JPS6316853B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a magnetron device, and particularly to a power supply circuit thereof. In general, magnetrons that apply a magnetic field at right angles to an electric field are now widely used in electronic equipment, such as microwave ovens, to which magnetrons are attached, and as a result, regulations on noise leakage are becoming stricter. Internationally, this noise regulation is being implemented or under consideration in each country based on the recommendations of the International Special Committee on Radio Disorders (CISPR). Therefore, measures to reduce the noise generated from the magnetron itself have become even more desirable. By the way, the cause of low frequency noise (e.g. below 100MHz) generated by magnetrons is
I have the following idea. That is, FIG. 1 schematically shows the anode vane 26 and cathode 25 that constitute the coaxially arranged anode of the magnetron.
When a high voltage of several thousand volts is applied between the cathode and the anode with the anode vane 26 as positive, and thermionic electrons are emitted from the cathode 25, in the electron action space 39, due to the space charge near the cathode, the dotted line curve in the figure As shown by a, the potential distribution has a downward concave portion that is more negative than the cathode potential. On the other hand, as shown by arrow B, a DC magnetic field of 1000 to 2000 Gauss is applied to the electron action space 39 in the cathode axial direction, so the electrons leaving the cathode 25 are moved to the cathode 2 by the action of the electric and magnetic fields.
orbit around 5. Especially for orthogonal electromagnetic fields,
Since the electrons travel a long distance, there is a high probability that the electrons will collide with residual gas, and they generate significantly more positive ions than other straight tubes. The generated positive ions flow into the valley of the potential distribution shown by curve a, that is, the potential minimum (indicated by the symbol m in the figure), and the electrons in the space charge and positive ions gradually become neutralized, and as a result, this The potential near the valley rises to a potential equal to or slightly higher than that of the cathode 25, as indicated by the symbol n. In this state, the potential distribution in the working space becomes like a solid line curve b. Positive ions flow into the cathode. In the next step, a potential valley m is again formed by space charges. This series of processes is repeated periodically. As a result, a complicated pulsation phenomenon occurs in the current between the cathode and the anode, that is, the anode current, and it can be assumed that this leaks into the external circuit as noise. Such noise mainly appears as so-called line noise that leaks along the input line, causing various radio interference. Therefore, as one measure to reduce such noise, by providing a third electrode near the cathode and applying a negative potential of several tens to several hundreds of volts to the third electrode with respect to the cathode, it is possible to eliminate the valleys in the potential distribution, that is, the potential.・The positive ions that gather to the minimum m are
It is considered that the noise caused by positive ions can be reduced by capturing them with electrodes. This example is shown in FIGS. 2 and 3, and FIG. 3 is an enlarged view of the main part of FIG. 2. That is, the rod-shaped cathode support 32 arranged on the tube axis
At one end, there is a cathode end chip 53, a third
An electrode end tip 52 and an end hat 51a are fixed, and the other end is fixed to a terminal plate 35a following the cathode terminal 35. A cylindrical cathode support 33 and a cylindrical third electrode support 57 are coaxially arranged at a predetermined interval on the outside of the rod-shaped cathode support 32 on the cathode stem side. Another cathode end chip 56 is fixed to one end, and the other end is connected to the cathode terminal 3.
It is fixed to 4. Further, another third electrode end tip 59 is fixed to one end of the cylindrical third electrode support 57, and the other end hat 51b is fixed to this end tip 59.
The other end of the electrode support 57 is fixed to a cathode terminal 58. A thorium-tungsten directly heated cathode 25 wound into a coil is disposed on the output side of the rod-shaped cathode support 32, and both ends thereof are fixed to cathode end chips 53 and 56, respectively. Furthermore, near the cathode 25,
A coiled third electrode 60 is disposed between the lines of the cathode 25, and both ends thereof are fixed to the third electrode end tips 52 and 59, respectively. This third electrode 60 is made of, for example, W, Mo,
It is made of a single substance or an alloy selected from refractory metals such as Ta and Ti, and the cathode 2
5 and at a position that does not impede the flow of electrons from the cathode 25 to the anode.
As described above, the coiled filaments of the cathode 25 and the coiled filaments of the third electrode 60 are alternately arranged so that their respective outer peripheral surfaces are on the same or substantially the same surface. In the figure, 26 is an anode vane, 27 is an anode cylinder, and 28 is a strap ring, which constitute a plurality of cavity resonators and form an anode as a whole. Also, 2
9 is an output part, 29a is an antenna conductor, 30 is a pole piece, 31, 31a, 31b is an insulating cylinder, 3
9 is an electron action space, 54 is an exhaust pipe, and 55 and 56 are insulating rings. Next, the operation will be described. The cathode 25 is heated and emits thermoelectrons. A high voltage of several thousand volts is applied between the cathode 25 and the anode vane 26, and a DC magnetic field of approximately 1500 gauss of magnetic flux parallel to the tube axis is applied to the electron action space 39, causing oscillation. do. The microwave energy generated in the cavity resonator is transmitted from the output section 29 to an external load through the antenna conductor 29a. Now, when the cathode 25 is heated, the emitted electrons cause the front surface of the cathode 25 to be approximately several 10 μm to several
A potential valley m is formed around 100 μm (in the absence of the third electrode), but if the third electrode 60 is set to a negative potential of, for example, about 10 to 100 V with respect to the cathode 25, the potential valley m is formed. The positive ions that gather toward m are immediately captured by the third electrode 60 because the third electrode 60 has a more negative potential than this. In other words, the positive ions do not stay near the cathode but flow into the third electrode 60, and the unstable electron-ion neutralization phenomenon near the cathode does not occur. As a result, noise below 100MHz is significantly reduced. An example of this noise reduction result is shown in FIG. By the way, if the potential of the third electrode is set to a high negative potential, it will be very effective in reducing noise.
It has been found that the more negative the potential, the more the stability of the magnetron's oscillation tends to suffer. An example is shown in FIG. That is, as is clear from FIG. 5, as the absolute value of the bias voltage of the third electrode increases, the maximum anode current for stable oscillation decreases. On the other hand, when examining the relationship between anode current and noise, as shown in Figures 6 and 7, continuous wave magnetrons generally generate large noise when the anode current is small, for example, about 0.15A or less, and about 0.2A. It can be seen from the above that the noise is rapidly decreasing. Therefore, if the anode current is always used at approximately 0.2A or more, noise will be generated very little and there will be few problems, but in actual microwave ovens, the anode power supply is a half-wave voltage doubler power supply due to cost reasons. is generally used, and the instantaneous anode current ranges from zero to
It has repeatedly fluctuated up to 1A. If you try to apply a negative high potential to the third electrode for the purpose of reducing noise in this way, the operation stability will decrease slightly, and conversely, the
There is a contradictory tendency that lowering the electrode potential tends to generate noise. This invention was made in view of the above circumstances, and aims to reduce noise and improve the stability of oscillation.
Another object of the present invention is to provide a magnetron device that does not require an external power source for the third electrode. Hereinafter, one embodiment of the present invention will be described in detail with reference to the drawings. Generally, it is necessary to reduce noise by applying the bias voltage of the third electrode only when the anode current is approximately 0.15A or less, and when the anode current is 0.2A or more, it is better not to apply the bias voltage of the third electrode. , is desirable as seen from the relationship with the magnetron stability in FIG. That is, Fig. 8 shows an example of the characteristics of the anode current and anode voltage of a magnetron. It can be seen that the difference between the anode voltage at approximately the maximum instantaneous anode current generated in the power supply and the anode voltage at an anode current of 0.15A is approximately 500V. It can be seen from FIG. 4 that if this potential difference is applied as a bias voltage to the third electrode, it is sufficiently effective in reducing noise. Therefore, if the voltage between the third electrode and the anode is always kept almost at the maximum value of the anode voltage, the bias voltage of the third electrode (negative potential with respect to the cathode) will be large when the anode current is low, and noise will be reduced. can be sufficiently reduced, and as the anode current increases, the bias voltage of the third electrode approaches zero, so that the influence on deterioration of oscillation stability can be reduced. Therefore, in the present invention, the bias voltage (potential) of the third electrode of the magnetron is set so that it becomes a negative high potential when the anode current is low, and becomes zero or a negative low potential when the anode current is high. For this purpose, in the embodiment of the present invention, a power supply circuit as shown in FIG. 9 is used. In the figure, 61
is a leakage transformer, and the primary winding L ₁
is connected to a commercial power source, and has a cathode heating winding L ₂ and a high voltage winding L ₃ on the secondary side, and there is no independent third electrode winding. The cathode heating winding _L2 is connected to a cathode K of a magnetron 62 having a third electrode similar to that shown in FIGS. 2 and 3 above. Further, one end of the high voltage winding _L3 is grounded, and the other end is connected in series to the anode pole of the forward rectifier _SR1 and to the cathode K of the magnetron 62 via a capacitor _C1 . rectifier
The cathode of SR ₁ is grounded. Further, the third electrode D of the magnetron 62 is a forward rectifier SR ₂
It is connected to the cathode K via the capacitor C2 and grounded via the capacitor _C2 . Further, the anode A of the magnetron 62 is also grounded. In addition, the capacitor _C1 above is 0.5μF, and the capacitor _C2 is
It is 0.05μF. Now, during operation, as time passes, the voltage or current waveforms of each part, that is, between 1 and 2, between A and K, between anode A, and between A and D, become as shown in Figures 10a to d, and Figure 10b. From the waveform of and c, eb
-ib waveform (Lissajyu waveform) is as shown in FIG. And, between A and K and between A and D, there is a T.
The maximum value ebm (e.g. -4kV) is reached at = T ₂ , and then when T = T ₃ , the voltage between A and K becomes the forward voltage of rectifier SR ₁ , so it is the same as T = T ₁ .
It becomes 0V. However, the voltage between A and D is
Although SR ₂ is in the forward direction as seen from the anode A, it is in the opposite direction with respect to the polarity of the charge on the capacitor C ₂ , and there is no electron emission from the third electrode D (if there is electron emission, Since the charge of capacitor _C2 remains constant due to some discharge, the potential difference (voltage) between D and K
The third electrode D has a negative potential with respect to the cathode K, which is about 4 kV. Actually, in Fig. 11, the value on the vertical axis with an arrow (about 4 kV when ib = 0, ib
= 0V for IBM) will be applied between D and K. The magnetron device of the present invention is constructed as described above and shown in the drawings, and uses a power supply circuit as shown in FIG. 9, thereby reducing noise, improving oscillation stability, and External power supply for electrodes is no longer required. That is, in the range of ib = 0 to 0.1 A where a lot of noise occurs, the bias voltage of the third electrode has a negative high potential and has a large noise reduction effect, and in the range of large ib, the bias voltage of the third electrode becomes low. The stability of magnetron oscillation does not deteriorate. Also, rectifier SR ₂ and capacitor C ₂ are several kV
It can be constructed at a relatively low cost. Incidentally, FIGS. 12, 14, and 15 show modifications of the present invention, and the same effects as in the above embodiment can be obtained. That is, in the case of FIG. 12, the above embodiment (No. 9
A resistor R is additionally connected in parallel to the capacitor C ₂ in Figure), and the time constant γ = C ₂ R = approximately 100 msec. When this resistance R is added,
The electric charge charged in the capacitor _C2 is discharged through the resistor R, as shown in Fig. 13.
It changes like ebm′. In other words, while ib increases from 0 to the maximum value (ibm) (from T ₁ to T ₂ in Figure 10), the bias voltage that changes with the potential difference shown by the vertical arrow in Figure 13 changes between D and K. It takes. Then, while ib decreases from the maximum value (ibm) (from T ₂ to T ₃ in Figure 10), the above bias voltage, that is, the potential difference shown by the vertical arrow in Figure 13, is applied, and ebm in the same figure A bias voltage is applied by adding the potential difference with ebm′. In this way, the third electrode is biased to a high negative potential when the anode current is low, and to zero or a very small negative potential when the anode current is high. Therefore D-K
The maximum voltage applied between them is not ebm but ebm′ (ebm′<ebm). For example, for ebm=4kV
ebm′ is approximately 3kV. By lowering the maximum voltage applied between D and K in this manner, dielectric breakdown between D and K can be avoided. In addition, magnetrons are generally supplied to microwave oven manufacturers with a shield box containing a choke coil and a feedthrough capacitor in order to prevent leakage of noise and harmonics. Therefore, within this shield box, there is a rectifier SR ₂ and a capacitor C ₂ (or a resistor R) that applies voltage to the third electrode.
By providing a circuit consisting of the following, it is possible to complete a microwave oven with reduced noise without making any changes to the power supply of the microwave oven. Examples of this are shown in FIGS. 14 and 15, where 63 is a shield box. And inside this shield box 63,
In addition to the rectifier SR ₂ and capacitor C ₂ , a choke coil 64 and a feedthrough capacitor 65 are provided. As explained above, according to the present invention, a magnetron device with great industrial value can be provided.

[Brief explanation of the drawing]

Figure 1 is a schematic diagram showing the noise generation mechanism in a magnetron, Figure 2 is a cross-sectional view of an example of a magnetron equipped with a third electrode to reduce noise, and Figure 3 is the main part of Figure 2. FIG. 4 is a characteristic curve diagram showing noise reduction due to the bias voltage of the third electrode, and FIG. 5 is a characteristic curve diagram showing the influence of the third electrode bias voltage on the stability of magnetron oscillation. , FIGS. 6 and 7 are characteristic curve diagrams showing changes in noise due to anode current, and FIG.
The figure is a characteristic curve diagram showing the anode current vs. anode voltage characteristic, Figure 9 is a circuit configuration diagram showing the power supply circuit used in the magnetron device of the present invention, and Figures 10a to 10 are
d is a waveform diagram showing the voltage or current of each part in the power supply circuit of FIG. 9, FIG. 11 is a Lissage waveform diagram, and FIGS. 12, 14, and 15 are circuit configuration diagrams showing modifications of the present invention. , FIG. 13 is a resurge waveform diagram in the power supply circuit of FIG. 12. 25, K... cathode, 26... anode vane,
27... Anode cylinder, 28... Strap ring, 39... Electron action space, 60, D... Third electrode, 61... Leakage transformer, 62... Magnetron, L ₁ ... Winding wire, L ₂ ... Winding wire for cathode heating, L ₃
…High voltage winding, C ₁ , C ₂ … Capacitor, SR ₁ , SR ₂ …
Rectifier, A...anode.

Claims (1)

[Scope of Claims] 1. A spirally wound directly heated cathode, an anode with a built-in cavity resonator arranged coaxially around the cathode, and an electron action space between the cathode and the anode along the cathode axis. In a magnetron device comprising a magnetron equipped with a magnet that provides a parallel magnetic field, and a power supply circuit device that applies a pulsating anode voltage between the cathode and anode of the magnetron, A spiral third electrode is provided without contacting the spiral, and the power supply circuit device has a series circuit including a capacitor C ₂ and a rectifier SR ₂ in the forward direction when viewed from the anode A, and the series circuit is connected to the anode A of the magnetron. and the cathode K, and the connection point between the capacitor C ₂ and the forward rectifier SR ₂ is the third one of the magnetron 62.
A magnetron device characterized by being connected to an electrode D.