JPS6014479B2 - Power supply circuit for high frequency heating equipment - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a power supply circuit for a high frequency heating device, and particularly to a small and efficient power supply circuit using power transistors.

The induction heating phenomenon in which a good conductor or magnetic material placed in an alternating magnetic field is heated by electromagnetic induction is well known, and several high-frequency heating devices using this heating phenomenon have been put into practical use as hardening devices and the like.

The frequencies used for induction heating range over a very wide range, but usually a high frequency of Hz or higher is used for one dish. Vacuum tube oscillators, which were suitable for handling large military forces, were commonly used as this type of high-frequency power source. However, the vacuum tube oscillator has disadvantages in that the high-voltage direct current source circuit and tank circuit become large and expensive, making it unsuitable for anything other than large-scale installation equipment as factory equipment. The present inventor has proposed that when high-frequency induction heating is employed in the heat-sealing process when manufacturing a storage container for cooked food and the heat-sealing process in which the storage container is sealed after being filled with cooked food, the high-frequency fin We focused on converting the source circuit into a transistor. The process of heating and sealing storage containers is extremely suitable for use with a high-frequency induction heating device. A typical storage container is made of a triple-layered sheet made of aluminum or other metal foil laminated with a resin film on both sides, and after this sheet is shaped into a bag or other container shape, the joint is heat-sealed, leaving a portion behind. . The storage container thus manufactured is filled with cooked food, and the filling opening is immediately heat-sealed. Conventional heat sealing means is known to press a heating element against the sealing part and melt and bond the resin film at the joint part by heat conduction, but in order to prevent the resin film on the outside of the metal foil from melting, Since the temperature of the pressing heating element cannot be raised above a certain level, it takes a long time for the inner resin film that is the joint to melt. In particular, when high-temperature, short-time sterilization is performed in order not to impair the flavor of food and to improve the efficiency of heat sterilization work, the melting temperature of the inner resin film must withstand high temperatures, and the outer resin film must withstand high temperatures. Although it is disadvantageous in terms of price to use a resin film with a high melting temperature, the difference in melting temperature between the inside and outside becomes smaller, and when the inside is melted,
It takes quite a long time. In addition, it is preferable to use strong nylon as the inner resin film to prevent damage to the storage container, but nylon easily absorbs water due to its characteristics, so when melting and bonding the inner resin film, nylon absorbs moisture. The moisture in the nylon evaporates and the inner resin film foams, so the temperature at the joint must be lowered to a temperature at which the evaporated water is absorbed by the nylon again while the pressure remains in place. If high-frequency induction heating is used in such a heat-sealing process, the metal foil of the sheet will be directly heated, and the resin film inside will be effectively melted and bonded, dramatically improving the working efficiency. If the supply of high-frequency power to the coil is stopped, the heat of the heated sheet is transferred to the lower temperature heating coil, and the above-mentioned foaming can also be suppressed.

When heat-sealing, the heating coil is pushed onto the sheet, so the heating coil and the metal foil that is the object to be heated come very close to each other, the phase induction coefficient between the heating coil and the metal foil is large, and the power factor of the heating coil is used under high conditions.

In order to connect the fin to a load with such a high power factor, the optimal high-frequency power source is a switching type inverter using wing power transistors. That is, this type of high-frequency power source does not require a large tank circuit like the vacuum tube oscillator type described above, so it is small, inexpensive, and highly efficient. Conventionally, a push-pull type DC-AC switching type inverter is known as an oscillation power supply circuit. This inverter is suitable for obtaining high-frequency power with high efficiency and high output, but since the output switching transistor is used in a saturated state, a phenomenon occurs in which the collector current continues to flow for a short period of time at cut-off due to accumulated charge. This phenomenon occurs because both switching transistors connected in parallel turn on at the same time, resulting in a current spike that reduces the efficiency of the inverter and, in extreme cases, destroys the transistors.
In order to eliminate this conventional drawback, there is a multipipulator type inverter using a supersaturated reactor.

However, in this conventional example, the use of a special supersaturated IJ vector is limited, and since it requires a DC power supply, a large smoothing circuit is required to obtain DC from a commercial power supply, or the oscillation frequency cannot be varied. There were various drawbacks such as: SUMMARY OF THE INVENTION In view of the above-mentioned conventional problems, an object of the present invention is to provide a small and inexpensive power supply circuit for a high-frequency heating device that can obtain high-efficiency, high-output high-frequency power using power transistors.

Preferred embodiments of the present invention will be described below based on the drawings.
FIG. 1 is a first embodiment showing the basic configuration of a power supply circuit according to the present invention. One output transformer includes a primary winding 11 and a secondary winding 12, and the primary winding 11 has an intermediate tap 13 to which two power supply circuits are connected. The secondary winding 12 of the output transformer 10 is connected to a high frequency heating coil (not shown). The power supply circuit 20 includes a commercial power supply 21 and a full-wave rectifier circuit 22
and a high-frequency bypass capacitor 23, and applies full-wave rectified power to the intermediate tap 13 of the output transformer 10. Output transistor circuits 30 and 40 are connected to both ends of the primary winding 11 of the output transformer 10, and both output transistor circuits 30 and 40' are connected to output transistors 31 and 41, respectively.
, current limiting resistors 32 and 42, and reactive power return diodes 33 and 43. The collectors of the output transistors 31 and 41 are connected to both ends of the primary winding 11, respectively, and the signal from the oscillation circuit 50 is connected to the base of the drive circuit 34.
, 44, the increasing voltage is applied. Note that the transistors 35, 36, 45, and 46 of the drive circuit are used in a saturated state.
The oscillation circuit 5 includes a flip-flop 51, and one output terminal thereof is connected to the base of the transistor of the drive circuit 34 via a differentiating circuit 52, a diode 53, and a monostable multilayer 54. Similarly, the other output terminal of the flip-flop 51 is connected to the base of the transistor of the drive circuit 44 via a differentiating circuit 55, a diode 56, and a monostable multilayer 57. Three input signals are applied to the input terminal of the flip-flop 51 via a differentiating circuit 58 and an OR gate 59. The first input signal is the start circuit 60
The second and third input signals are applied from the monostable multi 61 of
It is applied from 1,72. In this embodiment, feedback circuits 71, 72 include differentiating circuits 73, 74 connected to the collectors of output transistors 31, 41. The output of the monostable multi 61 is connected to the bases of transistors 75 and 76 which nullify the signals from the feedback circuits 71 and 72.
The monostable multi 61 includes a start pulse generation junction transistor 62, a start pulse blocking transistor 63, a capacitor 64, and a resistor 65.

This start circuit 601 is connected to the signal e from the zero volt start circuit 66 shown in FIG. 2 to prevent confusion caused by starting the oscillation operation from an irregular phase state of the commercial source AC. That is, if the power source of this high frequency oscillator is a pulsating current obtained by full-wave rectification of the commercial AC voltage, and the high frequency power is generated from zero volts of the pulsating voltage of the power source, at the start of switching of the output transistors 31 and 41, Since the voltage supplied to the output transistors 31 and 41 is low, the DC component flowing to the output transformer 10 at the start of switching is small, and the output transformer 10
Since the magnetic core of the output transformer is not saturated, the output transformer can be made smaller, and the output transistors 31 and 41 are not destroyed by the transient current at the start of switching, so the output transistors 31 and 41 can be made smaller. The zero port start circuit 66 is turned on when the zero volt start timing transistor 67 is turned off. It includes a volt start timing thyristor 68, the output of which controls transistor 63. Further, signals from feedback circuits 71 and 72 are also applied to the base of transistor 63. The zero volt start circuit 66 is provided with a start switch 69. The first embodiment of the present invention has the above-mentioned configuration,
Next, its effect will be explained. Closing the start switch 69 activates the zero volt start circuit 66. That is, when a positive voltage is applied from the switch 69 to the anode of the thyristor 68, preparation for turn-on is completed;
Since the collector of the zero-volt start timing transistor 67 is connected to the gate of the transistor 8, the transistor 68 is kept in the off state while the transistor 67 is in the on state. At the moment the pulsating voltage 1 due to full-wave rectification of the commercial power supply applied to the base of the transistor 67 becomes zero volts, the transistor 67 is turned off and the thyristor 68 is turned on. As a result, the transistor 63 turns off, and accordingly, the capacitor 64 is charged via the resistor 65, and when this voltage exceeds the standoff ratio, the junction transistor 62 becomes conductive and a negative impulse is generated. A pulse is generated from the monostable multi when applied to the monostable multi. The output pulse of the monostable multi 61 is applied to the flip-flop 51 through the OR gate 59 and the differentiating circuit 58, and the positive applied pulse causes the flip-flop 51 to change state.

The output of the monostable multi 61 is simultaneously connected to transistors 75 and 7.
6 is turned on to short-circuit the feedback signals of the feedback circuits 71 and 72, making them invalid. Although the initial state of the flip-flop 51 is undefined, for example, when the state of the flip-flop 51 changes, a negative impulse from the differentiating circuit 52 causes a predetermined pulse from one monostable multi 54 to turn on the output transistor 31. Consider the case.

By turning on the output transistor 31, the potential of a on the output transistor circuit 30 side becomes zero, and the potential of b on the output transistor circuit 40 side becomes twice the power supply voltage due to the transformer action of the output transformer. In this starting state, a negative impulse is generated from the differentiating circuit 73 and a positive impulse is generated from the differentiating circuit 74, but as described above, both the feedback circuits 71, 7
Since both impulses 2 and 2 are in an invalid state, neither of these impulses is applied to the OR gate 59. Even when the pulse from the monostable multi-channel transistor 54 disappears, the output transistor 31 remains in a nearly on state due to the accumulated charge.

During this time, no input is applied to the flip-flop 51, so the other output transistor circuit 40 does not act. Due to the disappearance of the accumulated charge, the output transistor 31
is turned off and the potential of a rises. monostable multi 54
, 57 are set to be substantially the same, but the monostable multi-pulse 61 is set to be slightly shorter than these. As a result, it can be understood that when the output transistor 31 is turned off, the feedback suppression effect by the monostable multi-layer 61 has already been released. Therefore, the positive impulse generated from the differential circuit 73 changes the state of the flip-flop 51 via the OR gate 59 and the differential circuit 58. The monostable multi 57 turns on the output transistor 41 for a predetermined period of time using a signal caused by this state change, and the differentiating circuit 74 detects the off operation of the output transistor 41 and provides an oscillation signal to the oscillation circuit 50 through the feedback circuit 72. The above operation continues until the voltage at the intermediate tap 13 becomes zero volts, and a high frequency rectangular wave signal is generated from the output transformer 10 and applied to the heating coil.

During this time, since a signal is input to the base of the transistor 63 via the feedback circuits 71 and 72, the charge in the capacitor 64 is discharged before the junction transistor 62 becomes conductive, so that the start circuit 601 does not function. When the voltage at the intermediate tap 13 eventually reaches zero volts, the signals from the feedback circuits 71 and 72 naturally become zero, so oscillation stops, and oscillation starts again with a signal from the next start circuit. As described above, in the power supply circuit for a high-frequency heating device according to the present invention, since the off-operation of one output transistor is detected and the other output transistor is turned on, both drive transistor circuits 30 and 40 can be turned on at the same time. Therefore, generation of current spikes and the like that adversely affect the circuit is prevented, and damage to the drive transistor is prevented.

In the power supply circuit of FIG. 1, control transistors 77 and 78 are provided to turn off the output transistor circuits 30 and 40 according to certain needs.

These control transistors 77 and 78 are normally kept off, but are turned on during power control or overcurrent protection. A magnetic force control circuit is shown in FIG. 3, in which the collector potential c of a transistor 81 controlled by a thyristor 80 is connected to the bases of control transistors 77 and 78. Thyristor 80 is fired by a firing circuit including a unijunction transistor 82, a capacitor 83, a variable resistor 84, and transistors 85 and 86. Transistor 86 turns off at zero volts of pulsating voltage 1 applied to its base, and at this time transistor 85 turns on and discharges capacitor 83. From this point on, the capacitor 83 is charged with a time constant set by the variable resistor 84, and the junction transistor 82 is turned on at a predetermined position determined by the standoff ratio, causing the thyristor 8
0 is turned on. Turning on thyristor 80 turns off transistor 81 and control transistors 77,7
8 is turned on to invalidate the signals to the output transistors 31 and 41. Since this state lasts until the pulsating voltage 1 of the power supply next becomes zero volts, the power control action is achieved by changing the time constant by the variable resistor 84. As explained above, in this power control method, high-frequency power is generated from zero volts of the pulsating voltage of the power supply, and power generation is stopped at a phase in the middle of one cycle. The transient current that sometimes occurs may saturate the output transformer 10 or cause the output transistors 31 and 41 to become saturated.
will not be destroyed. The control transistors 77 and 78 are also used to protect the output transistors 31 and 41 from current flow.

That is, the current flowing through the output transistors 31 and 41 is detected by the conductive coil 9, and the outputs f and g are rectified by the rectifier circuit 91 shown in FIG. 4 and applied to the Schmitt circuit 92. If the output transistor current increases for some reason,
When this applied voltage exceeds a predetermined value, the Schmitt circuit 92 applies a pulse to the d terminals of the control transistors 77 and 78 to turn off the output transistor circuits 30 and 40.
Due to this protective action, the overcurrent in the output transistors 31 and 41 disappears, but along with the overcurrent, the output of the Schmitt circuit 92 also disappears, and oscillation starts again, and if the cause of the current increase is not removed, the overcurrent will continue. It flows again. In order to prevent this drawback, the output of the Schmitt circuit 92 is applied to the gate terminal h of the thyristor 80 of the power control circuit, and the output transistor circuit 30, 40 is applied to the gate terminal h of the thyristor 80 of the power control circuit until the next zero volt of the pulsating voltage 1, similar to the power control action described above. Hold in off state. Even in this case, since the response speed of thyristor control is relatively slow, the Schmitt circuit 92
It is necessary to apply a pulse to the d terminals of the control transistors 77, 78 immediately after. FIG. 5 shows the second embodiment of the present invention.
An embodiment will be shown, and the same components as in the first embodiment will be given the same reference numerals and their explanation will be omitted.

In the second embodiment, the oscillation circuit 50 is a well-known rectangular wave generation circuit, and its outputs j and k are out of phase with each other by 1800 degrees. , 41 base. - A zero volt start signal e, a power control signal c, and an overcurrent protection signal d are connected to the inputs of the NOR gates 103 and 104, and although normally they are zero, if any of the signals is applied, the corresponding output transistor circuit 30 may 40 is turned off.

The other circuits are the same as those in the first embodiment and will therefore be omitted.
In the second embodiment, the feedback circuits 71 and 72 include a detection winding 105 that detects the secondary voltage of the output transistor 10. When the zero port start signal e is turned off, starting is performed through one of the NOR gates 103 or 104 to which the off signal of the oscillation signal i or k is applied. Assuming that the output transistor 31 is now turned on, the primary winding 11 and the detection winding 105 are wound with the polarities shown, so the feedback circuit 71 sends an OFF signal to the NOR gate 103, and the feedback circuit 72 sends an OFF signal to the NOR gate 104. An on signal is applied to the output transistor circuit 40, and the output transistor circuit 40 is maintained in the off state. When a positive oscillation signal i is applied from the oscillation circuit 50 to the NOR gate 103, the NOR gate 103 turns off, but the output transistor 31
There is a slight delay in the off operation due to the accumulated charge. During this delay, gate 104 is maintained off by a positive feedback signal from feedback circuit 72. Output transistor 3
1 is turned off, the detection winding 105 causes the Noah gate 1 to turn off.
04, the NOR gate 104 is turned on, and the output transistor circuit 40 is activated. Thereafter, this oscillation effect continues and a rectangular wave output is obtained from the output transformer 10. FIG. 6 shows a third embodiment of the present invention,
Components that are the same as those in the first embodiment and the second embodiment are given the same reference numerals and their explanations will be omitted. The collector of the output transistor 31 is connected to the base of the output transistor 41 via the drive circuit 44, and similarly the collector of the output transistor 41 is connected to the base of the output transistor 31 via the drive circuit 34. In this embodiment, the drive circuits 34 and 44 are provided to reduce power loss caused by the feedback signals 271 and 272 being applied from points a and b at fairly high voltages, and the transistors in these circuits are in a saturated state. used in In other words, since the base voltages of the output transistors 31 and 41 need only be low, the low power supply voltage 10E is sufficient.
, 1E are provided, and a feedback signal 27 is provided.
By increasing the current of 1,272 in the drive circuits 34, 44, the current values of the feedback signals 271, 272 can be reduced, and the power loss in the feedback resistors 111, 112 can be reduced. The drive circuits 34 and 44 include NPN transistors 35 and 45 to which a positive voltage of 1E is applied to the collectors, and a PNP transistor 3 to which a negative voltage of -E is applied to the collectors.
6,46. The zero volt start signal e is turned off, and the pulsating voltage at the intermediate tap 13 is applied to the output transistor 3.
1 and 41, and one of the output transistors 31 and 41 is undefined, but for example, the output i of the square wave generator forming the oscillation circuit 50 is positive and the output transistor 31 is turned on. shall be.

Then, the voltage at the collector a of the output transistor 31 becomes zero, and the voltage at the collector b of the output transistor 40 becomes twice the voltage at the intermediate tap 13 due to the transformer action of the output transformer. Therefore, output transistor 31 is kept on and output transistor 41 is kept off. When the output i of the square wave generator eventually becomes negative and the output k becomes positive, the drive signal for the output transistor 31 turns off, but there is a slight delay in turning off the output transistor 31 due to the accumulated charge, and eventually the output When the transistor 31 is turned off,
The collector a of the output transistor 31 becomes positive, and the feedback signal 272 is activated in the drive circuit 44, turning the output transistor 41 on. As described above, in the third embodiment, as in the other embodiments, after confirming the off operation of one output transistor, the other output transistor is turned on, thereby preventing both output transistor circuits from operating at the same time. be done. One of the features of the present invention is that the power source of the high frequency oscillator is a pulsating voltage obtained by full-wave rectification of the commercial AC voltage, and for this purpose, special signals are used to drive the output transistors 31 and 41. .

Since the magnitude of the collector current of the output transistors 31, 41 changes in proportion to the pulsating voltage of the power supply, the drive current supplied to the bases of the output transistors 31, 41 to shorten the storage time also changes in proportion to the pulsating voltage of the power supply. shall be proportionate to For that purpose, the output transistor 31
, 41, the power supply pressure 18 of the drive circuit is DC pressure +E. and the voltage +E which is proportional to the pulsating voltage of the power supply, and the transistor of the drive circuit must be used in a saturated state. This DC voltage 1 Eo is necessary because the collector current hardly flows until the base of the output transistors 31 and 41 reaches a certain value. is chosen so that it is effectively zero. In addition, in order to ensure that the output transistors 31 and 41 are turned off, and to reduce the delay time when the output transistors 31 and 41 are turned off due to accumulated charge, the base of the output transistors 31 and 41 is driven when the output transistors 31 and 41 are turned off. A negative voltage -E is supplied from the circuit. In order to provide the driving voltage as described above, the power supply voltage of the driving circuit is supplied from the circuit shown in FIG. This drive power supply circuit is a rectifier circuit 11
5, 116, one terminal 117 of the rectifier circuit 115
is used as a positive terminal, the other terminal is connected to the output terminal of rectifier circuit 116 via transistor 118, and the other output terminal 119 of rectifier circuit 116 is used as a negative terminal. A Zener diode 120 is connected to the base of the transistor 118, and a DC voltage +Eo is obtained. 131, 132 are smoothing capacitors 133, 13
4 is a high frequency bypass capacitor.

The voltage 117 of the drive power supply circuit in FIG. 7 is the sum of the positive pulsating current waveform 1E^ and the DC voltage 1Eo as shown in FIG. 8, and the voltage 119 is the negative DC voltage -E. A certain power supply waveform is obtained and supplied to the drive circuits 34, 44 of the embodiments shown in FIGS. 1, 5 and 6. In the embodiment described above, overcurrent detection is performed by the induction coil 9 provided in the primary winding 11 of the output transformer 10, but the detection means includes the output transistors 31 and 41 as shown in FIG. Means for detecting current by resistors 135, 136 or a Hall element 1 as shown in FIG.
37, etc. exist. It is known that when an overvoltage is applied outside the output transistor, the transistor is destroyed.

Such overvoltage is known as a spike voltage that occurs when the drive transistor turns off due to leakage magnetic flux in the output transformer. The first protection circuit absorbs this overvoltage.
This is shown in Figure 1. In FIG. 11, the collectors of output transistors 31 and 41 are connected to a capacitor 23 via diodes 121 and 122. The capacitor 123 is charged with a voltage 22 times the maximum value of the power supply voltage via a transformer 124 that boosts the commercial power supply 21 at a turns ratio of 2:1 and a rectifier circuit 125. In normal normal operation, the collectors of the output transistors 31 and 41 are at 2 of the wire voltage.
A voltage more than double the voltage is not applied, and the diodes 121, 122
There is always a reverse voltage applied and no current flows. However, if an overvoltage is applied to the output transistor 31 or 41 for some reason, a forward voltage is applied to the diodes 121 and 122, making them conductive. This current is discharged by a resistor 126 connected in parallel to the capacitor 123. As described above, the output transistors 31 and 41 are regulated so that a voltage higher than a predetermined voltage is not applied. The power supply circuit for a high frequency induction heating device according to the present invention requires a heating coil with a high power factor.

In order to increase the power factor of the heating coil, it is preferable to make the mutual induction coefficient between the heating coil and the heated object as close to 1 as possible. When heat sealing cooked food storage containers, it is relatively difficult to obtain heating coils with high power factors. One difficulty arises from the fact that the heating when sealing the storage container must be formed into a narrow band inside. FIG. 12 shows the basic flat spiral coil shape of a normal heating coil.

This heating coil 31 is pressed against the heated object in an insulated state, and a portion corresponding to the shape of the coil is heated. 13th
The figure shows an intermediate stage of manufacturing a bag-like storage container, in which two triple-layer laminated sheets 311 are stacked on top of each other, and a heating coil 310 is moved over them in the direction of the arrow to form a joint indicated by diagonal lines. 312 is heat sealed. Then, by cutting the joint portion 312 as shown by the chain line, a bag-shaped storage container with three joined sides can be obtained. During this production,
The flat spiral coil 310 shown in FIG. 12 cannot be used because, as is clear from the slightly exaggerated view of FIG. 13, the portion shown by the broken line is heat-sealed. For this reason, in actual use, it is probably necessary to separate one side 310A of the heating coil 310 from the laminated sheet 311, which is the object to be heated, so as to make it an ineffective side. FIG. 14 shows a state in which the storage container manufactured as described in FIG. 13 is filled with cooked food and then the opening 313 is sealed by heating from the heating coil 31. Even in this case, it is easily understood that the ineffective side 310A of the heating coil 310 does not come close to the object to be heated. In a heating coil having such an ineffective side, the ineffective side does not electromagnetically couple with the object to be heated, so the mutual induction coefficient decreases, and it is impossible to obtain a heating coil with a high power factor. In FIG. 12, it appears that one narrow band-shaped heating seal is achieved by bringing the ineffective side 310A of the heating coil 310 close to the heating side 310B. However, more realistically, this idea would be rejected because the mutual concession coefficient itself would decrease as a result.
FIG. 15 shows a conventional improved heating coil that airtightly seals the opening of a storage container.
A ferrite magnetic core 314 is fixed to the ferrite core 314.

In this conventional example, most of the magnetic flux generated from the heating coil 310 passes through the magnetic core 314 as shown by arrow P, contributing to an increase in the mutual induction coefficient. However, even in this case, the mutual induction coefficient of the entire heating coil is controlled due to the presence of the magnetic flux Q that does not interlink with the heated body due to the ineffective side 310A. FIG. 16 shows a schematic configuration diagram of a high-frequency heating coil suitable for the present invention, in which a short-circuit coil 315 is provided to reduce leakage magnetic flux Q that interlinks only with the ineffective side 310A.

One side of the short circuit coil 315 is connected to the heating coil 310.
The magnetic core 314 is placed in close proximity to the ineffective side 310A of the magnetic core 314 to form a short-circuit current path surrounding the magnetic circuit of the magnetic core 314. Short circuit coil 31
5 is provided as shown in the figure, the leakage magnetic flux Q interlinks with the short circuit coil 315, so a current flows in the short circuit coil 315 in a direction that cancels out the leakage magnetic flux Q as shown in the figure. As a result, it is understood that the leakage magnetic flux Q is canceled by the short circuit coil 315, and the mutual induction coefficient of the heating coil increases. In the embodiment of FIG. 16, the shorting coil 315 consists of a wound coil of copper wire, but it is also possible to form the shorting coil with a conductive metal plate.

An embodiment in which a metal mount for fixing a heating coil also serves as a short-circuiting coil is shown in FIGS. 17 and 18. In this embodiment, the mount 316 is made of brass that has high electrical conductivity and mechanical strength and is easy to process, and serves as a shorting coil. The mounting base 316 is made of a rod having a substantially U-shaped cross section, and is firmly fixed to the movable arm 317 of the storage container heat sealing machine with screws 318 and 319, as shown in FIG. A magnetic core 314 made of ferrite and having a U-shaped cross section is fixed to the mounting base 316 in the longitudinal direction. A heater 320 is further embedded in the magnetic core 314, and this heater 320 prevents the heating coil device itself from losing heat from the storage container so that the storage container and the heating coil device come into contact during the heat sealing process of the storage container. do.
This heater 320 is extremely suitable for a contact-type high-frequency induction heating device, and if this heater 320 is not provided, a situation may occur in which the surrounding area of the desired seal portion is also heated unnecessarily. Dew. The heating side 310B of the heating coil 310 is fixed to the front surface of the heater 320, and the ineffective side 310A thereof is fixed to the mounting base 316, so that the heating coil 310 is arranged so as to surround the heating core 314.

In this state, the mounting base 316 connects the magnetic core 316 with the adjacent side 316A of the ineffective side 310A and the opposite end 3168.
forming a short-circuit current path surrounding the magnetic circuit of the ineffective side 310
Absorbs leakage magnetic flux caused by A. Copper protection plates 321 and 322 are fixed to the front surfaces of the heating side 310B and the ineffective side 310A of the heating coil 310 to prevent the heating coil 31 from being damaged. FIG. 19 shows another embodiment of the heating coil, in which the ineffective side 310A of the heating coil is located on the opposite side of the heating side 3108 with the heater 320 in between.

An opening portion 316a is formed in a part of the mounting base 316, and the invalid side 310A is inserted into this opening portion 316a. According to this embodiment, the heating coil device can be miniaturized and the mutual concession coefficient between the ineffective side 310A of the heating coil 310 and the object to be heated is extremely small, so that a band-shaped seal during bag making as shown in FIG. It is also preferable when carrying out. When performing sealing by high-frequency induction heating using a heating coil suitable for the present invention, there is a method of pressing the sealing part with the heating side of the heating coil using two substantially identical heating coils as described above; There is a method in which the heating side of one heating coil is pressed against the sealing part, and the magnetic core that is to form a magnetic circuit with the magnetic core of the heating coil is placed on the opposite side.
There is no major difference in heating characteristics between the two.

The high-frequency induction heating coil used in the present invention has a large mutual induction coefficient between the heated side and the heated object, a 4.0-low mutual conduction coefficient between the ineffective side and the heated object, and a desired current density in the heated part. In addition to reducing the current density in other parts, the short-circuiting coil reduces the leakage magnetic flux generated at the ineffective side, making it a coil with a high power factor, making it an efficient coil for high-frequency transfer heating sealing.

Next, we will explain how to use this high-frequency induction heating coil to seal a sheet that has a hygroscopic resin film such as nylon on the inside of the metal foil.

According to this heating coil, only the desired portion can be effectively heated, so that a good seal can be obtained even if the heating temperature of the heater that heats only the heating piece described above is not so high. Therefore, when sealing a sheet containing a hygroscopic resin, high-frequency power is supplied after the heating coil presses the sealed portion, and once the seal portion has melted, the supply of high-frequency power is stopped. At the temperature where the seal part melts, the water absorbed in the resin film evaporates,
The seal part foams, but when the high frequency power supply is stopped,
The temperature of the seal part is transferred to the lower temperature heating coil, and the foaming of the seal part disappears. When the temperature of the seal part has decreased sufficiently, it is sufficient to stop pressing the seal part by the heating coil. Even in this case, since the higher the temperature of the heating piece of the coil, the more efficient heating can be performed, it is preferable to keep the temperature at a high temperature to such an extent that no foaming is observed after the sealing part has finished sealing. As explained above, according to the high frequency induction heating coil according to the present invention, an extremely high power factor can be obtained.

The power factor of the coil according to the present invention can be universally set to a value of 0.9 or more, and the power factor value of the conventional general induction coil is 0.
．． It is clear that the improvement has an extremely large effect compared to the case where the value is 1 or less. A high power factor heating coil can dramatically improve its heating efficiency.

That is, since the electric power supplied to the object to be heated is proportional to the power factor of the heating coil, when the same electric power is supplied to the object to be heated, the current value can be reduced in a heating coil with a high power factor.
Reducing the current value of the heating coil offers various advantages in the fabrication of high frequency conductive heating devices.

This can be understood from the fact that the heating coil of the present invention can have a power factor of more than 1 tone and a current value of less than 1'10 compared to the conventional heating coil. These values mean that the heating coil wire diameter can be reduced to 1'10 or less to supply the same electric power, and this point is extremely important. Reducing the diameter of the heating coil wire makes it easier to form the heating coil into an arbitrary shape. Further, the reduction in the current value has the advantage that the structure of the conducting wire portion can be simplified and the conducting wire can be made thinner, thereby eliminating the need for a cooling device. Particularly in devices where the heating coil must be movable, there is an advantage that a flexible conducting wire with a small diameter can be used.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing a preferred first embodiment of the power supply circuit for a high-frequency heating device according to the present invention, FIG. 2 is a circuit diagram showing a zero port start circuit connected to FIG. 1, and FIG. 1st
4 is a circuit diagram showing the overcurrent protection circuit connected to FIG. 1. FIG. 5 is a circuit diagram showing the second embodiment of the present invention. 6 is a circuit diagram showing a third embodiment of the present invention, FIG. 7 is a drive circuit diagram of an output transistor, FIG. 8 is a waveform diagram of FIG. 7, and FIGS. 9 and 10 are overcurrent detection circuit diagrams, respectively. Figure 11 is an overvoltage protection circuit diagram of the output transistor, Figure 12 is a schematic diagram showing the basic flat spiral coil shape of a normal heating coil, and Figure 13 is a bag-shaped storage container manufactured using the heating coil in Figure 1. 14 is a plan view showing the step of airtightly sealing the closing part of the bag-shaped storage container with the heating coil of FIG. 12; FIG. 15 is a schematic diagram showing the conventional heating coil;
Figure 6 is a schematic diagram of the high-frequency heating coil used in the present invention;
FIG. 17 is a perspective view showing a preferred embodiment of the high-frequency heating coil used in the present invention, FIG. 18 is a sectional view of FIG.
FIG. 9 is a sectional view showing another embodiment of the present invention. 10...Output transformer, 11...Primary side, 12,310
...High frequency heating coil, 13...Middle tap, 20...Power circuit, 21...
Commercial power supply, 22... Rectifier circuit, 30, 40...
... Output transistor circuit, 50 ... Oscillation circuit, 71, 72 ... N feedback circuit. Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 9 Figure 6 Figure 7 Figure 10 Figure 12 Figure 14 Figure 15 Figure 16 Figure 11 Figure 13 Figure 17 Figure 19 Figure 18

Claims (1)

[Claims] 1. A power supply circuit having a commercial power supply and a rectification circuit that rectifies the power supply voltage so as to periodically repeat a low potential;
an output transformer with an intermediate tap on the primary side connected to the power supply circuit and a secondary side connected to the high-frequency heating coil; a pair of output transistor circuits connected to both ends of the primary side of the output transformer; and an output of the rectifier circuit. a start pulse generating circuit which receives the input voltage and generates a pulse at the start of the rise of the voltage; and a pulse which drives one of the output transistors at the input of the output of the start pulse generating circuit; A detection signal that detects that the collector current of one of the output transistor circuits has become zero is used to output a pulse that drives one of the opposing output transistor circuits, which is further driven by the low potential output of the power supply circuit. 1. A power supply circuit for a high-frequency heating device, comprising: a pulse generation circuit for stopping.