JPS5931839B2 - High frequency heating device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a power supply device for a high-frequency heating device that converts commercial peripheral power into high-frequency power, boosts the voltage using a step-up transformer, and supplies high-frequency, high-voltage power to a magnetron, and which controls radio wave output. The present invention aims to provide a high-frequency heating device that not only provides a free power supply device but also stabilizes the cathode temperature of the magnetron to improve the life of the magnetron and has significantly improved reliability.

Recently, in high-frequency heating devices, a power supply device using a thyristor inverter or the like has been proposed in order to make the power supply device smaller, lighter, and lower in cost, and has been attracting attention.

The configuration will be explained below based on FIG. 1. Picture number is cool.
C, 1, 1' are commercial power supply terminals, 2 is a rectifier, and 3 is a capacitor, forming a unidirectional power supply. 4 is an inductor,
Together with the primary winding W of the step-up transformer 6, a series resonant circuit consisting of the capacitor T, and the reverse conduction thyristor 5, a simple series inverter is formed.

Now, the reverse conduction thyristor 5 is controlled by the switching control circuit 8.
is an ultrasonic frequency range of, for example, 18 KHz to 28 KHz, and when triggered, high-frequency power having a frequency equal to the trigger frequency is generated in the direct-wavelength oscillator circuit.

Therefore, high frequency high voltage power is generated in the secondary winding W2 of the step-up transformer 6, and DC high voltage is supplied to the magnetron 11 via a rectifier circuit including diodes 9a, 9b and capacitors 10a, 10b. In addition, step-up transformer 6
The second low-voltage secondary winding W3 supplies cathode heating power to the cathode of the magnetron 11 to increase the cathode temperature.

Therefore, the magnetron oscillates and dielectric heating becomes possible. A power supply device for such a high-frequency heating device can be smaller, lighter, and lower in cost than a power supply device that directly boosts commercial frequency power to high-voltage power using a leakage transformer. However, the power supply device shown in FIG. 1 has the following problems. That is, when the trigger frequency of the thyristor 5 is lowered in order to reduce the radio wave output of the magnetron 11 using the circuit shown in FIG. If it is too low, it will cause problems such as moding, and the magnetron 11
There is also a risk of significantly damaging the reliability range of the heater power (1).
Since the power supplied to the cathode also increases, when the temperature rise due to back bombardment of the magnetron cathode is large, the heater power also increases, and the reliability of the cathode is inevitably reduced further. I didn't get it.

Further, in such a power supply device, it is desirable that the high voltage power is low and the heater power is high at the time of startup, but it has been difficult to supply such high voltage and low voltage power.

That is, when trying to shorten the rise time of the magnetron by increasing the heater power at startup, the trigger frequency of the thyristor 5 is increased to increase the output voltage of the inverter, and the output voltage of the secondary winding W3 of the step-up transformer 6 is increased. Although it is necessary to increase the generated frost pressure, this rubbing also causes a very high voltage to be generated in the high-voltage secondary winding W2. Therefore, the voltage conditions for the diodes 9a, 9b and capacitors 10a, 10b have to be extremely severe. The present invention has been made in view of the above-mentioned conventional drawbacks, and embodiments of the present invention will be described below with reference to FIGS. 2 to 10.

Note that the same numbers are used for the same parts as in the conventional configuration described above, and the explanation thereof will be omitted. In FIG. 2, 12 is a heater transformer, the primary winding of which is connected in series with a DC blocking capacitor 13. This DC blocking capacitor 13
Without it, starting such an inverter would have to be done at the same time as commercial power is turned on, which would be practically impossible. With this configuration, high voltage power and heater power are supplied to the magnetron 11, and the trigger frequency FO of the thyristor 5 (
=L) by changing the magnetron radio wave output P
Looking at the change in the AC component s of the terminal voltage of the thyristor 5 when O is changed from 600W to 60W, it is found that 100(
It only changes by about 90% from f).

In other words, when the value of Vs when PO is 600W is 100, the value of Vs when PO is 60W is approximately 90, and for a change in PO from 600W to 60W, 1
Vs changes only by about 0%. This principle will be explained with reference to FIG. 7a, which shows only the heater power supply circuit of the magnetron 11 in FIG. 2. That is, the seventh
In Figure a, the AC component Vs of the terminal voltage of the thyristor 5 is considered as a power source. Now, the capacitance of the capacitor 13 is C, the primary and secondary inductances of the heater transformer 12 are Lp,
Lsl order, the coupling coefficient of the secondary winding is K, the turns ratio is n, the filter yoke 15a, 15b of the magnetron heater circuit
The impedance including Zin=RK+JCl)LK
When expressed as an equivalent circuit as , it becomes as shown in FIG. 7b.
RK and LK are the resistance value of the force sorter and the inductance of the heater circuit. In Fig. 7b, the inductance K
Let the current flowing in the branch with Lp be I(KLp), the current flowing in the branch with inductance (1-K) Lp, LK-N2, and resistance RK-N2 be 1(RK-
N2), and the terminal voltage of the inductance KLp is Vs'
Then, however, N)/Re・N2)2{2 slope δ・{(
1-K)Lp+N2Lml]2.

Here, if FO, K, Lp, RK, and LK are selected so that 2πFO−K−Lp>A, then

Therefore, I(KLp). Ignoring this, the circuit of FIG. 7b can be approximated by the circuit of FIG. 7c.

In Figure 7c, L=2・(1−K)Lp+N2・L
It is K.

Considering the power P supplied to the heater, however, ? 2πFO,
It can be expressed as l゜iζノ4, and -. If we choose the value of C and FO so that O and it becomes ω2LC, then I
H can be a power supply circuit with decreasing characteristics.

In addition, by appropriately designing the heater transformer 12 and capacitor 13, the degree of change in IH with respect to PO can be
It can be designed in the most favorable condition.

That is, in FIG. 8, PO and PH as in conventional 4
What used to be the relationship 8 can be changed to 8.

Furthermore, it has the following advantages at startup.

This will be explained with reference to FIG. 、． ．． 71:==:X.
By changing ``==.; 4 visit name:, if the inverter is a thyristor inverter as in the embodiment, commutation failure can be prevented, and furthermore, sudden inflow of current from the commercial power line can be prevented. It can prevent sudden drops in power supply voltage due to line impedance, and
The effect on equipment can be reduced. When such startup control is performed, the power PHC supplied to the heater changes as shown in the diagram. In other words, conventionally, PH and TO were equal to 1, as shown by the broken line.
However, according to the present invention, the PH gradually becomes smaller from the larger side as shown by the solid line. Then, as shown in diagram C, the anode-cathode voltage VAK of the magnetron changes, and the anode current 1
A rises as shown in figure d. That is, according to the present invention, the start time of the rise of magnetron oscillation becomes faster, and the rise time Tr is also shortened.

Therefore, it is suitable for quick cooking, and
Since the operating time of the magnetron in the abnormal oscillation mode during the rise time Tr is shortened, the life of the magnetron can be significantly improved. Furthermore, A that occurs at startup
The K(7) starting voltage VAK2 is lower than that of the conventional AKl, making it possible to reduce the cost and improve the reliability of the high voltage circuit.

3 to 6 show other embodiments of the present invention, which can achieve the same effects as the above embodiments. In other words, the present invention provides that ``when the switching frequency of the switching means that energizes the resonant circuit is changed to change the voltage excited in the resonant circuit (output voltage), the alternating current component of the terminal voltage of the switching means does not change much.'' Since it takes advantage of this fact, it can be implemented in various ways. In particular, FIGS. 5 and 6 show an embodiment using two semiconductor switch elements. In addition, Figure 2~
It is also possible to remove the rectifier 2 in the embodiment shown in FIG. 6 and use a reverse blocking thyristor in antiparallel in place of the reverse conduction thyristor 5, and the present invention is limited to the embodiment shown in FIGS. It is not something that can be done. As is clear from the above description, according to the present invention, it is possible to provide a high-frequency heating device that has a wide radio wave output range, significantly improves the life of the magnetron, and is small, lightweight, and low in cost.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram of a power supply device in a conventional high-frequency heating device using an inverter circuit, FIG. 2 is a circuit diagram showing an embodiment of the power supply device in a high-frequency heating device of the present invention, and FIG.
Figures 6 to 6 are circuit diagrams showing other embodiments of the present invention, Figures 7A, b, and c are equivalent circuit diagrams of heater circuits, and Figure 8 shows the relationship between heater power PH and radio wave output PO. Figures 9 and 9 are explanatory diagrams showing operating states of the circuit of the present invention, Figures 10a-d
FIG. 2 is an explanatory diagram showing a state at startup. 5... Semiconductor switch element, 6... Step-up transformer, 8... Switching control circuit, 1
1... Magnetron, 12... Heater transformer, 13... Capacitor.

Claims (1)

[Claims] 1. One or more semiconductor switching elements, switching control means for controlling the semiconductor switching elements,
A series or parallel resonant circuit energized by the semiconductor switch element, a step-up transformer connected to the resonant circuit, a magnetron energized by the step-up transformer, and a magnetron connected in parallel to one of the semiconductor switch elements. A high-frequency heating device including a heater transformer that supplies cathode heating power of the magnetron. 2. The high frequency heating device according to claim 1, wherein a capacitor is connected in series to the primary winding of the heater transformer. 3. The high-frequency heating according to claim 1, wherein the switching control means is configured to increase the switching frequency continuously or stepwise from a predetermined low frequency to a set frequency at startup to control the semiconductor switching element. Device.