JP3152202B2 - High frequency heating equipment - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to power control of a power supply for driving a magnetron of a high-frequency heating apparatus using a magnetron.

[0002]

2. Description of the Related Art FIG. 10 is a circuit diagram of a main part of a conventional high-frequency heating device. Reference numeral 25 denotes a device control circuit that controls the entire device. Reference numeral 32 denotes a magnetic leakage type step-up transformer having a silicon steel sheet as a core. When the relay 31 that is turned on / off by the command signal of the device control circuit 25 from the commercial power supply 1 is turned on, the voltage of the commercial power supply frequency is applied to the primary winding 28 of the step-up transformer 32 and the secondary winding 29 is High pressure is generated.
One end of the secondary winding 29 is a chassis ground 26. Further, a half-wave voltage is applied by the high voltage circuit 16 including the capacitor 33 and the diode 34, and the magnetron 24
A high voltage of about 4 kV is generated between the anode and the cathode every half cycle of the power supply frequency. Here, the cathode at one end of the diode 34 is the chassis ground 26.

On the other hand, the magnetron 2
Electric power is supplied to the heater No. 4 and the cathode is directly heated, thereby making the emission of electrons easy.

[0004] In this case, too, the anode at one end of the diode 34 is a chassis ground 26, so that when the cut-off voltage of the magnetron is exceeded, electrons emitted from the cathode reach the anode, and the high voltage circuit and the secondary winding 29 To form a closed loop, and a magnetron current (anode current) flows between the anode and the cathode. The electric power generated at this time is converted into microwaves with a certain conversion efficiency, and the food in the oven storage is dielectrically heated.

[0005] This is the most commonly used driving power supply circuit for microwave ovens at present. In this circuit, as the aging of the operation proceeds, the temperature of the magnet of the magnetron rises, and the cutoff voltage described above decreases. However, due to the electrical characteristics of the magnetic leakage type step-up transformer, the anode current is fixed at a substantially constant level with a slight increase, and the input current gradually decreases until the temperature is saturated.

FIG. 11 is a circuit diagram of a main part of a conventional high-frequency heating device. This is a magnetron driving power supply using a single-type voltage resonance type inverter circuit. 1 is a commercial power supply, and 2 is a diode bridge that performs full-wave rectification to obtain a DC power supply by performing full-wave rectification on the commercial power supply 1. The choke coil 3 smoothes the fluctuation of the current, and the smoothing capacitor 4 smoothes the fluctuation of the voltage. The rectifying filter unit 5 composed of these capacitors, inductors and diode bridges supplies a unidirectional voltage to a subsequent circuit. Energy is accumulated from the rectifying filter unit 5 to the winding of the magnetic leakage type step-up transformer 7. The primary winding 28 of the step-up transformer 7 and the resonance capacitor 6 arranged in parallel with it constitute a tank circuit, and resonate with the energy stored in the winding of the step-up transformer 7. Switching means including a semiconductor switching element 8 and a diode 9 arranged in parallel with the semiconductor switching element 8 are connected in series to the tank circuit. The AC power of the commercial power frequency is converted to a high frequency power by the inverter unit 10 constituted by the tank circuit and the switching means shown here.

The secondary side of the step-up transformer 7 has a secondary winding 29
And a tertiary winding 30. The voltage induced in the secondary winding 29 includes capacitors 14, 15 and diodes 12, 1
3 is converted to a DC high voltage by the high voltage circuit 16 which functions as a full wave voltage doubler rectifier circuit comprising
A high voltage of about 4 kV is applied between the anode and the cathode. In this way, the inverter power supply circuit 18 as the power supply for driving the magnetron is configured.

The first current transformer 17 detects the anode current flowing through the magnetron 24 and the other current flowing through the branch of the high voltage circuit 16 as a voltage generated in its secondary winding, and controls the inverter power supply circuit 18. The signal is transmitted to the inverter control unit 11.

The first current transformer 17 has a circuit system such as a high voltage circuit 16 having a chassis ground 26 connected to the equipment chassis and having a ground potential, and a ground 27 comprising an emitter line of the semiconductor switching element 8.
Has a function of transmitting a signal by electrically insulating the inverter control unit 11 having a ground potential. Here, as the detection current on the primary side of the first current transformer 17, an average current of about several hundred mA flows.

The inverter control section 11 controls the ON time of the semiconductor switching element 8 by performing negative feedback control so that the signal from the secondary side of the first current transformer 17 becomes substantially constant, and boosts the voltage from the inverter section 10. The power transmitted to the secondary side of the transformer 7 is controlled.

Further, a signal transmitted from the device control circuit 25 is transmitted to the inverter control unit 1 using the photocoupler 19.
1 and electrically insulated.

Also in this case, according to the control law, when the operation aging is performed, the anode current is fixed at a substantially constant level in the form of a slight increase as in the above-described conventional example, and the input current gradually decreases until the temperature is saturated. .

This gradual decrease characteristic is a control in which the input current is reduced and the rating is reduced by reducing the input current when the temperature rises, so that the temperature duty of each electric component is reduced. I can say something. Especially when the equipment is installed in a closed state and the cooling air intake and exhaust are delayed and the cooling capacity is reduced, the environment becomes extremely severe in terms of temperature.However, the input current also drops significantly and each electrical component of the equipment is excessively The temperature can be prevented from rising.

[0014]

However, in the conventional magnetron drive power supply as shown in FIGS. 10 and 11, since the input current of the device gradually decreases as described above, the temperature of the device can be sufficiently increased in the atmosphere. 1.5 to 2.0 from the familiar cold state to the start of operation and temperature saturation
A has also been found to decrease. Further, in the Electrical Appliance and Material Control Law, the timing of measuring the high-frequency output is this temperature saturation state.

[0015] On the other hand, current breaker, which is installed in the indoor wiring is generally Japan is the upper limit of 15A.
It is a fact that many users still use the 15A breaker. When a fuse having a rating of 15A is used, the input current is not allowed to exceed 15A . Therefore, it is an indispensable restriction to use an input current within 15 A in electrical equipment in Japan.

In view of the above, considering a high-frequency heating device having a large high-frequency output, if the high-frequency output is determined at time (b) as shown in FIG. As shown in the above, the current exceeds 15 A, and the above-described restriction on the input current in the market cannot be observed.

In other words, there is a constraint that the design must be made to be slightly less than 15 A at the start of heating. Unless a power supply, a magnetron, and a food supply system with high efficiency for converting input power into high-frequency output is achieved, the maximum high-frequency output is limited to 700 W at most, which is an obstacle to increasing the output of a high-frequency heating device. On the other hand, if the control is performed with a constant input current, it is not possible to use the power gradual decrease characteristic which is very small for the equipment, and it is disadvantageous in satisfying the temperature performance.

[0018]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, the present invention provides a magnetron drive system in which a microcomputer provided in a device control circuit for controlling the entire high-frequency heating apparatus has a predetermined high-frequency output set value. A second current transformer for detecting the current input to the power supply for use, and the detected current value is converted to a DC voltage. The output of the input current detection circuit is controlled to be constant by negative feedback control, thereby controlling the input current to be constant. I do. Other than that, the microcomputer uses a signal detected by the first current transformer to negatively control the current flowing in the branch of the high-voltage circuit, thereby controlling the current to be constant.

According to the invention, when the high-frequency output is high and the input current may exceed 15 A, the output of the input current detection circuit is controlled to a value not exceeding 15 A by negative feedback control. Limit the input current by 1
5A constraints can be observed.

On the other hand, when the operation aging proceeds to some extent,
Negative feedback control is selected so that the current flowing through the branch of the high-voltage circuit is constant, and thereafter, the power control is switched to a conventional power control having a gradually decreasing characteristic, and the temperature is reduced to a temperature saturation value.

As described above, by adding the function of limiting the input current to a constant value, the output can be increased as much as possible within the input current limit frame of 15 A without fear of breaking the current breaker. Become. Also, depending on the selection of the control loop, it is possible to positively utilize the gradually decreasing characteristic of the electric power, which has a very small burden on the device.

Further, for a model which can sufficiently enter the input current limit frame of 15 A, the input current detection circuit is removed, and the power of the negative feedback control is set such that the current flowing in the branch of the high voltage circuit becomes constant. It can be realized as a device with control and can achieve the commonality that the same magnetron drive power supply can be used, while exhibiting a great economic effect by reducing the number of circuits in design freedom.

[0023]

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a magnetron for radiating microwaves, a rectifying filter section for performing full-wave rectification on a commercial power supply and removing a high-frequency component to convert the commercial power supply into a DC power supply, and at least one semiconductor switching element. An inverter that turns on / off the DC power supply to convert it to high-frequency power, a step-up transformer that steps up the high-frequency power of the inverter, and a rectifier or multiplied voltage rectifier that converts the output of the step-up transformer into a high-voltage DC voltage and converts it into a magnetron. A magnetron drive power supply including a high-voltage circuit for applying a high-voltage DC voltage, a first current transformer for detecting a current flowing in a branch of the high-voltage circuit, and an inverter control unit for turning on / off the semiconductor switching element; An equipment control circuit that controls the entire high-frequency heating device equipped with a microcomputer, and a power supply for driving the magnetron A second current transformer for detecting a current input, the detected current value and an input current detecting circuit for converting the DC voltage, branch of the high-voltage circuit in the signal detected by the first current transformer using a microcomputer High-frequency output to determine whether the current flowing in the circuit is controlled to be constant by negative feedback control, or the input current detection circuit is negatively controlled by negative feedback control of the input current to the magnetron drive power supply. The configuration is changed in accordance with the set value.

Therefore, when the total input current is high, the negative feedback control in which the current input to the magnetron driving power supply is constant, that is, the input current is constant is selected. By selecting negative feedback control that keeps the current flowing in the path constant, the function of suppressing the generation of the initial excessive input current while maintaining the gradually decreasing characteristic is realized, and it is easy to increase the output of the high-frequency heating device. be able to.

On the other hand, for a model which can sufficiently enter the input current limit frame of 15 A, the input current detection circuit is removed and negative feedback control is performed so that the current flowing in the branch of the high voltage circuit becomes constant. It can be realized as a device with power control, and it can be realized while exhibiting a great economic effect by reducing the number of circuits in design freedom and a common use that a magnetron drive power supply can be the same as it is.

The present invention also has a short-time high-output function,
At least at the time of the high-frequency output set value, the input current to the magnetron drive power supply is controlled to be constant by negative feedback control.

Therefore, at the time of short-time high output, constant negative feedback control can be performed at least so that the total input current does not exceed 15 A, and no problem occurs due to an excessive input current exceeding 15 A. For high-frequency output values other than short-time high-power output, select negative feedback control to keep the current flowing in the branch of the high-voltage circuit constant under severe temperature conditions, and take advantage of the gradually decreasing characteristics. Thus, the duty on parts can be gradually reduced, and the reliability can be improved by derating the parts.

According to the present invention, the input current detection circuit is configured to detect the input current of the entire device.

As for the total input current of the equipment, there is a possibility that offset currents such as a control circuit, cooling, lamp, etc., other than the current of the power supply for driving the magnetron, also fluctuate or include variations from part to part. Therefore, by performing constant control including these total input currents, more accurate input current limitation can be realized.

[0030]

Embodiment (Embodiment 1) Hereinafter, an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a circuit diagram of a power supply for driving a magnetron according to an embodiment of the present invention. In FIG. 11, the same functions and the same parts are denoted by the same reference numerals and their description is omitted.

The difference from the conventional example is that the current transformer for detecting the circuit current includes a second current transformer 35 in addition to the first current transformer 17, and the input current detection circuit 62 feeds back to the equipment control circuit 26. There.

The first current transformer 17 is a high-voltage circuit 1
The current of the diode 13 is detected. This current has an average current that is substantially proportional to the anode current.

The second current transformer 35 heats the food table to reduce the current flowing to the magnetron drive power supply of the device, the lamp for illuminating the interior, the current flowing to the device control circuit 25, and the radio wave unevenness. The current flowing through the inverter power supply circuit 18 excluding the current flowing through the device load 61 such as a turntable motor to be rotated is detected.

A load resistor 36 is arranged in parallel with the first current transformer 17. The voltage at both ends represents a voltage waveform that matches the AC component of the current flowing on the primary side of the current transformer 17. This is full-wave rectified by the diode bridge 37, and a smooth average waveform from which high-frequency components have been removed by the low-pass filter 59 formed by the resistor 39 and the capacitor 59 is obtained at both ends of the capacitor 59. Incidentally, the discharge resistor 38 discharges the charge of the capacitor 59.

The voltage across the capacitor 36 is coupled to the second connector 21 and input to the device control circuit 25.
Here, terminal (b) is a signal. The terminal (c) serves as a base line and is connected to the GND line of the device control circuit 25. The terminal (a) is connected to a signal line for transmitting a control signal for driving the inverter control unit 11 via the photocoupler 19 after performing signal processing in the device control circuit 25.

On the other hand, a load resistor 41 is arranged in parallel with the second current transformer 35. The voltage at both ends represents a voltage waveform that matches the AC component of the current flowing on the primary side of the current transformer 35. This is diode bridge 4
2, a smooth average waveform is obtained at both ends of the capacitor 45 from which high-frequency components have been removed by a low-pass filter 60 formed by a resistor 44 and a capacitor 45. Similarly, the discharge resistor 43 discharges the charge of the capacitor 45. Here, the voltage across the capacitor 45 represents the total input current flowing through the device and is coupled to the device control circuit 25.

Here, the device control circuit 25 performs the negative feedback control and performs the power control of the inverter power supply circuit 18 with the function shared with the inverter control unit 11, and also has the function of the control unit that controls the entire device. ing.

In recent years, control using a microcomputer has become mainstream, and control using a microcomputer is used in the present embodiment in the present invention. By doing so, since the entire power control function is included as a program in the microcomputer, the circuit scale (mounting area) does not increase at all by transferring the function of the inverter control unit 11 to the device control circuit 25. Breakthrough effects can be found. First. FIG. 2 shows the power control of the present invention in the device control circuit 25 including the microcomputer.
This will be described with reference to FIG.

The AC current Ia flowing through the first current transformer 17 is converted into a voltage by a resistor 36 at both ends of the secondary winding with a predetermined gain. A high-frequency component of ripple is removed by a low-pass filter 59 composed of an integrating circuit composed of a resistor 39 and a capacitor 40 and a discharge resistor 38, and a voltage having a fluctuation of a power supply cycle is present in the equipment control circuit 25. 1 is input to the A / D converter 47, and the average value of the signal is read. The output of the first A / D converter 47 is set to Viad.

An input current Iin, which is an alternating current flowing through the second current transformer 35, is connected to a resistor 41 at both ends of the secondary winding.
Is converted to a voltage with a predetermined gain. The high-frequency component of the ripple is removed by the low-pass filter 60 composed of an integrating circuit composed of the resistor 44 and the capacitor 45 and the discharge resistor 43, and the voltage having the fluctuation of the power supply cycle is present in the device control circuit 25. 2 is input to the A / D converter 49, and the average value of the signal is read. The output of the second A / D converter 49 is Vii
n.

On the other hand, the reference value 39 for determining the magnitude of the microwave output is expressed as Vref. The microcomputer 46 performs the operation of (Vfef-Viad), and the operation result is input to the first conversion function unit 51. The first conversion function unit 51 calculates and converts the small fluctuation value dD from (Vfef-Viad) and outputs the result to the integration unit 56 via the switch 55. The integrator 56 performs integration by cumulatively adding dD, and the time resolution of integration is V
iad reads the average value, and since the input of the first and second A / D converters has a half cycle of the power supply cycle, it calculates every half power supply cycle. Operation result Idd
(∫ dDdt) is converted into a PWM signal having a duty ratio τ in accordance with the Idd the PWM signal 57.

The limit value 50 for determining the magnitude of the input current to the inverter power supply circuit 18 is expressed as a limit. The microcomputer 46 is (Vii
(n-limit) operation, and the operation result is input to the second conversion function unit 52. The second conversion function unit 52 calculates and converts the minute fluctuation value dD from (Viin-limit), and outputs it to the integration unit 56 via the switch 55. The integrator 56 performs integration by accumulating and adding dD, and the time resolution of integration is such that Viin reads the average value and the input of the first and second A / D converters is a half cycle of the power supply cycle. Calculate every half power cycle. Operation result Idd (∫ dDdt) the PWM signal unit 5
In step 6, the signal is converted into a PWM signal having a duty ratio τ according to Idd.

FIG. 3 shows the τ shown here and the behavior as a device. (A) is a diagram showing the relationship between the integration output Idd output from the integration unit 56 and the duty ratio τ of the PWM signal output from the PWM signal unit 57, which is proportional. Next, FIG. 2B shows the relationship between the duty ratio τ of the PWM signal and the current to be controlled (the current flowing in the branch of the high voltage circuit or the input current of the inverter power supply circuit 18). This is also in a proportional relationship. Therefore, the current, that is, the power (high-frequency output) handled by the inverter power supply circuit 18 changes in proportion to the output of the integration section 56.

Here, the function of the conversion function section will be described.
FIG. 4 is a diagram illustrating the input / output relationship of the first conversion function unit 51. The figure shows an example in which the argument (Vref-Viad) is used. A plurality of range groups are provided for this argument. If the argument is less than -1 or -2, function output d
D is -1, +1 when the argument is +1 to +2, -1
0 to +1, -2 if the argument is -2 to -4, +2 if the argument is +2 to +4, -5 if the argument is less than -4, +5 if the argument is more than +4 Is set to As described above, the output values are weighted for the respective range groups. FIG. 5 shows a time-series change of each parameter in the microcomputer 46 when this conversion function is used. (A) As shown in the figure, when the Vref of the reference value 48 for determining the high-frequency output changes at a certain timing, it shows how each parameter changes accordingly. The movement of dD behaves as shown in FIG. Idd and τ are as shown in waveforms (d) and (e) obtained by cumulatively adding them. PWM
The drive of the inverter power supply circuit 18 is controlled by the signal, resulting in a Viad waveform as shown in FIG.

When (Vref-Viad) is large, the amount of negative feedback becomes large, so that the parameter Viad representing the high-frequency output quickly approaches the target value and is stabilized.

Although the description has been given along the signal flow of the first current transformer 17, the characteristics are exactly the same even along the signal flow of the second current transformer 35.

Returning to FIG. 2, the microcomputer 46
Can control the switch 55 to "L" or "H" while controlling the power of the device. In the case of "H", the input current of the inverter power supply circuit 18 is controlled to be constant. On the other hand, when "L" is selected, the current flowing in the branch of the high voltage circuit, that is, equivalently, the anode current of the magnetron 24 is controlled to be substantially constant, and the threshold voltage of the magnetron 24 decreases due to the temperature rise. Accordingly, the input power and, consequently, the input current exhibit a gradually decreasing characteristic.

Therefore, when the total input current is high, the current input to the magnetron driving power supply is constant, that is, the switch 55 is selected to the “H” side so that the input current is constant, and the negative feedback control is performed. Is sufficiently warmed up, the switch 5 is controlled so that the current flowing through the branch of the high voltage circuit becomes constant.
5 is selected on the "L" side to perform a negative feedback control to realize a function of suppressing the generation of an initial excessive input current while maintaining a gradual decrease characteristic, thereby facilitating an increase in output of the high-frequency heating device.

Further, in the case of a low output with a light duty and no need for a gradual decrease characteristic, the constant input current control can be selected with emphasis on the stability of the high frequency output. As described above, since the power pattern can be freely selected, the valuation of power supply is expanded.

FIG. 6 shows an example of a time transition of the input current by the power control according to the present invention. (A) shows the case where the switch 55 is selected to the “H” side and the input current is controlled to be constant. The 15 A constraint shown by the dotted line is kept constant at a slightly lower level, and the power is drawn to the maximum within the range of the current constraint. Next, in FIG. 5B, the switch 55 is selected to the “H” side and the input current is controlled to be constant up to the point (A) where the high-frequency output is set low. Next, in the time period from the point (a) to the point (b), the high-frequency output is set to be high and the temperature duty is large, so that the temperature duty is reduced by derating by using the gradually decreasing characteristic of the input current. Here, the switch 55 is selected on the "L" side and the current flowing through the branch of the high voltage circuit is controlled to be constant. As a result, a gradually decreasing characteristic as shown in the figure can be obtained. Further, after the point (b), the switch 55 is set to the "H" side to control the input current to be constant because the high-frequency output is low and it is not necessary to derate using the gradually decreasing characteristic.

In this manner, various power patterns can be obtained by freely selecting the constant input current control and the gradual decrease control. For example, a limiter-like application that does not exceed an input current of 15 A, an application for derating by the input current gradual decrease characteristic at the time of high output, and an improvement in power supply accuracy by stabilizing the input current at a low output with low temperature duty. And the performance can be improved by improving the controllability of the device.

For a model which can sufficiently enter the input current limit frame of 15 A, the input current detection circuit is removed, and the power of the negative feedback control is set such that the current flowing through the branch of the high voltage circuit becomes constant. Since the inverter power supply circuit 18 can be used in common, it can be realized as a device having control, and a shared design can be realized while exhibiting a great economic effect by reducing the degree of freedom of design and the circuit.

(Embodiment 2) Recently, as a control method for drawing out the features of the inverter power supply, a boost in which components are sufficiently cooled (when there is no previous use history), a high-frequency output is increased to a rating or higher, and cooking is shortened in a short time. Has functions. For example, 3
The use of this boost function for minutes allows most of the benefits of this function for cooking that requires a relatively short time such as reheating.

However, the control of only the inverter power supply circuit having the gradually decreasing characteristic cannot comply with the restriction of 15A as shown in FIG. Therefore, this problem can be overcome by utilizing the negative feedback control via the input current detection circuit 62.

FIG. 7 shows a time transition of the input current at the time of power control including the boost function. (A) shows an output exceeding the rating for a certain period of time up to the initial point (a) of the operation. At this time, the switch 55 is selected on the “H” side to control the input current to be constant. From point (a), the output is reduced to the rated value, and thereafter, the switch 55 is selected to the “L” side to control the current flowing through the branch of the high-voltage circuit to be constant. As a result, derating can be realized by the gradually decreasing characteristic, which is advantageous in temperature performance. Further, in the diagram (b), the power pattern is such that the output further drops from the point (b). With this output, the temperature performance can be ensured without using the gradual decrease characteristic. Therefore, the control is switched to the constant input current control, which has an advantage in cooking software that a constant high-frequency dielectric heating power can be supplied to food.

As described above, when the high-output function (boost function) is in operation for a short time, the maximum electric power is drawn at a point where the input current does not exceed 15 A. The input current gradual decrease control or the constant input current control can be selected according to the high accuracy requirement of the heating output. Therefore, it is possible to observe the restriction of not exceeding 15 A in the short-time high-output period while having the valuation of the power control pattern.
High functionality as a device can be realized.

(Embodiment 3) A description will be given with reference to a circuit diagram of a magnetron driving power supply shown in FIG. In FIG. 1, the same functions and the same parts have the same numbers and their explanations are omitted. Here, the configuration of the second current transformer 35 is largely different from that of FIG. 1 in that the current flowing through the magnetron drive power supply of the device, the lamp for interior lighting, the current flowing through the device control circuit 25, and the elimination of radio wave unevenness The point is that both currents flowing to the device load 61 such as a turntable motor for rotating the mounting table of food for heating during use flow. Therefore, by adopting such a configuration, it is possible to realize a control in which the total input current of the device is adjusted to be constant by adjusting the current flowing to the magnetron driving power supply.

FIG. 9A shows the distribution of the total input current of the device. (1) is the total input current of the device.
The breakdown is the current of the magnetron drive power supply of (2),
(3) the current of the heater, which is another heating means provided in the device, and (4) the lamp for interior lighting, the current flowing in the device control circuit 25, and the food mounting table for eliminating radio wave unevenness. The current of the sum of (3) and (4) is equivalent to the current flowing to the device load 61 shown in FIG. 8. This is a heating method generally called simultaneous heating of dielectric heating by microwave and heating by heater.

FIG. 7B shows the transition of the current of each component over time. (3) The heater current has a low impedance when cold, and the current gradually decreases as the impedance of the resistor increases due to heating. In the dark current portion (4), the portion related to the copper loss is also large, and similarly exhibits a gradually decreasing characteristic.

The second current transformer 35 controls the sum of these currents and the current of the magnetron driving power supply of (2), that is, the total input current of the equipment of (1), to make the (2) constant. The current of the power supply for magnetron driving of (3) gradually increases in such a manner as to correct the current change of (3) and (4). Here, it goes without saying that the total input current of (1) is set so as not to exceed 15 A.

As described above, by monitoring the current of the entire apparatus and making correction with the current of the magnetron driving power supply, the total input current of the apparatus combined with the electric power of the apparatus load 61 including the second heating means heater is obtained. Since it can be controlled to be constant, the reliability with respect to not exceeding 15 A is further improved.

[0062]

As described above, according to the present invention, the input current to the magnetron driving power supply and the current flowing in the branch of the high voltage circuit can be selectively controlled to be constant, so that the input current can be controlled to be constant and the food can be controlled. The microcomputer pre-programs a method of heating the food with a constant power and a method of heating the food with a constant power, but gradually reducing the input current to reduce the temperature burden by reducing the rating of each power component. The sequence can be freely determined according to the determined sequence, and the degree of freedom of power control can be greatly expanded. The restriction of 15 A can also be cleared by selecting the control for keeping the input current constant and setting it to 15 A or less. For models that use low power without having to worry about the upper limit of the input current,
If the input current detection circuit is removed, the magnetron drive power supply alone can be operated as it is, and the economic effect is large, and the design flexibility and commonality between models are expanded.

Further, since a short-time high-output function is provided and the input current to the magnetron drive power supply is controlled to be constant by negative feedback control at least at the high-frequency output set value, at least during the short-time high output, Negative feedback constant control can be performed with the total input current not exceeding 15 A,
No problem occurs due to excessive input current exceeding 15A. For high-frequency output values other than short-time high-power output, select negative feedback control to keep the current flowing in the branch of the high-voltage circuit constant under severe temperature conditions, and take advantage of the gradually decreasing characteristics. Thus, the duty on parts can be gradually reduced, and the reliability can be improved by derating the parts.

Further, in the present invention, since the input current detection circuit is configured to detect the input current of the entire apparatus, the current of the power supply for driving the magnetron and the offset current of the control circuit, cooling, lamps, etc., and the consumption by other heating means are provided. By controlling the total input current to the device including the power constant, more accurate input current limitation can be realized.

[Brief description of the drawings]

FIG. 1 is a circuit diagram of a power supply for driving a magnetron of a high-frequency heating device according to a first embodiment of the present invention.

FIG. 2 is a circuit diagram of a main part of a power supply for driving a magnetron of the high-frequency heating device.

FIG. 3A is a characteristic diagram showing a relationship between a duty ratio of the PWM signal and an integral output. FIG. 3B is a characteristic diagram showing a relationship between a current to be controlled and a duty ratio of a PWM signal.

FIG. 4 shows correction values dD and (Vr) of the microcomputer.
ef-Viad)

FIG. 5A shows a reference value Vre of the microcomputer.
(b) Timing chart showing the time transition of the output Viad of the A / D conversion unit (c) Timing chart showing the time transition of the output dD of the A / D conversion unit (d) The integration unit (E) A timing chart showing a time transition of the output τ of the PWM signal section.

FIG. 6A is a timing chart showing another embodiment of the current control pattern according to the first embodiment of the present invention. FIG. 6B is a timing chart showing a current control pattern showing the other embodiment.

FIG. 7A is a timing chart illustrating a current control pattern according to a second embodiment of the present invention. FIG. 7B is a timing chart illustrating a current control pattern according to another embodiment.

FIG. 8 is a circuit diagram of a power supply for driving a magnetron of a high-frequency heating device according to a third embodiment of the present invention.

9A is a characteristic diagram showing current sharing for each function, and FIG. 9B is a timing chart of current for each function.

FIG. 10 is a main circuit diagram of a conventional high-frequency heating device.

FIG. 11 is a main circuit diagram of a high-frequency heating device using the power supply for driving the magnetron.

FIG. 12 is a timing chart of the input current and the anode current of the magnetron.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Commercial power supply 5 Rectification filter part 7 Step-up transformer 10 Inverter part 11 Inverter control part (power supply for magnetron drive) 16 High voltage circuit 17 First current transformer 24 Magnetron 25 Equipment control circuit 35 Second current transformer 46 Microcomputer 62 Input current Detection circuit

──────────────────────────────────────────────────続 き Continuation of the front page (72) Inventor Hideaki Moriya 1006 Oaza Kadoma, Kadoma City, Osaka Prefecture Matsushita Electric Industrial Co., Ltd. (56) References JP-A-8-96947 (JP, A) JP-A-4- 62789 (JP, A) JP-A-4-104497 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H05B 6/66-6/68

Claims (3)

(57) [Claims] 1. A magnetron for emitting microwaves,
A rectifying filter unit for full-wave rectifying a commercial power supply to convert it to a DC power supply; an inverter unit for turning on / off at least one semiconductor switching element to convert the DC power supply to high-frequency power; A step-up transformer for boosting, a high-voltage circuit for rectifying or multiplying the output of the step-up transformer to a high-voltage DC voltage and applying a high-voltage DC voltage to the magnetron; and detecting a current flowing in a branch of the high-voltage circuit. A magnetron driving power supply including a first current transformer, an inverter control unit for controlling on / off of the semiconductor switching element, a device control circuit for controlling an entire high-frequency heating device including a microcomputer, and the magnetron a second current transformer for detecting a current input to the driving power source, the detected current An input current detection circuit that converts the current into a DC voltage, and performs negative feedback control on the current flowing through the branch of the high-voltage circuit with the signal detected by the first current transformer using the microcomputer to control the current to be constant. Or a high-frequency heating apparatus configured to change according to a set value of a high-frequency output whether to perform negative feedback control on the input current detection circuit and perform negative feedback control on the input current to the magnetron drive power supply and control the input current to be constant. . 2. The high-frequency heating apparatus according to claim 1, further comprising a short-time high-output function, wherein the input current to the magnetron driving power supply is controlled to be constant by negative feedback control at least when the high-frequency output set value is reached. . 3. The high-frequency heating apparatus according to claim 1, wherein the input current detection circuit is configured to detect an input current of the entire apparatus.