JP3374845B2 - Power supply for magnetron drive - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high-frequency heating apparatus using a magnetron, and more particularly to a power supply for driving a magnetron. 2. Description of the Related Art A conventional magnetron driving power supply is shown in FIG.
0 is used. The high-voltage transformer 54 generates a high voltage on the secondary side, and the magnetron 56
Is supplied with high voltage. The capacitor 55 forms a resonance circuit together with the high-voltage transformer 54, and the switching waveform of the semiconductor switching element 53 is as shown in FIG.
As shown in FIG. 11B, the waveform becomes a sine wave. At this time, since the capacitor 55 and the high-voltage transformer 54 form a resonance circuit, a current starts to flow in the semiconductor switching element 53 after the voltage becomes zero. That is, the semiconductor switching element 53
, The switching loss at the time of turning on is reduced.
Also, when the current is turned off, the current is sharply cut off, but since the voltage gradually rises in a sine wave shape, the switching loss of the semiconductor switching element 53 is reduced even when the current is turned off. As described above, the resonance type circuit has an effect of reducing the switching loss of the semiconductor switching element. A magnetron is a vacuum tube having reverse blocking characteristics, and its voltage-current characteristics are as shown in FIG.
That is, when the voltage becomes approximately −4 kV, oscillation starts, and a dynamic load change occurs in which the impedance rapidly decreases. [0005] However, the magnetron driving power supply of the above-mentioned conventional configuration has a problem that the voltage applied to the semiconductor switching element and the magnetron becomes extremely high. That is, a very high voltage of about 500 V is applied to the semiconductor switching element and about 20 kV to the magnetron. As for the voltage applied to the magnetron, since the turns ratio of the high voltage transformer is about 40, when a peak voltage of about 500 V generated by resonance is applied to the primary side of the high voltage transformer, about 20 V is applied to the secondary side.
kV is generated. [0006] The present invention solves the problems of the above-mentioned conventional structure, and comprises a magnetron,
A high-voltage transformer for supplying a high voltage to the magnetron;
A first and a second capacitor connected to a primary side of the high-voltage transformer; a first semiconductor switching element connected to a resonance circuit including the high-voltage transformer and first and second capacitors; And a second semiconductor switching element connected in series to the first capacitor. The second semiconductor switching element drives the first and second semiconductor switching elements alternately, and a voltage applied to the first semiconductor switching element is a predetermined voltage. by exceeding the drive of the second semiconductor switching element, the first, the total capacitance of the second capacitor is assumed to depend on the voltage level applied to the first semiconductor switching element, the semiconductor switching element The power supply device for driving the magnetron can reduce the voltage applied to the magnetron and the voltage applied to the magnetron. According to the first aspect of the present invention, there is provided a magnetron, a high voltage transformer for supplying a high voltage to the magnetron, and first and second capacitors connected to a primary side of the high voltage transformer. And a first circuit connected to a resonance circuit including the high-voltage transformer and first and second capacitors.
, And a second semiconductor switching element connected in series to the second capacitor, and alternately drives the first and second semiconductor switching elements and the first semiconductor switching element. When the voltage applied to the first semiconductor switching element exceeds a predetermined voltage, the second semiconductor switching element is driven to reduce the total capacitance of the first and second capacitors to the voltage level applied to the first semiconductor switching element. Depend on
The voltage of the semiconductor switching element can be clamped to a certain level to reduce the voltage applied to the magnetron. An embodiment of the present invention will be described below with reference to the drawings. Embodiment 1 FIG. 1 is a circuit diagram showing a configuration of a power supply unit for driving a magnetron according to this embodiment. The rectifier 2 rectifies the commercial power 1 and converts it into a DC voltage, and supplies the DC voltage to the resonance circuit 3 and the semiconductor switching element 6. The resonance circuit 3
It comprises a capacitor 5 and a high voltage transformer 4 for generating a high voltage. The capacitor 5 has a voltage-dependent capacitance characteristic in which the capacitance changes according to the magnitude of the applied voltage, and is connected to the primary side of the high-voltage transformer 4. The magnetron 7 is connected to the secondary side of the high voltage transformer 4. The operation of the embodiment will be described below with reference to FIG. FIG. 2A shows a semiconductor switching element 6.
FIG. 2B shows the voltage waveform of the semiconductor switching element 6.
2 (c) shows a current waveform flowing to the primary side of the high-voltage transformer 4. FIG. When the switching element 6 is turned on and the current Ic is flowing, the high-voltage transformer 4
The current shown as Ia in FIG.
When the semiconductor switching element 6 is turned off, the current flowing on the primary side of the high-voltage transformer 4 starts flowing toward the capacitor 5, and at the same time, the voltage starts to be applied to the semiconductor switching element 6. That is, this is the state of the area a in FIG. When the voltage level applied to the semiconductor switching element 6 reaches V1, the capacitance of the capacitor 5 increases significantly (about 10 times) due to the voltage dependency. For this reason, as shown in the area b, the slope of the voltage applied to the semiconductor switching element 6 becomes sharp and gentle, and the rise of the peak value of the voltage is suppressed (clamped). High voltage transformer 4
Is transferred to the capacitor 5, a current starts to flow from the capacitor 5 to the primary side of the high-voltage transformer 4 as shown in a region c. When the voltage level applied to the semiconductor switching element 6 decreases and reaches V1 again, the capacitance of the capacitor 5 returns to its original state due to the voltage dependency of the capacitor 5, and as shown in a region d, the capacitance of the capacitor 5 is reduced. Such a voltage drops sharply. Thereafter, the semiconductor switching element 6 is turned on again, and the operation in the region a and below is repeated. As described above, according to the present embodiment, the voltage applied to the semiconductor switching element 6 can be reduced by using a capacitor having a voltage-dependent capacitance characteristic as the capacitor 5. According to the results of the experiment, the voltage applied to the semiconductor switching element 6 can be set to about 350 V in the device according to the present embodiment, which can be greatly reduced from 500 V of the conventional single-type voltage resonance type circuit. Further, since the voltage applied to the semiconductor switching element 6 can be reduced, the high voltage generated on the secondary side of the high voltage transformer 4 can also be reduced, and the voltage applied to the magnetron 4 can also be reduced. Second Embodiment Next, a second embodiment of the present invention will be described with reference to FIG. In the present embodiment, a first capacitor 10 and a second capacitor 8 having a larger capacity than the first capacitor 10 are connected to the primary side of the high-voltage transformer 4. Also,
The first capacitor 10 is connected to the first semiconductor switching element 6, and the second capacitor 8 is connected to the second semiconductor switching element 9. Reference numeral 11 denotes a drive circuit that drives the first semiconductor switching element 6 and the second semiconductor switching element 9. The operation of this embodiment will be described below with reference to FIG. FIG. 4 is a waveform diagram showing operation waveforms of each unit of the present embodiment. 4A shows a voltage waveform applied to the semiconductor switching element, FIG. 4B shows the same current waveform, and FIG.
(C) shows a current waveform flowing on the primary side of the high-voltage transformer 4,
4D shows a current waveform flowing in the first capacitor 10, FIG. 4E shows a current waveform flowing in the second capacitor 8, and FIG. 4F shows a voltage applied to the first semiconductor switching element 6. 4 (g) shows a voltage waveform applied to the second semiconductor switching element 9, FIG. 4 (h) shows a current waveform flowing through the magnetron 7, and FIG.
2 shows a voltage waveform generated on the high voltage side of FIG. The operation of clamping the voltage applied to the first semiconductor switching element 6 shown in FIG. 4A is the same as in the first embodiment. When the voltage of the first switching element 6 exceeds V1, a charging current starts to flow through the diode constituting the second switching element 9 to the second capacitor 8, as shown in a region b. This voltage V1 is an initial voltage of the second capacitor 8. When all the electric charge of the primary winding of the high-voltage transformer 4 is transferred to the second capacitor 8, as shown in a region (c), the second capacitor 8 transfers the charge to the primary side of the high-voltage transformer 4. Discharge to the winding starts. Since this discharge current flows through the transistor constituting the second semiconductor switching element 9, the voltage applied to the second semiconductor switching element 9 has a waveform as shown in FIG. When the transistor forming the second semiconductor switching element 9 is turned off by this drive signal,
The discharge current from the second capacitor 8 is cut off. At this time, the voltage of the second capacitor 8 is equal to the voltage V
Determine 1 As described above, in the present embodiment, the capacitances of the first capacitor 10 and the second capacitor 8 are made voltage-dependent by the second capacitor 8 and the second semiconductor switching element 9. . Therefore, compared to the configuration of the first embodiment, a normal fixed-capacitance type capacitor can be used as a variable-capacity type, and the configuration can be made inexpensively. The configuration shown in FIG. 5 is a configuration in which the second capacitor 8 and the second semiconductor switching element 9 are connected in series, and the second capacitor 8 and the second semiconductor switching element 9 are connected in parallel to the first semiconductor switching element 6. There is a function that is equivalent to that described in FIG. Third Embodiment Next, a third embodiment of the present invention will be described with reference to FIG. In the present embodiment, a first winding 12 for generating a high voltage and a second winding 13 are provided on the secondary side of the high-voltage transformer 4. The first winding 12 has a first diode 1
4, a second diode 15 is connected to the second winding 13, and a high voltage is supplied to the magnetron 7 from the first diode 14 and the second diode 15. At this time, the first winding 12 and the second winding 13
And have the same polarity. The operation of the embodiment will be described below. The configuration of the high-voltage transformer 4 used in the first and second embodiments has a leakage inductance, which causes a surge voltage on the secondary side of the high-voltage transformer 4. . That is, since the magnetron 7 has reverse blocking characteristics, when the applied voltage is in the reverse direction, the impedance becomes extremely high, and a surge voltage is generated by the leakage inductance. In this embodiment, as shown in FIG.
The first winding 12 and the second winding 12 are provided on the secondary side so as to have the same polarity.
Is provided so as to be tightly coupled, and a high voltage is supplied to the magnetron 7 via the first diode 14 and the second diode 15, so that the surge voltage can be reduced. Can be done. (Embodiment 4) Next, a fourth embodiment of the present invention will be described with reference to FIG. In the present embodiment, 4
A full-wave rectifier circuit composed of a plurality of diodes is connected, and the DC high voltage obtained by the full-wave rectifier circuit is supplied to the magnetron 7. The operation of this embodiment will be described below. Although the magnetron 7 has a reverse blocking characteristic, by using the full-wave rectifier circuit 15, a voltage in one direction (negative direction) can always be applied to the magnetron 7. That is, it can be always in an oscillation state. The magnetron in the oscillating state has an impedance of 300Ω
The surge voltage does not occur due to the action of leakage inductance. As described above, according to the present embodiment, similarly to the third embodiment, the surge voltage can be reduced. (Embodiment 5) Next, a fifth embodiment of the present invention will be described. FIG.
(A) is a winding voltage on the primary side of a high-voltage transformer, and this voltage is boosted and supplied to a magnetron. The winding voltage has a positive voltage V2 of about 140V and a negative voltage V3 of about 210V. Since the voltage level is different between the positive direction and the negative direction as described above, when a voltage obtained by boosting this voltage is supplied to the magnetron, the current shown in FIG. 8B flows through the magnetron. This current waveform is 0.5 A for I2 and 2 A for I3
Has a peak value of This current is a current flowing through the filament of the magnetron, and the peak value has a causal relationship with the life of the filament. The higher the peak value, the shorter the life of the magnetron. This embodiment relates to a means for reducing the peak value. The circuit configuration of this embodiment is the same as that shown in FIG. In this embodiment having the above configuration, the voltage V2 applied to the primary side of the high-voltage transformer 4 during the period when the first semiconductor switching element 6 is on, and the high-voltage transformer during the period when the first semiconductor switching element 6 is off. 4 is controlled so that the voltage V4 applied to the primary side is substantially the same. That is,
The time of the drive signal given to the second semiconductor switching element 9 is increased so that the discharge time of the second capacitor 8 is increased. As a result, the current flowing through the magnetron 9 has a balanced shape with a reduced peak value as shown in FIG. The waveform of the voltage applied to both ends on the primary side of the high-voltage transformer 4 shown in FIG. 9A is V2 = V4 as a result of executing the above control. As described above, according to the first aspect of the present invention, there is provided a magnetron drive power supply device capable of reducing the voltage applied to the magnetron by clamping the voltage of the semiconductor switching element to a certain level. It will be realized.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a circuit diagram showing a configuration of a magnetron driving power supply device according to a first embodiment of the present invention. FIG. 2 is a waveform diagram showing a waveform of a current flowing through each part. FIG. 4 is a circuit diagram showing a configuration of a magnetron driving power supply device according to a second embodiment of the present invention. FIG. 4 is a waveform diagram showing voltage / current waveforms of various parts. FIG. 5 shows a configuration of another embodiment. FIG. 6 is a circuit diagram showing a configuration of a magnetron driving power supply device according to a third embodiment of the present invention. FIG. 7 is a diagram showing a configuration of a magnetron driving power supply device according to a fourth embodiment of the present invention. FIG. 8 (a) is a waveform diagram showing a waveform of a voltage applied to a primary side of a high voltage transformer, and FIG. 9 (b) is a waveform diagram showing a waveform of a current flowing through a magnetron. With the circuit configuration of the fifth embodiment, the waveform of the voltage applied to the primary side of the high-voltage transformer FIG. 10 (b) is a waveform diagram showing a waveform of a current flowing through a magnetron. FIG. 10 is a circuit diagram showing a configuration of a conventional magnetron driving power supply device. FIG. 11 (a) is a voltage applied to a semiconductor switching element. FIG. 12 is a waveform diagram showing a waveform of a current flowing through a semiconductor switching element. FIG. 12 is a characteristic diagram showing operation of a magnetron. [Description of References] 3 Resonant circuit 4 High voltage transformer 5 Capacitor 6 Semiconductor Switching element 7 Magnetron 8 Second capacitor 9 Second semiconductor switching element 10 First capacitor 11 Drive circuit 12 First winding 13 Second winding 14 First diode 15 Second diode

────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Hideki Omori 1006 Oaza Kadoma, Kadoma City, Osaka Prefecture Matsushita Electric Industrial Co., Ltd. (56) References JP-A-10-50471 (JP, A) (58) Field (Int.Cl. ⁷ , DB name) H05B 6/66-6/68 H02M 7/48 H02M 3/28 H02M 3/335 H02M 7/537

Claims (1)

(57) [Claim 1] A magnetron, a high voltage transformer for supplying a high voltage to the magnetron, first and second capacitors connected to a primary side of the high voltage transformer, and the high voltage transformer A first semiconductor switching element connected to a resonance circuit composed of the first and second capacitors; and a second semiconductor switching element connected in series to the second capacitor. The second semiconductor switching elements are alternately driven, and the voltage applied to the first semiconductor switching elements exceeds a predetermined voltage
And driving the second semiconductor switching element , the total capacitance of the first and second capacitors is changed to the first capacitance.
And a magnetron driving power supply device depending on a voltage level applied to the semiconductor switching element.