JPH0432186A - High frequency heat-cooking apparatus - Google Patents

Abstract

PURPOSE:To obtain a high frequency heat-cooking apparatus wherein a power source circuit of a control circuit of a frequency converter can be inexpensively formed in a compact size by rectifying and supplying a high frequency output from the frequency converter by means of a rectifying circuit as a power source for operating the control circuit of the frequency converter. CONSTITUTION:A power source circuit 31 for operating a control circuit 10 of a frequency converter 1 is provided with a rectifying circuit 32 for rectifying a high frequency output on receipt of the high frequency output from the frequency converter 1. The rectifying circuit 32 is constituted similar to a so-called half-wave rectification type voltage doubler rectifying circuit, that is, it comprises two capacitors 33, 34 and two diodes 35, 36. The capacitor 33 on an input side is connected between a primary coil 6a of a step-up transformer 6 and a resonance capacitor 7. The capacitor 33 and a series circuit of the diode 35 are connected in parallel to the resonance capacitor 7.

Description

[Detailed Description of the Invention] [Objective of the Invention] (Industrial Application Field) The present invention converts a commercial power source into a high-frequency power source using a frequency converter, and supplies the high-frequency output to a magnetron via a step-up transformer. The present invention relates to a high-frequency heating cooking device that drives.

(Prior Art) Conventionally, a high-frequency heating cooking apparatus equipped with this type of frequency converter has a step-down transformer 51 and a rectifier circuit 52 as a power supply circuit for operating a control circuit of the frequency converter, as shown in FIG. A rectifier circuit 52 was provided to supply direct current a from the rectifier circuit 52 to the control circuit.

(Problems to be Solved by the Invention) In the above conventional configuration, the step-down transformer 51 must be provided in addition to the rectifier circuit 52 as a power supply circuit for the control circuit of the frequency conversion section, which increases the size and cost of the power supply circuit. It had the disadvantage of becoming

The present invention has been made in consideration of such circumstances, and an object thereof is to provide a high-frequency heating cooking device that can make the power supply circuit of the control circuit of the frequency converter more compact and lower in cost.

[Configuration of the Invention (Means for Solving the Problems) The high-frequency heating cooking device of the present invention comprises: a frequency conversion section having a control circuit for controlling the conduction time width of a switching element that converts a commercial power supply frequency into a high frequency; In a device comprising a step-up transformer that steps up the high-frequency output from the frequency converter and a magnetron connected to the secondary side of the step-up transformer, the frequency converter serves as a power source for operating a control circuit of the frequency converter. The high frequency output is rectified by a rectifier circuit and then supplied.

In this case, after the start of supply of commercial power to the frequency converter and until the output of the frequency converter is converted into a high frequency, the frequency converter serves as a power source for operating the control circuit of the frequency converter. The DC output may be supplied via a resistor.

(Function) During operation of the magnetron, the high frequency output of the frequency converter is supplied to the magnetron via the step-up transformer, and a part of the high frequency output of the frequency converter is rectified by the rectifier circuit to control the frequency converter. Supplied as power for the circuit. Therefore, the step-down transformer, which is indispensable for conventional power supply circuits, is not required in the present invention, and the power supply circuit is made more compact and lower in cost.

In this case, after the supply of commercial power to the frequency converter starts, there will be a slight time delay until the output of the frequency converter is converted to a high frequency, but during that time, the DC output of the frequency converter is connected to the resistor. If the frequency converter is supplied to the control circuit via the converter, the output of the frequency converter can be used as a power source for the control circuit during that time.

(Example) Hereinafter, a first example of the present invention will be described with reference to FIGS. 1 to 3.

Reference numeral 1 denotes a frequency converter that converts a commercial power supply frequency to a high frequency, and a rectifier circuit 2 that full-wave rectifies the AC voltage of the commercial power supply connected to terminals t1 and t2, and smoothes the full-wave rectified voltage to obtain a DC voltage. The filter 5 includes a choke coil 3 and a capacitor 4. The oscillation circuit for frequency conversion is composed of a primary winding 6a of a step-up transformer 6, a resonant capacitor 7, a switching transistor 8 and a diode 9 as switching elements, and a control circuit 1o controls switching transistor 8 on and off. As a result, a high frequency current is generated in the primary winding 6a of the step-up transformer 6.

As a result, in the magnetron drive unit 11, a high frequency voltage is induced in, for example, two secondary windings 6b and 6c of the step-up transformer 6, and the high frequency voltage induced in the secondary winding 6b is transmitted to the diode 12 and the smoothing capacitor 13
The magnetron 15 is connected through a voltage doubler rectifier circuit 14 consisting of
A voltage is applied between the anode and the cathode of the secondary winding 6c, and a voltage induced in the secondary winding 6c is applied to the cathode. Furthermore, an anode current detection circuit 18 consisting of a current transformer is provided in the current conduction path on the anode side of the magnetron 15. on the other hand,
A conduction timing detection circuit 21 constituted by a voltage dividing circuit including resistors 19 and 20 is connected in parallel to the primary winding 6a of the step-up transformer 6, and a conduction timing detection circuit 21 is connected in parallel to the primary winding 6a of the step-up transformer 6. In order to detect the magnitude, a power supply voltage detection section 24 constituted by a voltage dividing resistor circuit including resistors 22 and 23 is connected to the DC output side of the rectifier circuit 2.

Next, a specific configuration of the control circuit 10 for controlling the switching transistor 8 on and off will be described with reference to FIG. 2. The detected current 1a from the anode current detection circuit 18 is rectified and smoothed for one cycle by the current averaging circuit 25, and the average anode current value I
The aV signal is compared with a set value Vr by an error amplifier 26. The difference signal S1 is then supplied to the conduction timing determining circuit 27. This conduction timing determining circuit 2
7 is for determining the conduction start time and conduction time width of the switching transistor 8, and outputs a base signal S3 at a predetermined timing based on the voltage waveform signal S2 received from the conduction timing detection circuit 21. . This base signal S is supplied to the base of the switching transistor 8 via the AND gate 28.

On the other hand, the detected voltage Va from the power supply voltage detection section 24 is
The voltage is averaged by being rectified and smoothed for one period by the voltage averaging circuit 29, and the average voltage value is provided to the voltage range comparator 30. This voltage range comparator 3o determines whether the commercial power supply voltage belongs to the usable range (in this embodiment, the range of 80 V or more and 120 V or less) from the input average voltage, and if it is outside the range, it will be set to low level. A stop signal S4 is output to the AND gate 28 to make it non-conductive.

Next, based on FIG. 1, the control circuit 10 of the frequency converter 1
The configuration of the power supply circuit 31 that operates the will be explained. This power supply circuit 31 includes a rectifier circuit 32 that receives the high frequency output of the frequency converter 1 and rectifies it. This rectifier circuit 32 has a configuration similar to a kind of half-wave rectifier voltage doubler rectifier circuit, and includes two capacitors 33, 34 and 2.
It consists of two diodes 35 and 36. The input side capacitor 33 is connected to the primary winding 6a of the step-up transformer 6.
A series circuit of this capacitor 33 and a diode 35 is connected in parallel to the resonance capacitor 7. Then, the diode 3 is connected from the common connection point 37 between the capacitor 33 and the diode 35.
6, and both terminals of this capacitor 34 serve as both output terminals of the rectifier circuit 32.

A constant voltage diode 39 is connected between both output terminals of the rectifier circuit 32 via a resistor 38, thereby making the output voltage constant. Furthermore, this constant voltage diode 39
A smoothing capacitor 40 is connected to the latter stage, and DC power smoothed by this is supplied to the control circuit 10 as a power source.

On the other hand, the output side of the filter 5 is connected to the common connection point 37 in the rectifier circuit 32 via the resistor 40, so that after the commercial power supply starts to be supplied to the frequency converter 1, the output of the frequency converter 1 is Until it is converted to a high frequency, the DC output of the frequency converter 1 (output of the filter 5) is supplied via a resistor 41 as a power source for operating the control circuit 10.

In addition, both terminals of commercial power supply 1. ．． A motor 42 that drives a cooling fan (not shown) of the magnetron 15 and an interior light 43 are connected in parallel between the magnetron 12 and the refrigerator 12 .

Next, the operation of the above configuration will be explained.

When the user operates a cooking start switch (not shown) to start supplying commercial power to the frequency converter 1, the AC current from the commercial power is rectified by the rectifier circuit 2 and boosted through the filter 5. The current flows into the primary winding 6a of the transformer 6.

Then, the control circuit 10 turns on and off the switching transistor 8 to convert the output of the frequency converter 1 into a high frequency to operate the magnetron 15. After the power is turned on, the control circuit 1o finishes the initialization operation. There is a slight time delay until the on/off control of the switching transistor 8 is started. Therefore, immediately after the power is turned on, the output of the frequency converter 1 is DC.
After the supply of commercial power supply power is started, there is a slight time delay before the output of the frequency converter 1 is converted to a high frequency.

Therefore, while the output of the frequency converter 1 is DC immediately after the power is turned on, a part of the DC output of the frequency converter 1 is supplied as a power source to the control circuit 10 in the following manner. That is, the DC output of the frequency converter 1 (output of the filter 5) is supplied to the power supply circuit 31 via the resistor 41, charged to two capacitors 34 and 40 and smoothed, and outputted by the constant voltage diode 39. The voltage is made constant and supplied to the control circuit 10. Using this as a power source, the control circuit 1
0 executes the initialization operation.

Thereafter, when the control circuit 10 finishes the initialization operation and starts on/off control of the switching transistor 8, the output of the frequency converter 1 is converted to a high frequency and the magnetron 1
5 starts. After this, a part of the high frequency output of the frequency converter 1 is supplied as a power source to the control circuit 10 in the following manner. That is, when the output of the frequency converter 1 is converted to a high frequency, a high frequency voltage as shown in FIG. 3 is generated across the resonance capacitor 7, and this high frequency voltage is rectified by the rectifier circuit 32 of the power supply circuit 31. Ru.

This rectification effect occurs during a half cycle in which the potential on the a side of the resonant capacitor 7 in FIG. When the potential becomes high, the capacitor 33 is discharged, the diode 36 becomes conductive, and the capacitor 34 is charged. By repeating such an operation every half cycle, a DC voltage is generated across the capacitor 34, and this DC voltage is regulated by the voltage regulator diode 39, and is charged to the capacitor 40 and smoothed. Control circuit 1
0. Using this as a power source, the control circuit 10 executes on/off control of the switching transistor 8 as described later, and starts the operation of the magnetron 15.

That is, an oscillating current flows through the oscillating circuit consisting of the primary winding 6a of the step-up transformer 6 and the resonant capacitor 7 due to the on/off control of the switching transistor 8, and the high-frequency voltage V induced in the primary winding 6a and FIG. 3 shows the state of the high frequency current 11. Such a high frequency voltage V1 is further boosted by the step-up transformer 6 and supplied to the magnetron 15 to drive it. In this frequency conversion operation, the switching transistor 8
The conduction time width T1 is forcibly controlled by a gate signal S1 so as to correspond to the magnitude of the commercial power supply voltage, which will be described later. It is determined by the energy stored in the inductance and the size of the resonance capacitor 7. That is, the non-conduction time of the switching transistor 8 is set until the timing To when the high frequency current 11 becomes approximately zero, and this time To is also the time when the next period of conduction starts. The conduction timing determination circuit 27 receives the voltage waveform signal S2 of the high frequency voltage v1 from the constant timing detection circuit 21, and from the voltage value Vo in this signal S2,
Determine the timing To when the high frequency current 11 becomes zero,
The timing for outputting the gate signal S is obtained.

On the other hand, during the oscillation operation of the magnetron 15, the anode current value 1a of the magnetron 15 is detected by the anode current detection circuit 18, this anode current value 1a is averaged by the current averaging circuit 25, and the average anode current value I av The error amplifier 26
It compares it with the set value Vr and outputs a difference signal S1 according to the difference. This difference signal S1 is applied to terminal 1. ．． The higher the commercial power supply voltage applied to the base signal S12, the larger the value becomes.The conduction timing determining circuit 27 sets the time width of the base signal S4 so that the conduction time width of the switching transistor 8 becomes shorter as the difference signal S1 becomes larger. Control. This prevents the anode current from increasing as the voltage increases.In other words, the anode current is controlled to decrease and increase as the commercial power supply voltage rises and falls, so that it does not respond to fluctuations in the commercial power supply voltage. On the other hand, the high frequency output is made constant.

Further, in parallel with this operation, the voltage range comparator 30 converts the detected voltage Va from the power supply voltage detection section 24 into the voltage averaging circuit 2.
9, and the commercial power supply voltage is 80V or higher 12
When it is out of the range of 0V or less, a stop signal S4 is output to cut off the AND gate 28, stop the on/off operation of the switching transistor 8, and turn off the magneto.
Stop the operation of Ron 15. In this case, the lower limit value is 80V
If the voltage is lower than this, the anode current of the magnetron 15 will become excessive, and the upper limit value of 120V
It is determined to be the upper limit of the withstand voltage.

According to the embodiment described above, while the magnetron 15 is in operation, a part of the high frequency output of the frequency converter 1 is transferred to the rectifier circuit 3.
2 and is supplied as the power to the control circuit 10 of the frequency converter 1, so the step-down transformer that is essential to conventional power supply circuits is not required in this embodiment, and the power supply circuit 31 is made more compact accordingly.・Cost can be reduced.

In this case, after the start of supply of commercial power to the frequency converter 1, there will be a slight time delay until the output of the frequency converter 1 is converted to a high frequency, but during that time, the frequency converter 1
Since the DC output is supplied to the control circuit 10 via the resistor 41, the output of the frequency converter 1 can be used as a power source for the control circuit 10 during that time as well.

Note that in the first embodiment, the rectifier circuit 32 of the power supply circuit 31
The capacitor 33 of the rectifier circuit 32 is connected to one end of the resonance capacitor 7, but as in the second embodiment of the present invention shown in FIG. You may also connect it.

Further, in the first embodiment, the usable range of the commercial power supply voltage is set to 80 V or more and 120 V or less, but for example, 10
The magnetron 15 can be used in the range of 80V or more and 260V or less so that it can be used with either 0V or 200V commercial power supply.
It may be configured such that it can be driven.

[Effects of the Invention] As is clear from the above description, during the operation of the magnetron, a part of the high frequency output of the frequency converter is rectified by the rectifier circuit and is supplied as power to the control circuit of the frequency converter. Therefore, a step-down transformer, which is indispensable for conventional power supply circuits, is not required in the present invention, and the power supply circuit can be made more compact and lower in cost.

In this case, after the start of supply of commercial power to the frequency converter, there will be a slight time delay until the output of the frequency converter is converted to a high frequency, but during that time, the DC output of the frequency converter is passed through the resistor. During this time, the output of the frequency converter can be used as a power source for the control circuit.

[Brief explanation of the drawing]

1 to 3 show a first embodiment of the present invention, in which FIG. 1 is an electric circuit diagram of the high-frequency heating cooking device, FIG. 2 is a block diagram showing details of the control circuit, and FIG. 3 is a block diagram showing details of the control circuit. 1 is a diagram showing the relationship between high frequency voltage and high frequency current in the primary winding of a step-up transformer. FIG. 4 is a diagram corresponding to FIG. 1 showing a second embodiment of the present invention, and FIG. 5 is a diagram showing the configuration of a conventional power supply circuit. In the drawing, 1 is a frequency conversion section, 6 is a step-up transformer, 7 is a resonant capacitor, 8 is a switching transistor (switching element), 15 is a magnetron, 18 is an anode current detection circuit, 24 is a power supply voltage detection section, and 25 is a current An averaging circuit, 26 an error amplifier, 27 a conduction timing determining circuit, 29 a voltage averaging circuit, 30 a voltage range comparator, 31
32 is a rectifier circuit, and 41 is a resistor. Applicant: Toshiba Corporation

Claims (1)

[Claims] 1. A frequency converter having a control circuit that controls the conduction time width of a switching element that converts a commercial power supply frequency to a high frequency, a step-up transformer that boosts the high-frequency output from the frequency converter, and In a high-frequency heating cooking device equipped with a magnetron connected to the secondary side of a step-up transformer,
As a power source for operating the control circuit of the frequency converter,
A high-frequency heating cooking device, characterized in that the high-frequency output of the frequency conversion section is rectified and supplied by a rectifier circuit. 2. After the start of supply of commercial power to the frequency converter, until the output of the frequency converter is converted to high frequency,
As a power source for operating the control circuit of the frequency converter,
2. The high-frequency heating cooking apparatus according to claim 1, wherein the DC output of the frequency conversion section is supplied through a resistor.