the magnetron drive power supply circuit according to the first embodiment illustrated in FIG. 1;

FIG. 3 is a timing chart of drive signals Q1 to Q4 generated by a gate drive signal generation unit according to the first embodiment in FIG.

FIG. 4A is an operation state diagram of the magnetron drive power supply circuit in a period A of FIG. 3, and FIG.
FIG. 7 is an operation state diagram of the magnetron drive power supply circuit in a period B of FIG.

5A is an operation state diagram of the magnetron drive power supply circuit in a period D in FIG. 3, and FIG.
FIG. 7 is an operation state diagram of the magnetron drive power supply circuit in a period E of FIG.

6 (a) is a configuration diagram showing an improved example of the inverter control unit, and FIG. 6 (b) is a flowchart showing an operation sequence of the inverter control unit shown in FIG. 6 (a).

7A is a diagram showing a microwave oscillation frequency spectrum in a conventional magnetron drive power supply circuit, and FIG. 7B is a diagram showing microwave oscillation in a magnetron drive power supply circuit according to Embodiment 1 of the present invention; FIG. 7C is a diagram illustrating a frequency spectrum, and FIG. 7C is a diagram illustrating a microwave oscillation frequency spectrum in the magnetron drive power supply circuit according to the second embodiment of the present invention.

FIG. 8 is a circuit diagram showing an improved example of the magnetron drive power supply circuit of the first embodiment shown in FIG.

FIG. 9 is a circuit diagram of a magnetron drive power supply circuit according to a second embodiment of the present invention.

10 is a flowchart showing an operation sequence of an inverter control unit of the magnetron drive power supply circuit shown in FIG.

FIG. 11 is a circuit diagram of a conventional magnetron drive power supply circuit.

[Explanation of symbols]

 1,19 magnetron drive power supply circuit 2 solar cell 3 magnetron 4,5 voltage dividing capacitor 6 full bridge inverter circuit 7 high voltage transformer 8 cathode heating transformer 9 full wave voltage doubler rectifier circuit 10,30,31 inverter control unit 12 control amount calculation Unit 13 Gate drive signal generation unit 16 Command signal monitoring unit 17 Smoothing capacitor 18 Switching means 20 Current detection means 21 Control amount monitoring unit

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Masaki Shinohara Gokasho, Uji City, Kyoto Prefecture Inside the High-rise Radio Research Center, Kyoto University (72) Inventor Kazuhito Nishimura 22-22 Nagaikecho, Abeno-ku, Osaka-shi, Osaka In-house (72) Inventor Masaki Eguchi 22-22 Nagaike-cho, Abeno-ku, Osaka City, Osaka F-term (reference) 3K086 AA09 BA08 BB03 BB08 CA16 CB12 CC02 CD03 CD19 DA12 DB03 DB11 DB13 DB18 DB21 FA02 FA04 FA05 FA10 5H007 AA05 BB04 BB07 CB05 CC32 DB01 DC02 GA08

Claims (9)

[Claims] 1. A high voltage transformer for applying a high voltage between an anode and a cathode of a magnetron via a rectifier circuit, a cathode heating transformer for heating a cathode of the magnetron, a high voltage transformer and a cathode A full-bridge inverter circuit for supplying power to the heating transformer, and a full-bridge inverter circuit for supplying constant AC power to the cathode heating transformer while supplying variable AC power to the high-voltage transformer. A magnetron drive power supply circuit, comprising: an inverter control unit for controlling the power supply. 2. A full-bridge inverter circuit connected to a DC power supply and having four switching elements,
A magnetron drive power supply circuit for driving a magnetron including a high-voltage transformer, a cathode heating transformer, and a rectifier circuit, wherein the voltage divider circuit is provided at a stage preceding the full bridge inverter circuit and has at least first and second voltage dividing capacitors. A middle point between two of the four switching elements of the full-bridge inverter circuit, one of the former or the latter, and one end of the primary winding of the high-voltage transformer and the one of the cathode heating transformer. One end of the primary winding is connected to the other end of the primary winding of the high-voltage transformer. The other end of the next winding is connected to the middle point between the first voltage dividing capacitor and the second voltage dividing capacitor, The on-time of one of the two preceding switching elements connected to one end of the wire and one end of the primary winding of the cathode heating transformer is always constant, and the two switching elements are alternately switched. While conducting for a fixed time at a time, the on-time of the other two switching elements of the preceding stage or the succeeding stage connected to the other end of the primary winding of the high-voltage transformer is made variable, and the two switching devices are connected. A magnetron drive power supply circuit, comprising: an inverter control unit that conducts the ON time alternately each time. 3. The magnetron drive power supply circuit according to claim 1, wherein the inverter control unit generates a signal for driving the full-bridge inverter circuit, and the gate drive signal generation unit. And a variable amount of on-time data to be given to the gate drive signal generation unit until a predetermined time elapses after the start of the full-bridge inverter circuit, and a set value. A magnetron drive power supply circuit, comprising: a command signal monitoring unit for controlling the power so as not to exceed the power supply. 4. The magnetron drive power supply circuit according to claim 3, wherein the command signal monitoring unit is configured to store the variable on-time data and the variable on-time data in advance for a predetermined time after the full-bridge inverter circuit is started. A magnetron drive power supply circuit, which compares the variable on-time data or the set value, whichever is smaller, to the gate drive signal generator, by comparing the set value with a predetermined set value. 5. The magnetron drive power supply circuit according to claim 2, wherein a smoothing circuit is provided between the voltage dividing circuit having the first and second voltage dividing capacitors and the full bridge inverter circuit. A magnetron drive power supply circuit comprising a capacitor. 6. The magnetron drive power supply circuit according to claim 1, wherein a switch is connected to one end or the other end of a primary winding of the cathode heating transformer, and the cathode heating is performed. A magnetron drive power supply circuit characterized in that energization to a primary winding of a transformer for use can be controlled. 7. The magnetron drive power supply according to claim 1, wherein current detection means is provided between the rectifier circuit and an anode of the magnetron. circuit. 8. The magnetron drive power supply circuit according to claim 7, wherein the switch is turned off when the switch is turned on and the output from the current detector is equal to or higher than a predetermined value. A magnetron drive power supply circuit comprising a control amount monitoring unit. 9. The magnetron drive power supply circuit according to claim 8, wherein the control amount monitoring unit is configured to control the control amount monitoring unit when the switch unit is in a non-conductive state and an output from the current detection unit is equal to or less than a predetermined value. A magnetron drive power supply circuit, which outputs a stop signal for stopping the driving of the full-bridge inverter circuit to a gate drive signal generation unit.