JPS625590A - Cooker - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION (Technical Field of the Invention) The present invention relates to a cooking appliance in which a magnetron is driven at high frequency.

[Technical background of the invention and its problems]

Conventionally, in a cooking appliance such as a microwave oven, a commercial AC power supply voltage is boosted by a high voltage transformer, rectified by a voltage doubler rectifier circuit, and then applied to a magnetron.

However, in such conventional microwave ovens, the high voltage transformer is large and heavy, so
The microwave oven as a whole inevitably becomes larger and heavier, making it extremely difficult to use. Also, turn on the power to the magnetron.

Continuous output adjustment was not possible because the output was adjusted by turning it off.

Recently, we have recently rectified the commercial AC power supply voltage, supplied it to a resonant circuit consisting of the primary winding of the step-up transformer and a resonant capacitor, and excited the resonant circuit with a switching element. There is one in which high-frequency power of a predetermined frequency (and voltage) is obtained in the next winding, rectified by a double-wave voltage doubler rectifier circuit, and applied to the magnetron. Note that the double wave voltage doubler rectifier circuit includes a diode and a pair of capacitors.

In other words, it drives the magnetron at high frequency.
This makes it possible to employ a transformer that is small in size and light in fiffi, making it possible to make the entire microwave oven smaller and lighter, and also to enable continuous output adjustment. (For example, Japanese Patent Publication No. 52-4121, Utility Model Application Publication No. 56-148894).

However, in such microwave ovens, the voltage generated in the primary winding of the step-up transformer that makes up the resonant circuit does not form a neat sine wave, but rather an unbalanced waveform with different magnitudes of change for each half wave. . For this reason, a voltage with a different magnitude of change is generated in each half wave in the secondary winding of the step-up transformer, and the anode current (anode current) flowing from the double-wave voltage doubler rectifier circuit to the magnetron is shown in Figure 3. As shown in the figure, the waveforms have alternately different peak values, which disturbs the stable operation of the magnetron. That is, if the magnetron does not operate stably, it not only adversely affects the life of the magnetron itself but also the quality of cooking.

[Purpose of the invention]

This invention was made in view of the above circumstances,
The purpose is to provide a cooking appliance that allows stable operation of the magnetron, thereby extending the life of the magnetron, and, moreover, enabling cooking with good quality.

[Summary of the invention]

This invention employs a pair of capacitors with different capacities in a double wave voltage doubler rectifier circuit.

[Embodiments of the invention]

An embodiment of the present invention will be described below with reference to the drawings.

In FIG. 2, reference numeral 1 denotes a commercial AC power source, and a rectifier circuit 3 is connected to this power source 1 via an N source switch 2. A series circuit consisting of a primary winding 4a of a step-up transformer 4 and a resonant capacitor 5 is connected to the output end of the rectifier circuit 3, and a switching element such as an NPN transistor 6 is connected in parallel between the collector and emitter of the resonant capacitor 5. connected to. That is, a parallel resonant circuit is formed by the negative winding 4a and the resonant capacitor 5, and the resonant circuit is excited by turning the transistor 6 on and off.

Note that a protection diode 7 is connected between the collector and emitter of the transistor 6 to prevent application of a reverse voltage to the transistor 6.

Therefore, the secondary winding 4b of the step-up transformer 4 includes a diode 8 and a pair of capacitors 9a having different capacities.
The anode and cathode of the magnetron 10 are connected through a double wave voltage doubler rectifier circuit 9b. in this case,
The container of the capacitor 9a is made smaller than the capacitance of the capacitor 9b, and the ratio of the capacitances of the capacitors 9a and 9b is set at 1=1.degree. 5 to 1:2. The anode of the magnetron 10 is grounded, and the heater (
The cathode) is connected to a heater power source (not shown) via a heater transformer 11.

Furthermore, a control unit 13 is connected to the N source 1 via a power switch 2 and a step-down transformer 12 .

The control section 13 is made up of a microcomputer and its peripheral circuits, and controls the transistor 6 to be turned on or off in accordance with the operating state of the operating section 14.

Next, the operation of the above configuration will be explained with reference to FIG.

The power switch 2 is turned on and the operation to start cooking is performed using the operation unit 14. Then, the control unit 13 turns on and off the transistor 6 with a predetermined duty.

When the transistor 6 is turned on and off, a resonant circuit consisting of the negative winding 4a and the resonance capacitor 5 is excited, and a high frequency voltage is generated in the negative winding 4a.

As shown in the figure, when the transistor 6 is on, this negative winding voltage changes small in the form of a rectangular wave, and
When is off, the resonant capacitor 5 is charged based on the energy stored in the primary winding 4a, causing a large change in the shape of a sine wave. As a result, a high frequency current of a predetermined frequency is generated in the secondary winding 4b, and the magnetron 10 thereby operates in oscillation.

In other words, high frequency radio waves are emitted from the magnetron 10,
The high-frequency radio waves dielectrically heat the food in the heating chamber.

Incidentally, when the transistor 6 is on, the capacitor 9a is charged and the capacitor 9b is discharged, and as a result of the discharge, an anode current (anode current) Ib shown by a dashed line in the figure flows through the magnetron 10. Furthermore, when the transistor 6 is off, the capacitor 9b is charged, and
The capacitor 9a discharges, and the discharge causes the magnetron 10 to have an anode current (anode current) Ia indicated by the broken line in the figure.
flows. At this time, since the negative winding voltage has an unbalanced waveform every half wave, the capacitor 9a and the capacitor 9
There is going to be a difference in the charge for b, but since the capacitance of capacitor 9a is made small, that capacitor 9a
Mitsuru I against! This reduces the amount of capacitor 9a.
The distribution value of the current la based on the discharge of the capacitor 9b can be made approximately the same as the distribution value of the current 1b based on the discharge of the capacitor 9b.

In other words, the difference between the average value of the anode current in the magnetron 1o and the shear values of the anode currents Ia and Ib can be reduced, and the magnetron 10 can perform stable oscillation operation.

Therefore, not only can the life of the magnetron 1o be extended, but also the cooking can always be of good quality.

In the above embodiment, the ratio of the capacitances of the capacitors 9a and 9b was set to 1:1.5 to 1:2, but this ratio may be set to an optimal value depending on the design situation of the step-up transformer 4, etc. . In addition, although the case where the resonant circuit is a series resonant circuit formed by connecting the primary winding 4a of the step-up transformer 4 and the resonant capacitor 5 in series has been described, the -order winding 4a
The same can be applied to the case where a parallel resonant circuit is formed by connecting the resonant capacitor 5 and the resonant capacitor 5 in parallel. others,
This invention is not limited to the above-mentioned embodiments, but can be modified in various ways without changing the gist.

[Effects of the Invention] As described above, according to the present invention, there is provided a cooking appliance that enables stable operation of the magnetron, thereby extending the life of the magnetron, and furthermore, enabling cooking with good quality. can be provided.

[Brief explanation of the drawing]

Fig. 1 is a time chart for explaining the operation of an embodiment of the present invention, Fig. 2 is a diagram showing the configuration of a control circuit in the same embodiment, and Fig. 3 is a diagram showing the anode current of a magnetron in a conventional microwave oven. FIG. 3... Rectifier circuit, 4... Step-up transformer, 5... Resonant capacitor, 6... NPN transistor (switching element), 8... Diode, 9a, 9b...
- Capacitor, 10... Magnetron, 13... Control unit.

Claims (1)

[Claims] A double wave voltage doubler consisting of a rectifier circuit connected to an AC power source, a transformer with a primary winding connected to the output end of this rectifier circuit, a diode in the secondary winding of this transformer, and a pair of capacitors with different capacities. A magnetron connected through a rectifier circuit, a resonant capacitor forming a resonant circuit together with the transformer, a switching element for exciting this resonant circuit, and a control means for turning on and off the switching element. A cooker featuring: