JPH0636872A - Microwave oven - Google Patents

Abstract

PURPOSE:To stabilize the output of a magnetron in low output cooking by detecting the oscillating state of the magnetron, and feedback-controlling the duty for driving an inverter circuit on the basis of the detection signal. CONSTITUTION:When an inverter start signal Sa is given from a microcomputer 18 to an inverter connecting circuit 10, an inverter circuit 2 is ON, and after the lapse of a slight delay time, a magnetron 12 is oscillated. When the magnetron 12 is oscillated, a current transformer 16 detects this positive electrode current and gives a detection signal Sb to the computer 18. When timer time reaches Ta, thereafter, the computer 18 changes the signal Sa to low level to make the circuit 2 OFF, and stops the oscillation of the magnetron 12. When the timer time reaches Tb, then, the circuit 2 is ON. By conforming the times Ta and Tb to a duty to be set, consequently, the magnetron can be intermittently ON/OFF in precise conformation to the duty.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a microwave oven configured to oscillate and drive a magnetron by a power source supplied from an inverter circuit.

[0002]

2. Description of the Related Art In this type of microwave oven, the oscillation output of a magnetron is 50% to 100% (for example, the rated output is 6%).
In the case of 00 W, it is configured to be adjustable in the range of 300 W to 600 W). The reason why the output is not adjustable between 0% and 50% is that there is a cost problem and a magnetron oscillation stability problem. Here, when performing low-power cooking such as thawing cooking, use a magnetron 30
It is necessary to oscillate at a low output of less than 0W.

In such a case, for example, one magnetron
When oscillating with an output of 00 W, the magnetron is conventionally driven on and off intermittently with a duty for turning on for 10 seconds and turning off for 20 seconds. When the magnetron is intermittently driven at the above duty, the inverter circuit is driven on and off at the above duty.

[0004]

By the way, there is a slight delay time after the inverter circuit is turned on and before the magnetron is actually driven to oscillate. This delay time is a time that varies considerably depending on the state of the magnetron when the inverter circuit is turned on, for example, the temperature of the magnetron. Therefore, in the above-mentioned conventional configuration, even if the inverter circuit is driven on and off with a duty corresponding to an output of 100 W, the actual oscillation time of the magnetron fluctuates considerably, and the output of the magnetron fluctuates and becomes unstable. There was a problem. When the output of the magnetron fluctuates in this way, low-power cooking, such as thawing cooking, may not be performed well.

Therefore, an object of the present invention is to provide a microwave oven capable of stabilizing the output of the magnetron when the magnetron is intermittently driven on and off to cook at a low output, and the cooking can be performed well. To provide.

[0006]

The microwave oven of the present invention comprises:
In a microwave oven configured to oscillate and drive a magnetron by a power source supplied from an inverter circuit, the microwave oven is provided with a detecting means for detecting an oscillating state of the magnetron, and the detecting means is provided when the magnetron is on-off intermittently driven. It is characterized in that a control means for feedback controlling the duty for driving the inverter circuit based on the detection signal from is provided.

[0007]

According to the above means, the detecting means detects the oscillating state of the magnetron, and the duty for driving the inverter circuit is feedback-controlled based on the detected signal. Therefore, the delay time when the magnetron oscillates is delayed. However, even if the frequency fluctuates, the actual oscillation time of the magnetron can be accurately associated with the duty corresponding to the oscillation output to be set. Therefore, even during low-power cooking, the output of the magnetron can be stabilized, and cooking can be performed well.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to FIGS. First, in FIG. 2 showing the electrical configuration of a microwave oven, an inverter circuit 2 is connected to a commercial AC power supply 1. This inverter circuit 2
Is a rectifier circuit 3 which converts commercial frequency power into high frequency power and outputs the high frequency power, and which is formed by connecting diodes in a bridge connection.
It is composed of a smoothing capacitor 4 and a switching circuit 5.

The switching circuit 5 includes a switching transistor 6, which is a switching element, a resonance capacitor 7, a primary winding 8a of a step-up transformer 8, and a counter electromotive force generation preventing diode 9. The switching transistor 6 of the switching circuit 5 is turned on and off by the inverter control circuit 10, and high frequency power is generated in the primary winding 8a in response to the turning on and off.

The step-up transformer 8 has a secondary winding 8b.
And a filament winding 8c, and the secondary winding 8b is connected to the anode 12a and the cathode 12b of the magnetron 12 via the voltage doubler circuit 11. The voltage doubler circuit 11 includes a capacitor 13 and diodes 14 and 15. Here, the anode 12a and the voltage doubler circuit 1
A current transformer 16, which is a detection means, is provided between the first and second terminals. This current transformer 16
The magnitude of the current flowing through the anode 12a of the magnetron 12 is detected, and the detection signal is given to the microcomputer 18 via the photocoupler 17.

In this case, the current transformer 16 is configured to detect the oscillating state of the magnetron 12, that is, whether or not it is oscillating, by detecting the anode current of the magnetron 12. Also, the filament winding 8c
Are connected to the cathode 12b or filament of the magnetron 12.

Then, the microcomputer 18
Stores a control program for controlling the cooking operation of the microwave oven in general, and receives various switch signals from an input circuit (not shown) having various switches provided on the operation panel. There is. The microcomputer 18 is configured to give a control signal to the inverter control circuit 10 via a photo coupler 19 based on the control program and various switch signals. The microcomputer 18 and the inverter control circuit 10 constitute control means 20.

Next, the operation of the above configuration will be described with reference to FIG. When performing, for example, thawing cooking as low-power cooking, the magnetron 12 is oscillated with an output of 100 W, for example. In this case, if the magnetron 12 is controlled to be on / off intermittently driven with a duty that is on for 10 seconds and off for 20 seconds, an output of 100 W can be obtained. Hereinafter, the control for accurately driving the magnetron 12 intermittently on and off with a set duty will be specifically described.

Now, the inverter starting signal S as shown in FIG. 1A is output from the microcomputer 18 as a control signal.
When a is given to the inverter control circuit 10, the time t
1, that is, the inverter circuit 2 is turned on when the inverter start signal Sa becomes high level. And
Some delay time Δt after the inverter circuit 2 is driven
After elapse of time, the magnetron 12 is driven to oscillate at time t2. This delay time Δt is a time that varies considerably depending on the state of the magnetron 12, for example, the temperature of the magnetron 12 itself.

When the magnetron 12 is driven to oscillate at time t2, the anode current of the magnetron 12 flows, so that the current transformer 16 detects the anode current and gives a high-level detection signal Sb to the microcomputer 18. The microcomputer 18 starts clocking at the time when the detection signal Sb becomes high level, that is, at time t2. After that, when the measured time reaches Ta (for example, 10 seconds in the case of output of 100 W), that is, at time t3, the microcomputer 18 sets the inverter start signal Sa to the low level and turns off the inverter circuit 2. At the same time, the oscillation of the magnetron 12 is stopped.

At the same time, the microcomputer 18
Starts timing from time t3. After that, when the time measured reaches Tb (for example, 20 seconds in the case of output of 100 W), that is, at time t4, the microcomputer 18
Sets the inverter activation signal Sa to a high level to drive the inverter circuit 2 on. Hereinafter, the same control as the control described above is repeatedly performed. As a result, in the above embodiment,
As shown in FIG. 1C, the magnetron 12 is turned on for a time Ta.
It becomes possible to perform on / off intermittent drive with a duty that turns on and turns off for a time (Tb + Δt). If the above duty, that is, Ta and Tb, are made to correspond to the duty to be set, the magnetron 12 will correspond to the duty accurately. It is driven on and off intermittently (especially, the on time is accurate). Therefore, the magnetron 12 is stably oscillated and driven at the set low output.

In this case, the inverter activation signal Sa output from the microcomputer 18 has a duty that is feedback-controlled based on the detection signal Sb, as shown in FIG. In particular, the high level section of the duty of the inverter activation signal Sa is feedback controlled.

Incidentally, the magnetron 12 of the conventional structure is used.
FIG. 3 shows the on / off intermittent drive control of. As shown in FIG. 3, in the conventional configuration, the high level section T1 and the low level section T2 of the inverter start signal Sa are configured to correspond to the set duty, so that the oscillation of the magnetron 12 is started. It can be seen that both the actual ON time Tp and OFF time Tq of the magnetron 12 do not correspond to the above duty because the delay time Δt exists. In particular, since the delay time Δt changes,
It can be seen that the on-off intermittent drive of the magnetron 12 becomes considerably unstable.

On the other hand, according to this embodiment having the above-mentioned structure, the magnetron 12 is driven by the current transformer 16.
Is configured to perform feedback control of the duty for driving the inverter circuit 2 on the basis of the detection signal Sb. Therefore, as shown in FIG. Even if it fluctuates, the actual oscillation time of the magnetron 12 can be accurately associated with the duty corresponding to the oscillation output to be set. As a result, magnetron 1
2 can be accurately driven on / off intermittently at the above-mentioned duty (in particular, the on-time can be accurately controlled). Therefore, even during low-power cooking such as thawing cooking, unlike the conventional configuration (see FIG. 3), the magnetron 12 The output of can be stabilized and cooking can be performed well.

[0020]

As is apparent from the above description, the present invention detects the oscillating state of the magnetron by the detecting means and feedback controls the duty for driving the inverter circuit based on the detected signal. ,
When the magnetron is intermittently driven on and off to cook at a low output, the output of the magnetron can be stabilized and excellent cooking can be performed.

[Brief description of drawings]

FIG. 1 is a time chart showing an embodiment of the present invention.

[Fig. 2] Electric circuit diagram

FIG. 3 is a time chart showing a conventional configuration.

[Explanation of symbols]

2 is an inverter circuit, 5 is a switching circuit, 6 is a switching transistor, 10 is an inverter control circuit, 1
2 is a magnetron, 16 is a current transformer (detection means), 18 is a microcomputer, and 20 is control means.

Claims (1)

[Claims] 1. A microwave oven configured to oscillate and drive a magnetron by a power source supplied from an inverter circuit, wherein a detecting means for detecting an oscillating state of the magnetron, and an on-off intermittent drive of the magnetron, A microwave oven, comprising: a control unit that feedback-controls a duty for driving the inverter circuit based on a detection signal from the detection unit.