JP3206512B2 - High frequency heating equipment - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a high-frequency heating apparatus using a magnetron such as a microwave oven.

[0002]

2. Description of the Related Art A conventional high-frequency heating apparatus will be described with reference to the drawings. Prior to the present invention, a magnetron driving power supply shown in FIG. 5 was proposed. In FIG. 5, 1 is a DC power supply, 4 is a first resonance capacitor, 5 is a second resonance capacitor, 6
Is a second semiconductor switching element, 3 is a first semiconductor switching element, 7 is a drive circuit, 2 is a leakage type transformer, 8 is a full wave voltage doubler rectifier circuit, and 9 is a magnetron.

The drive circuit 7 includes an oscillator 12 for generating drive signals for the first semiconductor switching element 3 and the second semiconductor switching element 6 therein. A signal of a predetermined frequency and a duty is generated by the oscillator 12, and a drive signal is given to the first semiconductor switching element 3. The second semiconductor switching element 6 is provided with a signal obtained by adding a delay time to the inverted signal of the drive signal of the first semiconductor switching element 3.

The operation of this circuit will be described with reference to FIGS. 6 and 7. First, the first semiconductor switching element 3
Is conducted, the equivalent circuit of the main circuit portion after the DC power supply 1 is as shown in FIG.
Are supplied from the smoothing capacitor 10 through the primary winding of the leakage type transformer 2. At this time, the collector current Ic is expressed by the equation (1) and increases linearly as shown in FIG.

Ic = Vc10 × tON / L1 (1) Next, when the first semiconductor switching element 3 is turned off,
The equivalent circuit is as shown in FIG. 6B, and is applied to the first semiconductor switching element 3 as shown in FIG. 7B by the resonance phenomenon of the primary winding of the leakage type transformer 2 and the first resonance capacitor 4. Voltage rises. When this voltage continues to rise and reaches the initial value of the second resonance capacitor 5, the diode constituting the second semiconductor switching element 6 becomes conductive, and charging of the second resonance capacitor 5 starts, and the equivalent circuit is shown in FIG. Move to the state of 6 (c). Since the capacitance of the second resonance capacitor 5 is set to a value larger than the capacitance of the first resonance capacitor 4, the state of FIG. The slope of the applied voltage becomes steep rapidly as shown in FIG. During this period, the second semiconductor switching element 6
When the charging is completed, the second resonance capacitor 5 starts discharging, and the voltage applied to the first semiconductor switching element 3 starts to decrease as shown in FIG. The circuit is in the state shown in FIG. When the transistor forming the second semiconductor switching element 6 is cut off at an arbitrary time, the equivalent circuit is in the state shown in FIG. 6E, and the first resonance capacitor 4 and the primary winding of the leakage type transformer 2 are connected again. Resonant operation occurs. Therefore, the first
7 (e), the slope of the voltage applied to the semiconductor switching element 3 of FIG.
It descends toward zero due to the energy it has. When the voltage applied to the first semiconductor switching element 3 becomes zero, the first semiconductor switching element 3
Are conducted, and the equivalent circuit is shown in FIG.
become that way. The voltage / current waveform of the first semiconductor switching element 3 is as shown in FIG. 7F, and the smoothing capacitor 10 is charged via the primary winding of the leakage type transformer 2. During this period, the first semiconductor switching element 3
, The same operation is repeated again from the state (a).

By performing such an operation, an operation of reducing the switching loss when the first semiconductor switching element 3 is turned off is realized, and the first semiconductor switching element 5 is operated by the second resonance capacitor 5. The voltage applied to the element 3 can be reduced.

[0007]

However, the magnetron driving power supply having such a configuration has the following problems.

That is, when the commercial power supply shows a clean sine wave shape as shown in FIG. 8A, the rectified waveform also becomes a waveform as shown in FIG. 8B. At this time, the envelope of the voltage waveform of the smoothing capacitor 10 has a sinusoidal shape as shown in FIG. The power supply for driving the magnetron operates with the sine-wave DC voltage as an input.
Similarly, the envelope of the voltage waveform applied to the semiconductor switching element 3 has a sine wave shape as shown in FIG.
Therefore, the voltage waveform of the primary winding of the leakage type transformer 2 becomes a waveform as shown in FIG. 8E, and similarly shows a sinusoidal envelope waveform.

However, depending on the environment in which the high-frequency heating device is installed, the input voltage waveform is not always a sine wave as shown in FIG. In other words, due to the influence of other equipment connected to the same commercial power system and the inductance component of the wiring to the high-frequency heating device,
The voltage waveform is distorted. FIG. 8F shows an example in which the voltage waveform of the commercial power supply is distorted. FIG.
When the voltage waveform of the commercial power supply is distorted as in (f),
The rectified waveform also causes the same distortion as shown in FIG. Therefore, the envelope of the voltage waveform of the smoothing capacitor 10 also has a distorted waveform as shown in FIG.
Since the magnetron driving power supply operates using the distorted waveform as an input voltage, the envelope of the voltage waveform applied to the first semiconductor switching element 3 is also the same as shown in FIG. Also cause distortion. As a result, the maximum value of the voltage waveform applied to the first semiconductor switching element 3 becomes larger than when a sine wave is input. Also, the voltage waveform of the primary winding of the leakage transformer 2 is distorted as shown in FIG. 8 (j), and the maximum voltage is increased. For this reason, there is a problem that the effect of reducing the voltage applied to the first semiconductor switching element 3 is impaired by the action of the second resonance capacitor 5.

The leakage type transformer 2 boosts the voltage of the primary winding and drives the magnetron 9 via the high voltage rectifier circuit 8. Therefore, when the voltage of the primary winding increases,
The voltage applied to the magnetron 9 increases accordingly. For this reason, there has been a problem that an excessive voltage is generated until the magnetron 9 starts oscillating.

When the magnetron 9 causes a sudden impedance change due to discharge in the tube or the like, the inductance value of the primary winding of the leakage type transformer 2 becomes small when considered in an equivalent circuit. The current flowing through the first semiconductor switching element 3 increases, and as a result, the voltage applied to the first semiconductor switching element 3 increases.
There is a problem that the effect of reducing the applied voltage of the first semiconductor switching element 3 is impaired by the function of the second resonance capacitor 5.

[0012]

In order to solve the above-mentioned problems, the present invention provides a DC power supply obtained by rectifying a commercial power supply,
A smoothing capacitor for smoothing the output of the DC power supply,
Step-up transformer connected in parallel with the smoothing capacitor
Series connection of the primary winding and the first semiconductor switching element
Series or in parallel with the primary winding of the step-up transformer
A first resonant capacitor connected to the step-up transformer;
Second semiconductor switch connected in series or parallel to the primary winding of
Series connection of switching element and second resonance capacitor
Receiving the output of the secondary winding of the step-up transformer
A high-voltage rectifier circuit for transmitting power to the TRON;
Detecting a voltage applied to one semiconductor switching element
And a driving circuit for detecting the voltage.
The circuit is configured to control the driving signal of the first semiconductor switching element.
A signal obtained by adding a delay time to the
The first and second semiconductor switches to be applied to the switching element.
Driving the switching element and the voltage detecting means.
If the detected voltage is equal to or higher than a predetermined value, the first semiconductor switch
The on-time of the switching element is controlled to be short.
You.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The first aspect of the present invention provides the above-mentioned solution.
With the configuration of the determining means, it is possible to control the voltage waveform applied to the first semiconductor switching element to a predetermined value when the voltage waveform of the commercial power supply is distorted.

According to a second aspect of the present invention, the voltage detecting means has a switching means, and the level of the detection signal is switched between a state where the magnetron is oscillating and a state where the magnetron is not oscillating.

[0015]

Embodiment (Embodiment 1) An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a circuit diagram showing a magnetron driving power supply according to the present embodiment.
Components denoted by the same reference numerals as in the conventional example are the same components, and detailed description thereof will be omitted. Reference numeral 14 denotes voltage detection means, and 15 denotes output command means. The output command means 15 detects the voltage of the first semiconductor switching element 3 by resistance division, and inputs a signal obtained by resistance division to the base of the transistor 14a. Therefore, when the base voltage is higher than the emitter voltage of the transistor 14a, the transistor 14a is turned on. With this operation, a voltage V1 is generated at the emitter of the transistor 14a. The voltage V1 is discharged with a time constant τ determined by the capacitor 14c and a resistor connected in parallel with the capacitor 14c. When the voltage V1 exceeds the reference voltage Vref, the comparator 14b generates a signal and transmits the signal to the output command means 15. Based on the transmitted signal, the output command means 15 transmits a signal to the oscillator 12,
Of the first semiconductor switching element 3
It works to shorten the on-time.

FIG. 2 shows operation waveforms of main parts of the magnetron driving power supply. FIG. 2A shows an example when the voltage waveform of the commercial power supply is sinusoidal, and FIG. 2E shows an example when the voltage waveform of the commercial power supply is distorted. When the voltage waveform of the commercial power supply is sinusoidal, the maximum value of the voltage applied to the first semiconductor switching element 3 is as shown in FIG.
V2 is shown as shown in (d). On the other hand, the voltage generated when the voltage waveform of the commercial power supply is distorted is v3 as shown in FIG. However, as described above, since the voltage detection means 14 transmits a signal to the output command means 15, v3 is controlled to a predetermined value and is limited to a value substantially equal to v2. At this time, the above-mentioned time constant τ is set to a value that can hold a voltage with respect to the cycle of the commercial power supply, thereby limiting the entire envelope to a low value.

Therefore, one of the leakage type transformers 2
The voltage generated in the next winding is also limited. As a result, there is an effect that an excessive voltage is not generated until the magnetron 9 starts oscillating.

Since the output signal of the output command means 15 is limited by the voltage detection means 14 even after the magnetron 9 starts oscillating, the first semiconductor switching element 3
Also, there is an effect that an excessive voltage is not applied to the substrate.

FIG. 3 shows an example in which the voltage detecting means 14 is switched between a start-up state and a steady state. The switching unit 14d provided in the voltage detecting means 14 switches the reference voltage Vref at the time of startup and at the time of steady state, so that the voltage applied to the first semiconductor switching element 3 is not only at the time of startup but also at the time of steady state. It can be less than or equal to a predetermined value. With this configuration, it is possible to arbitrarily set the voltage applied to the first semiconductor switching element 3 at the time of startup and at the time of steady state. In other words, in other words, the voltage applied to the magnetron 9 at the time of starting can be controlled. Therefore, there is an effect that not only an overvoltage is not applied to the first semiconductor switching element 3 but also an overvoltage is not applied to the magnetron 9 at the time of startup.

Embodiment 2 FIG. 4 is a circuit diagram showing a driving circuit 7 according to Embodiment 2. Components denoted by the same reference numerals are the same as those in the above-described embodiment, and description thereof will be omitted. 16 is a second voltage detecting means, and 17 is a stop command unit. Second voltage detecting means 17
Is configured to detect a voltage applied to the first semiconductor switching element 3, and when a voltage equal to or higher than the reference voltage Vref2 is detected, a signal is transmitted to the stop command unit 17, and the stop command unit 17 A stop command is transmitted to the output command section 15 and the oscillator 12 on the basis of the command, and the operation of the magnetron driving power supply is stopped.

When the operating frequency of the power supply for driving the magnetron is 20 kHz to 50 kHz, the capacitor 16a provided in the second voltage detecting means 16 is 500p.
By setting F or less, a value is set such that the detection voltage sufficiently follows the operating frequency. With this setting, the magnetron 9
When a sudden impedance change occurs during the operation, the voltage applied to the first semiconductor switching element 3 can be detected to prevent application of an overvoltage.

Also, two reference voltages Vref1 and Vre
The magnitude relationship of f2 is set so that Vref1 <Vref2 (2), and the output is limited by the first voltage detection means without stopping with respect to the power supply voltage distortion of the commercial power supply. When a sudden impedance change such as discharge in a tube occurs, not only the first semiconductor switching element 3 but also the high-voltage rectifier circuit 8 and the leakage type transformer 2 have a large responsibility. The operation of the magnetron drive power supply is stopped by 16 to prevent an excessive voltage and current duty from being applied.

[0023]

As described above, according to the present invention, it is possible to control the voltage waveform applied to the first semiconductor switching element to a predetermined value when the voltage waveform of the commercial power supply is distorted.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing a power supply for driving a magnetron of a high-frequency heating device according to a first embodiment of the present invention.

2A is a voltage waveform diagram of a commercial power source used for the magnetron driving power source. FIG. 2B is an output voltage waveform diagram of a power source used for the magnetron driving power source. FIG. 2C is a voltage of a smoothing capacitor used for the magnetron driving power source. Waveform diagram (d) Voltage waveform diagram of the semiconductor switching element used for the magnetron drive power supply (e) Voltage waveform diagram of the commercial power supply used for the magnetron drive power supply (f) Output voltage waveform of the power supply used for the magnetron drive power supply (G) Voltage waveform diagram of a smoothing capacitor used for the magnetron driving power supply (h) Voltage waveform diagram of a semiconductor switching element used for the magnetron driving power supply

FIG. 3 is a circuit diagram showing another example of the voltage detecting means of the magnetron driving power supply.

FIG. 4 is a circuit diagram showing a driving circuit of a power supply for driving a magnetron of a high-frequency heating device according to a second embodiment of the present invention.

FIG. 5 is a circuit diagram showing a power supply for driving a magnetron of a conventional high-frequency heating device.

FIG. 6A is an equivalent circuit diagram of a main circuit portion of the magnetron driving power source. FIG. 6B is an equivalent circuit diagram of a main circuit portion of the magnetron driving power source. FIG. 6C is an equivalent circuit diagram of a main circuit portion of the magnetron driving power source. Circuit diagram (d) Equivalent circuit diagram of the main circuit portion of the magnetron drive power supply (e) Equivalent circuit diagram of the main circuit portion of the magnetron drive power supply (f) Equivalent circuit diagram of the main circuit portion of the magnetron drive power supply

FIG. 7 is a voltage-current waveform diagram of a first semiconductor switching element of the power supply for driving the magnetron.

FIG. 8A is an AC voltage waveform diagram of a commercial power source of the magnetron driving power source. FIG. 8B is a power source output voltage waveform diagram of a conventional magnetron driving circuit of the high-frequency heating device. Voltage waveform diagram (d) Voltage waveform diagram of the semiconductor switching element in the magnetron drive circuit (e) Voltage waveform diagram of the primary winding of the leakage type transformer in the magnetron drive circuit (f) Commercial power supply of the magnetron drive power supply Voltage waveform diagram (g) Output voltage waveform diagram of a power supply in a magnetron drive circuit of a conventional high-frequency heating device (h) Voltage waveform diagram of a smoothing capacitor in the magnetron drive circuit (i) Voltage waveform of a semiconductor switching element in the magnetron drive circuit Fig. (J) Leakage type transistor in the magnetron drive circuit Voltage waveform diagram of a primary winding of Nsu

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 DC power supply 2 Leakage type transformer 3 1st semiconductor switching element 4 1st resonance capacitor 5 2nd resonance capacitor 6 2nd semiconductor switching element 7 Drive circuit 8 High voltage rectification circuit 9 Magnetron 14 Voltage detection means 15 Output command means

Continuing on the front page (72) Inventor Makoto Mihara 1006 Kadoma Kadoma, Osaka Prefecture Matsushita Electric Industrial Co., Ltd. References JP-A-4-62787 (JP, A) JP-A-5-199768 (JP, A) JP-A-1-186585 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB Name) H05B 6/66-6/68

Claims (2)

(57) [Claims] 1. A DC power supply obtained by rectifying a commercial power supply ,
A smoothing capacitor for smoothing the output of the DC power source, the
Step-up transformer connected in parallel with the smoothing capacitor
Series connection of the primary winding and the first semiconductor switching element
A first resonance capacitor connected in series or parallel to a primary winding of the step-up transformer, a second semiconductor switching element connected in series or parallel to the primary winding of the step-up transformer, and Receiving the output of the series connection of the second resonance capacitor and the secondary winding of the step-up transformer,
A high-voltage rectifier circuit for transmitting power to the TRON;
Detecting a voltage applied to one semiconductor switching element
A voltage detecting means because consists driving circuit, the driving
The circuit is configured to control the driving signal of the first semiconductor switching element.
A signal obtained by adding a delay time to the
The first and second semiconductor switches to be applied to the switching element.
Driving the switching element and the voltage detecting means.
If the detected voltage is equal to or higher than a predetermined value, the first semiconductor switch
A high-frequency heating device that controls the on time of the switching element to be short . 2. The method according to claim 1, wherein the voltage detecting means includes an oscillating state of the magnetron.
And the first semiconductor switching element by the non-oscillation state
Switch off the predetermined voltage level to control the ON time of
The high-frequency heating device according to claim 1, which is replaced .