JP2011103269A - Power source for magnetron driving - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To protect an inverter circuit from an abnormal operation caused by discharging inside a magnetron tube. <P>SOLUTION: The power source for magnetron driving is provided with an inverter circuit 1 which has a resonance circuit having a semiconductor switching element 8 and a high voltage transformer 7, and a high voltage rectifying circuit 9, and supplies power to a magnetron 10 by switching on/off of the semiconductor switching element 8, and a controlling part 11 for controlling on/off of the semiconductor switching element 8. The controlling part 11 is provided with: a driving circuit part 13 for driving the semiconductor switching element 8; a switching controlling part 12 for controlling timing of on/off; and a current detecting part 14 for detecting a current of the magnetron 10. The current detecting part 14, when the current of the magnetron 10 exceeds a prescribed value, transmits an operation stop instruction to the switching controlling part 12. <P>COPYRIGHT: (C)2011,JPO&INPIT

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. 5 is a circuit diagram of a conventional magnetron driving power source mounted in a so-called inverter type microwave oven sold mainly in Japan.

  A conventional magnetron driving power source converts an AC commercial power source 1 into a DC voltage once by a diode bridge 2, and an inverter circuit turns a high frequency voltage into a primary winding of a high voltage transformer 6 by turning on and off the DC voltage of the semiconductor switch element 5. The high voltage transformer 6 excites a high frequency high voltage in the secondary winding.

  The high frequency high voltage is rectified to a high DC voltage by the high voltage rectifier circuit 8 and applied to the magnetron 9. The magnetron 9 is driven by this high DC voltage and generates a radio wave of 2.45 GHz.

  An IGBT (insulated gate bipolar transistor) is generally used as the semiconductor switch element 5, and a high frequency voltage is generated in the high voltage transformer 6 by switching the element at a high frequency of several tens of kHz.

  In order to drive the magnetron 9, the high voltage rectifier circuit 8 must output a high voltage of 4 kV or more. In the magnetron 9 that operates by applying such a high voltage, it is rarely called an in-tube discharge inside the magnetron 9. A short circuit occurs. This in-tube discharge is characterized by being generated in a very short period. In particular, when the in-tube discharge phenomenon is eliminated, an excessive voltage may be generated in the high-voltage rectifier circuit 8 with respect to a voltage in a normal operating state.

  In this type of conventional magnetron driving power supply, in order to protect the semiconductor switching element, an overvoltage detection means for detecting an overvoltage of the semiconductor switching element is provided, and the semiconductor switching element is controlled by controlling the on-pulse of the semiconductor switching element by the feedback signal. (See, for example, Patent Document 1).

Japanese Patent Laid-Open No. 7-135076

  However, in the conventional configuration, as described below, the resonance operation of the inverter circuit is disturbed and may stop due to feedback control, but it is difficult to detect a single occurrence of abnormality, and when the discharge in the tube is resolved There was a problem that high voltage application to the high voltage rectifier circuit 8 could not be prevented in advance.

  For example, it is impossible to predict in advance that an in-tube discharge will occur when the semiconductor switching element is on or off.

  The resonance operation of the inverter circuit is determined by the resonance circuit configured on the primary side, the high voltage rectifier circuit magnetically coupled by the high voltage transformer, and the load impedance of the magnetron. Depending on whether or not an abnormal operation such as an in-tube discharge occurs, the resonance operation is disturbed, that is, the impedance changes, and the degree of change in the resonance voltage varies.

  For this reason, depending on the timing and time when the in-tube discharge occurs, the degree of change in the resonance voltage is small and it is very difficult to reliably detect abnormal operation.

  However, when an in-tube discharge occurs, a short-circuit current flows in the high-voltage rectifier circuit, and an excessive current flows in the high-voltage rectifier circuit with respect to the normal time. For this reason, if abnormal discharge cannot be detected by feedback control and the discharge in the tube is eliminated, the high voltage capacitor is charged by an excessive current. May cause serious damage.

  The present invention solves the above-described conventional problems, and directly detects a short-circuit current caused by a magnetron in-tube discharge and performs feedback control, thereby reliably detecting the in-tube discharge of the magnetron and stopping the protection of the inverter circuit. Therefore, it is an object of the present invention to provide a magnetron driving power source that can improve the reliability of the protection operation against discharge in the tube.

  In order to solve the above-described conventional problems, a magnetron driving power source according to the present invention includes a resonance circuit having a semiconductor switch element, a high-voltage transformer, and a high-voltage rectifier circuit, and supplies power to the magnetron by turning on and off the semiconductor switch element. An inverter circuit; and a control unit that controls on / off of the semiconductor switch element, wherein the control unit is a drive circuit unit that drives the semiconductor switch element, a switching control unit that controls on / off timing, and a current that detects a current of the magnetron The current detection unit is configured to transmit an operation stop command to the switching control unit when the current of the magnetron exceeds a predetermined value.

  As a result, a child that reliably detects the in-tube discharge generated by the magnetron can be detected by the current detector, so that the occurrence of the in-tube discharge ensures damage to the inverter circuit, particularly the primary side semiconductor switching element and the secondary high-voltage circuit. Can be avoided.

  According to the magnetron driving power source of the present invention, it is possible to reliably detect an abnormal current due to the in-tube discharge of the magnetron and prevent damage to inverter circuits such as semiconductor switching elements and high voltage circuits.

Configuration diagram of magnetron driving power source in Embodiment 1 of the present invention Operation waveform diagram of magnetron in steady state in Embodiment 1 of the present invention Operation waveform diagram of magnetron at the time of abnormality in Embodiment 1 of the present invention Enlarged view at time T1 of the operation waveform diagram of the magnetron at the time of abnormality Configuration diagram of conventional magnetron drive power supply

A first invention includes a resonance circuit having a semiconductor switch element and a high-voltage transformer, and a high-voltage rectifier circuit, and an inverter circuit that supplies power to the magnetron by the on / off of the semiconductor switch element, and a control for controlling on / off of the semiconductor switch element The control unit includes a drive circuit unit that drives the semiconductor switch element, a switching control unit that controls on / off timing, and a current detection unit that detects a current of the magnetron, and the current detection unit includes the magnetron When the current exceeds a predetermined value, an operation stop command is transmitted to the switching control unit.

  When the current detection unit detects a current of a predetermined value or more, the operation of the switching control unit is stopped. Therefore, the abnormality of the resonance operation due to the in-tube discharge of the magnetron does not continue. As a result, the semiconductor switch element can be protected from damage due to overvoltage, and the overload state of the high-voltage circuit can be minimized.

  According to a second aspect of the present invention, the current detection unit is composed of a resistor, a series connection body of a Zener diode and a photocoupler connected in parallel to the resistor, and a stop signal is transmitted to the switching control unit by the output of the photocoupler. It is.

  Since the primary side and the secondary side, which have different electrical potentials by the high-voltage transformer, can be connected by a photocoupler to transmit a signal, a stop signal can be directly transmitted to the switching control unit provided in the control unit of the inverter. And a high-speed response can be realized.

  In a third aspect of the invention, the current detection unit is configured by a resistor, a series connection body of a varistor and a photocoupler connected in parallel thereto, and a stop signal is transmitted to the switching control unit by the output of the photocoupler. is there.

  Since the primary side and the secondary side, which have different electrical potentials by the high-voltage transformer, can be connected by a photocoupler to transmit a signal, a stop signal can be directly transmitted to the switching control unit provided in the control unit of the inverter. And a high-speed response can be realized.

  According to a fourth aspect of the present invention, there is provided a timing unit in the control unit, the switching operation is stopped by a stop signal, the predetermined time is measured by the time measuring unit, and the operation of the inverter circuit is restarted again after the predetermined time has elapsed. It is a thing.

  Since it restarts after a predetermined time by the time measuring means, even if the current detection circuit should react due to noise etc., it can be restarted quickly and normal oscillation can be resumed, so it is possible to avoid problems such as defective heating it can.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. Note that the present invention is not limited to the embodiments.

  FIG. 1 is a configuration diagram of a magnetron driving power source according to an embodiment of the present invention.

  In FIG. 1, an inverter circuit 1 once rectifies an AC voltage obtained from a commercial power source 2 into a unidirectional voltage by a diode bridge 3 and smoothes it by a smoothing circuit including a choke coil 4 and a smoothing capacitor 5.

  This smoothing circuit does not have the ability to maintain and smooth the voltage with respect to the commercial power supply frequency of 60 Hz or 50 Hz, and the circuit is small enough to have a smoothing ability that can maintain a DC voltage with respect to the switching frequency of the inverter circuit 1. Is playing.

  Further, a high frequency high voltage is induced on the secondary side of the high voltage transformer 7 by exciting a resonance circuit composed of the resonance capacitor 6 and the high voltage transformer 7 by turning on and off the semiconductor switch element 8.

  The high voltage rectifier circuit 9 rectifies the high frequency high voltage and supplies a DC high voltage to the magnetron 10, and the magnetron 10 is configured to generate a 2450 MHz microwave by the DC high voltage.

  The control unit 11 includes a switching control unit 12 that controls the on / off timing of the semiconductor switch element 8 and a drive circuit unit 13 that drives the semiconductor switch element 8, and the drive circuit unit 13 outputs the output of the switching control unit 12. The semiconductor switch element 8 is turned on and off based on the pulse train to be performed.

  The current detector 14 is mounted between the high voltage rectifier circuit 9 and the ground connection so as to detect the current of the magnetron 10. The current detector 14 includes a resistor 14a, a Zener diode 14b connected in parallel thereto, and a series body on the light emission side of the photocoupler 14c, and is configured to transmit a signal through the photocoupler 14c when an overcurrent occurs. ing.

  The detailed operation and action of the magnetron driving power source configured as described above will be described below.

  FIG. 2 is a diagram showing the applied voltage Vak and the passing current Ia of the magnetron 10 when the inverter circuit 1 is normal. In order to show the change of the operating voltage with respect to the AC cycle, an AC voltage waveform Vac is added to the drawing. As described above, the smoothing circuit provided at the input of the inverter circuit does not have the ability to smooth the voltage of the commercial power source 2.

  For this reason, the input voltage of the inverter circuit 1 fluctuates in synchronization with the voltage of the commercial power supply 2. The resonance circuit excited by the semiconductor switch element 8 fluctuates due to this fluctuating voltage, and as a result, the output voltage of the high-voltage transformer 7 naturally fluctuates, and the voltage applied to the magnetron 10 is insufficiently boosted when the voltage of the commercial power supply 2 is low. However, the oscillation of the magnetron 10 is stopped.

  FIG. 3 is a diagram showing the applied voltage Vak and the passing current Ia of the magnetron 10 when an in-tube discharge is generated in the magnetron 10 during the operation of the inverter circuit 1. It is assumed that an in-tube discharge has occurred in the magnetron 10 at time T1.

  When the magnetron 10 causes an in-tube discharge, both ends of the magnetron 10 are in the same circuit state as when both ends are simply short-circuited, so that a negative high voltage stored in the high-voltage rectifier circuit 9 flows as a short-circuit current all at once.

  For this reason, immediately after the discharge in the tube occurs, an excessive current as a short-circuit current passes through the current detection unit 14 from the high-voltage rectifier circuit 9. FIG. 4 is an enlarged waveform diagram at time T1 in FIG. Since the state of the discharge inside the tube instantaneously changes, the applied voltage of the magnetron 10 changes to 0 almost instantaneously, and the current becomes a very large current transiently reaching several tens of A.

  When this short-circuit current flows through the resistor 14a of the current detector 14, a voltage drop occurs, and a voltage is generated across the resistor 14a.

  When this voltage exceeds the operating voltage of the Zener diode 14b connected in parallel, a current flows through the series circuit of the Zener diode 14b and the light emitting diode of the photocoupler 14c, and a signal is transmitted to the light receiving side of the photocoupler 14c. This signal is transmitted to the switching control unit 12 of the control unit 11 to immediately stop the switching operation of the semiconductor switch element 8.

By operating in this way, this is detected at the moment when the in-tube discharge occurs, and the operation of the inverter circuit 1 is stopped, so that the abnormal operation due to the in-tube discharge does not continue, and the instant at which the in-tube discharge occurs is directly captured. Therefore, it is possible to minimize the delay time of feedback control, stop the operation of the inverter circuit before the discharge phenomenon in the tube is eliminated, and prevent an excessive voltage from being applied to the high-voltage rectifier circuit.

  The time measuring means 15 detects an abnormal current by the current detection unit 14 and measures an elapsed time after the switching operation of the inverter circuit 1 is stopped. When this measurement time exceeds a predetermined time, the abnormal stop state is once released, the inverter circuit 1 is started again, and the switching operation is resumed. If the abnormal state of the magnetron 10 is eliminated, the normal oscillation state can be continued and the heating operation can be continued.

  With this configuration, the current detection unit is activated due to noises caused by an unexpected situation, and the inverter circuit 1 can be started again even if the protection operation is performed. There is nothing.

  As described above, the magnetron driving power source according to the present invention can detect an abnormal current due to the magnetron discharge in the tube, and can provide a magnetron driving power source that prevents the inverter circuit and the magnetron from being damaged. It can also be applied to applications such as a heating device using dielectric heating, a garbage disposal machine, or a microwave power source of a plasma power source that is a semiconductor manufacturing device.

DESCRIPTION OF SYMBOLS 1 Inverter circuit 7 High voltage transformer 8 Semiconductor switch element 9 High voltage rectifier circuit 10 Magnetron 11 Control part 12 Switching control part 13 Drive circuit part 14 Current detection part 14a Resistor 14b Zener diode 14c Photocoupler (light emission side)

Claims (4)

The control circuit includes a resonance circuit having a semiconductor switch element and a high-voltage transformer, and a high-voltage rectifier circuit. The inverter circuit supplies power to the magnetron by turning on and off the semiconductor switch element. The unit has a drive circuit unit for driving the semiconductor switch element, a switching control unit for controlling on / off timing, and a current detection unit for detecting the current of the magnetron, and the current detection unit has a predetermined value for the current of the magnetron. A magnetron driving power source configured to transmit an operation stop command to the switching control unit when exceeding. 2. The magnetron according to claim 1, wherein the current detection unit is configured by a resistor, a series connection body of a Zener diode and a photocoupler connected in parallel to the resistor, and a stop signal is transmitted to the switching control unit by an output of the photocoupler. Power supply for driving. 2. The magnetron drive according to claim 1, wherein the current detection unit is configured by a resistor, a series connection body of a varistor and a photocoupler connected in parallel to the resistor, and a stop signal is transmitted to the switching control unit by an output of the photocoupler. Power supply. 4. The time measuring means is provided in the control unit, the switching operation is stopped by a stop signal, the predetermined time is measured by the time measuring means, and the operation of the inverter circuit is restarted again after a predetermined time has elapsed. The magnetron drive power supply described in 1.

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