JP2007018841A - Magnetron filament power supply device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a small, low-loss and low-cost magnetron filament power supply device capable of using a conventional general-purpose magnetron and having a simple structure. <P>SOLUTION: The primary side of a filament transformer T1 is connected to a commercial power source 6, a capacitor C2, a choke coil L1, a capacitor C3 and a bidirectional switching element group 10. One end of the capacitor C3 is connected to the primary side of the filament transformer T1, and the other end thereof is connected to the bidirectional switching element group 10. The bidirectional switching element group 10 is composed by serially connecting unidirectional switching elements Q2 and Q3 in opposite polarity directions and by connecting diodes D2 and D3 in parallel to the switching elements Q2 and Q3 and in polarity directions opposite to the current carrying directions. The secondary side of the filament transformer T1 is connected to a filament F of a magnetron 9 through a low-pass filter 11 composed of a choke coil L2 and capacitors C4, C5 and C6. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a microwave oven and a magnetron filament power supply device used for industrial use, medical use and the like.

  As a magnetron filament power supply device using a switching power supply, in order to reduce the size and weight, a series resonant circuit formed by a primary winding 1a of a first transformer 1 and a resonant capacitor 2 as shown in FIG. The freewheeling diode 3, the transistor 4, and the output control circuit 5 constitute a first inverter device for converting the commercial power supply 6 into the first high-frequency voltage, and the resonance capacitor C1 and the second transformer 7 A parallel resonance circuit formed by the primary winding 7a, the transistor Q1, the freewheeling diode D1, and the power control circuit 8 constitute a second inverter device, and the second inverter device converts the second inverter device. The second high-frequency voltage is transformed using the second transformer 7, and the transformed predetermined heater voltage is supplied to the filament F of the magnetron 9. Those in so that there has been known (e.g., see Patent Document 1).

  However, in this configuration, since a high-frequency current is passed through the magnetron filament, a magnetron dedicated to the inverter power supply must be employed.

  This is because the feedthrough capacitor terminal and internal conductive part material used in the magnetron are made of inexpensive iron materials, so the loss and heat generation during high frequency driving here will increase and exceed the heat resistance rating of the capacitor. Because. Therefore, the feedthrough capacitor has a very short life and frequently suffers from short-circuit failures. Therefore, the material of the terminal of the feedthrough capacitor and the internal conductive part is changed from iron to brass exclusively for the inverter power supply to prevent loss and heat generation due to high frequency.

  Further, the choke coil in the magnetron filter case also has an inductance that was not a problem at a power frequency of 50/60 Hz, but has a large impedance at a high frequency of the inverter power source, so that the filament current does not flow so much that the magnetron does not reach an appropriate cathode temperature. Therefore, a choke coil with a small inductance dedicated to the inverter power supply has to be adopted. If the magnetron choke coil L is 1.5 μH, the switching frequency f is 40 kHz, and the filament current If is 10 A, the voltage drop generated in the choke coil is If × 2πfL = 3.77 V, and two magnetron choke coils are paired. Since it is used, the voltage drop becomes 7.54V. Compared with the ratings of Vf = 3.3V and If = 10A when driving at a power frequency of 50/60 Hz, the voltage applied to the filament in the high frequency operation is around 10V because the voltage drop is large in the high frequency operation with the inverter power supply as described above. Must be applied.

Therefore, an improved magnetron filament power supply device is provided with a rectifier for high-frequency switching current on the secondary side of the filament transformer so that a conventional general-purpose magnetron can be used under the same conditions, not a magnetron dedicated to an inverter power supply. There is known one that can supply a stable filament voltage when the voltage fluctuates. In this case, a rectifier circuit is provided on the secondary side of the filament transformer so that a high frequency current does not flow through the magnetron cathode and a current close to the commercial frequency flows. With this configuration, a conventional general-purpose magnetron can be used, and an appropriate cathode temperature can be defined by the conventional magnetron filament voltage Vf (see, for example, Patent Document 2).
Japanese Patent Laid-Open No. 1-183087 JP 2003-297545 A

  However, the magnetron filament power supply device is 3.3V, 10A for microwave ovens, and from 4V to 5V during preheating, 20A to 30A for industrial high-power magnetrons, and is called cutback during operation. The voltage / current value must be variable within a range of minimum 2.2V and 20A.

  As described above, the magnetron filament power supply device requires a large current, and several times as much current flows as the inrush current when the filament power supply is turned on.

  In such a magnetron filament power supply device, in order to form a low-voltage large-current rectifier circuit, the rectifier circuit must be enlarged. Although there are remarkable technologies in recent high-performance CPU power supplies and the like for large current circuits, there are many problems in using these synchronous rectification methods. This is because the secondary circuit on the rectifying side is a floating portion having a voltage to ground of 4000 V or more.

  Therefore, when a simple Schottky barrier diode is used, a forward loss, a recovery loss, and the like are generated. Therefore, the diode must be mounted on a large heat sink.

  However, since diodes and radiators have a voltage to ground of 4000 V or more, the rectifying element must also dissipate heat while ensuring insulation. Therefore, the circuit configuration is to ensure an insulation distance of 16 mm or more, large current and heat dissipation. As a countermeasure, there is a problem that the structure becomes large and the power supply is enlarged and the cost is increased.

  In view of these problems, an object of the present invention is to provide a magnetron filament power supply device having a simple configuration, low loss, small size, and low cost.

  In order to solve the above-described conventional problems, a magnetron filament power supply apparatus according to the present invention includes a commercial power supply, a noise filter, and a bidirectional switching element group connected to a primary side of a filament transformer, and a low-pass filter on the secondary side of the filament transformer. It has the structure connected to the filament of the magnetron via.

  According to this configuration, the magnetron filament can be operated with the same waveform as that of the commercial power supply, and a large current rectifier circuit is not required on the secondary side of the filament transformer, so that the size can be reduced.

  In the bidirectional switching element group, two unidirectional switching elements are connected in series in opposite polar directions, and two diodes are connected in parallel to the unidirectional switching element and in the opposite polarity direction to the current-carrying direction of the diodes. Or a configuration in which a collector or drain of a unidirectional switching element is connected to a positive electrode of a diode bridge in which four diodes are bridge-connected, and an emitter or a source of the unidirectional switching element is connected to a negative electrode of the diode bridge Is preferred.

  The low-pass filter provided on the secondary side of the filament transformer includes a plurality of capacitors connected in parallel and a choke coil connected in series to the plurality of capacitors.

  According to such a configuration, on the secondary side of the filament transformer, it is possible to remove the high frequency component and extract only the low frequency component of the commercial frequency.

  As described above, the magnetron filament power supply device of the present invention includes a bidirectional switching element on the primary side of the filament transformer, and a low-pass filter on the secondary side of the filament transformer, thereby reducing power source power factor and line harmonics. There is no deterioration, there is no problem of loss, heat dissipation and insulation due to the secondary side rectifier circuit, and the conventional general-purpose magnetron can be used without using a dedicated magnetron for the inverter power supply. A low-loss, low-cost magnetron filament power supply device can be provided.

  The best mode for carrying out the present invention will be described below with reference to the drawings.

(Embodiment 1)
FIG. 1 is a circuit diagram of a magnetron filament power supply apparatus according to Embodiment 1 of the present invention. In FIG. 1, the same components as those in the conventional diagram shown in FIG.

  In FIG. 1, the primary side of the filament transformer T1 includes a commercial power source 6, a capacitor C2 for preventing noise, a choke coil L1 for preventing outflow of high-frequency current to the power source, a capacitor C3 regarded as a high-frequency switching current supply source, and The bidirectional switching element group 10 is connected. One end of the capacitor C3 is connected to the primary side of the filament transformer T1, and the other end is connected to the bidirectional switching element group 10. In the bidirectional switching element group 10, unidirectional switching elements Q2 and Q3 are connected in series in opposite polarity directions, and diodes D2 and D3 are connected in parallel to the unidirectional switching elements Q2 and Q3 and in the opposite polarity direction to the energizing direction. It is configured.

  The secondary side of the filament transformer T1 is connected to the filament F of the magnetron 9 through a low-pass filter 11 composed of a choke coil L2 and capacitors C4, C5, C6.

  One end of the filament F of the magnetron 9 is connected to a high voltage power source Eb for driving the magnetron, and a power source of 300 mA for industrial use to 900 mA for industrial use and a voltage to ground of 4000 V to 5000 V is supplied.

  Next, the operation of the magnetron filament power supply device configured as described above will be described.

  First, the commercial power source 6 passes through a noise filter composed of a capacitor C2 and a choke coil L1, and charges the capacitor C3 with an AC voltage different from that of a normal switching power source. The voltage of the capacitor C3 is applied to the primary side of the filament transformer T1, and the bidirectional switching element group 10 performs high frequency switching as described below.

  When the power supply voltage is in the positive direction, current flows in the direction of C3 → T1 → D2 → Q3, and when the power supply voltage is in the negative direction, current flows in the direction of C3 → D3 → Q2 → T1. As a result of such a switching operation, a current as if the switching frequency was modulated by the commercial power supply flows continuously to the primary side of the filament transformer T1 in the order of C3, T1, Q2, Q3, D2, and D3.

  On the other hand, a voltage having a winding ratio N2 / N1 of the filament transformer T1 appears on the secondary side of the filament transformer T1. Since this voltage has a waveform in which the same switching frequency as that on the primary side is modulated by a commercial power supply, it contains a large amount of high frequency components.

  Therefore, in order to remove the high frequency component and extract only the low frequency component of the commercial frequency, a low pass filter 11 including a choke coil L2 and capacitors C4, C5 and C6 is provided. By this low-pass filter 11, only the commercial frequency component is supplied to the filament F of the magnetron 9. Here, the filament current is 3.3 V for a microwave oven and 10 A for a high-power magnetron, and a large current of 4 A to 5 V for a high-power industrial magnetron flows from 20 A to 30 A during preheating. Many capacitors are used in parallel to distribute the high-frequency current so that the current flowing through the capacitor does not exceed the rated value.

  As described above, according to the present embodiment, the switching operation by the filament transformer T1 and the bidirectional switching element group 10 and the low-pass filter 11 on the secondary side of the filament transformer T1 are provided on the primary side of the filament transformer T1. There is no need to provide a rectifier circuit, and since there is no need to provide a large current rectifier circuit on the secondary side of the filament transformer T1, there is no element of heat generation or loss due to the low voltage large current rectifier element, and there is no need to provide a large radiator. Further, since the circuit elements are only choke coils and capacitors, the structure is very simple. Therefore, it is possible to easily secure an insulation distance of 16 mm or more due to the application of a voltage to ground of 4000 V, and there is no need to worry about ensuring insulation of the low-voltage, high-current rectifier radiator. Further, since there is no smoothing circuit or phase control circuit on the primary side of the filament transformer, the power source power factor is not lowered and the line harmonics are not deteriorated.

  Therefore, according to the present invention, it is possible to provide a magnetron filament power supply device having a simple configuration, a small size, a low loss, and a low cost.

  In the above-described embodiment, choke coils are used for L1 and L2, but common choke coils may be used. Further, as the filament transformer T1, a ferrite core, a cut core or an EI core with good frequency characteristics can be used. MOSFETs, IGBTs, or transistors can be used for the unidirectional switching elements Q2, Q3.

(Embodiment 2)
FIG. 2 is a circuit diagram of a magnetron filament power supply apparatus according to Embodiment 2 of the present invention. 2 differs from the first embodiment shown in FIG. 1 in the configuration of the bidirectional switching element group 10 connected to the primary side of the filament transformer T1, and the other configurations are the same. Omitted.

  As shown in FIG. 2, the primary side of the filament transformer T1 is regarded as a commercial power source 6, a noise preventing capacitor C2, a choke coil L1 for preventing high-frequency current from flowing to the power source, and a high-frequency switching current supply source. The capacitor C3 and the bidirectional switching element group 10 are connected. One end of the capacitor C3 is connected to the primary side of the filament transformer T1, and the other end is connected to the bidirectional switching element group 10. The bidirectional switching element group 10 has a collector or drain of a unidirectional switching element Q4 connected to a positive electrode of a diode bridge DB (hereinafter simply referred to as DB) in which four diodes D4, D5, D6, and D7 are bridge-connected. The emitter or source of the unidirectional switching element is connected to the negative electrode of the DB.

  On the primary side of the filament transformer T1 configured as described above, the commercial power source 6 passes through a noise filter composed of the capacitor C2 and the choke coil L1, and charges the capacitor C3 with an AC voltage unlike an ordinary switching power source. The voltage of the capacitor C3 is applied to the primary side of the filament transformer T1, and the bidirectional switching element group 10 performs a high-frequency switching operation as described below.

  When the power supply voltage is positive, current flows in the direction of C3 → T1 → DB (D4) → Q4 → DB (D7), and when the power supply voltage is negative, C3 → DB (D6) → Q4 → DB. (D5) → Current flows in the direction of T1. By such a switching operation, a current as if the switching frequency was modulated by a commercial power supply flows continuously to the primary side of the filament transformer T1 in the order of C3, T1, DB, and Q4.

  The secondary side of the filament transformer T1 has the same configuration as that described in the first embodiment and performs the same operation.

  In the first embodiment, since two unidirectional switching elements are used in series, the drive circuit is complicated due to the floating operation of the high-side gate. However, in the second embodiment, the unidirectional switching element is used. Since there is one, the gate drive circuit is simple.

  In each of the above embodiments, only the basic circuit portion has been described and the control circuit portion has not been described. However, the following configuration can be easily considered. Needless to say, the magnetron filament power supply device is configured by sensing the power supply voltage, current and power, and the secondary side filament current as feedback elements to vary the gate PWM signal of the switching element.

  It is useful as a magnetron filament power supply device for driving a magnetron of a microwave application device used for a microwave oven, industrial use, medical use and the like.

Circuit diagram of magnetron filament power supply device according to Embodiment 1 of the present invention Circuit diagram of magnetron filament power supply apparatus according to Embodiment 2 of the present invention Circuit diagram of conventional magnetron filament power supply

Explanation of symbols

6 Commercial Power Supply 9 Magnetron 10 Bidirectional Switching Element Group 11 Low Pass Filter C2, C3, C4, C5, C6 Capacitor DB Diode Bridge D2, D3, D4, D5, D6, D7 Diode Eb High Voltage Power Supply F Filament L1, L2 Choke Coil Q2 , Q3, Q4 Unidirectional switching element T1 Filament transformer

Claims (4)

A magnetron filament power supply device characterized in that a commercial power supply, a noise filter, and a bidirectional switching element group are connected to the primary side of the filament transformer, and are connected to the filament of the magnetron via a low-pass filter on the secondary side of the filament transformer. . In the bidirectional switching element group, two unidirectional switching elements are connected in series in opposite polar directions, and two diodes are connected in parallel with the unidirectional switching element and in the opposite polarity direction to the current-carrying direction of each other diode. The magnetron filament power supply device according to claim 1, further comprising a configuration. In the bidirectional switching element group, a collector or drain of a unidirectional switching element is connected to a positive electrode of a diode bridge in which four diodes are bridge-connected, and an emitter or a source of the unidirectional switching element is connected to a negative electrode of the diode bridge. The magnetron filament power supply device according to claim 1. 4. The low-pass filter provided on the secondary side of the filament transformer includes a plurality of capacitors connected in parallel and a choke coil connected in series to the plurality of capacitors. The magnetron filament power supply device described in 1.

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