JP4363310B2 - Magnetron drive power supply - Google Patents

Description

  The present invention relates to a power source for driving a magnetron using a magnetron such as a microwave oven as a load.

  A conventional magnetron driving power supply will be described with reference to the drawings. FIG. 6 is a circuit diagram of a conventional magnetron driving power source. The magnetron driving power source shown in this figure includes a unidirectional power source unit 1, an inverter unit 2, a driving circuit 3, a high voltage rectifier circuit 4, a magnetron 5, and a current transformer 6. The unidirectional power supply unit 1 is a low-pass filter circuit including a diode bridge 102 that full-wave rectifies an AC power supply from a commercial power supply 101, a choke coil 103, and a capacitor 104. The unidirectional power supply unit 1 serves as a filter for high-frequency switching operation of the inverter unit 2. To fulfill. In the unidirectional power supply unit 1, a current transformer 6 is inserted on the AC input side of the diode bridge 102, and is used to detect an input current.

  The inverter unit 2 includes a resonant capacitor 201, a switching element 202, a commutation diode 203, and a step-up transformer 204. The switching element 202 performs a switching operation according to a switching control signal of 20 to 50 kHz given from the drive circuit 3. As a result, a high frequency voltage is generated in the primary winding of the step-up transformer 204.

  The drive circuit 3 includes a primary side current detection unit 301, an oscillation detection unit 8, and a switching element drive circuit 304. The primary current detection unit 301 detects an input current from the commercial power supply 101 and inputs the output and the reference voltage 802 to the comparator 801. When the input current exceeds the reference voltage 802, it is determined that the magnetron 5 can oscillate. The operation switching mode circuit 803 increases the suppressed input current I1 to the input current I2 simultaneously with this determination. Switch. That is, the reference voltage 802 sets the reference voltage 802 to switch the operation mode switching circuit 803 so as to increase the input current when the magnetron 5 starts to oscillate, and the magnetron 5 starts to oscillate. To do.

  Next, FIG. 4 illustrates the control of the input current at that time. Until the oscillation starts, the magnetron 5 has a current only flowing through the heater section and does not flow between the anode and the cathode. Therefore, if the input current is controlled to the value of I2 at the steady state, an excessive voltage is generated between the anode and the cathode. Is applied, and an excessive current flows through the heater to shorten the life of the magnetron 5. Accordingly, until the magnetron 5 starts to oscillate as shown in the figure, it is necessary to set the input current to be lower than that in the steady state (I1 <I2).

  Further, as shown in FIG. 7, a method of detecting oscillation of the magnetron 5 by inserting a current transformer 7 between the cathode side of the diode 404 of the high-voltage rectifier circuit 4 and the ground and detecting the secondary side current. A change to is also possible. Further, the switching element driving circuit 304 performs a switching operation of the base current supplied to the switching element 202 of the inverter unit 2 at a predetermined cycle duty (that is, an on / off time ratio).

The high-voltage rectifier circuit 4 includes capacitors 401 and 402 and diodes 403 and 404, and generates a high-voltage DC voltage by performing half-wave voltage double rectification on the voltage generated in the secondary winding of the step-up transformer 204. Applied to magnetron 5. An AC voltage for the heater is also applied to the magnetron 5 from the heater winding of the step-up transformer 204. When the AC voltage for the heater is applied to the magnetron 5, the cathode is heated side by side to be able to oscillate. When a high voltage voltage is applied in this state, electromagnetic energy is generated.
Japanese Unexamined Patent Publication No. 63-271886

However, in the conventional configuration, when noise is added to the input current, the oscillation detection unit 8 determines that the magnetron 5 oscillates even though the magnetron is not oscillated , and an overvoltage is applied to the high voltage circuit. May cause an excessive voltage to be applied to the components of the high voltage circuit. In other words, even though the magnetron is not ready to oscillate, the input current and the secondary current exceed the reference voltage, and the oscillation detector determines that the magnetron has oscillated. Since no current flows between the anode and the cathode, if the input current is controlled to a steady value, there is no force to suppress the voltage, and an excessive voltage is applied between the anode and the cathode. In this way, an excessive voltage may be applied to the components of the high-voltage circuit, which may cause a failure such as component destruction.

  The present invention has been made in view of such problems, and even if noise is added to the input current and the secondary current, the oscillation of the magnetron is determined until the magnetron can be oscillated reliably. An object of the present invention is to provide a power source for driving a magnetron.

In order to solve the conventional problems, a magnetron driving power source according to the present invention includes a unidirectional power source unit that converts a commercial power source into a unidirectional direction, and at least one switching element that converts an output of the unidirectional power source into a high frequency. An inverter circuit having a drive circuit for the switching element, a magnetron for generating a high frequency for heating food or fluid, a step-up transformer for boosting the output of the inverter circuit and supplying electric power to the magnetron The inverter circuit includes an oscillation detection unit that detects oscillation of the magnetron, and the oscillation detection unit includes a filter for noise to clearly determine the oscillation of the magnetron.

  Thereby, even if noise is added to the input current and the secondary current, it is possible to determine the oscillation of the magnetron until the magnetron can be oscillated reliably.

According to the magnetron driving power source of the present invention, even if noise is added to the input current and the secondary current, the magnetron transitions to oscillation by providing a filter for noise in the oscillation detection unit that detects the oscillation of the magnetron. Whether or not an excessively high voltage is continuously applied to the high-voltage circuit can be prevented.

According to a first aspect of the present invention, there is provided an inverter circuit comprising: a unidirectional power supply unit that converts a commercial power supply in a unidirectional direction; at least one switching element that converts an output of the unidirectional power supply into a high frequency; and a drive circuit for the switching element; A magnetron that generates a high frequency for heating food or fluid, and a step-up transformer that boosts the output of the inverter circuit and supplies electric power to the magnetron, and the inverter circuit detects oscillation of the magnetron has an oscillation detector for the oscillation detection section by a clearly determined form an oscillation of the magnetron with a filter to noise, even the noise is superimposed on the input current and secondary current, reliably Until the magnetron is ready to oscillate, the oscillation of the magnetron can be determined. It is possible to prevent applying an excessive voltage to the high voltage circuit of use power.

According to a second aspect of the invention, in particular, the oscillation detection unit of the first aspect of the invention includes a first comparison circuit having a first input unit for inputting a detection signal and a second input unit for inputting a first reference voltage; And a second comparison circuit having a second input unit for inputting a second reference voltage and a capacitor between the output of the first comparison circuit and a power source. In parallel, even if noise is added to the input current and the secondary current, the oscillation of the magnetron can be determined until the magnetron can oscillate reliably. It is possible to prevent an excessive voltage from being applied to the high voltage circuit.

Even if noise is added to the input current, the third invention detects the input current supplied from the commercial power supply to the magnetron driving power supply of the second invention and determines the oscillation of the magnetron. It is possible to determine the oscillation of the magnetron until the magnetron can oscillate surely, and it is possible to prevent an excessive voltage from being applied to the high voltage circuit of the magnetron driving power source.

According to the fourth aspect of the invention, it is assumed that noise is added to the secondary side current by detecting the secondary side current of the step-up transformer in the magnetron driving power source of the second aspect of the invention and determining the oscillation of the magnetron. However, it is possible to determine the oscillation of the magnetron until the magnetron can oscillate reliably, and it is possible to prevent an excessive voltage from being applied to the high voltage circuit of the magnetron driving power source.

  According to a fifth aspect of the invention, in particular, the oscillation detection unit according to any one of the first to fourth aspects includes a first input unit that inputs a detection signal and a second input unit that inputs a first reference voltage. A second comparison circuit having a comparison circuit, a first input section for inputting an output of the first comparison circuit, and a second input section for inputting a second reference voltage; By providing a capacitor in parallel between the output and the power supply, and connecting the capacitor to an external output pin of the drive circuit, the constants of the filter can be adjusted externally even if the drive circuit is integrated. It becomes possible.

  According to a sixth aspect of the present invention, in particular, the oscillation detection unit according to any one of the first to fourth aspects includes a first comparison circuit having a first input unit and a second input unit for inputting a first reference voltage; A second comparison circuit having a second input unit for inputting an output of the first comparison circuit and a second reference voltage, and a capacitor is provided in parallel between the output of the first comparison circuit and a power supply; By providing the connection portion of the capacitor inside the drive circuit, space can be saved by integrating the drive circuit.

  In the seventh aspect of the invention, in particular, the magnetron driving power source of any one of the first to sixth aspects of the invention is provided with a time measuring means, and when the oscillation of the magnetron cannot be detected within a predetermined time from the starting of the driving circuit, the power is restarted. By adopting the configuration, it is possible to eliminate the continuous application of a high voltage to the high voltage circuit.

  In the eighth invention, the magnetron driving power supply according to the seventh invention is provided with a counting means, and the operation is stopped when the driving power supply for the magnetron is repeatedly restarted a predetermined number of times or more after starting the driving circuit. Because the restart is limited to a predetermined number of times or less, it is possible to detect an abnormality in the magnetron or an abnormality in the power supply voltage, and to prevent an abnormally high voltage or large current from being applied to the magnetron driving power supply. it can.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. In addition, this invention is not limited by this embodiment.

(Embodiment 1)
FIG. 1 is a diagram showing a configuration of a magnetron driving power source according to the first embodiment of the present invention. In this figure, parts common to those shown in FIGS. 6 and 7 described above are denoted by the same reference numerals and description thereof is omitted.

In the magnetron driving power source of this embodiment, the first comparator 801 determines that the magnetron can oscillate once, and then the potential of the capacitor 807 increases and exceeds the reference voltage 806 of the second comparator 805. Sometimes it is determined that the magnetron 5 can oscillate normally. 2 and 3 illustrate the difference between the conventional oscillation detection method and the oscillation detection method of the present embodiment. In the conventional oscillation detection shown in FIG. 2, when the reference voltage 802 of the comparator 801 exceeds the input current, it is determined that the magnetron 5 can normally oscillate. However, when noise is included in the input current, it may be determined that the magnetron 5 can oscillate even though the magnetron 5 is not yet in an oscillatable state. There is a possibility of applying a voltage . However, in the oscillation detection of the present embodiment shown in FIG. 3, even if the reference voltage 802 of the first comparator 801 exceeds the input current, the potential of the capacitor 807 causes the reference voltage 806 of the second comparator 805 to be Unless it exceeds, it is not determined that the magnetron 5 can oscillate. That is, even if noise enters the input current, it is not determined that the magnetron 5 can oscillate until the potential of the capacitor 807 increases to the reference voltage 806. As a result, even if noise is added to the input current, it is possible to determine the oscillation of the magnetron 5 until the magnetron 5 can reliably oscillate, and an excessive voltage is applied to the high voltage circuit of the magnetron driving power source. Can be prevented.

  In this embodiment, the current transformer is used for detecting the input current. However, it is possible to change the method of detecting the current by the voltage drop by inserting a resistor into the system, and the circuit configuration shown in the figure is used. It is not limited.

(Embodiment 2)
A second embodiment of the present invention will be described with reference to FIG. The figure is a circuit diagram of the power source for driving the magnetron of this embodiment. In this figure, parts common to those in FIG. 1 described above are denoted by the same reference numerals and description thereof is omitted. Here, reference numeral 305 denotes time measuring means, which measures the time from when the drive circuit 3 starts operating and when a gate signal starts to be generated in the switching element 202. If a signal indicating that the oscillation of the magnetron 5 has been determined is not sent from the oscillation detector 8 after a certain period of time has elapsed since the drive circuit 3 started to operate, the drive circuit 3 is temporarily stopped, delayed for a predetermined time, and restarted. Functions to be activated. The counting means 306 counts the number of times the time counting means 305 has been instructed to restart, and the counting means 306 acts so as to stop the drive circuit 3 from being restarted when restarting more than a certain number of times. As a result, it is possible to prevent the high voltage from being continuously applied to the high voltage circuit even if the oscillation of the magnetron 5 cannot be detected when the power supply voltage is abnormally high or low with respect to the rated voltage.

As described above, the magnetron driving power source according to the present invention can determine the oscillation of the magnetron until the magnetron can reliably oscillate even if noise is added to the input current. It is possible to prevent an excessive voltage from being applied to the high voltage circuit of the power supply.

1 is a circuit diagram showing a configuration of a magnetron driving power supply in Embodiment 1 of the present invention. Operating characteristics of conventional oscillation detector Operation characteristic diagram of oscillation detection unit of the present invention Start-up characteristics of the magnetron drive power supply The circuit diagram which shows the structure of the power supply for magnetron drive in Embodiment 2 of this invention Circuit diagram showing the configuration of a conventional magnetron drive power supply Circuit diagram showing the configuration of a conventional magnetron drive power supply

DESCRIPTION OF SYMBOLS 1 Unidirectional power supply part 3 Drive circuit 5 Magnetron 8 Oscillation detection part 9 Inverter circuit 101 Commercial power supply 202 Switching element 204 Boosting transformer 305 Time measuring means 306 Counting means 801 1st comparator (1st comparison circuit)
802 First reference voltage 805 Second comparator (second comparison circuit)
806 Second reference voltage 807 Capacitor (filter)
808 power supply

Claims (5)

A unidirectional power supply unit that converts commercial power into a unidirectional; an inverter circuit that converts an output of the unidirectional power supply unit into a high-frequency high-frequency voltage; and a high-voltage rectifier circuit that converts the output of the inverter circuit into a high-voltage DC voltage; The inverter circuit has at least one switching element, a step-up transformer, and a driving circuit for the switching element, and the driving circuit detects a current used for detecting the oscillation of the magnetron. A current detection unit that detects the oscillation of the magnetron based on the output of the current detection unit and outputs a detection signal; a switching element drive circuit that drives the switching element based on the output of the oscillation detection unit; The oscillation detection unit includes a first input unit that inputs the detection signal, and a second input unit that inputs a first reference voltage. A first comparison circuit, a second comparison circuit having a first input section for inputting an output of the first comparison circuit, and a second input section for inputting a second reference voltage; A magnetron driving power source comprising: a power source for the driving circuit connected to the output of the comparison circuit; and a capacitor having one terminal connected to the power source and the other terminal grounded. The magnetron driving power source according to claim 1, wherein the current detection unit detects a current supplied from the commercial power source. The magnetron driving power source according to claim 1, wherein the current detection unit detects a secondary current of the step-up transformer. The magnetron driving power source according to any one of claims 1 to 3 , wherein a time-counting means is provided to restart the magnetron when the oscillation of the magnetron cannot be detected within a predetermined time from the starting of the driving circuit. The magnetron driving power source according to claim 4 , wherein the operation is stopped when the restart is repeated a predetermined number of times or more.

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