JP3206484B2 - High frequency heating equipment - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a high-frequency heating device using a magnetron, and more particularly to a power supply for driving a magnetron.

[0002]

2. Description of the Related Art FIG. 6 is a circuit diagram of a conventional magnetron driving power supply.

In FIG. 6, 1 is a DC power supply, 2 is a leakage transformer, 3 is a first semiconductor switching element,
Is the first capacitor, 5 is the second capacitor, 6 is the second capacitor
, A drive circuit, 8 a rectifier circuit, and 9 a magnetron.

The driving circuit 7 includes an oscillating unit 11 for generating pulses for driving the first semiconductor switching element 3 and the second semiconductor switching element 6 therein. The oscillating unit generates a signal of a predetermined frequency and a duty, and gives a pulse to the first semiconductor switching element 3. A pulse obtained by inverting the pulse of the first semiconductor switching element 3 is given to the second semiconductor switching element 6. The delay circuit 12 has a function of providing a fixed delay time between the trailing edge of the pulse of the second semiconductor switching element 6 and the leading edge of the driving pulse of the first semiconductor switching element 3.

The operation of this circuit will be described with reference to FIGS. First, when a pulse is given to the first semiconductor switching element 3 and a transistor constituting the same is turned on, an equivalent circuit of a main circuit portion after the DC power supply 1 is as shown in FIG. Current Ic
Is supplied from the third capacitor 10 through the primary side of the leakage transformer {state (a) in FIG. 8 (a)}. At this time, the secondary output of the leakage transformer starts charging the capacitor 13 of the full wave voltage doubler rectifier circuit. Capacitor 14
Since the initial voltage V2 is stored in the
When the voltage V3 of V.3 is in the relationship of V2 + V3> Vcut (1) Vcut: cutoff voltage of the magnetron, the magnetron can be oscillated, and the current starts to flow through the magnetron 9. When the first semiconductor switching element 3 is turned off, the equivalent circuit becomes as shown in FIG. 7B, and the current flowing on the primary side of the leakage transformer 2 starts flowing toward the first capacitor 4. At this time, the secondary output of the leakage transformer 2 starts charging the capacitor 14 (the state (b) in FIG. 8B). At this time, when Expression (1) is satisfied, the magnetron 9 starts oscillating again, and the anode current starts flowing. The current on the primary side of the leakage transformer 2 is as shown in FIG. The voltage of the first semiconductor switching element 3 is as shown in FIG. When this voltage reaches the initial voltage of the second capacitor 5, the diode constituting the second semiconductor switching element 6 is turned on, and charging of the second capacitor 5 is started {state (c) of FIG. C)｝. The equivalent circuit at this time is as shown in FIG. A parasitic inductor 15 exists in series with the first capacitor 4. The parasitic inductor 15 is formed by an inductor existing in a pattern on a printed circuit board, an inductor of the first capacitor 4, and the like. When the diode constituting the second semiconductor switching element 6 is turned on, the current flowing through the first capacitor 4 suddenly decreases, and an oscillating current is generated by the action of the parasitic inductor 15 and the first capacitor 4. I do. This oscillating current flows through a closed loop including the first capacitor 4, the parasitic inductor 15, the diode forming the second semiconductor switching element 6, and the second capacitor 5. FIG. 8B shows a state (c) of the current waveform of the first capacitor 4 which is an oscillating current. This oscillating current exists up to state (d). Also, an oscillating current exists in the second capacitor current waveform in FIG. In the oscillating current, a negative current flows through the second semiconductor switching element 6.
Through the diode that constitutes
Of the semiconductor switching element 6. The driving pulse supplied to the second semiconductor switching element 6 and the first semiconductor switching element 3 is supplied from the driving circuit 7, but the pulse of the second semiconductor switching element 6 is the pulse of the first semiconductor switching element 3. Are provided. However, the delay time Td3 is provided between the trailing edge of the pulse of the second semiconductor switching element 6 and the leading edge of the drive pulse of the first semiconductor switching element 3, No delay time is set between the trailing edge of the drive pulse and the leading edge of the drive pulse of the first semiconductor switching element 3, and the second semiconductor is almost simultaneously turned off when the first semiconductor switching element 3 is turned off. The transistor constituting the switching element is on. As a result, the oscillating current flows in the negative direction.

The state (c) of the voltage of the first semiconductor switching element shown in FIG. 8 (e) is such that the second capacitor 5 has a larger capacitance value than the first capacitor 4, so that the voltage gradient Suddenly slows down. When the current flowing from the primary side of the leakage transformer 2 toward the second capacitor 5 starts flowing from the second capacitor 5 toward the primary side, the state transits to the state (d). When the transistor constituting the second semiconductor switching element is cut off at an arbitrary time T1, the state shifts to a state (e) in which current starts to flow from the first capacitor 4 toward the primary side of the leakage transformer 2. At this time, the slope of the voltage of the first semiconductor switching element 3 becomes steep, and decreases toward zero due to the energy of the first capacitor 4. When the first semiconductor switching element 3 is driven again when this voltage becomes zero, the same operation is repeated from the state (a). Since the first semiconductor switching element is turned on after the voltage becomes zero, the switching loss at this point can be extremely small. In order to realize such an operation, the delay time Td3 corresponding to the time required until the voltage of the first semiconductor switching element 3 becomes zero is set to be equal to the trailing edge of the pulse of the second semiconductor switching element 6 and the first edge. It is provided between the semiconductor switching element 3 and the leading edge of the drive pulse. The pulse waveform of the first semiconductor switching element 3 and the pulse waveform of the second semiconductor switching element 6 are shown in FIG.
(F) and (g).

The initial voltage of the above-mentioned second capacitor is:
In the state (d), it is determined by turning on the second semiconductor switching element 6 for an arbitrary time T1. That is, the longer the ON time of the second semiconductor switching element 6, the lower the initial voltage of the second capacitor 5, and as a result, the voltage of the first semiconductor switching element 3 can be reduced. Things.

The generation of the oscillating current is the same in the circuit shown in FIG. FIG. 3A shows that a series circuit of a second capacitor 5 and a second semiconductor switching element 6 is connected in series with the primary side of the leakage transformer 2, and the first capacitor 4 is connected to the primary side of the leakage transformer. This is the case where they are connected in parallel.

FIG. 1 (b) shows that a series circuit of a second capacitor 5 and a second semiconductor switching element 6 is connected in parallel with the primary side of the leakage transformer 2, and the first capacitor 4 is connected to the leakage transformer. This is the case where the primary side is connected in series.

FIG. 1C shows that a series circuit of a second capacitor 5 and a second semiconductor switching element 6 is connected in parallel with the primary side of the leakage transformer 2, and the first capacitor 4 is connected to the leakage transformer. This is the case where they are connected in parallel to the primary side.

[0011]

However, in the conventional magnetron drive power supply, as described in the conventional example, the presence of the parasitic inductor 15 causes an oscillating current to be generated in the first capacitor and the second capacitor. However, it is necessary to increase the effective current of both capacitors and increase the volume of the capacitors to secure a heat radiation area, and there is a problem that the capacitors become large and noise is generated due to an oscillating current.

[0012]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, the present invention provides a pulse for driving a second semiconductor switching element so as not to inadvertently create a closed loop through which an oscillating current flows. It is.

Further, according to the present invention, when the voltage applied to the first semiconductor switching element becomes zero, a pulse signal for driving the first semiconductor switching element is provided so that a pulse signal for driving is given. A first delay time is provided between a trailing edge and a leading edge of a pulse for driving the second semiconductor switching element, and a trailing edge of a driving pulse of the second semiconductor switching element and driving of the first semiconductor switching element. The second delay time is provided separately from the leading edge of the pulse.

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION
A DC power supply, a leakage transformer connected to the DC power supply, a primary side of the leakage transformer, and the DC power supply
The first semiconductor switching element, the parasitic inductor above were parallel or on the primary side of the leakage transformer for connecting a first capacitor connected in series to said first capacitor in series to connect in series to the When, a second capacitor the second semiconductor switching elements connected in series, the
Second capacitor and second semiconductor switching element
Are connected in series, one end of the
Midpoint of a ditransformer and the first semiconductor switching element
And the other end to the positive or negative side of the DC power supply.
Connect, includes a drive circuit for generating a pulse for driving said first and second semiconductor switching elements, and a rectifier circuit connected to the secondary side of the leakage transformer, and said magnetron connected to said rectifying circuit , The first
Semiconductor switching element and second semiconductor switch
Drive the switching elements alternately, and drive each switching element.
When switching the motion, a delay time is provided . Therefore, the oscillating current becomes small.

A first delay circuit for providing a first delay time between a trailing edge of a pulse for driving the first semiconductor switching element and a leading edge of a pulse for driving the second semiconductor switching element; A second delay time is provided between the trailing edge of the drive pulse of the second semiconductor switching element and the leading edge of the drive pulse of the first semiconductor switching element.
And the first delay time and the second delay circuit
And the delay time can be set separately.

Then, the first semiconductor switching element voltage can be turned on when the voltage becomes zero, so that the switching loss can be reduced and the oscillating current of the first capacitor and the second capacitor can be reduced. Can be suppressed.

Hereinafter, embodiments of the present invention will be described with reference to the drawings. Embodiment 1 In FIG. 1, the same components as those in FIG. 6 are denoted by the same reference numerals, and detailed description is omitted. In addition, since the outline of the circuit operation is the same, detailed description is omitted. Pulse signals for driving the first semiconductor switching element 3 and the second semiconductor switching element 6 are given as shown in FIGS. 2 (c) and 2 (d). A first delay time (Td1) is provided between the trailing edge of the pulse signal of the first semiconductor switching element 3 and the leading edge of the second semiconductor switching element 6, and the pulse of the first semiconductor switching element 3 is provided. A second delay time (Td2) is provided between the leading edge of the signal and the trailing edge of the pulse signal of the second semiconductor switching element 6. The first delay time (Td1) is set so that the oscillating current generated in the current waveform of the first capacitor in FIG. In order to explain this point in detail, the operation will first be described using the ideal circuit of FIG. This ideal circuit is obtained by extracting only necessary parts from the components shown in FIG. 1, and the parasitic inductor 15 is removed for idealization. The waveform of the current flowing through the first capacitor 4 and the second capacitor 5 by the same circuit is as shown in FIGS. The current in the state (f) flowing through the second capacitor 5 in FIG. 4B flows through the diode constituting the second semiconductor switching element 6 in FIG.
The current in the state (g) flows through the transistor forming the same second semiconductor switching element 6. Therefore, since the transistor may be turned on at the time when this current flows, a driving pulse signal may be given at the timing shown in FIG. FIG. 4D shows a pulse signal for driving the first semiconductor switching element 3.
Between the trailing edge of the pulse signal of the first semiconductor switching element 3 and the leading edge of the second semiconductor switching element 6, the first
Is provided, and a second delay time (Td2) is provided between the leading edge of the pulse signal of the first semiconductor switching element 3 and the trailing edge of the pulse signal of the second semiconductor switching element 6. It may be provided. Such a first delay time (T
d1) and the second delay time (Td2)
When applied to an actual circuit in which is present, the current waveforms flowing through the first capacitor 4 and the second capacitor 5 are as shown in FIG.
(A) and (b) are obtained. FIGS. 4C and 4D show waveforms of pulse signals for driving the second semiconductor switching element 6 and the first semiconductor switching element 3.
FIG. 4C shows a drive pulse applied to the second semiconductor switching element 6, that is, a drive pulse applied to a transistor included in the semiconductor switching element. Compared with FIG. 8F, which is a conventional example, the ON width of the pulse signal is shorter. For this reason, in the present embodiment, even if the oscillating current of the second capacitor is going to swing in the minus direction, the transistor constituting the second semiconductor switching element 6 does not turn on at that time and does not flow in the minus direction. . As a result, the oscillating current can be attenuated without continuing. This is the current waveform of the first capacitor 4 shown in FIG.
(B) and FIG. 2 showing the current waveform of the second capacitor.
By comparing FIG. 8B with FIG. 8C of the conventional example, it is clear that the oscillating current is reduced in the present invention.

FIGS. 9 (a) and 9 (b) show a conventional example.
As for the circuit configuration (c), an equivalent operation can be obtained by the same means as described above, and a detailed description thereof will be omitted.

(Embodiment 2) The drive circuit 7 of FIG. 1 includes an oscillator 11 and a first delay circuit 16
And a second delay circuit 17. FIG.
(A) is an output pulse of the oscillator 11, which is the first pulse.
To the second delay circuit 17 and the second delay circuit 17. The first delay circuit 16 compares an output pulse of the oscillator 11 with a reference voltage generated by the resistors 18a and 18b. Since the resistor 16c and the capacitor 16d connected to the power supply are connected to the output terminal of the comparing means 16a, the rising of the pulse of the comparing means 16a is as shown in FIG. The falling of the pulse sharply falls because the comparing means 16a rapidly extracts the charge of the capacitor 16d. Since the comparing means 16b compares the output of the comparing means 16a with the reference voltage, the output pulse is as shown in FIG. The pulse drives the first semiconductor switching element 3.

The pulse transmitted to the second delay circuit 17 is inverted and output. The output terminal is connected to a resistor 17c and a capacitor 17d. These functions are different from those of the first delay circuit. The same is true. FIG. 5D shows the comparison means 17.
The output pulse a is the output of the comparison means 17b, and this pulse drives the semiconductor switching element 6.

When comparing FIG. 3C and FIG. 3E,
(C), that is, between the trailing edge of the pulse for driving the first semiconductor switching element 3 and the pulse in FIG. (E), that is, the leading edge of the pulse for driving the second semiconductor switching element 6 Is provided with a first delay time (Td1), and a second delay is provided between the trailing edge of the pulse driving the second semiconductor switching element 6 and the leading edge of the pulse driving the first semiconductor switching element 3. Is provided for the delay time (Td2).

The magnitudes of the first delay time (Td1) and the second delay time (Td2) can be set by the resistor 16c and the capacitor 16d or the resistor 17c and the capacitor 17d, respectively. Can be set separately. As described in the first embodiment, the first delay time (Td1) is from when the pulse driving the second semiconductor switching element 6 is turned off until the voltage of the first semiconductor switching element 3 becomes zero. May be set to a time corresponding to the time required for.

The first delay time (Td1) may be set so that the oscillating current generated in the current waveform of the first capacitor, that is, the second capacitor, is as small as possible.

In FIG. 1, a first semiconductor element 3 is connected in series with the leakage transformer 2, and a first capacitor 4 and a parasitic inductor 15 existing in series with the capacitor 4 are connected in parallel with the leakage transformer 2. And a circuit for connecting a second semiconductor switching element in series with the second capacitor 5 and the capacitor 5,
A conventional circuit as shown in FIG. 9 may be used. That is,
(A) is in series with the primary side of the leakage transformer 2,
Is connected in series with the capacitor 5 and the second semiconductor switching element 6, and the first capacitor 4 is connected in parallel to the primary side of the leakage transformer.

FIG. 2B shows that a series circuit of a second capacitor 5 and a second semiconductor switching element 6 is connected in parallel with the primary side of the leakage transformer 2 and the first capacitor 4 is connected to the primary side of the leakage transformer. It is a case where it is connected in series to the side.

FIG. 3C shows that a series circuit of a second capacitor 5 and a second semiconductor switching element 6 is connected in parallel with the primary side of the leakage transformer 2, and the first capacitor 4 is connected to the primary side of the leakage transformer. Side is connected in parallel.

[0027]

As described above, according to the present invention, the oscillating current generated by the first capacitor and the parasitic inductor can be suppressed by the timing of applying the pulse for driving the second semiconductor switching element. Having.

A first delay circuit for providing a first delay time between a trailing edge of a pulse for driving the first semiconductor switching element and a leading edge of a pulse for driving the second semiconductor switching element; A second delay time is provided between the trailing edge of the drive pulse of the second semiconductor switching element and the leading edge of the drive pulse of the first semiconductor switching element.
And the first delay time and the second delay circuit
And the delay time can be set separately, the first semiconductor switching element voltage can be turned on when the voltage becomes zero, the switching loss can be reduced, and the first capacitor and the This has an effect that generation of an oscillating current of the second capacitor 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 Embodiments 1 and 2 of the present invention.

FIG. 2 is a waveform diagram of the main circuit section.

FIG. 3 is an ideal circuit diagram of the main circuit section.

FIG. 4 is a waveform diagram in the ideal circuit diagram of FIG. 3;

FIG. 5 is a waveform chart illustrating a circuit operation according to a second embodiment of the present invention.

FIG. 6 is a circuit diagram of a power supply device for driving a magnetron of a conventional high-frequency heating device.

FIG. 7A is an equivalent circuit diagram in one state of the main circuit unit. FIG. 7B is an equivalent circuit diagram in another state of the main circuit unit. FIG. 7C is an equivalent circuit diagram in another state of the main circuit unit. Equivalent circuit diagram in other states of main circuit section

FIG. 8 is a waveform diagram of a conventional main circuit portion.

9A is a circuit diagram of a main part of a magnetron driving power supply unit of a conventional high-frequency heating apparatus. FIG. 9B is another circuit diagram of a main part of the magnetron driving power supply unit. Circuit diagram of the main part of the power supply device for driving

[Explanation of symbols]

 Reference Signs List 1 DC power supply 2 Leakage transformer 3 First semiconductor switching element 4 First capacitor 5 Second capacitor 6 Second semiconductor switching element 7 Drive circuit 8 Rectifier circuit 9 Magnetron 15 Parasitic inductor 16 First delay circuit 17 Second Delay circuit

Continued on the front page (72) Inventor Kenji Yasui 1006 Kadoma Kadoma, Osaka Pref. Matsushita Electric Industrial Co., Ltd. (72) Inventor Haruo Suenaga 1006 Odakadoma Kadoma, Osaka Pref. Matsushita Electric Industrial Co., Ltd. (56 References JP-A-5-199768 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H05B 6/66-6/68

Claims (2)

(57) [Claims] 1. A DC power supply, a leakage transformer connected to the DC power supply, a first semiconductor switching element connected in series to a primary side of the leakage transformer and the DC power supply, and a primary of the leakage transformer. the <br/> was parallel or on the side of the first capacitor connected in series, and parasitic inductance to be connected in series with said first capacitor, connects the second capacitor and the second semiconductor switching element in series And the second capacitor and the second semiconductor switch.
A series connection in which switching elements are connected in series has one end
The leakage transformer and the first semiconductor switch.
And the other end to the positive side of the DC power supply.
Or a drive circuit connected to the negative electrode side to generate a pulse for driving the first and second semiconductor switching elements, a rectifier circuit connected to a secondary side of the leakage transformer, and a rectifier circuit connected to the rectifier circuit. A magnetron, the first semiconductor switching element and the second semiconductor switching element.
The semiconductor switching elements are driven alternately and each switch is
A high-frequency heating device having a configuration in which a delay time is provided when switching of the driving of the switching element is performed . 2. A first delay for providing a first delay time between a trailing edge of a pulse for driving a first semiconductor switching element and a leading edge of a pulse for driving a second semiconductor switching element in a drive circuit. A circuit provided with a circuit and a second delay circuit for providing a second delay time between a trailing edge of the drive pulse of the second semiconductor switching element and a leading edge of the drive pulse of the first semiconductor switching element; The high-frequency heating device according to claim 1.