JP3206511B2 - 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. 10 was proposed. 10, 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.
, A drive circuit, 2 a leakage type transformer, 8 a full-wave voltage rectifier circuit, and 9 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. To the second semiconductor switching element 6, a signal obtained by adding a delay time to an inverted signal of the driving signal of the first semiconductor switching element 3 is given by the driving unit 13.

FIGS. 11 and 12 show the operation of this circuit.
This will be described with reference to FIG. First, when the first semiconductor switching element 3 is conducting, the equivalent circuit of the main circuit part after the DC power supply 1 is as shown in FIG. 12A, and the collector current Ic is changed to the primary winding of the leakage type transformer 2. Energy is supplied from the smoothing capacitor 10 through the wire. At this time, the collector current Ic is expressed by equation (1), and FIG.
As shown in (a), it increases linearly.

Ic = VC10 × tON / L1 (1) Next, when the first semiconductor switching element 3 is turned off,
The equivalent circuit is as shown in FIG. 12B, and is applied to the first semiconductor switching element 3 as shown in FIG. 11B 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, the charging of the second resonance capacitor 5 starts, and the equivalent circuit shifts to the state shown in FIG. Since the capacitance of the second resonance capacitor 5 is set to a value larger than the capacitance of the first resonance capacitor 4, by shifting to the state of FIG.
The slope of the voltage applied to becomes sharp gradually as shown in FIG. By sending an ON signal to the second semiconductor switching element 6 during this period, when the charging is completed, the second resonance capacitor 5 starts discharging, and the voltage applied to the first semiconductor switching element 3 decreases. 11
As shown in FIG. 12D, the equivalent circuit starts to fall, and the equivalent circuit is in the state shown in FIG. When the transistor constituting the second semiconductor switching element 6 is cut off at an arbitrary time, the equivalent circuit is in the state shown in FIG. 12E, and the first resonance capacitor 4 and the primary winding of the leakage type transformer 2 are again connected. Resonant operation occurs. Therefore, the slope of the voltage applied to the first semiconductor switching element 3 becomes steep as shown in FIG. 11E, and falls toward zero by the energy of the first resonance capacitor 4. When the voltage applied to the first semiconductor switching element 3 becomes zero, the diode constituting the first semiconductor switching element 3 conducts,
The equivalent circuit is as shown in FIG. The voltage / current waveform of the first semiconductor switching element 3 is as shown in FIG. 11 (F), and via the primary winding of the leakage type transformer 2,
The smoothing capacitor 10 is charged. By keeping the transistor constituting the first semiconductor switching element 3 conductive during this period, 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 9 serving as a load causes a sudden change in impedance, such as discharge in a tube. Such a sudden change in impedance affects the operation of the above-described resonance circuit. That is, the equivalent circuit of the leakage type transformer 2 has a configuration as shown in FIG. 13A, and can be expressed by an inductance corresponding to the leakage and an ideal transformer. On the other hand, when the magnetron 9 causes an impedance change such as discharge in a tube, the load on the secondary side of the leakage type transformer 2 is eliminated, and the equivalent circuit of the leakage type transformer 2 is as shown in FIG. It has only leakage inductance. Therefore, the slope of the current flowing through the first semiconductor switching element 3 represented by the equation (1) becomes large, and the operation waveform becomes as shown in FIG. For this reason, an excessive current and voltage are continuously applied to the first semiconductor switching element 3, and the voltage reduction effect obtained by the effect of the second resonance capacitor 5 is impaired. .

[0008]

[Means for Solving the Problems] In order to solve the above-mentioned problems
The present invention is a DC power supply obtained by rectifying a commercial power supply ,
A smoothing capacitor for smoothing the output of the DC power supply, a leakage type step-up transformer, a first semiconductor switching element connected in series to a primary winding of the step-up transformer, and a primary winding of the step-up transformer. A first resonance capacitor connected in series or in parallel, and one of the boost transformers
A series connection of a second semiconductor switching element and a second resonance capacitor connected in series or parallel to the next winding, a high-voltage rectifier circuit, a magnetron, and the smoothing capacitor.
A voltage detecting means for detecting an output voltage; and a driving circuit, wherein the high-voltage rectifier circuit receives an output of a secondary winding of the step-up transformer, transmits power to a magnetron, and outputs a primary winding of the step-up transformer. And a series connection of the first semiconductor switching element is connected in parallel to an output of the smoothing capacitor, and the drive circuit includes the first semiconductor switch.
Signal with a delay time in the inverted signal of the driving signal of the
To provide the second signal to the second semiconductor switching element.
While driving the second semiconductor switch element,
The voltage of the smoothing capacitor detected by the pressure detection means is negative.
Or the slope in the negative direction falls below a predetermined threshold
Or if the slope in the positive direction is
Stop command means for stopping the function of the drive circuit
By doing so , overcurrent and overvoltage are not continuously applied to the first semiconductor switching element.

Further, the stop command means is configured to issue a stop command after the first semiconductor switch element has been turned on for a predetermined time, thereby stopping the operation when the voltage of the smoothing capacitor is low. An increase in the voltage applied to the first semiconductor switching element due to the voltage can be suppressed.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The invention according to claim 1 is a DC power supply obtained by rectifying a commercial power supply, a smoothing capacitor for smoothing the output of the DC power supply, a leakage type booster transformer, and a booster transformer. A first semiconductor switching element connected in series with the primary winding, a first resonance capacitor connected in series or in parallel with the primary winding of the step-up transformer, and a primary winding of the step-up transformer. For detecting an output voltage of a series connection of a second semiconductor switching element and a second resonance capacitor connected in series or in parallel, a high voltage rectifier circuit, a magnetron, and the smoothing capacitor;
A voltage detecting means comprises a drive circuit, the high-voltage rectifier circuit receives an output of the secondary winding of the step-up transformer, to transmit power to the magnetron, the first semiconductor and the primary winding of the step-up transformer A series connection of switching elements is connected in parallel to an output of the smoothing capacitor, and the driving circuit
Is the reaction of the drive signal of the first semiconductor switching element.
A signal obtained by adding a delay time to the
First and second semiconductor switch elements to be applied to a switching element
While the voltage is being detected by the voltage detecting means.
When the voltage of the smoothing capacitor becomes negative,
It is configured to have a stop command means for stopping the function .

According to a second aspect of the present invention, the voltage detecting means detects the slope of the output voltage of the smoothing capacitor and transmits a signal to the stop command means when the slope in the negative direction falls below a predetermined threshold value. did.

According to a third aspect of the present invention, the voltage detecting means detects the slope of the output voltage of the smoothing capacitor, and transmits a signal to the stop command means when the slope in the positive direction exceeds a predetermined threshold value. did.

According to a fourth aspect of the present invention, the stop command means issues a stop command after the first semiconductor switching element has been turned on for a predetermined time.

[0014]

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

(Embodiment 1) FIG. 1 is a circuit diagram showing a first embodiment of the present invention. Components denoted by the same reference numerals as those of the conventional example are the same components, and detailed description thereof will be omitted. The voltage detecting means 16 is configured to detect the voltage of the smoothing capacitor 10. Reference numeral 15 denotes a stop command unit, which is configured to send a stop command to the drive unit 13 and the output command unit 14 based on an output signal of the voltage detection unit 16. Hereinafter, this operation will be described in detail.

During operation of the high-frequency heating device, the magnetron 9
Causes a sudden change in impedance due to discharge in the tube or the like, as already described in the conventional example, the inductance of the primary winding of the leakage type transformer 2 sharply decreases, and as shown at time T1 in FIG. The current flowing through the semiconductor switching element 3 of FIG. As a result, while the first semiconductor switching element 3 is conducting, the smoothing capacitor 10 is discharged through the primary winding of the leakage type transformer 2 and the voltage decreases. When the first semiconductor switching element 3 is turned off, charging is performed from the DC power supply 1, so that the voltage starts increasing.
When the diode forming the first semiconductor switching element 3 becomes conductive after the resonance period ends, the smoothing capacitor 10 is charged by this current. When the impedance of the magnetron 9 is extremely low due to discharge in a tube or the like, the power consumption on the secondary side of the leakage type transformer 2 becomes very small.
The current value is the same as when the semiconductor switch element 3 is turned off. Therefore, the charging current of the smoothing capacitor 10 increases, and the voltage peak increases. Next, when the transistor constituting the first semiconductor switching element 3 is turned on, the voltage of the smoothing capacitor 10 is high, so that a current having a larger gradient starts to flow. By repeating the charging / discharging operation of the smoothing capacitor 10, the amplitude of the voltage of the smoothing capacitor 10 increases. The operation is repeated several times, and at time T2 when the voltage of the smoothing capacitor 10 becomes equal to or less than the predetermined value, the diode provided in the voltage detecting means 16 conducts, and the voltage of the inverting input terminal of the comparator becomes as shown in FIG.
As shown in FIG. 2D, the output becomes lower than the reference signal, so that the comparator outputs the output shown in FIG. The stop command means 15 issues a stop command based on this signal, and has the effect that the operation of the high-frequency heating device is stopped and an excessive current voltage can be prevented from being continuously applied to the first semiconductor switching element 3. .

FIG. 3 shows an example in which the voltage detecting means 16 is configured to detect an overvoltage of the smoothing capacitor 10. With this configuration, the smoothing capacitor 10
The stop command means 15 issues a stop command by detecting that the voltage amplitude has increased to a predetermined value or more, stops the operation of the high-frequency heating device, and causes the first semiconductor switching element 3 to output an excessive current. Voltage can be prevented from being continuously applied.

FIG. 4 shows an example in which the voltage detecting means 16 is configured to detect the slope of the voltage of the smoothing capacitor 10. In this case, when the voltage amplitude of the smoothing capacitor 10 increases due to the impedance change of the magnetron 9, the slope of the positive voltage is detected before the voltage of the smoothing capacitor 10 reaches or exceeds a predetermined value. It has the effect of being able to.

FIG. 5 shows an example in which the negative gradient of the voltage of the smoothing capacitor 10 is detected, and the same effect is obtained.

FIG. 6 shows an example in which the voltage gradient of the smoothing capacitor 10 is detected in both positive and negative directions. With this configuration, the smoothing capacitor 1
There is an effect that the detection can be performed before the voltage of 0 becomes equal to or more than the predetermined value or less, and the detection probability can be increased.

(Embodiment 2) FIG. 7 is a circuit diagram showing a driving circuit according to a second embodiment. The stop command means 15 is configured to issue a stop command signal after the first semiconductor switching element 3 conducts for a predetermined ON time by a logic synthesis circuit. Hereinafter, this operation will be described with reference to FIG. FIG. 8A shows the voltage detecting means 1.
6 (b) is the output signal of the flip-flop circuit provided in the stop command means 15, and FIG.
Is a drive signal for the first semiconductor switching element 3.

When the voltage detecting means 16 generates an output signal, the output of the flip-flop circuit becomes low. At this time, when the drive signal of the first semiconductor switching element 3 is HIGH, the stop command signal is not generated by the operation of the NOR circuit, the first semiconductor switching element 3 conducts for a predetermined time, and the drive signal is Low. Then, a stop command signal is issued, the operation of the drive circuit 7 is stopped, and the high-frequency heating device stops. At this time, the voltage of the smoothing capacitor 10 is turned on when the first semiconductor switching element 3 is turned on.
Since the voltage is discharged through the primary winding of the leakage type transformer 2, the voltage is reduced. At that time, the high-frequency heating device stops its operation, so that the voltage of the smoothing capacitor 10 is gradually charged up to the output voltage value of the DC power supply 1, and FIG.
The voltage waveform is as shown in (b)-(a). Further, the voltage of the first semiconductor switching element 3 has an oscillation waveform centered on the voltage of the smoothing capacitor 3 due to the primary winding of the leakage type transformer 2 and the first resonance capacitor 4, as shown in FIG. 3 shows a voltage waveform. As described above, since the operation is stopped when the voltage of the smoothing capacitor 10 is low, the voltage applied to the first semiconductor switching element 3 does not become larger than the voltage during operation due to the oscillation voltage generated after the stop. .

[0023]

As described above , according to the first to fourth aspects of the present invention, it is possible to prevent an excessive current voltage from being continuously applied to the first semiconductor switching element.

Further, in particular, according to the invention described in claim 4,
For example, the stop command means is configured to issue a stop command after the first semiconductor switch element has been conducting for a predetermined time, so that the operation is stopped when the voltage of the smoothing capacitor is a low value. This has the effect that the voltage applied to the first semiconductor switching element can be suppressed.

[Brief description of the drawings]

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

FIG. 2 is an operation waveform diagram of the high-frequency heating device.

FIG. 3 is a circuit diagram showing an example of a voltage detecting means of the high-frequency heating device.

FIG. 4 is a circuit diagram showing another example of the voltage detecting means of the high-frequency heating device.

FIG. 5 is a circuit diagram showing another example of the voltage detecting means of the high-frequency heating device.

FIG. 6 is a circuit diagram showing another example of the voltage detecting means of the high-frequency heating device.

FIG. 7 is a circuit diagram illustrating a driving circuit of a high-frequency heating device according to a second embodiment of the present invention.

FIG. 8 is an operation waveform diagram of the drive circuit.

FIG. 9 is an operation waveform diagram of the high-frequency heating device.

FIG. 10 is a circuit diagram of a power supply for driving a magnetron of a conventional high-frequency heating device.

FIG. 11 is a voltage-current waveform diagram of a semiconductor switching element in an equivalent circuit of a power supply for driving a magnetron of a conventional high-frequency heating device.

12A is a circuit diagram showing an example of an equivalent circuit of a magnetron driving power supply of a conventional high-frequency heating device. FIG. 12B is a circuit diagram showing another example of the same equivalent circuit. (D) A circuit diagram showing another example of the same equivalent circuit (e) A circuit diagram showing another example of the same equivalent circuit (f) A circuit diagram showing another example of the same equivalent circuit

FIG. 13A is an equivalent circuit diagram of the leakage type transformer of the same circuit. FIG. 13B is an equivalent circuit diagram of the leakage type transformer when the magnetron of the same circuit causes an impedance change.

FIG. 14 is an operation waveform diagram when the magnetron of the circuit changes impedance.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 DC power supply 2 Leakage type transformer 3 1st semiconductor switching element 4 1st capacitor 5 2nd capacitor 6 2nd semiconductor switching element 7 Drive circuit 8 High voltage rectification circuit 9 Magnetron 10 Smoothing capacitor 15 Stop command means 16 Voltage detection means

Continuing on the front page (72) Inventor Makoto Mihara 1006 Kadoma Kadoma, Osaka Prefecture Matsushita Electric Industrial Co., Ltd. References JP-A-2-7385 (JP, A) JP-A-5-199768 (JP, A) JP-A-6-310267 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB Name) H05B 6/66-6/68

Claims (4)

(57) [Claims] 1. A DC power supply obtained by rectifying a commercial power supply, a smoothing capacitor for smoothing an output of the DC power supply,
A leakage type step-up transformer and one of the step-up transformers
A first semiconductor switching element connected in series to the secondary winding; a first resonance capacitor connected in series or in parallel to the primary winding of the boost transformer; and a serial connection to the primary winding of the boost transformer. Or a series connection of a second semiconductor switching element and a second resonance capacitor connected in parallel,
High voltage rectifier circuit, magnetron, and the smoothing capacitor
And a drive circuit. The high-voltage rectifier circuit receives an output of a secondary winding of the step-up transformer, transmits electric power to a magnetron, and outputs a primary winding of the step-up transformer. A series connection of a line and the first semiconductor switching element is connected in parallel to an output of the smoothing capacitor, and the driving circuit is connected to the first semiconductor switch.
Added delay time to inverted signal of driving signal
To apply a signal to the second semiconductor switching element.
1. While driving the second semiconductor switch element,
The voltage of the smoothing capacitor detected by the voltage detecting means
Stop command hand to stop the function of the drive circuit when is negative
A high-frequency heating device having a step . 2. A DC power supply obtained by rectifying a commercial power supply, a smoothing capacitor for smoothing an output of the DC power supply,
A leakage type step-up transformer and one of the step-up transformers
A first semiconductor switching element connected in series to the secondary winding; a first resonance capacitor connected in series or in parallel to the primary winding of the boost transformer; and a serial connection to the primary winding of the boost transformer. Or a series connection of a second semiconductor switching element and a second resonance capacitor connected in parallel,
High voltage rectifier circuit, magnetron, and the smoothing capacitor
And a drive circuit. The high-voltage rectifier circuit receives an output of a secondary winding of the step-up transformer, transmits electric power to a magnetron, and outputs a primary winding of the step-up transformer. A series connection of a line and the first semiconductor switching element is connected in parallel to an output of the smoothing capacitor, and the driving circuit is connected to the first semiconductor switch.
It gave a time delay to the inverted signal of the drive signal quenching element
To apply a signal to the second semiconductor switching element.
1. While driving the second semiconductor switch element,
The output of the smoothing capacitor detected by the voltage detecting means
If the slope of the voltage in the negative direction falls below a predetermined threshold,
A high-frequency heating device having stop command means for stopping the function of the drive circuit . 3. A DC power supply obtained by rectifying a commercial power supply, a smoothing capacitor for smoothing an output of the DC power supply,
A leakage type step-up transformer and one of the step-up transformers
A first semiconductor switching element connected in series to the secondary winding; a first resonance capacitor connected in series or in parallel to the primary winding of the boost transformer; and a serial connection to the primary winding of the boost transformer. Or a series connection of a second semiconductor switching element and a second resonance capacitor connected in parallel,
High voltage rectifier circuit, magnetron, and the smoothing capacitor
And a drive circuit. The high-voltage rectifier circuit receives an output of a secondary winding of the step-up transformer, transmits electric power to a magnetron, and outputs a primary winding of the step-up transformer. A series connection of a line and the first semiconductor switching element is connected in parallel to an output of the smoothing capacitor, and the driving circuit is connected to the first semiconductor switch.
Added delay time to inverted signal of driving signal
To apply a signal to the second semiconductor switching element.
1. While driving the second semiconductor switch element,
The output of the smoothing capacitor detected by the voltage detecting means
If the slope of the voltage in the positive direction exceeds a predetermined threshold,
A high-frequency heating device having stop command means for stopping the function of the drive circuit . 4. A stop command means according to claim issues a stop command after the first semiconductor switch element is turned a predetermined time 1
The high-frequency heating device according to any one of claims 1 to 3 .