CN1472990A - Apparatus and method for shortening heating time before starting magnetron - Google Patents

Abstract

A high-frequency heating apparatus for shortening a magnetron start-up heating time, comprising: a transformer connected with the DC power supply; the first resonant circuit is connected with the primary side winding of the transformer and comprises at least one switching device and at least one capacitor, and the first resonant circuit is formed by switching of the switching device and the primary side winding of the transformer; the rectifying device is connected with a secondary side coil of the transformer; a noise filter connected with the secondary side winding of the transformer; a resonant capacitor connected to the noise filter; and a magnetron connected to the noise filter, the resonant capacitor and the magnetron to form a second resonant circuit. With the invention, before the magnetron is started, the power supply is operated in a resonance mode, thereby increasing the output of the heating power of the magnetron and shortening the heating time before the magnetron is started, and after the magnetron is started, the operation mode of the power supply shifts the resonance point, thereby reducing the output of the heating power and maintaining the cathode temperature of the magnetron not lower than 2100K.

Description

Device and method for shortening heating time before magnetron start-up

(1) Technical field

The present invention relates to a device and method for shortening the heating time before the start-up of a magnetron.

(2) Background technology

FIG. 1 is a schematic diagram of a conventional magnetron circuit. As shown in Figure 1, a magnetron is a vacuum tube used to generate microwaves. The condition for its normal operation is: when the cathode temperature exceeds 2100K (absolute temperature), a negative high voltage ( thousands of volts). However, different magnetrons have different operating voltages, but their voltage and current characteristics are basically similar, as shown in Figure 2. When the voltage between the cathode and the anode reaches an operating voltage, the magnetron generates a microwave, and the voltage between the cathode and the anode is clamped near the operating voltage. At this time, the characteristics of the magnetron are quite In a regulator tube.

After the magnetron is activated, a microwave with a frequency of 2.45 GHz is generated, but other radio frequency waves are also generated at the same time. In order to eliminate these radio frequency waves, a noise filter is needed. As shown in FIG. 3 , the noise filter includes two inductors L1 and L2 and a capacitor C1 to eliminate other radio frequency waves.

The known device for shortening the heating time before the start-up of the magnetron is as follows: the cathode of the magnetron is a negative high-voltage terminal, and in practical applications, a winding is often directly added to a main transformer for heating the magnetron. , no need to use other high-voltage isolation transformers to provide a heating power supply for the cathode of the magnetron. As shown in FIG. 4 , n1 , n2 and n3 respectively represent the primary side winding and the secondary side winding of the main voltage transformer. The capacitor C1 is used to filter out the radio frequency ripple, and its value is small, so it can be neglected in the following analysis. Suppose the voltage of the heating winding n2 shown in Fig. 4 is:

u _n2 = Vsinωt (1)

Wherein, V is a peak voltage on the winding n2, and ω is a voltage angular frequency of the primary side of the main transformer.

The current flowing through the cathode is then: $i_{\mathrm{the\; heat}}=\frac{\mathrm{<figure-callout\; id="2"\; label="V\; R"\; filenames="A0212782600152.png,A0212782600181.png"\; state="\{\{state\}\}">V</figure-callout>}}{\sqrt{R^{}}}\sin (\mathrm{\&omega;t}-\mathrm{\&psi;})---\left(2\right)$

Wherein, R is the heating equivalent resistance of the cathode, and L is the sum of the inductances L1 and L2. $\mathrm{\&psi;}=\arctan \left(\frac{\mathrm{\&omega;\; L}}{R}\right)---\left(3\right)$

Its heating power is: $P={{\mathrm{<figure-callout\; id="2"\; label="i"\; filenames="A0212782600152.png,A0212782600181.png"\; state="\{\{state\}\}">i</figure-callout>}}^2}_{\mathrm{the\; heat}}R=\frac{V^{2}R}{2(R^2+{\mathrm{\&omega;}}^2{L}^2)}---\left(4\right)$

From the above deduction, it can be seen that the method of shortening the heating time before the magnetron is started: (1) increasing the peak voltage V; or (2) reducing the angular frequency ω of the input power.

However, in method one, that is, to increase the input voltage, the terminal voltage of the other secondary side winding n3 of the main transformer increases. At this moment, the magnetron has not started yet, which causes the voltage stress of the rectifier diode on the secondary side to increase. In the second method, for the magnetron power supply, there is still the problem of increased voltage stress of the rectifier diode on the secondary side. The specific description is as follows: the transformer applied to a microwave oven power supply is a high-voltage transformer, and the primary side and secondary side of the transformer are generally separated from the winding, thus generating a large leakage inductance. The magnetron power supply structure shown in Figure 4 can be equivalent to As shown in Figure 5. An inductance L _k in the figure is the leakage inductance of the high-voltage transformer, and _un2 and _un3 are the high-frequency AC voltages of the secondary windings n2 and n3 respectively.

Before the magnetron is started, the magnetron is equivalent to an open circuit. At this time, the voltage stress u of the rectifier diodes D1 and D2 is expressed by the following equation: $\mathrm{\&mu;}=\frac{{2\mathrm{\&mu;}}_{\mathrm{<figure-callout\; id="3"\; label="no"\; filenames="A0212782600152.png,A0212782600181.png"\; state="\{\{state\}\}">no</figure-callout>}3}}{1-(f_{\mathrm{the\; s}}/f_0)}---\left(5\right)$

Among them, f _s is the frequency of the power supply u _n3 , and f ₀ is a resonance frequency of leakage inductance and two capacitors C3 or C4:

Suppose, C=C3=C4, then ${\mathrm{<figure-callout\; id="0"\; label="f"\; filenames="A0212782600152.png"\; state="\{\{state\}\}">f</figure-callout>}}_0=\frac{1}{2\mathrm{\&pi;}\sqrt{L_{k}C}}---\left(6\right)$

A characteristic curve of voltage gain M=u _c3 /u _n3 and f=f _s /f ₀ can be obtained, as shown in FIG. 6 . Unless the frequency of the power supply drops to a very low value, 0.2 times the resonant frequency as an example, the voltage value on the load capacitor is still very large. And the reduction of the frequency of the power supply may saturate the transformer due to the increase of its excitation current.

From the above description, it can be seen that although the heating time is shortened by the method 1 and the method 2, the voltage stress of the rectifier diode is also increased.

(3) Contents of the invention

The main purpose of the present invention is to provide a device and method that can shorten the heating time before the magnetron is started, and shorten the heating time before the magnetron is started without increasing the voltage stress of the rectifier diode on the secondary side of a transformer. The effect of time.

According to one aspect of the present invention, there is provided a device for shortening the heating time before the start-up of the magnetron, connected to a DC power supply, comprising: a transformer connected to the DC power supply; a first resonant circuit connected to the primary side winding of the transformer, comprising At least one switch device and at least one capacitor, utilizing the switching of the switch device, forms the first resonant circuit with the primary side winding of the transformer; a rectifier device is connected to a secondary side coil of the transformer; a noise filter , is connected to the secondary side winding of the transformer; a resonant capacitor is connected to the noise filter; and a magnetron is connected to the noise filter, wherein the noise filter, the resonant capacitor and the magnetron The tube forms a second resonant circuit to shorten the start-up heating time of the magnetron.

According to the above idea, wherein the noise filter includes: a first inductor, one end of which is connected in series with one end of the magnetron; a second inductor, one end of which is connected in series with the other end of the magnetron; and A first capacitor is connected in parallel with the first inductor and the second inductor.

According to the above concept, the resonant capacitor is connected in series with any one of the first inductor and the second inductor.

According to the above idea, one end of the resonant capacitor is connected to the connection point of the first inductor and the first capacitor.

According to the above idea, one end of the resonant capacitor is connected to the connection point between the second inductor and the first capacitor.

According to the above idea, one end of the resonant capacitor is connected in series with the second inductor, and the other end is connected to one end of the first capacitor.

According to the above idea, one end of the resonant capacitor is connected in series between the first inductor and the first capacitor.

According to the above concept, the resonant capacitor is connected in series between the first inductor and the magnetron.

According to the above concept, the resonant capacitor is connected in series between the second inductor and the magnetron.

According to the above idea, the noise filter further includes a resonant inductor connected in series to the input end of the noise filter.

According to the above concept, the rectification device is one of the following devices: full wave voltage doubler rectification; half wave voltage doubler rectification; full wave rectification ( full wave rectification); full bridge rectification device (full bridge rectification).

According to the above idea, the transformer is a transformer with leakage inductance.

According to another aspect of the present invention, a method for shortening the start-up heating time of a magnetron is provided, which is applied to a magnetron high-frequency heating device, and the device includes a noise filter connected to the magnetron. The method includes the following steps: Steps: add a resonant capacitor to the noise filter; use the resonant capacitor to form a series resonant circuit with the noise filter and the magnetron, and make the device operate in a resonant mode before the magnetron starts, adding Large magnetron heating power output shortens the start-up heating time.

In order to further illustrate the purpose, structural features and effects of the present invention, the present invention will be described in detail below in conjunction with the accompanying drawings.

(4) Description of drawings

Fig. 1 is the circuit diagram of conventional magnetron (magnetron);

Fig. 2 is a schematic diagram of voltage-current characteristics of a conventional magnetron;

Fig. 3 is a conventional schematic diagram of a noise filter circuit applied to a magnetron heating circuit;

Fig. 4 is a conventional schematic diagram of a heating circuit applied to a magnetron;

Fig. 5 is the equivalent circuit schematic diagram of Fig. 4;

Fig. 6 is a schematic diagram of the voltage gain and frequency characteristic curve of the magnetron;

7 is a schematic diagram of a noise filter circuit of a magnetron heating circuit in a first preferred embodiment of the present invention;

Fig. 8 is the equivalent circuit diagram of Fig. 7;

Fig. 9 is a schematic diagram of the heating calibration power and frequency characteristic curve of the magnetron, wherein Fig. 9A is a schematic diagram of the characteristic curve of the heating calibration power P1 and the calibration frequency of the quality factor Q = 10, and Fig. 9B is the heating calibration power of the quality factor Q = 20 Schematic diagram of the characteristic curve of P1 and calibration frequency;

Fig. 10 is a schematic diagram of a magnetron heating circuit in a first preferred embodiment of the present invention;

Fig. 11 is a partial schematic diagram of the equivalent circuit of Fig. 10;

Fig. 12 is a partial schematic diagram of the magnetron heating circuit of the second and third preferred embodiments of the present invention;

Fig. 13 is a partial schematic diagram of the magnetron heating circuit of the fourth to fifth preferred embodiments of the present invention;

Fig. 14 is a partial schematic diagram of the magnetron heating circuit of the seventh to eighth preferred embodiments of the present invention; and

Fig. 15 is a partial schematic diagram of the heating circuit of the magnetron according to the tenth preferred embodiment of the present invention.

(5) specific implementation

In order to solve the problems of the prior art, the present invention utilizes the noise absorbing inductance of the magnetron and combines the working principle of series resonance to shorten the heating time of the magnetron. As shown in Figure 7.

A capacitor C1 is generally negligible due to its small capacitance, so a resonant capacitor C2 and two inductors L1 and L2 form a resonant circuit. Its equivalent circuit diagram is shown in Figure 8, wherein L is the sum of two noise absorbing inductances L1 and L2, and a resistor R is the equivalent resistance of the cathode heating of the magnetron.

u _n2 = Vsinωt (7)

Among them, V is the peak voltage on a winding n2, and ω is an angular frequency of the primary side voltage of the transformer.

And the current flowing through the cathode is: $i_{\mathrm{the\; heat}}=\frac{\mathrm{<figure-callout\; id="2"\; label="V\; R"\; filenames="A0212782600152.png,A0212782600181.png"\; state="\{\{state\}\}">V</figure-callout>}}{\sqrt{R^{}}}\sin (\mathrm{\&omega;t}-\mathrm{\&psi;})---\left(2\right)$

in, $\mathrm{\&psi;}=\arctan \left(\frac{\mathrm{\&omega;\; L}-\frac{1}{{\mathrm{\&omega;\; C}}_2}}{R}\right)---\left(9\right)$

Its heating power is: $P={{\mathrm{<figure-callout\; id="2"\; label="i"\; filenames="A0212782600152.png,A0212782600181.png"\; state="\{\{state\}\}">i</figure-callout>}}^2}_{\mathrm{the\; heat}}R=\frac{V^{2}R}{2({\mathrm{<figure-callout\; id="2"\; label="R"\; filenames="A0212782600152.png,A0212782600181.png"\; state="\{\{state\}\}">R</figure-callout>}}^2+{(\mathrm{\&omega;L}-\frac{1}{{\mathrm{\&omega;\; C}}_2})}^2)}---\left(10\right)$

Therefore, as long as the start-up is reduced ${(\mathrm{\&omega;\; L}-\frac{1}{\mathrm{\&omega;}{C}_2})}^2$ value, you can

To shorten the heating time before the magnetron starts.

suppose $\mathrm{<figure-callout\; id="1"\; label="P"\; filenames="A0212782600152.png"\; state="\{\{state\}\}">P</figure-callout>}1=\frac{\mathrm{<figure-callout\; id="2"\; label="P\; V"\; filenames="A0212782600152.png,A0212782600181.png"\; state="\{\{state\}\}">P</figure-callout>}}{V^{}};$ $f^{\&prime;}=f_{\mathrm{the\; s}}/f_{01};f_{01}=\frac{1}{2\mathrm{\&pi;}\sqrt{{\mathrm{<figure-callout\; id="2"\; label="LC"\; filenames="A0212782600152.png,A0212782600181.png"\; state="\{\{state\}\}">LC</figure-callout>}}_2}};$ $Q=\frac{{2\mathrm{\&pi;f}}_{01}L}{R}$

From this, the relationship between a heating calibration power P1 , a calibration frequency f′ and a quality factor Q can be obtained, as shown in FIG. 9 . Wherein, FIG. 9A is a schematic diagram of characteristic curves of heating calibration power P1 and calibration frequency f′ with quality factor Q=10. FIG. 9B is a schematic diagram of the characteristic curve of heating calibration power P1 and calibration frequency f′ with quality factor Q=20. Before the magnetron is started, if the operating frequency of the primary side power supply is near the resonant frequency f ₀₁ , the heating power will be greatly increased, and its maximum value is V ² /2R (full resonant state).

Therefore, according to the above analysis, the present invention not only greatly shortens the heating time, but also maintains the voltage stress of the rectifier diode basically unchanged. To further illustrate this problem, please refer to FIG. 10 , which is a schematic diagram of a magnetron heating circuit according to a first preferred embodiment of the present invention. The magnetron heating circuit is connected to a DC power supply V _dc and includes: a transformer T, a first resonant circuit 1 , a rectifier 2 , a noise filter 3 , a resonant capacitor C2 and a magnetron 4 . The transformer T is connected to the DC power source V _dc . The first resonant circuit 1 is connected to the primary side winding of the transformer T, and includes at least one switch device and at least one capacitor. By switching the switch device, a first resonant circuit is formed with the primary side winding of the transformer T. The rectifying device 2 is connected to a secondary coil of the transformer T. As shown in FIG. The noise filter 3 is connected to the secondary side winding of the transformer T. The resonant capacitor C2 is connected to the noise filter 3 . And, the magnetron 4 is connected to the resonant capacitor C2, wherein the noise filter 3, the resonant capacitor C2 and the magnetron 4 form a second resonant circuit to shorten the start-up heating time.

In addition, the noise filter 3 includes: a first inductor L1, one end of which is connected in series with the end of the magnetron; a second inductor L2, one end of which is connected in series with the other end of the magnetron 4; and A capacitor C1 is connected in parallel with the first inductor L1 and the second inductor L2.

In the circuit shown in FIG. 10 , because the transformer is a high-voltage transformer, the primary side and the secondary side winding are generally separated from each other according to insulation requirements, thus generating a large leakage inductance. For the convenience of analysis, please refer to FIG. 11 , which is a partial schematic diagram of the equivalent circuit of FIG. 10 . u _n2 and u _n3 are high-frequency AC voltages, and the inductance L _k is the leakage inductance.

Regarding the second part, the relationship between voltage gain and frequency before starting is still shown in Figure 6. For the first part of heating, the relationship between the calibration power P1, the calibration frequency f' and the quality factor (Quality factor) Q is shown in FIG. 9 . Before starting the magnetron, the power supply of the magnetron works at f ₀₁ frequency, and the heating power is very large at this time. By properly selecting the relative value of f ₀₁ and f ₀ , the voltage stress of the rectifier diode can be kept unchanged. After the magnetron is started, the power supply of the magnetron resumes normal frequency operation, and the heating power is reduced to only maintain the cathode not less than 2100K.

Please refer to FIG. 12 , which is a partial schematic diagram of the magnetron heating circuit according to the second and third preferred embodiments of the present invention.

Please refer to FIG. 13 , which is a partial schematic diagram of the magnetron heating circuit of the fourth to fifth preferred embodiments of the present invention. The difference from FIG. 12 is that the capacitor C1 is negligible because of its small capacitance.

Please refer to FIG. 14 , which is a partial schematic diagram of the magnetron heating circuit of the seventh to eighth preferred embodiments of the present invention. The biggest difference from the aforementioned preferred embodiments is that this embodiment also includes a resonant inductor L3.

Please refer to FIG. 15 , which is a partial schematic diagram of a magnetron heating circuit according to a tenth preferred embodiment of the present invention. The difference from FIG. 14 is that the capacitor C1 is negligible because of its small capacitance.

To sum up the above, the circuit structure shown in FIG. 7 , FIG. 12 to FIG. 15 disclosed by the present invention can be applied to any power supply circuit to shorten the start-up time of the magnetron, which all belong to the scope of this patent. It is known that the present invention can provide a magnetron high-frequency heating device to shorten the heating time before starting.

Of course, those of ordinary skill in the art should recognize that the above embodiments are only used to illustrate the present invention, rather than as a limitation to the present invention, as long as within the scope of the spirit of the present invention, the implementation of the above Changes and modifications of the examples will fall within the scope of the claims of the present invention.

Claims (13)

1. A high-frequency heating device that shortens the start-up heating time of the magnetron is connected to a DC power supply, and is characterized in that, comprising: A transformer connected to the DC power supply; A first resonant circuit, connected to the primary side winding of the transformer, including at least one switch device and at least one capacitor, using the switching of the switch device to form the first resonant circuit with the primary side winding of the transformer; a rectifying device connected to the primary and secondary side coils of the transformer; A noise filter is connected to the secondary side winding of the transformer; a resonant capacitor connected to the noise filter; and A magnetron is connected to the noise filter, wherein the noise filter, the resonant capacitor and the magnetron form a second resonant circuit to shorten the start-up heating time. 2. The high-frequency heating device according to claim 1, wherein the noise filter comprises: a first inductor, one end of which is connected in series with the end of the magnetron; a second inductor, one end of which is connected in series with the other end of the magnetron; and A first capacitor is connected in parallel with the first inductor and the second inductor. 3. The high-frequency heating device as claimed in claim 2, wherein the resonant capacitor is connected in series with one of the first inductor and the second inductor. 4. The high-frequency heating device according to claim 3, wherein one end of the resonant capacitor is connected to a connection point between the first inductor and the first capacitor. 5. The high-frequency heating device as claimed in claim 3, wherein one end of the resonant capacitor is connected to a connection point between the second inductor and the first capacitor. 6. The high-frequency heating device as claimed in claim 3, wherein one end of the resonant capacitor is connected in series with the second inductor, and the other end is connected to one end of the first capacitor. 7. The high-frequency heating device as claimed in claim 3, wherein one end of the resonant capacitor is connected in series between the first inductor and the first capacitor. 8. The high-frequency heating device as claimed in claim 3, wherein the resonant capacitor is connected in series between the first inductor and the magnetron. 9. The high-frequency heating device as claimed in claim 3, wherein the resonant capacitor is connected in series between the second inductor and the magnetron. 10. The high-frequency heating device according to any one of claims 4-9, characterized in that the noise filter further comprises a resonant inductor connected in series to the input end of the noise filter. 11. The high-frequency heating device as claimed in claim 1, wherein the rectifying device is one of the following devices: (1) Full-wave voltage doubler rectifier; (2) Half-wave voltage doubler rectifier; (3) Full-wave rectification device; (4) Full bridge rectifier. 12. The high-frequency heating device according to claim 1, wherein the transformer is a transformer with leakage inductance. 13. A method for shortening the start-up heating time of a magnetron, applied to a magnetron high-frequency heating device, the device includes a noise filter connected to the magnetron, characterized in that the method includes the following steps : adding a resonant capacitor to the noise filter; Using the resonant capacitor, the noise filter and the magnetron to form a series resonant circuit, before the magnetron is started, the device is operated in a resonant mode, and the heating power output of the magnetron is increased to shorten the start-up heating time .

Images