JPH0574562A - High-frequency heating device - Google Patents

Abstract

PURPOSE:To dispense with the connection of a step-up transformer and a printed wiring circuit by forming the windings for the step-up transformer on the printed wiring circuit board. CONSTITUTION:While a circular conductive pattern 49 is formed on a printed wiring circuit board 46, a voltage doubler rectifier circuit 36 is loaded thereon. The conductive pattern 49 is connected to the voltage doubler rectifier circuit 36. The primary winding 21a of a step-up transformer 21 is provided concentrically corresponding to the conductive pattern 49, and thereby, a filament winding 21c is composed from the conductive pattern 49. As a result, when a high-frequency power is generated in the primary winding 21a, a lighting current is induced from the filament winding 21c, and it is given to the cathode C of a magnetron.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high frequency heating apparatus having a filament winding for generating a lighting current to a filament forming a cathode of a magnetron or a timing detection winding for determining an operation timing of a frequency conversion circuit.

[0002]

2. Description of the Related Art For example, as an example of a microwave oven, a frequency conversion circuit for converting commercial power into high frequency power is provided on the primary side of a step-up transformer, and the high frequency power boosted by the step-up transformer is rectified on the secondary side to a magnetron. There is provided a rectifier circuit that outputs a DC voltage. In this case, since it is necessary to pass a lighting current through the filament of the magnetron, a filament winding is provided on the secondary side of the step-up transformer so that the lighting current generated in the filament winding is applied to the filament of the magnetron.

FIG. 7 shows an example of this type of step-up transformer. In FIG. 7, a bobbin 3 is fitted on a transferlite core 2 of a step-up transformer 1, and a primary winding 1a, a secondary winding 1b, and a filament winding 1c are wound around the bobbin 3. A frequency conversion circuit (not shown) is connected to the primary winding 1a, and commercial power is converted into high-frequency power by the conversion operation of the frequency conversion circuit and given to the primary winding 1a. The secondary winding 1b is connected to a voltage doubler rectifier circuit 5 mounted on the printed wiring circuit board 4 via a lead wire (not shown).
The high frequency power output from the converter is converted into DC power by the voltage doubler rectifier circuit 5 and output to a magnetron (not shown). The filament winding 1c is connected to the voltage doubler rectifier circuit 5 of the printed wiring circuit board 4 via the lead wire 6 and also to the filament of a magnetron (not shown). Therefore, when high frequency power is generated in the primary winding 1a by the frequency conversion operation by the frequency conversion circuit, a lighting current is generated in the filament winding 1c and is output to the filament of the magnetron, so that the magnetron is capable of outputting high frequency. ..

Further, in the above frequency conversion circuit,
A timing detection winding (not shown) for detecting the primary side voltage is provided on the primary side of the step-up transformer 1, and the frequency conversion timing is determined based on the timing signal from the timing detection winding. There is. in this case,
The timing detection winding is connected to the frequency conversion circuit mounted on the printed wiring circuit board via a lead wire.

[0005]

By the way, in the case of the above-mentioned conventional example, since the filament winding or the timing winding is connected to the printed wiring circuit board through the lead wire, the number of connecting points between the components increases. Reliability is reduced. Also, the large number of constituent parts has the drawbacks of lowering the reliability and increasing the assembly cost and the parts cost.

The present invention has been made in view of the above circumstances, and an object thereof is a filament winding for generating a lighting current to a filament of a magnetron or a timing detection winding for determining an operation timing of a frequency conversion circuit. In a device provided with a printed wiring circuit board on which electronic components connected to these are mounted, the work of connecting the filament winding or the timing detection winding to the printed wiring circuit board can be omitted, and the component parts can be provided. It is an object of the present invention to provide a high-frequency heating device that has effects such as reduction in assembly cost and parts cost.

[0007]

SUMMARY OF THE INVENTION The present invention is provided on a secondary side of a step-up transformer, and a printed circuit board provided with a rectifier circuit for applying a DC voltage to a magnetron, and a secondary side of the step-up transformer. A high-frequency heating device comprising a filament winding that generates a lighting current to the magnetron filament, wherein the filament winding generates a lighting current on the printed wiring circuit board according to an induced electromotive force generated by the step-up transformer. The conductive pattern is formed.

Also, a printed wiring circuit board having a frequency conversion circuit for converting commercial power into high frequency power and outputting the high frequency power to a step-up transformer, and the frequency conversion according to the primary side voltage provided on the primary side of the step-up transformer. In a high-frequency heating device including a timing detection winding that generates a timing signal for determining an operation timing of a circuit, the timing detection winding is provided on the printed wiring circuit board according to an induced electromotive force generated by the step-up transformer. It may be formed from a conductive pattern that outputs a timing signal.

Further, the filament winding or the timing detection winding may be divided in the conductive pattern in a direction orthogonal to the energization direction associated with the induced electromotive force.

[0010]

In the high frequency heating apparatus according to the first aspect, when high frequency power is applied to the primary side of the step-up transformer, the high frequency power is output from the secondary side and the high frequency power is rectified into DC power by the rectifier circuit. Given to the magnetron.

When high frequency power is applied to the primary side of the step-up transformer, an alternating magnetic field interlinks with the filament winding formed by the conductive pattern on the printed wiring circuit board, so that an electromotive force is generated in the filament winding. Occurs, a lighting current is output to the filament of the magnetron, and in response thereto, a high frequency is output from the magnetron.

In the high frequency heating device according to the second aspect, the frequency conversion circuit converts the commercial power into the high frequency power and outputs the high frequency power to the primary side of the step-up transformer. As a result, the timing detection coil formed by the conductive pattern on the printed wiring circuit board outputs the timing signal according to the primary side voltage to the frequency conversion circuit, so that the frequency conversion circuit performs the frequency conversion operation according to the timing signal. To execute.

Further, in the case of the high frequency heating device according to the third aspect, an eddy current is generated by the alternating magnetic field from the step-up transformer interlinking with the conductive pattern forming the filament winding or the timing detection winding, but the eddy current is generated. Since the current is divided by the conductive pattern, the eddy current loss can be reduced.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A first embodiment of the present invention will be described below with reference to FIGS. In FIG. 3 showing the electrical configuration, a cooling fan motor 13 is connected to the AC input terminals 11 and 12, and a high voltage component such as a magnetron is cooled by the air blown from the cooling fan 13 in the energized state.

A frequency conversion circuit 14 is connected to the AC input terminals 11 and 12. This frequency conversion circuit 1
Reference numeral 4 is for converting a commercial frequency into a high frequency and outputting the high frequency, and is composed of a rectifying circuit 15, a smoothing circuit 16, and a switching circuit 17.

The rectifying circuit 15 comprises a diode 18 connected in a bridge, which full-wave rectifies the AC voltage from the AC input terminals 11, 12. The smoothing circuit 16 is composed of a choke coil 19 and a capacitor 20, which rectifies the voltage including the pulsation, which is full-wave rectified by the rectifying circuit 15, into a DC voltage.

The switching circuit 17 is a step-up transformer 2.
1, a primary winding 21a, a resonance capacitor 22, a counter electromotive voltage generation preventing diode 23, a switching transistor 24, and a control circuit 25. One end of the primary winding 21a is connected to the smoothing circuit 16, and the other end is connected to the collector of the transistor 24. The transistor 24 is turned on and off by the control circuit 25, and high frequency power is generated in the primary winding 21a according to the turning on and off.

Here, the resistor 2 is provided on the input side of the smoothing circuit 16.
A voltage detection unit 28 composed of 6, 27 is connected, and its common connection point is connected to the control circuit 25. Also,
The output side of the smoothing circuit 16 is connected to the collector of the transistor 24 via the timing detection unit 31 including the resistors 29 and 30, and the common connection point of the resistors 29 and 30 is the control circuit 25.
Connected with. Further, a temperature sensor 32 is arranged near the transistor 24, which is a control circuit 25.
The temperature signal is output to.

The step-up transformer 21 is provided with a secondary winding 21b and a filament winding 21c.
b is an anode 3 of the magnetron 37 through a voltage doubler rectifier 36 composed of a capacitor 33 and diodes 34 and 35.
7a and the cathode 37b. Here, between the secondary winding 21b and the voltage doubler rectifier circuit 36, for example, an anode current detection circuit 38 constituted by a current transformer or the like.
Is provided, and its output is given to the control circuit 25. The filament winding 21c is connected to the cathode (filament) 37b of the magnetron 37.

In FIG. 4, which specifically shows the configuration of the control circuit 25, an anode current averaging circuit 39 averages the detected currents from the anode current detecting circuit 38. Error amplification circuit 40
Compares the averaged current from the anode current averaging circuit 39 with the set value Vref, and supplies the difference to the conduction time determining circuit 41. The conduction time determination circuit 41 determines the conduction start time and the conduction time width of the transistor 24, and outputs a high level signal to the AND circuit 42 at a predetermined timing based on the signal from the conduction time determination circuit 41.

The input voltage averaging circuit 43 includes a voltage detector 28.
The average voltage value is output to the comparison circuit 44. The comparison circuit 44 determines whether or not the commercial power supply voltage is in the usable range (for example, 80 V or more and 120 V or less) based on the input average voltage, and when it is within the range, a high level signal is output to the AND circuit 4.
Output to 2. Further, the temperature determination circuit 45 uses the temperature sensor 3
It is determined whether the temperature signal from 2 is within the allowable range, and if it is within the range, a high level signal is output to the AND circuit 42.
Output to.

In FIGS. 1 and 2 showing the plane and side surface of the printed wiring circuit board, a voltage doubler rectifier circuit 36 and an anode current detection circuit 38 are mounted on a printed wiring circuit board 46, and each component has a conductive pattern 47. Connected by. A hole 48 is formed at a predetermined position of the printed wiring circuit board 46, and an annular conductive pattern 49 is formed so as to surround the hole 48. One end of the conductive pattern 49 is directly connected to the diode 35 and also connected to the cathode 37b of the magnetron 37 via a lead wire (not shown). The other end of the conductive pattern 49 is connected to the cathode 3 of the magnetron 37.
7b and a lead wire (not shown). In this case, the bobbin 50 is positioned on the annular conductive pattern 49, and the bobbin 50 and the printed wiring circuit board 4 are positioned.
A transferlite core 51 is provided so as to penetrate through the holes 48 of No. 6. The primary winding 21a and the secondary winding 21b are wound around the bobbin 50, and the conductive pattern 49 on the printed wiring circuit board 46 is positioned coaxially with the bobbin 50. The pattern 49 constitutes the filament winding 21c shown in FIG. In this case, the primary winding 21a of the step-up transformer 21,
The number of turns of the secondary winding 21b and the filament winding 21c is set as shown in Table 1 below, and in the state where a high frequency voltage of 30 KHz is applied to the primary winding 21a,
The secondary winding 2 is stepped up and down by the step-up transformer 21.
The high frequency voltage and the high frequency current shown in Table 1 are generated in 1b and the filament winding 21c.

[0023]

[Table 1]

Next, the operation of the above configuration will be described. Immediately after the start of cooking, an oscillating current flows through the resonance circuit composed of the primary winding 21a of the step-up transformer 21 and the resonance capacitor 22 due to the on / off control of the transistor 24 by the control circuit 25, so that the primary winding 21a accordingly.
High-frequency voltage and high-frequency current are induced in. Then, the high frequency power induced in the primary winding 21 is increased by the step-up transformer 21.
The voltage is boosted by the secondary winding 21b and given to the voltage doubler rectifier circuit 36, and the DC power is output from the voltage doubler rectifier circuit 36 to the magnetron 37 accordingly. Therefore, a high voltage is applied between the anode 37a and the cathode 37b of the magnetron 37. DC voltage is applied.

In this case, when a high frequency voltage is generated in the primary winding 21a of the step-up transformer 21 due to the switching operation of the transistor 24 by the control circuit 25 as described above,
Due to the electromagnetic induction effect of the step-up transformer 21, an alternating magnetic field interlinks with the conductive pattern 49 on the printed wiring circuit board 46, and an induced electromotive force is generated in the alternating magnetic field. As shown, a high frequency current of 10 A is output. As a result, the cathode 37b of the magnetron 37 is turned on and high frequency is output from the magnetron 37.

In the frequency conversion operation, the control circuit 25 determines the conducting time of the transistor 24 according to the magnitude of the commercial power supply voltage. The non-conducting time of the transistor 24 depends on the transistor 24. Is determined by the energy stored according to the inductance of the step-up transformer 21 and the size of the resonance capacitor 22 within the conduction time. That is, the transistor 24
The non-conduction time is set to the timing at which the high-frequency current flowing through the primary winding 21a becomes substantially zero, and the time is set to the conduction start time of the next cycle. In this case, the conduction time determination circuit 41 always keeps the timing detection unit 3
The voltage signal corresponding to the high-frequency voltage induced in the primary winding 21a from 1 is input, and the timing at which the high-frequency current becomes zero is determined based on the voltage signal, and the AND circuit 4
The timing for outputting the high level signal to 2 is determined.

On the other hand, during the oscillation operation of the magnetron 37, the anode current averaging circuit 39 detects and averages the anode current value of the magnetron 37 from the anode current detecting circuit 38. Further, the error amplification circuit 40 compares the average current value by the anode current averaging circuit 39 with the set value Vref,
The difference is output to the conduction time determination circuit 41. in this case,
The difference between the average current value and the set value increases as the commercial power supply voltage increases. Then, the conduction time determination circuit 41 increases the transistor 24 as the difference between the error amplification circuits 40 increases.
Therefore, the anode current is controlled so as to suppress the fluctuation of the commercial power supply voltage, so that the high frequency output by the magnetron 37 becomes constant.

The input voltage averaging circuit 43 averages and outputs the detected voltage from the voltage detecting unit 28, and the comparing circuit 44 outputs the commercial power supply voltage by the input voltage averaging circuit 43 in the range of 80V to 120V. When it is out of the inside, a low level signal is output to the AND circuit 42. As a result, a low level signal is output from the AND circuit 42 to the base of the transistor 24.
Is turned off and the operation of the magnetron 37 is stopped. In this case, the lower limit value of 80V is determined because the anode current to the magnetron 37 becomes larger than the allowable value at a voltage lower than this, and the upper limit value of 120V is determined from the withstand voltage of the magnetron 37. There is.

According to the above structure, the filament winding 21c is constituted by the conductive pattern 49 formed on the printed wiring circuit board 46, and the filament winding 21c is formed.
c and the voltage doubler rectifier circuit 36 mounted on the printed wiring circuit board 46 are directly connected, the filament winding is different from the conventional example in which the secondary winding is provided in the step-up transformer. It is possible to reduce the connecting portion between the line 21c and the printed wiring circuit board 46 and omit the connecting process.

Since the work of winding the filament winding 21c around the step-up transformer 21 can be omitted,
Assembling cost and parts cost can be reduced.

FIG. 5 shows a second embodiment of the present invention,
The same parts as those in the first embodiment are designated by the same reference numerals, and the description thereof will be omitted. Only different parts will be described. The difference of the second embodiment from the first embodiment is that a timing detection winding 21d is provided on the primary side of the step-up transformer 21, and the timing detection portion 54 is composed of the timing detection winding 21d and the resistors 52 and 53. And their resistance 5
The common connection points of 2, 53 are connected to the control circuit 25.

In this case, although not shown, the timing detection winding 21d is formed of an annular conductive pattern on the printed wiring circuit board on which the frequency conversion circuit 14 is mounted, and the timing detection winding 21d is formed. And a series circuit of resistors 52 and 53 mounted on the printed wiring circuit board are directly connected.

In the case of the second embodiment, since the timing detection winding 21d is formed on the printed wiring circuit board, the work for connecting the timing detection winding 21d and the printed wiring circuit board is performed as in the first embodiment. Can be omitted.

FIG. 6 shows a third embodiment of the present invention,
In the third embodiment, the conductive pattern forming the filament winding 21c or the timing detection winding 21d is divided in the direction orthogonal to the energization direction. In this case, even if an eddy current is generated in the conductive pattern due to the alternating magnetic field generated by the step-up transformer 21, the eddy current can be divided, so that the eddy current loss generated in the conductive pattern can be reduced.

[0035]

As is apparent from the above description, the high frequency heating apparatus of the present invention has the following effects.

According to the high frequency heating device of the first and second aspects, since the filament winding or the timing detection winding is formed by the conductive pattern on the printed wiring circuit board, the filament winding or the timing detection winding and these With a printed wiring circuit board on which electronic components to be connected are mounted, the work of connecting the filament winding or the timing detection winding to the printed wiring circuit board can be omitted, and the number of components is reduced. Assembling cost and parts cost can be reduced.

According to a third aspect of the high-frequency heating apparatus of the present invention, in the high-frequency heating apparatus of the first and second aspects, the conductive pattern forming the filament winding or the timing detection winding is in the energizing direction thereof. Since it is divided in the orthogonal direction, the eddy current loss generated in the conductive pattern can be reduced.

[Brief description of drawings]

FIG. 1 is a plan view of a printed wiring circuit board showing a first embodiment of the present invention.

FIG. 2 is a vertical sectional view of a printed wiring circuit board.

FIG. 3 is a schematic circuit diagram showing a schematic configuration

FIG. 4 is a block diagram showing a configuration of a control circuit.

FIG. 5 is a view corresponding to FIG. 3 showing a second embodiment of the present invention.

FIG. 6 is an enlarged view of a filament winding showing a third embodiment of the present invention.

FIG. 7 is a view corresponding to FIG. 2 showing a conventional example.

[Explanation of symbols]

14 is a frequency conversion circuit, 15 is a smoothing circuit, 17 is a switching circuit, 21 is a step-up transformer, 21a is a primary winding,
24 is a switching transistor, 25 is a control circuit,
28 is a timing detector, 21b is a secondary winding, 21c is a filament winding, 46 is a printed circuit board, 49
Is a conductive pattern, and 21d is a timing detection winding.

Claims (3)

[Claims] 1. A printed wiring circuit board provided on a secondary side of a step-up transformer and having a rectifying circuit for applying a DC voltage to a magnetron, and a lighting current to a filament of the magnetron provided on a secondary side of the step-up transformer. In a high-frequency heating device including a filament winding that generates a filament winding, the filament winding is formed of a conductive pattern that is formed on the printed wiring circuit board and that generates a lighting current according to an electromotive force induced by the step-up transformer. High-frequency heating device characterized by. 2. A printed wiring circuit board having a frequency conversion circuit for converting commercial power into high frequency power and outputting the high frequency power to a step-up transformer; and the frequency conversion according to the primary side voltage provided on the primary side of the step-up transformer. In a high-frequency heating device including a timing detection winding that generates a timing signal for determining an operation timing of a circuit, the timing detection winding is formed on the printed wiring circuit board, and an induced electromotive force generated by the step-up transformer. A high-frequency heating device comprising a conductive pattern that outputs a timing signal in accordance with the above. 3. The filament winding or the timing detection winding is formed by dividing a conductive pattern in a direction orthogonal to a current-carrying direction associated with an induced electromotive force.
Alternatively, the high frequency heating device according to claim 2.