JP3152220B2 - High frequency heating equipment - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to relates to a high frequency heating apparatus which performs a dielectric heating using a magnetron such as electronic oven, and in particular the circuit construction of a power supply device for driving a magnetron.

[0002]

2. Description of the Related Art A power supply is mounted on various devices including a high frequency heating device for home use. Conventional power supplies are heavy,
And since it was large, it was desired to reduce its size and weight. For this reason, the reduction in size, weight, and cost by switching the power supply has been actively promoted in various fields. A high-frequency heating apparatus that cooks food using microwaves generated by a magnetron is also required to reduce the size and weight of a power source for driving the magnetron.
No. 0-241851.

In the above publication, in order to reduce the switching loss of a semiconductor switching element operating at a high frequency, a resonance type circuit system is used, and the voltage applied to the semiconductor switching element increases due to the action of the resonance circuit. As a result, the withstand voltage of the semiconductor switching element or related electric parts is increased, and as a result, the size is increased,
In order to solve the problem of high cost, the following configuration is adopted.

That is, as shown in FIG. 5, a DC power supply 1 obtained by rectifying a commercial power supply, a third capacitor 2 for smoothing the output of the DC power supply, a leakage transformer 3, a first semiconductor switching element 4, 1 capacitor 5, 2nd
, A second semiconductor switching element 7, a driving means 8, a full-wave voltage doubler rectifier 9, and a magnetron 10. The DC power supply 1 performs full-wave rectification of a commercial power supply and applies a DC voltage VDC to a series circuit of the second capacitor 6 and the primary winding 11 of the leakage transformer 3. The first semiconductor switching element 4 and the second semiconductor switching element 7 are connected in series, and a series circuit of the primary winding 11 of the leakage transformer 3 and the second capacitor 6 is connected to the second semiconductor switching element 7. Connected in parallel.

The first capacitor 5 is connected in parallel with the second semiconductor switching 7. The high voltage output generated in the secondary winding 12 of the leakage transformer 3 is converted into a high DC voltage by the full-wave voltage doubler rectifier 9 and applied between the anode and the cathode of the magnetron 10. The tertiary winding 13 of the leakage transformer 3 supplies a current to the cathode of the magnetron 10.

The first semiconductor switching element 4 is an IGB
T and a diode connected in parallel with T. Similarly, the second semiconductor switching element 7
It is composed of a GBT and a diode.

The driving means 8 has an oscillating section for generating driving signals for the first semiconductor switching element 4 and the second semiconductor switching element 7 therein. The oscillating section generates a signal of a predetermined frequency and a duty. The drive signal is generated and supplied to the first semiconductor switching element 4. The second semiconductor switching element 7 is supplied with a signal obtained by inverting the drive signal of the first semiconductor switching element 4 and having a delay time.

The operation of the circuit of FIG. 5 can be divided into the modes shown in FIG. This circuit operation will be described with reference to FIG. 6 and FIG. 7 showing a voltage-current waveform diagram of the semiconductor switching element.

In mode 1, a drive signal is supplied to the first semiconductor switching element 4. At this time, the current is
Flows through the primary winding 11 of the leakage transformer 3 and the second capacitor 6. In the mode 2, the first semiconductor switching element 4 is turned off, and the current flowing through the primary winding 11 and the second capacitor 6 is changed to the first capacitor 5
At the same time, the voltage of the first semiconductor switching element 4 rises. In mode 2, the voltage of the first capacitor 5 goes from VDC to 0V. In mode 3, the voltage across the first capacitor 5 reaches 0 V, and the diode constituting the second semiconductor switching element 7 is turned on. In mode 4, the direction of the current flowing through the primary winding 11 and the second capacitor 6 is reversed due to resonance, so that the second semiconductor switching element 7 needs to be on at this time. is there. During the periods of modes 2, 3, and 4, the voltage of the first semiconductor switching element 4 becomes equal to the DC power supply voltage VDC. In mode 5, the second semiconductor switching element 7 is turned off, the current flowing through the second capacitor 6 and the primary winding 11 starts to flow toward the first capacitor 5, and the voltage of the first capacitor 5 is reduced. Rise to VDC.

In mode 6, the voltage of the first capacitor 5 reaches VDC, and the diode constituting the first semiconductor switching element 4 is turned on. Due to the resonance, the direction of the current flowing through the primary winding 11 and the second capacitor 6 is reversed. At this time, the first semiconductor switching element 4 needs to be turned on, and this is the mode 1 Becomes In modes 6 and 1, the voltage of the second semiconductor switching element 7 becomes equal to the DC power supply voltage VDC.

According to such a circuit configuration, the first semiconductor switching element 4 and the second semiconductor switching element 7
Can be set as the DC power supply voltage VDC.

Modes 2 and 5 are resonance periods in which a current from the primary winding 11 flows through the first capacitor 5 and the second capacitor 6. The capacitance value of the first capacitor 5 is about 1/20 to 1/3 of the capacitance value of the second capacitor 6.
Since the value is set to 0, the combined capacitance is almost equal to the capacitance value of the first capacitor 5. Voltages in modes 3 and 5 applied to the first semiconductor switching element 4 and the second semiconductor switching element 7 change with a time constant determined by the combined capacitance and the impedance of the leakage transformer 3. Since this voltage change has a slope determined by the above time constant, the switching loss when the first semiconductor switching element 4 is turned off in mode 3 is reduced. Further, since the voltage becomes zero in mode 5, when the first semiconductor switching element 4 is turned on in mode 1, the applied voltage of the first semiconductor switching element 4 is zero, so that the switching loss at the time of on is reduced. This is called zero voltage switching, and these are the characteristics of the resonance circuit system. There is an advantage that the characteristics of the resonance circuit system are utilized and that the voltage of the semiconductor switching element does not exceed the DC power supply voltage VDC.

The second capacitor 6 is, as shown in FIG.
The capacitance is set to a sufficiently large value so that the voltage has a small ripple, which is a great feature. As shown in FIG. 8, the third capacitor 2 is one of the components of the DC power supply. The third capacitor 2 forms a filter with an inductor which is also one of the components of the DC power supply. It acts to prevent regeneration at the source.
The capacity of the second capacitor 6 is
It has a large capacity almost equivalent to.

[0014]

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

The magnetron 10 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 transformer 3 has a configuration as shown in FIG. 9A, and can be expressed by an inductance for leakage and an ideal transformer. On the other hand, when the magnetron 10 causes an impedance change such as discharge in a tube, the load on the secondary side of the leakage transformer 3 is eliminated, and the equivalent circuit of the leakage transformer 3 is shown in FIG.
As shown in (b), only the leakage inductance is provided. Therefore, Ic = VDC × Ton / L (1) VDC: output voltage of third capacitor Ton: conduction time of first semiconductor switching element 4 L: inductance of primary winding 11 of leakage transformer 3 The slope of the current (Ic) flowing through the first semiconductor switching element 4 as shown by becomes large, and the operation waveform is shown in FIG.
It becomes as shown in. For this reason, excessive current and voltage are continuously applied to the first semiconductor switching element 4, and the primary winding 11 of the leakage transformer 3 and the second
There is a problem that the effect of voltage reduction obtained by the effect of series connection with the capacitor 6 is impaired.

[0016]

Means for Solving the Problems The present invention has the following arrangement to solve the above-mentioned problems.

A DC power source obtained by rectifying a commercial power source,
A third capacitor for smoothing the output of the DC power source, and Rieke <br/> Jitoransu, first semiconductor is connected to the DC power supply
Body switching element and the second semiconductor switching element
A series body, and the second semiconductor switching element, respectively.
A first capacitor connected to a column and the leakage
Series body of primary winding of transformer and second capacitor
If consists of a driving means for driving the first semiconductor switching element and the second semiconductor switching element, a rectifying means connected to the secondary winding side of the leakage transformer, a magnetron connected to the rectifying means, The driving means has a voltage detection means and a stop command means, and the voltage detection means detects a voltage at a portion of the leakage transformer which is connected in series with the primary winding and the second capacitor, and sends a signal to the stop command means. By transmitting the signal, the stop command means is configured to stop the driving means based on this signal,
When a sudden impedance change occurs in the magnetron, the operation of the high-frequency heating device can be stopped without applying overvoltage and overcurrent to the first semiconductor switching element and the second semiconductor switching element.

Also, the voltage detected by the voltage detecting means may be set to the output voltage of the third capacitor or the voltage applied to the first semiconductor switching element. It can have a protective effect.

[0019]

A DC power source obtained by rectifying the commercial power PREFERRED EMBODIMENTS, a third capacitor for smoothing the output of said DC power source, a leakage transformer are connected to the DC power supply
A first semiconductor switching element and a second semiconductor switch.
A series body of switching elements and the second semiconductor switching
The first capacitor connected in parallel with the element and the first capacitor
A primary winding and a second capacitor of the leakage transformer;
Series of support, and drive means for driving said first semiconductor switching element and the second semiconductor switching element, a rectifying means connected to the secondary winding side of said leakage transformer, said rectifying means The driving means has voltage detecting means and stop command means, and the voltage detecting means is a serially connected part of the primary winding of the leakage transformer and the second capacitor. And a signal is transmitted to the stop command means, and the stop command means stops the driving means based on the signal.

Further, the detection location of the voltage detection means is determined by the third
And the output voltage of the capacitor.

Further, the detection location of the voltage detection means is determined by the first
And a voltage applied to the semiconductor switching element.

Further, overvoltage and overcurrent of the semiconductor switching element can be prevented.

[0023]

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

FIG. 1 is a circuit diagram showing a first embodiment of the present invention, in which components denoted by the same reference numerals as those of the conventional example are the same components, and a detailed description thereof will be omitted. The voltage detecting means 14 is configured to detect a voltage of a portion where the primary winding 11 of the leakage transformer 3 and the second capacitor 6 are connected in series. Reference numeral 15 denotes stop command means, which is configured to send a stop command to the driving means 8 based on an output signal of the voltage detection means 14.

During operation of the high-frequency heating device, the magnetron 1
0 is discharge in tube, or anode of magnetron 10-
If a sudden impedance change occurs between the cathodes and in a high voltage part of the full-wave voltage rectifier circuit due to the occurrence of a spark phenomenon, as described above, the inductance of the primary winding 11 of the leakage transformer 3 rapidly decreases. , The first semiconductor switching element 4 as shown after time T1 in FIG.
The current flowing through begins to increase sharply. As a result, during the period when the first semiconductor switching element 4 is conducting, the third
Of the primary winding 11 of the leakage transformer 3
And discharge through the second capacitor 6, and the voltage decreases. When the first semiconductor switching element 4 is turned off, charging is performed from the DC power supply 1, so that the voltage starts increasing. When the diode constituting the first semiconductor switching element 4 becomes conductive after the resonance period ends, the third capacitor 2 is charged by this current. When the impedance of the magnetron 10 is extremely low due to discharge in the tube, spark, or the like, the leakage transformer 3
Since the power consumption on the secondary side becomes very small, this diode current has the same current value as when the first semiconductor switching element 4 is turned off. For this reason, the charging current of the third capacitor 2 increases, and the voltage peak increases.

Next, when the transistor constituting the first semiconductor switching element 4 becomes conductive, the third capacitor 2
, The current of higher slope starts to flow. By repeating such charging and discharging operations of the third capacitor 2, the amplitude of the voltage of the third capacitor 2 increases. As described above, the third capacitor 2
Is the same as the voltage applied to the first semiconductor switching element 4 and the second semiconductor switching element 7.
The operation is repeated several times, and when the voltage of the third capacitor 2 becomes equal to or more than a predetermined value, a signal is transmitted to the stop command means 15 by detecting the voltage detection means 14, and the high frequency heating device is Is stopped, it is possible to prevent continuous application of an excessive voltage and current to the first semiconductor switching element 4 and the second semiconductor switching element 7.

Second Embodiment FIG. 3 shows a second embodiment. Even in a configuration in which the detection point of the voltage detection means 14 is set to the output voltage of the third capacitor 2,
It is possible to prevent continuous application of excessive voltage and current to the first semiconductor switching element 4 and the second semiconductor switching element 7.

Third Embodiment FIG. 4 shows a third embodiment. Even when the voltage detected by the voltage detecting means 14 is a voltage applied to the first semiconductor switching element 4, the first semiconductor switching element 4
In addition, it is possible to prevent an excessive voltage and current from being continuously applied to the second semiconductor switching element 7.

[0029]

According to the present invention as described above, the following effects can be obtained.

DC power obtained by rectifying commercial power,
A third capacitor for smoothing the output of the DC power supply ;
And over the cage transformer, a first connected to the DC power supply
Semiconductor switching element and second semiconductor switching element
And the second semiconductor switching element and the
A first capacitor connected in parallel and
Series of the primary winding of the storage transformer and the second capacitor
A drive unit for driving the body, the first semiconductor switching element and the second semiconductor switching element, a rectifier connected to a secondary winding of the leakage transformer, and a rectifier connected to the rectifier. A driving means having a voltage detecting means and a stop command means, and the voltage detecting means detects a voltage of a serially connected part of a primary winding of the leakage transformer and the second capacitor. The first semiconductor switching device and the second semiconductor switching device are configured to detect and transmit a signal to the stop command unit, and the stop command unit is configured to stop the driving unit based on the signal. This has the effect of preventing continuous application of excessive voltage and current to the element.

Further, the detection location of the voltage detection means is determined by the third location.
With this configuration, it is possible to prevent an excessive voltage and current from being continuously applied to the first semiconductor switching element and the second semiconductor switching element.

Further, the detection location of the voltage detecting means is determined by the first
Has the effect that an excessive voltage and current can be prevented from being continuously applied to the first semiconductor switching element and the second semiconductor switching element. .

[Brief description of the drawings]

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

FIG. 2 is an operation waveform diagram when the impedance of the circuit changes.

FIG. 3 is a circuit diagram of a magnetron driving power supply used in a high-frequency heating device according to a second embodiment of the present invention.

FIG. 4 is a circuit diagram of a magnetron driving power supply used in a high-frequency heating device according to a third embodiment of the present invention.

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

6A is a diagram for explaining a circuit operation for each operation mode. FIG. 6B is a diagram for explaining a circuit operation for each operation mode. FIG. 6C is a diagram for explaining a circuit operation for each operation mode. d) Diagram for explaining circuit operation for each operation mode (e) Diagram for explaining circuit operation for each operation mode (f) Diagram for explaining circuit operation for each operation mode

FIG. 7 is a waveform diagram showing voltages and currents of components of the circuit.

FIG. 8 is a circuit diagram showing a configuration of a DC power supply obtained by rectifying an AC power supply.

FIG. 9A is an equivalent circuit diagram of a leakage transformer of a power conversion device that drives a magnetron. FIG. 9B is an equivalent circuit diagram of a leakage transformer when the impedance changes.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 DC power supply 2 3rd capacitor 3 Leakage transformer 4 1st semiconductor switching element 5 1st capacitor 6 2nd capacitor 7 2nd semiconductor switching element 8 Drive means 10 Magnetron 11 Primary winding 12 Secondary winding 14 Voltage detection means 15 Stop command means

──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Makoto Mihara 1006 Kadoma Kadoma, Osaka Prefecture Matsushita Electric Industrial Co., Ltd. (72) Inventor Hideaki Moriya 1006 Odakadoma Kadoma, Osaka Pref. (56) References JP-A-4-32191 (JP, A) JP-A-7-320855 (JP, A) JP-A-6-310267 (JP, A) (58) Fields investigated (Int. ⁷ , DB name) H05B 6/66-6/68

Claims (3)

(57) [Claims] 1. A DC power supply obtained by rectifying a commercial power supply,
A third capacitor for smoothing the output of the DC power supply ;
And over the cage transformer, a first connected to the DC power supply
Semiconductor switching element and second semiconductor switching element
And the second semiconductor switching element and the
A first capacitor connected in parallel and
Series of the primary winding of the storage transformer and the second capacitor
A drive unit for driving the body, the first semiconductor switching element and the second semiconductor switching element, a rectifier connected to a secondary winding of the leakage transformer, and a rectifier connected to the rectifier. A driving means having a voltage detecting means and a stop command means, and the voltage detecting means detects a voltage of a serially connected part of a primary winding of the leakage transformer and the second capacitor. A high-frequency heating apparatus configured to detect and transmit a signal to the stop command unit, and the stop command unit stops the driving unit based on the signal. 2. A voltage detection means detecting箇plants the third output voltage claims 1 high frequency heating apparatus according capacitor. Wherein the voltage detecting means detects箇plant the high-frequency heating device according to claim 1, wherein the voltage applied to the first semiconductor switching element.