JPH02306577A - High frequency heating device - Google Patents

Abstract

PURPOSE:To prevent the primary and secondary coils of a step-up transformer from being mixed with and contacting each other so as to reduce induction heating loss by making a shielding portion electrically open along the winding direction of the primary coil of the step-up transformer, and electrically connecting the shielding portion to another shielding portion. CONSTITUTION:A control portion 29 controls a semiconductor switch so that the primary side circuit and secondary side high-tension circuit of a step-up transformer 19 are electrically shielded from each other by a shielding portion 111. The shielding portion 111 is electrically opened along the winding direction of the primary coil of the step-up transformer 19, and the shielding portion is electrically connected to a shielding portion 106, thereby completely preventing the primary side and secondary side circuits of the step-up transformer from being mixed with and contacting each other, and besides reducing loss caused by the high frequency induction heating of the shielding portion 111 to a remarkably small amount. Moreover, the noise source of a power converter and a magnetron, etc., is shielded to prevent noise and unnecessary radiation.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to improvements in high frequency heating devices such as microwave ovens.
More specifically, the present invention relates to a power supply device using semiconductor switching elements such as transistors in the power supply circuit of the magnetron.

2. Description of the Related Art Conventionally, as is well known, a power supply device for a microwave oven consists of a power supply circuit mainly composed of a ferro-resonant transformer 50 as shown in FIG. 12 magnetrons usually 3-4
Since the operating voltage is kV, the circuit voltage of the secondary circuit of the high voltage transformer 50 is extremely high and dangerous. That is,
In FIG. 5, the point P of the primary winding 53 and the point P of the secondary winding 5
If the point Q of 4 is short-circuited due to some kind of failure, if the casing 51 is not installed at the earth ground 52,
This was very dangerous because the voltage on the housing 51 would be extremely high. Therefore, the casing 51 of the microwave oven was always grounded to the earth 52 during use.

In addition, in recent years, a power supply device using a voltage resonant inverter with a parallel resonant circuit as shown in Figure 6 has been proposed. It is used for.

This circuit rectifies a commercial power supply 1 with a bridge diode 2, an inductor 3, and a capacitor 4, and a pulsating DC voltage source (
A parallel resonant circuit consisting of a resonant capacitor 5 and a step-up transformer 6 that also serves as a resonant inductor, a transistor 7, and a diode 8 form a voltage resonant inverter circuit, and the high-voltage output of the step-up transformer 6 is connected to a capacitor. 9, diode)" 10.11 and supplies it to the magnetron 12. Note that 13.
Reference numerals 14 and 15 are the primary, secondary and heater windings of the step-up transformer 6, respectively, and 16 is a control circuit for driving the l.

In this power supply circuit, the transistor 7 is connected to the control circuit 16
Therefore, the conduction time To is controlled by so-called pulse width control.
n is controlled (by controlling Ton', T
on). That is, the switching operation by the transistor 7 and diode 8 is performed by the gate signal VGH as shown in FIG. 7(a) and the voltage waveform VCE as shown in FIG. On the other hand, since the amount of power converted by the inverter circuit is determined by TON, the amount of power supplied to the magnetron 12 is determined by TOH. The supply power increases.The control circuit 16 controls the magnetron 1 by controlling this TON.
This function adjusts the magnitude of the second output and stabilizes the output against fluctuations in power supply voltage.

However, even with such a power supply device, if an electrical connection (contact) occurs between the primary winding 13 and the secondary winding 14 of the step-up transformer 6, as in the case shown in FIG. 5, it is extremely dangerous. One thing didn't change. In particular, as the transformer 50 has become smaller, it has become extremely difficult to prevent this contact, and as the operating frequency of the power converter increases, it becomes even more difficult to guarantee safety. Ta.

Problems to be Solved by the Invention As mentioned above, the conventional technology cannot prevent the risk of contact between the primary and secondary windings, and it is necessary to always ground the casing, which prevents movement. There are disadvantages such as being troublesome and requiring grounding work.

Furthermore, when incorporating these power supply devices into a microwave oven, it was necessary to incorporate the magnetron and its power supply section separately, and to perform a wiring process for the high-voltage section. As a result, assembly costs increased and product defects were likely to occur due to wiring errors.

Furthermore, especially when a power converter is used, terminal noise conducted through the power line and interference waves radiated into the air are large, making it difficult to suppress them.

Furthermore, as shown in FIGS. 5 and 6, the magnetrons 5 and 12 have so-called choke boxes containing choke coils 57 and 58 and capacitors 59 and 60, and the magnetrons themselves have a choke box. Noise generation in the band of several tens of MHz to several hundred Mllz is prevented. These parts require high voltage resistance, are not only expensive, but also tend to suffer from dielectric breakdown, resulting in a lack of reliability. In addition, especially when a power converter is used, the influence of these parts on the magnetron heater circuit becomes large, so it becomes necessary to set the output voltage of the heater winding 15 of the step-up transformer to a large value, or the choke coil This has the disadvantage that the high-frequency magnetic flux generated by this process heats surrounding metal.

The present invention solves the problems of the conventional technology, and prevents cross contact between the primary and secondary circuits of a step-up transformer, and suppresses the generation of noise and unnecessary radiation from power converters, magnetrons, etc. be.

Means for Solving the Problems In order to solve the problems of the prior art, the present invention has the configuration described below.

That is, a power supply unit obtained from a commercial power source, a battery, etc., a power converter made of a semiconductor switch element, etc., a step-up transformer that boosts the output voltage of the power converter and supplies it to the magnetron, and a controller that controls the semiconductor switch. a shielding part that electrically shields the secondary high voltage circuit and the primary circuit of the step-up transformer; and a shielding part that shields part or all of the power converter, the step-up transformer, etc. The shielding section is configured to be electrically open along the winding direction of the primary winding of the step-up transformer, and the shielding section is configured to be electrically connected to the shielding section. It is.

Further, the shield part is provided with a power terminal for supplying power from a commercial power source, a battery, etc., and a signal terminal for supplying a control command signal to the control part, and is configured as one unit.

A filter section is provided near at least one of the power terminal and the signal terminal, and at least one of the power and the control command signal is supplied into the shield section through the filter section.

Furthermore, the capacitor constituting the filter section is constructed using a two-core type feedthrough capacitor, and this feedthrough capacitor is electrically connected to the shield section, so that the terminal and filter section have a simple structure. .

Effects With the above configuration, the present invention has the following effects.

That is, a shield part that shields a power supply part, a power converter, a step-up transformer, a magnetron, etc., and a shield part configured to be electrically open along the winding direction of the primary winding of the step-up transformer are provided, Since this shielding part and the shield part are electrically connected, it is possible to completely prevent contact between the primary and secondary circuits of the step-up transformer, and also prevent noise sources such as power converters and magnetrons. can be shielded to suppress the generation of noise and unnecessary radiation.

In addition, by providing power terminals and signal terminals in the shield part, all the main components for generating microwaves can be housed within the shield part, and the power supply unit can be extremely easily supplied with power and signals. realizable.

By providing a filter section near this terminal, leakage of noise voltage from this terminal can be significantly reduced and
can be easily reduced.

Further, by configuring the capacitor of this filter as a two-core feedthrough capacitor, it is possible to easily prevent high frequency noise generated by the magnetron from leaking to the outside from the shield portion.

EXAMPLES Hereinafter, examples of the present invention will be described 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 the same reference numerals as in FIG. 6 are components corresponding to those in FIG. 6.

The power of the commercial power supply 1 is transferred to the diode bridge 2 (power supply section 1
00), resulting in a full-wave rectified voltage waveform output. This output is provided by a series resonant circuit consisting of an inductor 17, a capacitor 18, and a step-up transformer 19 that function as a constant current power supply, a switching circuit consisting of an insulated gate bipolar transistor (IGBT) 7 and a diode 8, and a resistor 20. Power conversion circuit (inverter) 1 composed of a snubber circuit consisting of a capacitor 21
01 and is converted into frequency power of 100-300 KHz. Since this high frequency power is generated as a high frequency voltage in the primary winding 22 of the step-up transformer 19, high frequency high voltage and high frequency low voltage power are induced in the secondary winding 23 and the heater winding 24, respectively. High frequency and high voltage are connected to diodes 25, 26 and capacitors 27. '2B
DC high-voltage power is supplied to the magnetron 12 after rectification, while high-frequency low-voltage power is directly supplied to the cathode of the magnetron 12 to heat the cathode.

The current and voltage waveforms flowing through this IC; Br3 and diode [8 are as shown in FIGS. 2(a) and 2(b), respectively. The IGBT 7 is driven by a control section 29, which will be described later, using a gate voltage waveform VGE shown in FIG.

In the control unit 29, a switch 30 such as a relay is connected to the heating controller 10.
2, the resistor 31, diode 32,
Operation is started by forming a control power source consisting of a capacitor 33 and a Zena diode 34. When the control command signal voltage of the heating controller 102 is supplied between the signal terminals 103 and 104, the voltage controlled oscillator 35 is activated in response to the signal, and its output energizes the timer circuit 36. The timer circuit 36 can be easily realized by a monostable multi-high break with a cent terminal, for example, and the voltage controlled oscillator 35 can be easily realized by an astable multi-high break with a voltage control terminal. The signal of the timer circuit 36 is sent to the output circuit 37.
After the impedance is converted, the signal is supplied to the IGBT 7 through a resistor. As is clear from FIG. 2, when the gate pulse VGE is supplied to the IGBT 7, its collector current IC begins to flow resonantly as shown. After 13 hours have elapsed, the current becomes zero, and then the diode current 1d flows, and this Id also becomes zero after the time t2.

The gate pulse voltage VGE that drives IGBT7 is this t.
It is extremely important for the safe operation of the IC and Br3 that the pulse width ton be longer than t2 and shorter than t2. If ton is shorter than Ll, the IGBT 7 will be turned off while Ic is flowing, resulting in a large turn-off loss.

Conversely, if it is longer than t2, a so-called commutation failure phenomenon occurs, and a short circuit current flows through the IGBT 7, resulting in destruction. That is, when using a switching element having a self-commuting function such as an IGBT, the conduction time ton of the resonant circuit is shorter than 2, and the resonant half-period jUl 1. The condition that the length is longer than + is extremely important and indispensable in order to guarantee safe and reliable operation and to operate with high efficiency and high frequency.

The reverse bias detection circuit 39 in FIG. 1 detects the point in time when Id starts to flow (after 1+ time has elapsed) in FIG. 2, and resets the timer circuit 36 to cut off the output pulse VGE after delaying Δ. It is something to do. Due to this reverse bias detection circuit 39, the characteristics of the magnetron 12, capacitor 1, transformer 19, etc. change greatly,
Even if the circuit constants of the series resonant circuit change, the gate pulse V
The pulse width (that is, conduction time) ton of the GE can satisfy the condition that it is always longer than t and shorter than t2, and stable and low-loss switching operation can be realized. Of course, the reverse bias detection circuit 3
9 is not necessarily necessary. For example, if the variation range of the circuit constants of the series resonant circuit due to changes in the characteristics of the magnetron 12, capacitor 18, transformer 19, etc. described above is relatively small, the timer circuit 3
If the count time of is set to be the conduction time ton in Figure 2, even if there is some variation in the circuit constant of the series resonant circuit, the period during which Id is flowing (that is, when [c becomes zero) and VCE is zero), the game I.
Pulsed VGE can be turned off. Therefore, in this case, only the timer circuit 36, such as a simple monostable multi-by-break circuit, is required, resulting in a simple and inexpensive configuration.

40 is for detecting the current flowing through the current transformer. This diode current is the anode current (
(proportional to radio wave output), so a signal corresponding to the anode current can be obtained with a small amount of current detection. Therefore, a small Karen 1-lance can be used. The output of this current transformer 40 is sent to an error amplifier 41, and the error amplifier 41 controls the oscillation frequency of the voltage controlled oscillator 35 so that the signal of the current transformer 40 becomes a set value. That is, if the output of the Karen 1 to lance 40 is smaller than the set value, the error amplifier 41 controls the oscillation frequency of the voltage controlled oscillator 35 to be increased, and conversely, if the output is larger than the set value, the oscillation frequency is increased. So-called negative feedback control is used to lower the temperature.

The error amplifier 41 can be realized very easily by using a known operational amplifier or the like. A control command signal voltage is given from the controller 102 via the filter unit 105. That is, the signal voltage corresponding to the set value of the radio wave output is received, and the oscillation frequency of the voltage control oscillator 35 is controlled so that the signal voltage becomes the signal voltage. It is something to do.

The signal terminals 103 and 104 are provided on the shield part 106 as shown in FIG. 1, and the filter part 105 is also grounded to the shield part 106 as shown in the figure. Therefore, unnecessary radiation leakage of the magnetron from this signal terminal can be prevented.

Similarly, power from the commercial power source 1 is supplied from power terminals 107 and 108 provided on the shield section 106, and is supplied to the diode bridge 2 via the filter section 109 which is also grounded to the shield section 106. It is connected to the. Therefore, the noise generated by the magnetron 12 and power converter 101 is transmitted from this terminal to the shield part 1.
It is possible to suppress leakage to the outside of 06.

When using noise prevention capacitors in the filter sections 105 and 109, by configuring the two terminal pairs with two-core feedthrough capacitors, leakage of high-frequency noise voltage from the magnetron from these terminals can be effectively and effectively prevented. , can be realized at low cost. As shown in Figure 3, 2
Core feedthrough capacitor 109A and choke coil 109B
, 109C constitutes the filter section 109, and if it is attached to the shield section 106 as shown in the figure, the above-mentioned effects can be obtained.

Of course, such a structure can also be adopted for the filter section 105.

Each winding 22, 23, 24 of the step-up transformer 19 is provided in a ferrite core 110, but a shielding portion 111 is provided between the primary side circuit and the secondary side circuit, and this shielding portion 111 is electrically connected to the shield part 106. Therefore, the winding 23.2 which is the secondary circuit
4. Diodes 25, 26, capacitors 27, 28 are:
Since the shielding part 111 and the shielding part 106 completely isolate each other, the structure is such that there is no risk of the high-voltage secondary circuit and the primary circuit coming into contact with each other. FIG. 3 is a block diagram showing the configuration of a secondary side circuit centering on this step-up transformer 19, and the same reference numerals as in FIG. 1 indicate corresponding components.

In FIG. 3, a core 110 is secured by a fixture 113 between two cores having an air gap 112, and each winding is applied to a bobbin 114, 115 as shown. Diode 25.26, capacitor 27.
28 is molded with resin and fixed to the bobbin 115 as a rectifying unit 116. Since the shielding part 111 is electrically connected to the shielding part 106 at point A, if a magnetron is provided on the left side of this step-up transformer and a primary side circuit such as the power converter 101 is placed on the right side, the high voltage secondary It is possible to completely isolate the side circuit from the primary circuit, achieve high safety, and eliminate the need for troublesome earthing.

This shielding portion 111 is configured to form an electrical open circuit with respect to the winding direction of the primary winding 22 .

FIG. 4 is a block diagram of this shielding section 111, and the same reference numerals as in FIG. 3 are corresponding components. The shielding part 111 has a discontinuous part 117 so as to form an electrically open circuit' in the winding direction of the primary winding shown by the arrow in the figure, and is also provided with many slits 118. This discontinuous portion 117 prevents the generation of a large induced current that would flow around the core 110, and
By providing a large number of 8, small loop induced currents that tend to flow within the plane of the shielding portion 111 are suppressed.

In addition, this shielding part 111 is made of a non-magnetic metal material, such as aluminum, copper, 5U, etc., in order to suppress Joule loss due to induced current due to high-frequency magnetic flux.
A metal material such as S304 is suitable.

By configuring the shielding part 111 in this way, induction heating of the shielding part due to the high-frequency magnetic flux generated by the primary winding is significantly reduced, and a safe structure is realized that completely prevents contact between the primary and secondary windings. can do.

Effects of the Invention As described above, according to the present invention, there is provided a power supply section obtained from a commercial power source, a battery, etc., a power converter made of a semiconductor switch element, etc., and a magnetron that boosts the output voltage of the power converter. a step-up transformer for supplying the step-up transformer to the step-up transformer; a control section that controls the semiconductor switch;
The shielding part electrically shields the next high voltage circuit and the primary circuit, and the shielding part shields part or all of the power converter, step-up transformer, etc., and the shielding part is connected to the step-up transformer. Since the circuit is configured to be electrically open along the winding direction of the primary winding, and the shielding portion is electrically connected to the shielding portion, the primary and secondary sides of the step-up transformer are It completely prevents cross-contact between circuits, and also significantly reduces loss due to high-frequency induction heating in the shielding part.
It is possible to shield noise sources such as radio waves and suppress the prevention of noise and unnecessary radiation.

Furthermore, when incorporating these power supplies into a microwave oven, it is only necessary to assemble one unit, which simplifies the wiring process, reduces assembly costs, and prevents wiring errors. It is.

Furthermore, even if we eliminate the so-called choke box containing the choke coil and capacitor of the magnetron, which was indispensable in the past, the number of magnetrons generated +
Since noise generation in the MIIz to several hundred MHz band can be prevented, these high-frequency components (lower costs and higher multipliers due to the omission of pressure-performance parts), rationalization of the step-up i-lance heater winding design, and high-frequency reduction of surrounding components It is possible to prevent inconveniences such as heating.

In addition, by providing power terminals and signal terminals in the shield part, all the main components for generating microwaves are housed within the shield part, and the wiring process for supplying power and signals to them is extremely easy. A power supply unit can be realized. In other words, it is extremely easy to handle the power supply unit as a component consisting only of power terminals, signal terminals, and microwave output antennas, which makes it very easy to design high-frequency heating devices such as microwave ovens.

- Manufacturing, assembly, etc. can be made extremely simple and low cost.

A filter section is provided near at least one of the power terminal and the signal terminal, and at least one of the power and the control command signal is passed through the filter section to the seal 1.
By configuring the power supply to be supplied inside the section, noise sources such as power converters and magnetrons can be more reliably shielded, and the generation of noise and unnecessary radiation can be extremely effectively suppressed.

Furthermore, by configuring the capacitor constituting the filter section using a two-core feedthrough capacitor, and configuring the feedthrough capacitor to be electrically connected to the shield section, it is possible to reduce the high frequency generated by the magnetron. It is possible to more reliably and easily prevent noise from leaking to the outside from the shield part at low cost.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram of a high-frequency heating device showing one embodiment of the present invention, and FIGS. 2(a), (b), and (c) respectively show the collector current 1c of an insulated gate bipolar transistor of the same device. A waveform diagram, a waveform diagram of the collector voltage VCE, and a waveform diagram of the gate voltage VGIi, FIG. 3 is a partial sectional view showing the structure of the step-up transformer of the same device, FIG. 4 is a structural diagram of the shielding part of the same device, and FIG. The figure shows a circuit diagram of a conventional high-frequency heating device using a ferro-resonant lance, FIG. 6 is a circuit diagram of a conventional high-frequency heating device using a conventional power converter, and FIG.
), (b), and (C) are a gate voltage waveform diagram, a collector current waveform diagram, and a collector voltage waveform diagram, respectively, of the insulated gate type high-bolar transistor of the same device. 19...Step-up transformer, 100...Power supply section, 101...Power converter, 103.104
...Signal terminal, 105.109...Filter part, 106...Shield part, 107°108...Power terminal, 111... Shielding part.

Claims (4)

[Claims] (1) A power source obtained from a commercial power source, battery, etc.
a power converter made of a semiconductor switch element or the like; a step-up transformer that boosts the output voltage of the power converter and supplies it to a magnetron; a control unit that controls the semiconductor switch;
The shielding portion includes a shielding portion that electrically shields a secondary high voltage circuit and a primary side circuit of the step-up transformer, and a shielding portion that shields part or all of the power converter, the step-up transformer, etc. The high-frequency heating device is configured to be electrically open along the winding direction of the primary winding of the step-up transformer, and the shielding portion is electrically connected to the shielding portion. (2) High-frequency heating according to claim (1), wherein the shield part is provided with a power terminal for supplying power from a commercial power source, a battery, etc., and a signal terminal for supplying a control command signal to the control part. Device. (3) Claim (2) wherein a filter section is provided near at least one of the power terminal and the signal terminal, and at least one of the power and the control command signal is supplied into the shield section through the filter section. The high-frequency heating device described in Section 1. (4) High-frequency heating according to claim (3), wherein the capacitor constituting the filter section is constructed using a two-core feedthrough capacitor, and the feedthrough capacitor is electrically connected to the shield section. Device.