JPS593037B2 - High frequency heating device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an improvement in a power supply device for a high-frequency heating device, and its purpose is to improve the power supply device for a high-frequency heating device using a frequency converter. It is an object of the present invention to provide a high-frequency heating device that is highly reliable and inexpensive.

Fig. 1 is a circuit diagram showing a conventional example. It is becoming.

4 is an inductor, 5 is a thyristor, 6 is a diode, T
is a linear transformer, 8 is a capacitor, and the size is 0.
A rest inverter is configured.

The primary winding W1 of the transformer 7 and the capacitor 8 form a series resonant circuit, while the inductor 4 connects the primary winding W1 to the capacitor 8.
The inductance is selected to have a sufficiently large inductance relative to the inductance of 1, and is a kind of relaxation oscillation type inverter. When the thyristor 5 is triggered by the control circuit 14, the capacitance charge of the capacitor 8 is resonantly discharged through the primary winding W1 and the thyristor 5.

Therefore, once the thyristor 5 is 0, the capacitor 8
The source voltage is reversed to the polarity before being triggered, and then the diode 6
is again resonantly recharged to its original polarity through the thyristor 5, in the process of which the thyristor 5 is turned off. In response to the trigger signal from the control circuit 14, the thyristor 5 is fired at the trigger frequency, and the inverter repeats the above operation. An intermittent positive strong wave-like current flows due to the 3-channel operation, and therefore high-frequency power equal to the trigger frequency is generated in the primary winding W1.

Therefore, the high voltage high frequency power generated in the high voltage secondary winding W2 is transmitted through the diodes 9a and 9b1 and the capacitor 10a910b.
The rectified signal is then supplied to the magnetron 13. On the other hand, the high-frequency power generated in the low-voltage secondary winding W3 is applied to the cathode of the magnetron in the chiyoke coil 11a. 11b to raise the temperature of the cathode. In this way, the magnetron 13 oscillates and the required radio wave output can be obtained. In such a circuit system, the trigger frequency of the thyristor 5 is controlled to be close to the resonant frequency of the resonant circuit made up of the primary winding W1 and the capacitor 8 mentioned above,
On the other hand, by lowering the trigger frequency, the resonant voltage generated in the resonant circuit can be controlled, and as a result, the high frequency voltage of the primary winding W can be easily controlled by the trigger frequency. become.

Utilizing this, the magnetron output PO can be easily controlled by the trigger frequency. FIG. 5 shows the trigger frequency F. magnetron output P. It is a graph showing a change in the cathode heater power PH. As shown in the figure, the inverter operating frequency F.

Radio wave output P for a change in . The reason why the heater power PH and the heater power PH exhibit two different changes is that the voltage/current characteristics of the magnetron are nonlinear, and when a voltage smaller than a predetermined voltage is applied, no radio wave output can be output. Once a voltage higher than a predetermined voltage is supplied, even a slight increase in voltage will significantly increase the radio wave output level. This is because the bell changes.
Therefore, when FO changes from f1 to F2 and the magnitudes of the two (W2 and W3) output voltages of the step-up transformer 7 change accordingly, PO changes from O to 100%, whereas PO changes from O to 100%. The pH shows a change of about 60% to 100%. However, as is clear from FIG. 5, the inverter operating frequency F.

By controlling the radio wave output P. When changing from O to 100%, the change in cathode heater power PH is P
It is said that it is a change smaller than O, about 6 from 100%.
It was not preferable for magnetron cathodes because it varied up to 0%. In other words, in order to guarantee stable and reliable magnetron oscillation, it is necessary that the temperature of the cathode remains constant; if it becomes too high, the cathode will melt or deform, and if it becomes too low, the emission The shortage causes moding and cathode surface deterioration. In order to prevent such inconvenience, conventionally the radio wave output P.

Alternatively, the low voltage secondary winding W3 in Fig. 1 can be removed and the cathode heater can be heated using commercial frequency power instead. The cathode temperature was stabilized by installing a heater transformer to heat the cathode. However, in the former method,
Radio wave output P.

The adjustable range was very narrow, making the high-frequency heating device difficult to use. Furthermore, the latter method has disadvantages such as a considerable increase in cost and an increase in the weight and dimensions of the entire power supply device. The present invention has been made in view of these points, and FIG. 2 shows one embodiment thereof.

In addition, in the figures, the same symbols as in FIG. 1 are equivalents.
An inductor 16 is connected in series to the low voltage secondary winding 7WW3 of the linear transformer 7, and is also connected in series to a parallel circuit consisting of the cathode of the magnetron 13 and the thyristor 15.

Furthermore, a series circuit of a capacitor 18 and a resistor 17 is connected in parallel with the thyristor 15, and a trigger element 19 is connected between the midpoint of the capacitor 18 and the resistor 17 and the gate of the thyristor 15. . Next, the circuit operation will be explained with reference to FIG.

FIG. 6a shows a voltage waveform generated in the next winding W3 at a low voltage, which is at the operating frequency F of the inverter as described above. By changing , when FO is high, the broken lines b1 and F in the same figure. When the voltage is low, the voltage waveform becomes as shown by the solid line a in the figure. Figure b shows the terminal voltage V of the capacitor 18.

Figure c is a diagram showing a current 1H flowing through the magnetron cathode, and to simplify the explanation, only the response to the first half-wave-like voltage in the upper half of figure a is shown. It shows. When a voltage as shown by the solid line a in FIG. is charged as shown by the solid line a in Figure b. Then, when the normal voltage of the trigger element (diac) 19 reaches +5, the diac 19 becomes conductive and discharges. Due to this discharge of the diode 19, the thyristor 15 becomes conductive and cuts off the current 1H that had been flowing to the cathode heater until then. That is, the thyristor 15 is electrically connected in parallel to the cathode heater, so that the heater current 1
H almost becomes O as the capacitor 18 is discharged. Also, the inverter operating frequency F.

When is high, VL in FIG. 6 Af) becomes the broken line b in FIG. 6 a. Since the peak value of this voltage is higher than that shown by the solid line a in the figure a, the photoelectric speed of the capacitor 18 is faster, and therefore the change in VO is also as shown by the broken line b in the figure b. Therefore, the normal timing of the diac 19 is the above-mentioned F. This is faster than when the current is low, and the time for which the heater current 1H is supplied is shortened. As a result, the heater current 1H shown in figure c also becomes as indicated by the broken line b in figure c. That is, the radio wave output P.

In order to increase the inverter's operating frequency F. When increasing the heater current 1H, the peak value of the heater current 1H becomes large and the repetition period becomes short.
When IH is lowered, the IH peak value is lower and the repetition period is longer, but the energization width becomes larger. Therefore, the effective value of the heater current 1H does not change much with respect to changes in FO, and therefore the inverter operating frequency F
.

The change in the heater power PH with respect to 5 is as shown in B shown in FIG. 7, and compared to the conventional change as shown in A in the same figure, the change in the heater power PH [F] is as shown in FIG. lfC. The stability has been greatly improved. Such a circuit configuration (Fig. 2) does not require the three-terminal thyristor 15 to be controlled by an external control circuit, especially considering that the cathode 1 reaches a high potential (3 to 4 Kv). , is extremely effective. FIG. 3 shows another embodiment of the present invention, and the same symbols as in FIG. 2 are equivalents. 20 is a two-terminal thyristor connected in parallel with the magnetron cathode, and a second terminal in series.
It has an inductor 21 of.

In this example, the trigger frequency F. As you increase the
When the frequency F3 is reached such that the breakover voltage of the thyristor 20 has a waveform similar to that applied to the thyristor 20 in FIG. While a voltage is applied, an inductor 21 is connected to the cathode of the magnetron 13.
F of the heater power (i.e., heater current) compared to the conventional configuration in which the thyristors 20 are kept connected in parallel and the thyristor 20 is not provided. There will be less change in . That is, as shown in Figure 7C, when FO is lower than F3, the thyristor is off, and when FO is set higher, P
H increases. And F. At =F3, the thyristor becomes conductive, changing to a circuit in which the inductor 21 is connected in parallel to the cathode of the magnetron, and the PH decreases to a value determined by the intersotance of the inductor 21. More F. When the pH is increased, the pH becomes F again. increases as . However, in the case of such a circuit, as is clear from FIG. 7C, the range of PH change can be reduced to about half that of the conventional case A. Figure 4 shows
This is another embodiment of the present invention.

In FIG. 4, the same symbols as in FIG. 2 are equivalents. In FIG. 4, 5a, 5b, 5e, and 5d are thyristors, and 22 is an inductor.Thyristors 5a, 5b are such that the firing order is controlled according to the phase of the commercial power supply, and the commercial AC is directly converted into high-frequency power. It consists of a cycloconverter that converts into Next, explanation will be given according to FIG. a
is the voltage VL generated between the terminals of the thyristor 20,
b is a current 1H flowing through the cathode of the magnetron 13. In Figure a, VBO is the voltage at which the thyristor 20 breaks over. Now, the output frequency F of the cycloconverter. When is low, VL becomes as shown in Fig. 8Af) a. As the value increases, it changes to B9C.
When VL reaches VBO, the magnetron cathode current 1H stops flowing, so IH changes from A7→d→♂ as FO becomes higher, as shown in FIG. 8b. That is, as shown in FIG. 7D, the VBO of the thyristor 20
By appropriately selecting , or by appropriately selecting the design of transformer 7, FOof/C can be obtained! The change in PI becomes the largest when it is extremely low, and even when FO becomes high,
is a characteristic that does not change significantly. In the embodiments shown in FIGS. 2 to 4, the inductor 16 may be replaced by a leakage inductance by appropriately selecting the degree of coupling between the primary winding W of the linear transformer 7 and the low-voltage secondary winding W3.

As described above, according to the present invention, by simply adding a simple circuit configuration, it is possible to freely control the radio wave output level while keeping the fluctuation range of the magnetron's heater power small, thereby increasing the reliability of the magnetron. It is possible to provide a high-frequency heating device that can be arbitrarily selected from low output to high output without impairing the output, and has extremely great effects.

[Brief explanation of the drawing]

Fig. 1 is a circuit diagram showing a conventional example, Fig. 2 is a circuit diagram of a high frequency heating device showing one embodiment of the present invention, Fig. 3 is a circuit diagram showing another embodiment, and Fig. 4 is a circuit diagram of a high frequency heating device showing an embodiment of the present invention. Furthermore, a circuit diagram showing another embodiment, FIG. 5 is a diagram showing the relationship between the frequency converter output frequency, the radio wave output of the magnetron, and the heater power in the conventional example,
Figure 6a is a diagram of the terminal voltage waveform of the thyristor in the same main part, b is a diagram of the terminal voltage waveform of the capacitor in the main part, c is a current waveform diagram of the magnetron heater in the main part, and Fig. j is the output of the frequency converter of the present invention. A diagram showing the relationship between frequency and magnetron heater power, Figure 8a is a voltage waveform diagram of the thyristor terminal of the same main part, and b
is a current waveform diagram of the same magnetron heater. 1, V... Commercial power supply terminal, 2... Rectifier 3... Capacitor, 4... Inductor, 5... Thyristor, 7 ...Linear transformer, 8...Capacitor, 13...
・Magnetron, 15... Thyristor, 17.
...Resistor, 18 ...Capacitor, 19
...Trigger element.

Claims (1)

[Claims] 1. A semiconductor frequency converter that operates at a frequency higher than a commercial frequency, and at least one linear transformer for supplying the output of the semiconductor frequency converter as high-voltage power and cathode heating power for a magnetron. . A high-frequency heating device comprising: frequency control means for controlling the operating frequency of the semiconductor frequency converter; and a semiconductor switch element connected in parallel with the cathode of the magnetron. 2. The high-frequency heating according to claim 1, wherein the semiconductor switching element is a bidirectional or reverse blocking three-terminal thyristor, and is configured to be triggered by a CR series circuit connected in parallel with the semiconductor switching element. Device. 3. The high-frequency heating device according to claim 1, wherein the first inductor is connected in series with a parallel circuit consisting of a magnetron cathode and a semiconductor switch element. 4. The high-frequency heating device according to claim 3, wherein the second inductor is connected in series with the semiconductor switch element. 5. The high-frequency heating device according to claim 3, wherein the first inductor is configured to also serve as a leakage inductance of a linear transformer.