JPH01221882A - High-frequency heating device - Google Patents

Abstract

PURPOSE:To make the power consumption of a control unit lower and to realize compact size at low cost by providing resonance circuits and a semiconductor switch with an electric field effect function at a power transducer, and connecting a parallel circuit of a resistor and a diode to the gate of the semiconductor switch in series. CONSTITUTION:This heating device is composed of a power transducer 41 having resonance circuits 5 and 6 and a semiconductor switch 42, a high-frequency heating device 15 to heat a food, a fluid, and the like, and a semiconductor switch control unit 46. The semiconductor switch 42 is composed of a voltage control type switch having an electric field effect function, and a parallel circuit consisting of a resistor 43 and a diode 44 is arranged to the gate of the switch in series. As a result, a surge voltage generated at the gate of the voltage control type switch which is generated by the resonance of a resonance circuit 45, and the turnoff loss of this switch can be suppressed. Consequently, the control electric power of the control unit 46 can be reduced, and the heating device can be made compact and at a low cost.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention is applicable to so-called microwave ovens that heat food by dielectric heating, and induction ovens that heat food by heating cooking utensils such as pots by induction heating. Regarding heating cookers, etc., more specifically, it relates to high-frequency heating devices such as microwave ovens and electromagnetic cookers that receive power from a commercial power supply or battery and are equipped with a power converter that generates high-frequency power. Technology Regarding high-frequency heating devices of this type, for example, in the case of microwave ovens, various configurations have been proposed in order to reduce the size, weight, or cost of the power transformer.

FIG. 8 is a circuit diagram of a conventional high frequency heating device. In the figure, power from a commercial power source 1 is rectified by a diode bridge 2 to form a unidirectional power source. 3 is an inductor, and 4 is a capacitor, which serves as a filter for the high frequency switching operation of the inverter.

The inverter includes a resonant capacitor 5, a step-up transformer 6, a transistor 7, a diode 8, and a drive circuit 9.

The transistor 7 performs a switching operation at a predetermined period and duty (ie, on-off time ratio) by a base current supplied from the drive circuit 9.

As a result, the current Xala as shown in FIG. 9 (IL), that is, the collector current Xc of the transistor 7 and the current Id of the diode 8 flow.

On the other hand, when the transistor 7 is off, the resonance between the capacitor 6 and the primary winding 1o occurs.
occurs between collector emitter (C-IC) of transistor 7. Therefore, high frequency power is generated in the negative winding 1°. Therefore, high frequency high voltage power and high frequency low voltage power are generated in the secondary winding 11 and the tertiary winding 12, respectively. This high frequency high voltage power is supplied to a capacitor 13 and a diode 14.
The high-frequency low-voltage power is rectified and supplied between the anode and cathode of the magnetron 16, while the high-frequency low-voltage power is supplied to the cathode heater. Therefore, the magnetron 16 oscillates and dielectric heating becomes possible. The magnetron 16 consists of a magnetron main body 151L, capacitors 16, 17, 18 and choke coils 19, 20 that constitute a filter. Further, 21 is a power transformer of the drive circuit 9.

In such a configuration, the core cross-sectional area of the step-up transformer 6 becomes smaller as the frequency of the power supplied to both ends of the primary winding 1o increases.
When operated at a frequency of around 0 KHz, the weight and size of the step-up transformer can be reduced from a few minutes to a dozen times less than when boosting the voltage at the commercial power frequency, making it possible to reduce the cost of the power supply section. It has the following features.

The pace current Ib supplied to the pace of the transistor 7 is composed of a positive current Ib and a negative current xb-, as shown in FIG. 9(0).
Composition. The positive current Ib needs to be larger than the maximum value Ia of the collector current 1c of the transistor 7 shown in FIG. 9 (IL) by its current amplification factor (hr, for example, 30). Further, the negative current Xb- is a current that flows by reverse biasing between the pace epigraphs of the transistor in order to increase the switching speed of the transistor T and prevent an increase in switching loss. As is clear from FIGS. 9(IL) and (C), the positive current Ib has a value Ibm determined by the maximum value Iam (for example, 60 μm) of the collector current Ic during the conduction period of the transistor 7.
+ (for example, 2 mm). Further, the negative current Ibm- is also determined according to the maximum value Iam of the collector current Ia (for example, 16 μm), and the larger Iam is, the more power is required. Furthermore, the collector current Ia continues to flow for a certain period of time toff after the base current Ib+ is cut off due to the so-called minority carrier accumulation effect, and this tofT changes depending on K such as the variation in characteristics of the transistor 7 and the temperature. . And this 1o
A change in tf results in a change in the output of the inverter.

In order to drive the transistor 7 under such conditions, the drive circuit 9 required a configuration as shown in FIG. 8, for example.

That is, a DC power source 22 obtained from a power transformer 21,
23, oscillation circuit 24, transistors 25, 26.27,
It is composed of resistors 28 to 36 and a diode 37.

In order to supply the base current as shown in Fig. 9 (0),
It was necessary to use transistors 25 and 26 with a considerably large capacity, and also to have a DC power supply 22 and 23 with a considerably large capacity. Therefore, the power transformer 21 also needs to be a large power transformer, for example, 20~SO
A power transformer with a capacity of about W must be used, and the power transformer 2
1 and the drive circuit 9 cannot be made compact as a whole, and are large and expensive, which hinders the compactness of the high-frequency heating device as a whole and makes it larger and more expensive.

Problems to be Solved by the Invention As mentioned above, such conventional high-frequency heating devices have the following drawbacks.

In the conventional high-frequency heating device, a step-up transformer e is energized by an inverter constituted by a transistor 7, etc., in order to reduce the size, weight, and cost of the power supply device.

- However, it is necessary to supply the pace current Ibm corresponding to the peak value Icm of the collector current Ic to the transistor 7, as shown in the *th (a) O and (0), and it is necessary to supply the pace current Ibm corresponding to the peak value Icm of the collector current Ic. The power was quite large. For example, if Icm=60 and hfe of the closing transistor 7 is 30, then Xb11I+=2mu, and the power consumption of the drive circuit 9 becomes extremely large, and the power consumption of the drive circuit e and the power transformer 21, therefore,
It has been difficult to avoid increasing the size and price of the entire power supply device.

Furthermore, changes in the storage time of the transistor 7 (the main cause of toff in FIG. 9) due to temperature changes, etc.
In order to cope with a 1 cm change in the collector current caused by temperature changes or changes over time in the magnetron 15, it is necessary to supply a sufficient base current. This not only increases the price, but also increases the output fluctuation of the high-frequency heating device, making it unstable, and causes unnecessary loss in the transistor 7, etc., which reduces power supply efficiency and reliability. Ta.

In particular, when trying to further increase the frequency and achieve further miniaturization, the above-mentioned tendency is extremely noticeable, and with the current level of semiconductor technology, it is practically difficult to achieve practical performance at frequencies above about 30 to 40 KHz. Therefore, sufficient downsizing and cost reduction could not be achieved.Means for Solving the ProblemsThe present invention aims to provide a high-frequency heating device that eliminates such conventional drawbacks, and has the configuration described below. Consists of.

That is, a power supply unit obtained from a commercial power supply, etc., a power converter having a series or parallel resonant circuit and a semiconductor switch, and the output of the power converter is output as high-frequency power to directly or indirectly heat food, fluid, etc. and a control unit that controls the semiconductor switch, the semiconductor switch being a voltage-controlled switch having a field effect, and a resistor connected in series with the gate of the voltage-controlled switch. and a parallel circuit consisting of a diode.

Effects According to the above configuration, the present invention suppresses the switching surge voltage generated at the gate of the voltage-controlled switch due to resonance of the resonant circuit, and suppresses the turn-off loss of the voltage-controlled switch. Therefore, the control power of the control section for controlling the semiconductor switch of the power converter can be significantly reduced, and as a result, the size and cost of the high-frequency heating device can be significantly reduced.

Example An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a circuit diagram of a high-frequency heating device showing one embodiment of the present invention, and since the components correspond to those with the same reference numerals as those in FIG. 8, detailed explanations thereof will be omitted.

In the figure, a power source section 40 is constructed from a commercial power source 1 or the like and has a similar configuration to a conventional high-frequency heating device. The power converter 41 includes a resonant circuit including a resonant capacitor 6 and a primary winding 10 of a step-up transformer 6, a transistor 42 having a field effect, and a flywheel diode 8. The transistor 42 has a conductivity modulation function and conduction characteristics close to that of a bipolar transistor, and is a so-called insulated gate bipolar transistor (IGBT).
).

The high-frequency heating means includes a magnetron 16, and is configured to heat foods, fluids, etc. using the output radio waves of the magnetron 16.

The transistor 42 includes a resistor 43 and a diode 44.
The switching operation is controlled by the control section 46 through a parallel circuit 46 consisting of the following.

Power for the control section 46 is supplied from the output of the diode bridge 2 via a resistor 47. A capacitor 48 and a resistor 49 are used to protect the gate of the transistor 42 from destruction or malfunction.

FIG. 2 shows a more detailed embodiment of the control circuit 46 of FIG. 1, and the same reference numerals as in FIG. 1 represent corresponding components.

The control circuit 46 in FIG. 2 is a control circuit that supplies a gate pulse to the transistor 42 in synchronization with the resonance operation of the resonance circuit consisting of the resonance capacitor 6 and the primary winding 10 of the step-up transformer 6, and controls its switching operation. The structure and operation will be explained with reference to the operation waveforms of each part shown in FIG.

When the power switch 60 in FIG. 1 is turned on, power is supplied to the control circuit 4e through the resistor 47 in FIG.

When the power is turned on, the voltage Va of the capacitor 63 is zero, while the voltage vb of the variable reference power supply 64 is controlled by the power control circuit 55 to be a predetermined voltage.

Therefore, the output of the comparator 56 becomes High, and the output enable of the R/S flip-flop (R/5-FF) 60 becomes High by the logic control circuit 67. As a result, the capacitor 53 begins to be charged via the resistor 61 by the output of the R/5-FF. At the same time, the output of the buffer circuit 62 becomes High, the gate of the transistor 42 becomes High through the resistor 43, the transistor 42 becomes conductive, and the collector current Ia flows. Since the first collector current flows through the resonant capacitor 6, it becomes a considerably large short-circuit current as shown in FIG. 3 Φ). Therefore, the pulse width ton of the gate pulse applied to the transistor 42 needs to be as small as possible to prevent the transistor 42 from being destroyed, as shown in FIG. For this purpose, the same figure ((1
), the voltage vb of the variable reference power supply 54 is controlled to a low value when the power is turned on (1=0), and then gradually increases to a voltage at which a predetermined output is obtained. This voltage vb
As described above, the value of is controlled by the power control circuit 66 and changes as shown in (11) in the figure.

When the voltage v1 of the capacitor 63 reaches the voltage vb, the output of the comparator 66 is inverted and the output enable of R/5-FF becomes Low, so the charge of the capacitor 63 is discharged through the diodes 63 and 64, and at the same time, the output of the comparator 66 is The positive input voltage of 66 is controlled to almost zero voltage by resistor 65 and diode 6e.

Therefore, the voltage vIL of the capacitor 63 is the voltage V1
) according to the voltage value as shown in (d) of the same figure.

As a result, as shown in the figure (sL), the pulse width ton of the gate pulse vG is kept small at the first time, and then gradually increases to a predetermined pulse width.

Next, the timing of the second and subsequent gate pulse vG generation will be explained. In FIG. 3, when the gate pulse vG becomes Low at 1=1°, the transistor 42 is turned off and the collector current Xa becomes zero.

Therefore, the primary winding 1o of the transformer 6 and the resonant capacitor 5 resonate, and the collector voltage VI4 has a resonant voltage waveform as shown in FIG. This collector voltage VOX and the voltage vh of the line 12 are monitored by a cross detection circuit 67 in FIG. 2, and a point P at t=t2 is detected. The output Vc of this cross detection circuit is the delay circuit 6
#8) A signal vd delayed by td is generated at t=t4. In response to this Vd, the logic control circuit 67
Since a control signal is given to the -FF, a gate signal 'lac' as shown in FIG. 3 (IL), that is, the Q output of the R/5-FF is generated. Figure 3(e) shows the timing relationship of these signals.

(shown in 0 and (g).

That is, as shown in FIG. 3(b), the gate signal VG changes from t=t3 to t when current is flowing through the diode 8.
It becomes High at t=ta during =t5, and is controlled to become Low after a ton time determined by the charging time of the capacitor 63, making it possible to perform pulse width control in synchronization with the resonant operation of the resonant circuit.

By configuring the power supply circuit of the high-frequency heating device using a power converter having such a configuration, the control section thereof can be made extremely compact, with low power consumption, and low cost. That is, as shown in FIGS. 1 and 2, the output voltage of the control circuit 46, that is, the gate pulse V
, since the transistor 42 switches by field effect, the input capacitance (1o
o.

~5000pF) is sufficient for charging and discharging. Therefore, the buffer 62 can be configured with, for example, 0MO8, and may be of low power consumption and low cost. Therefore, the current supplied to the control circuit 46 via the resistor 47 can be approximately 6 to 10 mm.
If the operating voltage of the Zener diode is 167, the power consumption of the control circuit 46 is about 0.2 to 0.3 W at most. Compared to the conventional configuration shown in Figure 8, which required a control power of about 20 to 30 W, the control power is only about 1/1ω of that, making it possible to achieve significant energy savings, compactness, and cost reduction. It is something to do.

However, when starting up the power converter 41 having a resonant circuit as shown in FIG. 1, the following problem may occur, and the gate-emitter connection may be destroyed.

In FIG. 3(b), the collector current at the first start-up becomes extremely large as described above.

This collector current IC is a current that flows when the capacitor 4 is short-circuited by the resonant capacitor 6 and a switch circuit consisting of the transistor 42 and the diode 8.

This current path includes the inductance and resistance of the wiring, the internal inductance and resistance of the capacitors 4 and 5, the internal resistance of the transistor 42, etc.
The actual collector current 1c has an oscillating waveform with an extremely large peak current as shown in FIG. In other words, Fig. 4 (
As shown in IL), while v6 is High, the same figure (b)
An oscillating current flows through the throat. V, is High
, that is, when the transistor 42 is in a conductive state,
The current flowing in the opposite direction generates a voltage spike between the gate and emitter.

FIG. 6 is an equivalent circuit diagram of the transistor 42 and diode 8 showing the mechanism of this spike voltage generation. Since the start of current flowing through the diode 8 is delayed by the turn-on time tDo)1 of the diode 8, as shown in Fig. 6 (I
The reverse current xd' of the collector current shown in L) is the current X flowing through the emitter lead of the transistor 42.
It is a composite current of the current 1(i) flowing through the diode 8 and the current 1(i) that flows through the diode 8. In other words, I(1 starts flowing with a delay of tDOI+ after Xa' starts flowing, as shown in FIG. 6(b). , only during this tno*, Fig. 6(C)
Ic flows through the emitter lead of transistor 42.

This current XC is equal to the equivalent MO of transistor 42.
8) Langister 42! A current XX flows in the opposite direction to the equivalent diode 42b, and the MOS transistor 421L
This is the sum of the current X flowing to the gate side through the gate-emitter capacitance 420 and the like. In particular, during the period when this Xd' flows, as is clear from FIG. 4, VG is High, so 1. 1. If there is no current limiting element in the flow path, an extremely large spike voltage will occur between the gate and emitter.

This spike voltage VGP is shown in Fig. 7 (a) and (b).
As shown in FIG. 3, the turn-on time tDON of the diode 8 is delayed from when Id' starts flowing. This causes transistor 42 to turn on due to diode 8 turning on.
The inductance component 42 (1) of the emitter lead wire and bonding wire, and the capacitance 42 between the gate emitter and the bonding wire
It is thought that this is caused by the resonance phenomenon of spike voltage caused by 0, etc.

Therefore, as shown in FIGS. 1 and 2, by providing a resistor 43 in series with the gate of the transistor 42, this spike voltage vap can be attenuated to a small value. FIG. 7(0) shows the resistance value RAS of this resistor 43.
The values of the spike voltage VGF and the spike voltage VGF were obtained through experiments, and the larger the value of RAS, the smaller the vep can be suppressed.

If R45 is increased, the turn-off time of the transistor 42 becomes longer, the switching (turn-off) loss increases, and the reliability of the transistor 42 decreases.
Larger heat dissipation fins may be required. diode 4
4 is for preventing this. By inserting the diode 44, the spike voltage VGP is suppressed by inserting the resistor 43 without increasing the switching loss of the transistor, and the reliability of the transistor 42 is increased. can be guaranteed.

That is, by inserting the parallel circuit consisting of the resistor 43 and the diode 44 in series with the gate of the transistor 42, the transistor 42 having a field effect can be used as a power converter having a resonant circuit with high reliability. As a result, the control circuit of the power converter can be made compact, low in power consumption, and low in cost.

In the embodiments described above, a magnetron is used as the high-frequency heating means, and a high-frequency heating device is shown that directly heats food or the like using radio waves, but the present invention is not limited to this embodiment. For example, the high-frequency heating means may be a high-frequency heating device that indirectly heats food, etc. by induction heating cooking utensils such as pots using a heating coil, or the high-frequency heating means may be a power converter. It may also be configured such that the output of the power converter is directly extracted as radio waves from the antenna to heat food or the like.

Effects of the Invention As described above, the present invention includes a power converter including a resonant circuit and a semiconductor switch having a field effect, a high-frequency heating means, and a control section for controlling the semiconductor switch. A parallel circuit of a resistor and a diode is connected in series with the gate of the switch, which prevents a high gate spike voltage from occurring in a semiconductor switch with field effect and increases loss. A power converter can be constructed with high reliability guaranteed. Therefore, the control section can be made extremely compact, with low power consumption, and low cost, and the entire high-frequency heating device can be made compact, highly efficient, and low cost, and high reliability can be guaranteed. It is something that has value.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing an embodiment of the high-frequency heating device of the present invention, and FIG. 2 is a more detailed circuit diagram of the control circuit of the same device.
Figure 3 is an operational waveform diagram of each part of the circuit, Figure 4 is a waveform diagram of the first conduction operation of the transistor in the circuit, and Figure 6 explains the current flow path during the first conduction operation of the transistor. Equivalent circuit diagram, Figure 6 is a waveform diagram showing the correlation of each current in the equivalent circuit, Figure 7 is the generation timing and magnitude of the spike voltage that occurs during the first transistor conduction, and the gate insertion resistance value. An explanatory diagram explaining the relationship between
FIG. 8 is a circuit diagram of a conventional high-frequency heating device, and FIG. 9 is a diagram of operation waveforms of each part of the device. 5.6... Resonant circuit (6... Resonant capacitor, 6... Step-up transformer), 16...
・High frequency heating means (magnetron), 4o...
・Power supply section, 41...Power converter, 42...
...Semiconductor switch, 46...Parallel circuit (43
...Resistor, 44...Diode),
46...Control unit. Name of agent: Patent attorney Toshio Nakao and 1 other person No. 3
Figure 4 Figure 6 Figure 7 Figure 8 Figure 9

Claims (4)

[Claims] (1) A power supply unit, a power converter having a series or parallel resonant circuit and a semiconductor switch, a high-frequency heating means that outputs the output of the power converter as high-frequency power to heat an object to be heated, and controls the semiconductor switch. the semiconductor switch is a voltage-controlled switch having a field effect, and a parallel circuit consisting of a resistor and a diode is provided in series with the gate of the voltage-controlled switch. Device. (2) The high-frequency heating device according to claim 1, wherein a parallel circuit is configured such that the gate of the voltage-controlled switch and the anode of the diode are connected. (3) The high-frequency heating means includes a magnetron,
Claim 1: The object to be heated is heated by dielectric heating.
Or the high frequency heating device according to 2. (4) The high-frequency heating device according to claim 1 or 2, wherein the high-frequency heating means includes an induction heating coil, and is configured to indirectly heat an object to be heated by heating a cooking utensil such as a pot.