WO2012081221A1 - Magnetron-driving power supply and high-frequency heating device equipped with same - Google Patents

Abstract

Provided are a magnetron-driving power supply and a high-frequency heating device equipped with the same, such that the power supply can operate with a high power factor without being affected by variations in the type or characteristics of the magnetron. A voltage from an alternating current power supply (20) is rectified; one of input voltage waveform information (92) and input current waveform information (91) of an inverter circuit which conducts high-frequency switching to transmit electric power is selected, wherein the one having a greater amplitude than the other is selected; the selected one of input voltage waveform information (92) and input current waveform information (91) is superimposed on electric power control information (93) by a mixing circuit (73) to pulse-width modulate the switching of a switching transistor (37); and the signal amplitude is changed between start-up control and steady-state control. In this way, the pulse-width modulation control pattern for each of the start-up control and the steady-state control can be optimally designed according to respective control requirements, and therefore, more stable control of the magnetron-driving power supply can be achieved.

Description

Magnetron driving power source and high-frequency heating apparatus including the same

The present invention relates to a magnetron driving power source having a magnetron used for a microwave oven or the like as a load.

Conventional known magnetron driving power supplies adjust the power supplied to the magnetron by adjusting the output pulse width of the inverter control circuit. The power supplied to the magnetron is increased by increasing the output pulse width of the inverter control circuit, and conversely, the power is reduced by decreasing the output pulse width. With this configuration, the heating output of the magnetron can be continuously varied.

In addition, since the heater also serves as the magnetron cathode, the transformer that supplies power to the magnetron also supplies power to the heater. Therefore, the power supplied to the heater also follows the change in power supplied to the magnetron. It was changing.

Magnetron is a vacuum tube that generates microwaves inside by emitting thermoelectrons from the cathode, so it is necessary to control the temperature of the heater (cathode) within an appropriate range in order to maintain stable oscillation.

However, as described above, the power supplied to the heater also changes following the change in the power supplied to the magnetron. Therefore, if the temperature of the heater is kept within an appropriate range, only a slight change in the output power can be obtained. There was a problem that the heating output could not be changed continuously.

There are a high-frequency heating device and a control method thereof disclosed in Patent Documents 1 and 2 as a high-frequency heating device that solves this problem. FIG. 11 is a block diagram of the magnetron driving power source disclosed in Patent Document 1. In FIG.

In FIG. 11, this heating control system includes a magnetron 101, a high voltage transformer 103 that supplies high voltage power to the high voltage rectifier circuit 102 that supplies secondary winding power to the magnetron 101, and simultaneously supplies power to the heater 115 of the magnetron 101, The inverter circuit 105 that rectifies the AC power supply 104 and converts it into AC having a predetermined frequency and supplies the AC voltage to the high-voltage transformer 103, the power detection means 106 that detects input power or output power of the inverter circuit 105, and a desired heating output An output setting unit 107 that outputs an output signal corresponding to the setting, and a power adjustment unit 116 that compares the output of the power detection means 106 with the output setting signal to control the DC level of the power adjustment signal so as to obtain a desired heating output; The output 106 of the power detection means is the output level 11 of the reference voltage generation means. When the above is reached, the oscillation detection means 119 whose output oscillation detection signal changes from LO to HI, the comparison voltage generation circuit 120 that generates a voltage corresponding to the output setting signal, and the waveform shaping that compares the output signal with the level conversion circuit A waveform shaping circuit 121 that shapes the signal and the output of the rectifier circuit 110 that rectifies the voltage of the AC power supply 104 based on the waveform shaping signal and the oscillation detection signal, and the output signal of the waveform shaping circuit 121 is the comparison voltage generation circuit. A comparison circuit 111 that outputs a comparison reference voltage when the output is smaller than the output 120 and an inverting amplification when larger, and a signal that outputs a pulse width control signal by superimposing the output signal of the comparison circuit 111 on the power adjustment signal The output of the superimposing means 112, the oscillation circuit 113, and the oscillation circuit 113 is pulse width modulated by the pulse width control signal, and this modulation output It has a structure comprising an inverter control circuit 114 for driving the more the inverter circuit 105.

The above high-frequency heating device adjusts the power supplied to the magnetron 101 by the output pulse width of the inverter control circuit 114. When the output voltage of the signal superimposing means 112 becomes high, the output pulse width of the inverter control circuit 114 becomes wide and the power supplied to the magnetron 101 becomes large.

In this apparatus, the heating output of the magnetron 101 can be continuously varied by continuously changing the output voltage of the signal superimposing means 112. According to this configuration, the waveform shaping circuit 121 that inputs the rectified voltage of the AC power supply 104 and outputs the rectified voltage to the comparison circuit 111 performs shaping according to the output setting.

The output of the waveform shaping circuit 121 is inverted and amplified by a comparison circuit 111 having a reference voltage generation circuit 120 that generates a reference signal of a level corresponding to the heating output setting signal as a reference voltage, and the inverted amplification signal and the power adjustment unit By superimposing the output, the pulse width control signal, which is the output signal of the signal superimposing means 112, has a lower level near the maximum amplitude of the AC power source 104 when the heating output setting is low than when the heating output setting is high. Accordingly, the non-oscillation portion of the magnetron 101 becomes higher, and the oscillation period per cycle of the AC power supply of the magnetron 101 becomes longer. As a result, the power supplied to the heater 115 increases.

Furthermore, at the time of high output, the input current waveform of the inverter circuit 105 is convex upward near the envelope peak and becomes a waveform close to a sine wave, and the power source current harmonic is suppressed.

In this way, the waveform shaping circuit 121 controls the power supply current harmonics to be low by controlling the power supply current harmonics to be small at high output so that a large amount of heater current is input when the pulse width modulation signal is low output. In addition, since the change in the heater current can be reduced, a highly reliable high-frequency heating device can be realized.

However, in this control, the ON / OFF drive pulse of the switching transistor is subjected to pulse width modulation using a modulated waveform obtained by processing and shaping the commercial power supply waveform, and waveform shaping by prospective control so that the input current waveform approaches a sine wave. Therefore, the waveform shaping cannot keep up with fluctuations in the characteristics of the magnetron, fluctuations in the voltage between the anode and the cathode due to the anode temperature of the magnetron and the load in the microwave oven, and fluctuations in the power supply voltage.

Therefore, there is a control method disclosed in Patent Document 2 for the above problem. FIG. 12 is a block diagram of a magnetron driving power source disclosed in Patent Document 2. In FIG.

12, the high-frequency heating device includes an inverter circuit, a control circuit that controls the switching transistor 239 of the inverter circuit, and a magnetron 250. The inverter circuit includes an AC power supply 220, a diode bridge type rectifier circuit 231, a smoothing circuit 230, a resonance circuit 236, a switching transistor 239, and a voltage doubler rectifier circuit 244.

The AC voltage of the AC power source 220 is rectified by the diode bridge type rectifier circuit 231 and converted into a unidirectional voltage by the smoothing circuit 230 including the inductor 234 and the capacitor 235. The high frequency high frequency power is transmitted to the secondary winding 243 through the high voltage transformer 241 by the inverter circuit including the resonance circuit 236 including the primary winding of the resonance capacitor 237 and the high voltage transformer 241 and the inverter circuit including the switching transistor 239. The

The high-voltage and high-frequency power induced in the secondary winding 243 is converted into a DC high voltage by a voltage doubler rectifier circuit 244 including high- voltage capacitors 245 and 247 and high- voltage diodes 246 and 248, and between the anode 252 and the cathode 251 of the magnetron 250. Supplied.

The high-voltage transformer 241 has a tertiary winding 242, and the heater power of the magnetron 250 is supplied by the tertiary winding 242 to heat the heater.

The control circuit for controlling the switching transistor 239 of the inverter circuit is configured by CT 271 and the like, and is configured to control the power from the input current detection unit for detecting the input current to the inverter circuit, the input voltage detection unit for detecting the voltage of the AC power supply, and the comparison circuit 274. A drive circuit for turning ON / OFF the switching transistor 239 of the inverter circuit, which is composed of a mix circuit 275 that mixes information 291, a sawtooth wave generation circuit 283, and a PWM comparator 282, is pulse width modulated.

In this configuration, since not only the input current waveform information 290 but also the input voltage waveform information 294 is input to the mix circuit 275, the characteristics between the magnetron 250, the anode temperature of the magnetron 250, and the anode-cathode due to the load in the microwave oven Input voltage waveform shaping that is not affected by voltage fluctuations and power supply voltage fluctuations can be realized with a relatively simple configuration.

Japanese Unexamined Patent Publication No. 7-176375 Japanese Unexamined Patent Publication No. 2007-149446

However, the conventional magnetron driving power supply has the following problems. That is, particularly when the input current to the inverter circuit is small, the signal amplitude of the input current detector may be lower than the signal amplitude of the input voltage detector.

In this case, the pulse width modulation of the drive signal transmitted to the switching transistor has a degree of modulation suitable to some extent in order to maintain the power factor, and the effect of preventing an extreme decrease in the power factor can be exhibited. A situation occurs in which the on-time for the switching transistor to perform the soft switching operation is insufficient.

Especially, since the maximum conversion power is large in the magnetron drive power supply, soft switching technology is applied to reduce the switching loss of the switching transistor. Soft switching technology is a technology that reduces the switching loss by slowing the voltage or current change at the switching timing by the action of the resonant circuit, but it is necessary to store a predetermined energy in the resonant circuit for the soft switching operation. is there.

The circuit method described in the prior art document is a method of voltage resonance type soft switching. However, in this method, if the on-time of the switching transistor is not more than a certain level, the accumulation of energy in the resonance circuit is insufficient and the soft circuit is soft. When the switching transistor is turned on, the switching operation is lost, and the switching transistor is turned on in a state where a voltage is applied.

If this happens, there is a possibility that the loss at turn-on will be excessive and the switching transistor will generate excessive heat.

Also, the magnetron cannot generate microwaves unless the cathode is heated to a predetermined temperature as described above.

For this reason, the operation of the magnetron has a steady state in which microwaves are generated and a start-up control state in which the cathode is heated, and the operating condition requirements for each state are different. Naturally, pulse width modulation control is also performed. Although different controls are required, since the conventional power supply for driving a magnetron does not separate the pulse width modulation control for start-up control and steady control, if the operating conditions such as the power supply voltage are different, both pulse width modulation controls There is a possibility of interfering and inhibiting stable operation.

In addition, the conventional magnetron driving power source has the following problems. That is, particularly when the input current to the inverter circuit is small, the signal amplitude of the input current detector may be lower than the signal amplitude of the input voltage detector. In this case, the pulse width modulation of the drive signal transmitted to the switching transistor has a degree of modulation suitable to some extent in order to maintain the power factor, and the effect of preventing an extreme decrease in the power factor can be exhibited. A situation occurs in which the on-time for the switching transistor to perform the soft switching operation is insufficient.

Especially, since the maximum conversion power is large in the magnetron drive power supply, soft switching technology is applied to reduce the switching loss of the switching transistor. Soft switching technology is a technology that reduces the switching loss by slowing the voltage or current change at the switching timing by the action of the resonant circuit, but it is necessary to store a predetermined energy in the resonant circuit for the soft switching operation. is there. The circuit method described in the prior art document is a method of voltage resonance type soft switching. However, in this method, if the on-time of the switching transistor is not more than a certain level, the accumulation of energy in the resonance circuit is insufficient and the soft circuit is soft. When the switching transistor is turned on, the switching operation is lost, and the switching transistor is turned on in a state where a voltage is applied. If such an operation occurs, the loss at turn-on becomes excessive, and there is a possibility that the heat generated in the switching transistor becomes excessive.

Also, the magnetron cannot generate microwaves unless the cathode is heated to a predetermined temperature as described above. For this reason, the operation of the magnetron has a steady state in which microwaves are generated and a start-up control state in which the cathode is heated, and the operating condition requirements for each state are different. Naturally, pulse width modulation control is also performed. Although different controls are required, since the conventional power supply for driving a magnetron does not separate the pulse width modulation control for start-up control and steady control, if the operating conditions such as the power supply voltage are different, both pulse width modulation controls There is a possibility of interfering and inhibiting stable operation.

SUMMARY OF THE INVENTION The present invention solves the above-described conventional problems, and an object thereof is to provide a magnetron driving power source that can operate with an optimum pulse width modulation pattern for each control request by separating start-up control and steady-state control. .

Further, the present invention solves the above-described conventional problems, and separates start-up control and steady-state control, can operate with an optimum pulse width modulation pattern for each control request, and can control the magnetron at a low output. However, an object of the present invention is to provide a magnetron driving power source that does not increase the turn-on loss of the switching transistor.

In order to solve the above-described conventional problems, the magnetron driving power source according to the present invention is a magnetron that rectifies the voltage of an AC power source, modulates the on-time of the high-frequency switching of the switching transistor, and converts it to high-frequency power. A driving power source for detecting an input current from an AC power source to the inverter circuit and outputting input current waveform information; and detecting an input voltage input from the AC power source to the inverter circuit An input voltage detector that outputs input voltage waveform information; a selector that selects one of the input current waveform information and the input voltage waveform information; and the input current waveform information selected by the selector and the input Switching that converts any of the voltage waveform information into a drive signal for the switching transistor of the inverter circuit And a section, the selection unit are those magnetrons to select the input voltage waveform information in a period of active state, the magnetron is configured to select the input current waveform information and becomes the oscillation state.

As a result, the startup control when the magnetron is in the non-oscillation state can generate a pulse width modulation control pattern based on the input voltage waveform information, and when the magnetron shifts to the oscillation state, the pulse width modulation control pattern can be generated based on the input current waveform information. .

In addition, since pulse width modulation control can be generated with completely different signal relationships between startup control and steady state control, an optimal pulse width modulation pattern can be generated for each control requirement, and a more stable magnetron drive power supply Control can be realized.

In order to solve the above-described conventional problems, the magnetron driving power source of the present invention controls an inverter circuit that rectifies the voltage of the AC power source and modulates the on-time of the high-frequency switching of the switching transistor to convert it to high-frequency power. And a magnetron driving power source for supplying power to the magnetron via a rectifier circuit for rectifying the high-frequency power, wherein the input current from the AC power source to the inverter circuit is detected and input current waveform information is output. A current detection unit; an input voltage detection unit that detects an input voltage input from the AC power supply to the inverter circuit and outputs input voltage waveform information; and one of the input current waveform information and the input voltage waveform information. A selection unit to be selected, and any of the input current waveform information and the input voltage waveform information selected by the selection unit A switching conversion unit that converts the drive signal of the switching circuit of the inverter circuit into a drive signal; and a power command unit that commands the power that the inverter circuit supplies to the magnetron. The selection unit includes the input voltage detection unit and the input current. When the signal waveform information having the larger output amplitude is selected from among the detection units, and the magnetron is ready to oscillate, the signal amplitude of the input voltage waveform information is reduced, and the power indicated by the power command unit is a predetermined value. In the following cases, the signal amplitude obtained by the selection unit is reduced, and the switching conversion unit compares the signal waveform information selected by the selection unit with a triangular wave using a PWM comparator, and drives the switching transistor based on the magnitude relationship. The signal is configured.

As a result, the start-up control when the magnetron is in the non-oscillation state generates a pulse width modulation control pattern based on the input voltage waveform information, and the signal amplitude based on the input voltage waveform information decreases when the magnetron enters the oscillation state. The pulse width modulation control pattern can be generated according to the information, and the pulse width modulation control can be generated with completely different signal relations between the start control and the steady control, so the optimum pulse width modulation pattern for each control requirement Can be realized, and more stable control of the magnetron drive power supply can be realized, and even if the magnetron is controlled to a low output state, the on-time of the switching transistor of the inverter circuit is not reduced too much, and soft switching Because it can operate reliably, it can always operate with low loss. That.

The power source for driving the magnetron of the present invention can optimally design the pulse width modulation control pattern of the start control and the steady control according to each control request, so that it is possible to realize more stable control of the power source for driving the magnetron. it can. In addition, the magnetron driving power source according to the present invention can optimally design the pulse width modulation control patterns for start-up control and steady control according to the respective control requirements, so that more stable control of the magnetron driving power source and low power can be achieved. Loss operation can be realized.

1 is a block diagram of a magnetron drive power supply according to a first embodiment of the present invention. Configuration diagram of the input current detection unit according to the first embodiment Configuration diagram of the mix circuit according to the first embodiment Waveform diagram showing input voltage waveform information, input current waveform information, and output signal of the mix circuit according to the first embodiment Block diagram of magnetron drive power supply according to the second embodiment of the present invention Waveform diagram showing input voltage waveform information, input current waveform information, and output signal of the mix circuit according to the second embodiment Waveform diagram showing input voltage waveform information, input current waveform information, and output signal of the mix circuit according to the third embodiment of the present invention Block diagram of magnetron drive power supply according to Embodiment 4 of the present invention Circuit diagram showing a mix circuit of a magnetron drive power supply according to a fourth embodiment of the present invention. Waveform diagram of magnetron drive power supply according to the fourth embodiment of the present invention Block diagram of a conventional magnetron drive power supply Block diagram of a conventional magnetron drive power supply

A first invention is a magnetron driving power source that controls an inverter circuit that rectifies a voltage of an AC power source, modulates a high-frequency switching on-time of a switching transistor, and converts it into high-frequency power, and converts the AC power source to the inverter An input current detector that detects an input current to the circuit and outputs input current waveform information, and an input voltage detector that detects an input voltage input from the AC power source to the inverter circuit and outputs input voltage waveform information A selection unit that selects any one of the input current waveform information and the input voltage waveform information, and any one of the input current waveform information and the input voltage waveform information selected by the selection unit. A switching conversion unit that converts the driving signal of the switching transistor into a drive signal. The input voltage waveform information is selected during the period of the state, and the input current waveform information is selected when the magnetron is ready to oscillate. When the magnetron is in the activated state, the pulse width is determined by the input voltage waveform information. A modulation control pattern is generated, and after the oscillation is enabled, a pulse width modulation control pattern is generated based on the input current waveform information. Therefore, in each state, the inverter circuit is operated with the optimum pulse width modulation pattern to increase switching loss and power factor. It is possible to perform an operation for preventing the deterioration of the image.

In the second invention, in particular, the selection unit of the first invention is connected between the input current detection unit and the input voltage detection unit and the switching conversion unit, and either of the input current waveform information and the input voltage waveform information and the inverter circuit Combining power control information for controlling the input current to be a predetermined value, it is composed of a synthesis circuit that generates an on-voltage signal for the switching transistor, and the switching converter is turned on so that the peak voltage of the semiconductor switch element is suppressed. The voltage signal is converted into a drive signal for the switching transistor.

According to the present invention, the pulse width modulation control pattern is generated from the input voltage waveform information when the magnetron is in the activated state, and the pulse width modulation control pattern is generated from the input current waveform information after the oscillation is enabled. It is possible to operate the inverter circuit with an optimal pulse width modulation pattern to prevent an increase in switching loss and a decrease in power factor.

According to a third aspect of the invention, a clock generator is provided in the magnetron driving power supply of the first or second invention, and the clock generator generates a clock in synchronization with the cycle of the AC power supply. The selection switching of the input voltage waveform information is synchronized with the clock output of the clock generator.

According to the present invention, the pulse width modulation control pattern is generated from the input voltage waveform information when the magnetron is in the activated state, and the pulse width modulation control pattern is generated from the input current waveform information after the oscillation is enabled. It is possible to operate the inverter circuit with an optimal pulse width modulation pattern to prevent an increase in switching loss and a decrease in power factor.

Also, since the switching timing between the start control and the steady control can be performed at a predetermined timing by the clock pulse, the unstable elements of the control accompanying the control switching can be reduced.

In the fourth aspect of the invention, in particular, the clock generation unit of the third aspect of the invention generates a clock pulse at a timing when the absolute value of the AC power supply voltage changes from a decrease to an increase, and the selection unit generates an input current waveform by the clock pulse of the clock generation unit. The information and the input voltage waveform information are selectively switched.

According to the present invention, the pulse width modulation control pattern is generated from the input voltage waveform information when the magnetron is in the activated state, and the pulse width modulation control pattern is generated from the input current waveform information after the oscillation is enabled. It is possible to operate the inverter circuit with an optimal pulse width modulation pattern to prevent an increase in switching loss and a decrease in power factor.

In addition, since the switching timing between the start control and the steady control can be performed at the time when the amplitude of the AC voltage is the lowest, it is possible to prevent the switching control from becoming unstable due to the control switching.

In the fifth aspect of the invention, in particular, the clock generation unit of the third aspect of the invention generates a clock that divides the period of the AC power supply by 2, and the selection unit generates a clock for selecting and switching input current waveform information and input voltage waveform information. It is configured to synchronize with the clock output of the unit.

According to the present invention, the pulse width modulation control pattern is generated from the input voltage waveform information when the magnetron is in the activated state, and the pulse width modulation control pattern is generated from the input current waveform information after the oscillation is enabled. It is possible to operate the inverter circuit with an optimal pulse width modulation pattern to prevent an increase in switching loss and a decrease in power factor.

In addition, since the switching timing between the start control and the steady control can be performed at the time when the amplitude of the AC voltage is the lowest, it is possible to prevent the switching control from becoming unstable due to the control switching.

According to a sixth aspect of the invention, the selection unit is configured to perform selection switching between input current waveform information and input voltage waveform information, particularly at the rising or falling edge of the clock output of the clock generation unit of the fifth invention. .

According to the present invention, the pulse width modulation control pattern is generated from the input voltage waveform information when the magnetron is in the activated state, and the pulse width modulation control pattern is generated from the input current waveform information after the oscillation is enabled. It is possible to operate the inverter circuit with an optimal pulse width modulation pattern to prevent an increase in switching loss and a decrease in power factor.

In addition, since the switching timing between the start control and the steady control can be performed at the time when the amplitude of the AC voltage is the lowest, it is possible to prevent the switching control from becoming unstable due to the control switching.

A seventh invention is a magnetron driving power source that controls an inverter circuit that rectifies the voltage of an AC power source and modulates the on-time of high-frequency switching of a switching transistor to convert it into high-frequency power, and from the AC power source to the inverter circuit An input current detector that detects input current to output input current waveform information; an input voltage detector that detects input voltage input from the AC power supply to the inverter circuit; and outputs input voltage waveform information; A selection unit that selects either the input current waveform information or the input voltage waveform information, and converts either the selected input current waveform information or the input voltage waveform information into a drive signal for a switching transistor of the inverter circuit A switching converter that generates a clock and a clock generator that generates a clock in synchronization with the cycle of the AC power supply. The selection unit is configured to select a larger one of the output signals of the input current detection unit and the input voltage detection unit, and the output of the input voltage detection unit is gradually decreased by a predetermined number of steps. The timing of gradual decrease is synchronized with the clock output of the clock generator.

According to the present invention, the pulse width modulation control pattern is generated from the input voltage waveform information when the magnetron is in the activated state, and the pulse width modulation control pattern is generated from the input current waveform information after the oscillation is enabled. It is possible to operate the inverter circuit with an optimal pulse width modulation pattern to prevent an increase in switching loss and a decrease in power factor.

In addition, since the switching timing between the start control and the steady control can be performed at the time when the amplitude of the AC voltage is the lowest, it is possible to prevent the switching control from becoming unstable due to the control switching.

In the eighth aspect of the invention, in particular, the output of the input voltage detection unit of the seventh aspect of the invention is stepwise so that the output voltage is reduced to half the amplitude in the first stage and the output voltage becomes zero in the second stage. It is configured to decrease to

According to the present invention, the pulse width modulation control pattern is generated from the input voltage waveform information when the magnetron is in the activated state, and the pulse width modulation control pattern is generated from the input current waveform information after the oscillation is enabled. It is possible to operate the inverter circuit with an optimal pulse width modulation pattern to prevent an increase in switching loss and a decrease in power factor.

In addition, since the switching timing between the start control and the steady control can be performed at the time when the amplitude of the AC voltage is the lowest, it is possible to prevent the switching control from becoming unstable due to the control switching.

In the ninth invention, a predetermined delay time is particularly provided between the first stage and the second stage of the eighth invention.

According to the present invention, the pulse width modulation control pattern is generated from the input voltage waveform information when the magnetron is in the activated state, and the pulse width modulation control pattern is generated from the input current waveform information after the oscillation is enabled. It is possible to operate the inverter circuit with an optimal pulse width modulation pattern to prevent an increase in switching loss and a decrease in power factor.

In addition, since the switching timing between the start control and the steady control can be performed at the time when the amplitude of the AC voltage is the lowest, it is possible to prevent the switching control from becoming unstable due to the control switching.

According to a tenth aspect of the invention, in particular, the magnetron driving power source of the seventh aspect is provided with a clock count unit, and the clock count unit counts the clock of the clock generation unit and counts the clock a predetermined number of times from the first stage. It is set as the structure which transfers to the stage.

According to the present invention, the pulse width modulation control pattern is generated from the input voltage waveform information when the magnetron is in the activated state, and the pulse width modulation control pattern is generated from the input current waveform information after the oscillation is enabled. It is possible to operate the inverter circuit with an optimal pulse width modulation pattern to prevent an increase in switching loss and a decrease in power factor.

In addition, since the switching timing between the start control and the steady control can be performed at the time when the amplitude of the AC voltage is the lowest, it is possible to prevent the switching control from becoming unstable due to the control switching.

In the eleventh aspect of the invention, in particular, the input voltage detection unit of the seventh aspect of the invention is configured to reduce the output voltage amplitude by a predetermined value every time the clock is counted by the clock counting unit.

According to the present invention, the pulse width modulation control pattern is generated from the input voltage waveform information when the magnetron is in the activated state, and the pulse width modulation control pattern is generated from the input current waveform information after the oscillation is enabled. It is possible to operate the inverter circuit with an optimal pulse width modulation pattern to prevent an increase in switching loss and a decrease in power factor.

In addition, since the switching timing between the start control and the steady control can be performed at the time when the amplitude of the AC voltage is the lowest, it is possible to prevent the switching control from becoming unstable due to the control switching.

In a thirteenth aspect of the invention, the inverter circuit that rectifies the voltage of the AC power supply, modulates the on-time of the high-frequency switching of the switching transistor and converts it to high-frequency power, and controls the inverter circuit to the magnetron via the rectifier circuit that rectifies the high-frequency power. A power source for driving a magnetron that supplies power, an input current detection unit that detects an input current from the AC power supply to the inverter circuit and outputs input current waveform information, and is input from the AC power supply to the inverter circuit An input voltage detection unit that detects input voltage and outputs input voltage waveform information; a selection unit that selects one of the input current waveform information and the input voltage waveform information; and the input selected by the selection unit Either the current waveform information or the input voltage information is converted into a drive signal for the switching transistor of the inverter circuit. A switching converter that performs power conversion, and a power command unit that commands the power supplied to the magnetron by the inverter circuit, and the selection unit is a signal having a larger output amplitude of the input voltage detection unit and the input current detection unit. When the waveform information is selected and the magnetron is ready to oscillate, the signal amplitude of the input voltage waveform information is reduced, and the signal obtained by the selection unit when the power indicated by the power command unit is a predetermined value or less. The amplitude is reduced, and the switching converter compares the signal waveform information selected by the selector with a triangular wave by a PWM comparator, and uses the magnitude relationship as a drive signal for the switching transistor. When the is in the startup state, the input current waveform is very small, so the input voltage waveform The pulse width modulation control pattern is generated according to the input voltage waveform information, and the signal based on the input voltage waveform information is gradually reduced after the oscillation is enabled, so the input current waveform information is prioritized and the pulse width modulation control pattern is gradually given priority. Therefore, it is possible to operate the inverter circuit with an optimal pulse width modulation pattern in both the start-up state and the oscillation state to prevent an increase in switching loss and a decrease in power factor. Even when the output power is low, the pulse width modulation pattern is output so that the switching transistor of the inverter circuit performs a soft switching operation, so that a low-loss circuit operation is always possible, and an abnormal temperature of the switching transistor due to an increase in switching loss. It is possible to prevent the rise.

According to a fourteenth aspect of the invention, in particular, the selection unit of the thirteenth aspect is constituted by a voltage-current conversion unit and a current injection unit is provided, and the current injection unit is a signal amplitude waveform selected by injecting a current into the selection unit. When the magnetron is in the starting state, the input current is at a very low level, so the input voltage waveform information is prioritized and the pulse width modulation control pattern is generated based on the input voltage waveform information. After that, since the signal based on the input voltage waveform information is gradually reduced, the input current waveform information is gradually prioritized and the pulse width modulation control pattern is generated. Therefore, the optimum pulse width modulation is performed in each of the magnetron in the activated state and the oscillation state. The inverter circuit can be operated with a pattern to prevent the switching loss from increasing and the power factor from being lowered. Even when the output power of the magnetron is low, since the pulse width modulation pattern is output so that the switching transistor of the inverter circuit performs soft switching operation, circuit operation with low loss is always possible, and switching transistor abnormalities due to increased switching loss It is possible to prevent a significant temperature rise.

In the fifteenth aspect of the invention, in particular, the amount of current injected by the current injection section of the fourteenth aspect of the invention is configured to be inversely proportional to the output voltage of the power command section. Since the amount of injected current in the current injection section changes at the same time as the conversion power of the inverter changes, the amount of current injection in the current injection section changes according to the conversion power of the inverter circuit. There is no point where the pulse width modulation control pattern changes. For this reason, since the discontinuity of the control is eliminated, the unstable element of the control is eliminated, and the magnetron can be driven stably with respect to all the converted power.

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.

(Embodiment 1)
FIG. 1 is a block diagram for explaining a magnetron driving power source according to a first embodiment of the present invention. In FIG. 1, the magnetron driving power source includes an inverter circuit including a switching transistor 37 and a resonance circuit 34, a control unit that controls on / off of the switching transistor 37, and a magnetron 50.

The control unit includes a PWM comparator 79 that transmits a drive pulse to the switching transistor 37, a sawtooth wave generation circuit 78, a mix circuit 73 as a selection unit, and a shunt resistor 70 as an input current detection unit.

The AC voltage of the AC power supply 20 is rectified by a bridge-type rectifier circuit 30 composed of four diodes, rectified to a unidirectional voltage, and supplied to the inverter circuit by a smoothing circuit 31 including an inductor 32 and a capacitor 33. Is done.

An inverter circuit composed of a resonance circuit composed of a capacitor 35 and a primary winding 36 of a high-voltage transformer 40 and a switching transistor 37 excites high-frequency power by controlling the switching transistor 37 on and off, High voltage and high frequency power is induced in the secondary winding 41.

The high-frequency and high-frequency power induced in the secondary winding 41 is supplied between the anode 52 and the cathode 51 of the magnetron 50 through a voltage doubler rectifier circuit 47 including capacitors 44 and 45 and diodes 43 and 46. The high-voltage transformer 40 is provided with a tertiary winding 42 and is configured to simultaneously supply heater power for heating the cathode 51 to the magnetron 50 simultaneously with the above-described operation.

Next, a control circuit (control unit) that controls the switching transistor 37 of the inverter circuit will be described.

As shown in FIG. 2, the shunt resistor 70 provided between the bridge-type rectifier circuit 30 and the smoothing circuit 31 and the amplifier circuit that amplifies the voltage at both ends form an input current shaping circuit 71 to generate input current waveform information 91. An input current detection unit.

The input current waveform information 91 is smoothed by the smoothing circuit 75, and this is compared with a signal from the output setting unit 76 that generates an output setting signal corresponding to the heating output setting by the comparison circuit 77. The comparison circuit 77 compares the input current signal smoothed by the smoothing circuit 75 with the setting signal generated by the output setting unit 76 in order to control the magnitude of the input power of the inverter circuit.

Therefore, the current may be detected by a shunt resistor as in the configuration of the present embodiment, the input current may be detected by a current transformer, or a signal such as a collector current or a collector voltage of a switching transistor may be used. Good. That is, the information for power control input to the comparison circuit 77 is not restricted to the configuration shown in this embodiment mode.

The control circuit also includes an input voltage detection unit including a pair of diodes that detect and rectify the voltage of the AC power supply 20 and a shaping circuit 72 that shapes the rectified voltage and generates input voltage waveform information 92.

The input voltage waveform information 92, the input current waveform information 91, and the power control information 93 from the comparison circuit 77 are mixed and filtered by the mixing circuit 73 to output the ON signal width information 94 of the switching transistor 37, and the sawtooth wave generating circuit. The sawtooth wave from 78 is compared with the PWM comparator 79 and the switching transistor 37 of the inverter circuit is ON / OFF controlled by pulse width modulation.

The on / off control of the switching transistor 37 with respect to the input current waveform information is converted with a polarity that shortens the on-time when the input current is large, and conversely increases it when it is small. Similarly, the input voltage waveform information is also converted with a polarity that shortens the on-time when the input voltage is high, and conversely lengthens the on-time when the input voltage is low.

FIG. 3 shows an example of the mix circuit 73. The mix circuit 73 has four input terminals, each of which receives input current waveform information 91, input voltage waveform information 92, power control information 93, and switching signal 95. The circuit shown in FIG. It is configured to transmit to.

With the configuration as described above, the mix circuit 73 selects any one of the input current waveform information 91 and the input voltage waveform information 92 and converts the selected one into an on / off control signal for the switching transistor 37 of the inverter circuit. To use.

By adopting such a configuration, correction is made so that the on-time of the switching transistor 37 is shortened in a period in which the voltage amplitude of the AC power supply is large so as to correct distortion of the input current waveform in a state where the magnetron 50 is oscillating constantly. Conversely, the ON signal width of the switching transistor 37 is subjected to pulse width modulation so that the ON time of the switching transistor 37 is corrected to be increased in a period in which the amplitude of the AC power supply voltage is small. The voltage waveform applied to the switching transistor 37 can be expressed as Equation (1). In Equation (1), V is the maximum value of the voltage applied to the switching transistor 37, E is the voltage of the capacitor 33, LP is the primary winding inductance of the high-voltage transformer 40, C is the capacitance of the capacitor 35, and Ton is the switching transistor 37. Indicates on-time. Therefore, the applied voltage can be controlled by increasing / decreasing the ON time of the switching transistor 37. That is, when the ON time is shortened, the peak voltage applied to the switching transistor 37 can be suppressed.

As a result, the sum of the instantaneous error or the correction amount of the ideal signal waveform and the input current waveform information 91 in a short period such as a half cycle of the AC power supply is substantially zero because the magnitude of the input current is controlled by other means. It is. In addition, since the portion where the input current does not flow due to the non-linear load is corrected in the flowing direction, the portion where the input current is large is decreased on the contrary to establish the above substantially zero.

This is to correct the current waveform so that it can be regarded as a linear load even if it is a non-linear load, and since the commercial power supply voltage waveform is a sine wave, the ideal waveform is a sine wave as well as the current waveform flowing through the linear load. In this way, the input current is corrected with the reverse polarity of the waveform so as to cancel the change in the input current waveform and the excess or deficiency with respect to the ideal waveform.

Therefore, a steep current change in a commercial power supply cycle caused by a non-linear load such as the magnetron 50, that is, distortion is canceled out by this control loop, input current waveform shaping is performed, and operation with low distortion and high power factor is realized. I can do it.

On the other hand, the magnetron 50 cannot oscillate microwaves unless the cathode 51 is heated to an appropriate temperature. In this state, the magnetron 50 exhibits an almost infinite resistance value. For this reason, in order to start the magnetron 50 at high speed, it is necessary to increase the power supplied to the cathode 51 as much as possible in the start-up control.

When the pulse width modulation of the ON signal width of the switching transistor 37 is compared with the case where the pulse width modulation is not performed based on the input current waveform information 91, when the pulse width modulation is applied, the envelope waveform of the supply current of the cathode 51 is trapezoidal. And more power can be supplied. As a result, the cathode 51 can be heated to an appropriate temperature in a shorter time.

The mix circuit 73 of the power source for driving the magnetron according to the present embodiment is configured to connect the input voltage waveform information 92 and the input current waveform information 91 to a common emitter resistor 737 through buffer transistors 735 and 739, respectively. With this configuration, the emitter voltage of the buffer transistor 735 or 739 operates so as to output the voltage of the input current waveform information 91 or the input voltage waveform information 92.

The emitter resistor 737 is connected to each of the buffer transistors 735 and 739 through a common emitter. Therefore, the signal information having the larger amplitude of the input voltage waveform information 92 and the input current waveform information 91 is reflected in the ON signal width information 94. It becomes the composition which is done. The voltage divided by the resistors 731 and 732 causes a voltage drop corresponding to the current flowing through the buffer transistors 735 and 739, and generates a signal obtained by inverting the waveform information.

The buffer circuit 733 is inserted in order to separate the impedance between the voltage dividing point and the capacitor 741 so that the impedance influence from the capacitor 741 does not affect the divided voltages of the resistors 731 and 732. The above waveform information is superimposed as voltage information on the ON signal width information 94 via the capacitor 741, and the ON signal width of the switching transistor 37 is subjected to pulse width modulation.

FIG. 4 is a waveform diagram showing the input voltage waveform information 92, the input current waveform information 91, the switching signal 95, and the ON signal width information 94 which is the output signal of the mix circuit of the magnetron driving power source of this embodiment. It is the wave form diagram which expanded the timing which changes to a steady state from a starting state.

During a period in which the cathode of the magnetron 50 is not heated to a sufficient temperature, the magnetron 50 exhibits an almost infinite impedance, so that the input current waveform is substantially zero. Therefore, the output signal of the mix circuit 73 is the input voltage waveform information 92. A signal amplitude reflecting the above is output. (Period T0 to T1) When the cathode 51 of the magnetron 50 is heated and ready to oscillate, the impedance decreases and the input current begins to flow.

In the start-up control state of heating the cathode 51 of the magnetron 50, the amplitude of the input voltage waveform information 92 is adjusted so that the power supplied to the cathode 51 can be maximized. If this signal amplitude is large, Since the input voltage waveform information 92 is output from the mix circuit even in the steady oscillation state, a high power factor cannot be realized in the steady oscillation state.

Therefore, in this embodiment, the switching circuit 74 is provided so as to cut the input voltage waveform information 92 when it is detected that the magnetron 50 is in an oscillation state. With this configuration, when the magnetron 50 shifts to the oscillation state, the output of the mix circuit 73 can be determined by the input current waveform information 91. Therefore, even when the input current is small, a high power factor can always be maintained. It becomes possible.

Further, when the input current waveform is small, the amplitude of the output signal of the mix circuit 73 is also small, so that the degree of modulation near the voltage peak point of the AC power supply 20 is also small. As a result, the ON time of the switching transistor 37 is set to be somewhat long. Will do.

As a result, the energy accumulated during the switching period can be secured in the resonance circuit 34 provided in the inverter circuit, and the soft switching operation can be stably performed even when the conversion power of the inverter circuit is low. It is possible to prevent an excessive increase in loss of 37.

(Embodiment 2)
FIG. 5 is a block diagram showing a magnetron driving power source according to the second embodiment of the present invention. The components denoted by the same reference numerals as those of the above-described embodiment perform the same functions, and detailed description thereof is omitted here. The difference from the above-described embodiment is that the control unit of the magnetron driving power supply includes a clock generation circuit 81 which is an input voltage detection unit, and the clock generation circuit 81 which is an input voltage detection unit determines the timing at which the switching circuit 74 operates. This is a point synchronized with a generated clock pulse.

Since the clock generation circuit 81 detects the timing of changing the clock from the input voltage waveform information 92, it can generate a clock pulse synchronized with the cycle of the AC power supply 20. The clock generation circuit 81 generates a clock that divides the cycle of the AC power supply by two.

The switching circuit 74 operates so as to switch the signal of the input voltage waveform information 92 at the timing when the signal of the clock generation circuit 81 changes after the switching signal 95 is determined to be steady. The switching timing may be the rising edge of the clock pulse, the falling edge, or the timing at which the absolute value of the AC power supply voltage starts to increase from the decrease.

FIG. 6 shows the signal waveform of the input voltage waveform information 92, the signal waveform of the input current waveform information 91, the output signal waveform of the steady state determination circuit 80 (switching signal 95), and the output of the clock generation circuit 81 in the magnetron drive power supply of this embodiment. It is a waveform diagram showing a signal waveform and a signal waveform of ON signal width information 94.

The difference from the above embodiment is that the signal waveform of the input voltage waveform information 92 is switched at a timing synchronized with the clock waveform of the clock generation circuit 81. Since the switching signal 95 can be randomly generated with respect to the cycle of the AC power supply 20, the stationary determination cannot always be determined at the best time for the stability of the control.

That is, there is a possibility that the steady state determination is confirmed when the amplitude of the AC power supply 20 becomes maximum, and when the waveform information is switched in this state, the instantaneous conversion power of the inverter circuit near the peak point of the AC power supply 20 is included. Since the value is also the maximum, a slight fluctuation in control may cause the switching operation to become unstable.

When a clock pulse synchronized with the AC power supply 20 is generated by the clock generation circuit 81 as in the present embodiment and the waveform information is switched using this clock pulse as a trigger, the control is switched with respect to the phase of the AC power supply 20. It becomes possible to fix the phase, and it is possible to eliminate an unstable element of control accompanying switching.

(Embodiment 3)
FIG. 7 is a waveform diagram showing an example of the third embodiment of the present invention. Since the configuration of the inverter circuit is the same as that of the second embodiment, the drawings are omitted here.

In the present embodiment, the signal amplitude of the input voltage waveform information 92 is divided into several steps in synchronization with the clock pulse of the clock generation circuit 81 and gradually decreased. For example, the output of the input voltage detecting unit is reduced stepwise so that the output voltage is reduced to ½ amplitude in the first stage and the output voltage becomes 0 (zero) in the second stage. Also, a predetermined delay time may be provided between the first stage and the second stage. Further, the inverter circuit may further include a clock count unit. The clock count unit counts the clock of the clock generation unit, and shifts to the second stage when the clock is counted a predetermined number of times from the first stage. Further, the input voltage detection unit may reduce the output voltage amplitude by a predetermined value each time the clock is counted by the clock counting unit. In the figure, the solid line of the signal waveform of the input current waveform information 91 indicates a signal waveform in a state where a high power output is instructed by the output setting unit, and the broken line indicates a signal in a state where a relatively low power output is instructed. The waveform is shown.

The signal amplitude of the input current waveform information 91 has a large amplitude at the time of predetermined power conversion in a state where a high power output is instructed, but in a state where a relatively low power output is instructed, stable control is achieved. However, the amplitude of the input current waveform information 91 remains small.

For this reason, when the waveform information is switched suddenly, the signal amplitude of the on signal width information 94 also changes abruptly, and there is a large change in the on signal width of the switching transistor 37 before and after the control is switched, and power stabilization control is not performed. May lead to stability.

However, in the present embodiment, the signal amplitude of the input voltage waveform information 92 is gradually reduced at several stages, so that a rapid change accompanying switching can be mitigated, and unstable elements of control accompanying switching can be eliminated. I can do it.

(Embodiment 4)
FIG. 8 is a block diagram for explaining the magnetron driving power source according to the first embodiment of the present invention.

8, the magnetron driving power source includes an inverter circuit including a switching transistor 37 and a resonance circuit 34, a control unit for controlling on / off of the switching transistor 37, and a magnetron 50. The control unit includes a PWM comparator 79 that transmits a drive pulse to the switching transistor, a sawtooth wave generation circuit 78, a mix circuit 73 as a selection unit, an input current detection unit, an input voltage detection unit, and the like. The AC voltage of the AC power supply 20 is rectified by a bridge-type rectifier circuit 30 composed of four diodes, rectified to a unidirectional voltage, and supplied to the inverter circuit by a smoothing circuit 31 including an inductor 32 and a capacitor 33. Is done.

An inverter circuit composed of a resonance circuit 34 and a switching transistor 37 constituted by a capacitor 35 and a primary winding 36 of a high-voltage transformer 40 excites high-frequency power by controlling on / off of the switching transistor 37. High voltage high frequency power is induced in the secondary winding 41. The high-voltage and high-frequency power induced in the secondary winding 41 is supplied between the anode 52 and the cathode 51 of the magnetron 50 through the voltage doubler rectifier circuit 47 including the capacitors 44 and 45 diodes 43 and 46. The high-voltage transformer 40 is provided with a tertiary winding 42 and is configured to simultaneously supply heater power for heating the cathode 51 to the magnetron 50 simultaneously with the above-described operation.

Next, a control circuit that controls the switching transistor 37 of the inverter circuit will be described.

As shown in FIG. 2, an input current shaping circuit 71 includes a current detection unit as an input current detection unit including a shunt resistor 70 provided between the bridge-type rectifier circuit 30 and the smoothing circuit 31, and an amplifier circuit that amplifies the voltage at both ends thereof. And an input current detector for generating the input current waveform information 91. The input current waveform information 91 is smoothed by the smoothing circuit 75, and the signal from the output setting unit 76 that generates an output setting signal corresponding to the heating output setting is compared by the comparison circuit 77. The comparison circuit 77 compares the input current signal smoothed by the smoothing circuit 75 with the setting signal generated by the output setting unit 76 to control the magnitude of the input power of the inverter circuit, and inputs the magnetron driving power source. Feedback control is performed so that the current becomes equal to the setting signal.

The input current may be detected by a voltage generated by passing a current through a resistor such as a shunt resistor as in the configuration of the present embodiment, or the input current may be detected by a current transformer. The output may be obtained by rectifying and smoothing, or a signal such as a collector current or a collector voltage of a switching transistor that changes according to the magnitude of the input current may be used. That is, the information for power control input to the comparison circuit 77 is not restricted to the configuration shown in this embodiment mode.

The control circuit also includes an input voltage detection unit including a pair of diodes that detect and rectify the voltage of the AC power supply 20 and a shaping circuit 72 that shapes the rectified voltage and generates input voltage waveform information 92. The input voltage waveform information 92, the input current waveform information 91, and the power control information 93 from the comparison circuit 77 are mixed and filtered by the mixing circuit 73 to output the ON signal width information 94 of the switching transistor 37, and the sawtooth wave generating circuit. The sawtooth wave output from 78 is compared with the PWM comparator 79, and the pulse width modulation is performed to control on / off of the switching transistor 37 of the inverter circuit.

The on / off control of the switching transistor 37 with respect to the input current waveform information 91 is converted with a polarity that shortens the on-time when the input current is large and conversely increases it when it is small. Similarly, the input voltage waveform information 92 is also converted with a polarity that shortens the on-time when the input voltage is high and conversely increases the on-time when the input voltage is low.

FIG. 9 shows an example of the mix circuit 73. The mix circuit 73 has five input terminals, each of which receives input current waveform information 91, input voltage waveform information 92, power control information 93, steady state determination signal 97, and output setting signal 96. Information 94 is transmitted to the PWM comparator 79.

With the configuration as described above, the input current waveform information 91 and the input voltage waveform information 92 are converted into an on / off control signal for the switching transistor 37 of the inverter circuit and used.

By adopting such a configuration, correction is made so that the on-time of the switching transistor 37 is shortened in a period in which the voltage amplitude of the AC power supply is large so as to correct distortion of the input current waveform in a state where the magnetron 50 is oscillating constantly. Conversely, the ON signal width of the switching transistor 37 is subjected to pulse width modulation so that the ON time of the switching transistor 37 is corrected to be increased in a period in which the amplitude of the AC power supply voltage is small. As a result, the sum of the instantaneous error or the correction amount of the ideal signal waveform and the input current waveform information 91 in a short period such as a half cycle of the AC power supply is substantially zero because the magnitude of the input current is controlled by other means. is there. In addition, since the portion where the input current does not flow due to the non-linear load is corrected in the flowing direction, the portion where the input current is large is decreased on the contrary to establish the above substantially zero. Even if it is a non-linear load, it is corrected so that the current waveform can be regarded as a linear load, and since the commercial power supply voltage waveform is a sine wave, the ideal waveform is a sine wave as well as the current waveform flowing through the linear load. In this way, the input current is corrected with the reverse polarity of the waveform so as to cancel the change in the input current waveform and the excess or deficiency with respect to the ideal waveform. Therefore, a steep current change within a commercial power cycle caused by a non-linear load such as the magnetron 50, that is, distortion is canceled out by this control loop, input current waveform shaping is performed, and operation with low distortion and high power factor is realized. I can do it.

On the other hand, the magnetron 50 cannot oscillate microwaves unless the cathode 51 is heated to an appropriate temperature. In this state, the magnetron 50 exhibits an almost infinite resistance value. For this reason, in order to start the magnetron 50 at high speed, it is necessary to increase the power supplied to the cathode 51 as much as possible in the start-up control. When the pulse width modulation of the ON signal width of the switching transistor 37 is compared with the case where the pulse width modulation is not performed based on the input voltage waveform information 92, the envelope waveform of the supply current of the cathode 51 is trapezoidal when pulse width modulation is applied. More power can be supplied. As a result, the cathode 51 can be heated to an appropriate temperature in a shorter time.

The mix circuit 73 of the power source for driving the magnetron according to the present embodiment is configured to connect the input voltage waveform information 92 and the input current waveform information 91 to a common emitter resistor 737 through buffer transistors 735 and 739, respectively. With this configuration, the emitter voltage of the buffer transistor 735 or 739 operates so as to output the voltage of the input current waveform information 91 or the input voltage waveform information 92. The emitter resistor 737 is connected to each of the buffer transistors 735 and 739 through a common emitter. Therefore, the signal information having the larger amplitude of the input voltage waveform information 92 and the input current waveform information 91 is reflected in the ON signal width information 94. It becomes the composition which is done. The voltage divided by the resistors 731 and 732 causes a voltage drop corresponding to the current flowing through the buffer transistors 735 and 739, and generates a signal obtained by inverting the waveform information. The buffer circuit 733 is inserted in order to separate the impedance between the voltage dividing point and the capacitor 741 so that the impedance influence from the capacitor 741 does not affect the voltage divided by the resistors 731 and 732. The above waveform information is superimposed as voltage information on the ON signal width information 94 via the capacitor 741, and the ON signal width of the switching transistor 37 is subjected to pulse width modulation.

The amplitude of the input voltage waveform information 92 applied to the buffer transistor 735 is switched by the amplitude switching means 98 between the non-oscillation state and the oscillation enabled state. When the steady state determination circuit 80 detects that the magnetron 50 is ready to oscillate, a steady state determination signal 97 is issued. The steady determination signal 97 charges the capacitor 748 with a constant current by turning on the switch of the switching circuit 74. As a result, the voltage of the capacitor 748 increases with a constant slope with respect to time. Since the buffer transistor 749 operates to flow a current corresponding to this voltage to the resistor, a current corresponding to the voltage of the capacitor 748 flows to the current mirror 747. On the other hand, since the buffer transistor 749 allows a current corresponding to the input voltage waveform information 92 to flow through the resistor, the current mirror 746 allows a current corresponding to the input voltage waveform information 92 to flow. Here, since the current of the resistor 780 is a difference between the currents of the current mirror 747 and the current mirror 746, the current decreases as the voltage of the capacitor 748 increases. For this reason, when the voltage of the capacitor 748 rises, the voltage applied to the resistor 780 decreases to substantially zero. Therefore, the input current waveform information 91 always indicates the current value of the emitter resistor 737 after a certain time has elapsed since the steady state determination signal 97 is generated. Therefore, the ON signal width information 94 is created based on the input current waveform information 91.

In addition, when the output setting signal 96 is small, the current value of the constant current source 750 is configured to be large so that the current injected into the voltage dividing points of the resistors 731 and 732 increases. As a result, the input current waveform information 91 converted into current by the buffer transistor 739 is canceled. For this reason, when the output setting signal 96 is small, the output of the mix circuit is not affected by the input current waveform information 91 and outputs the ON signal width information 94 of the switching transistor 37. When the output setting is small, Since the pulse width modulation control cannot be performed, it is possible to prevent the soft switching operation from being disabled due to a short on-time of the switching transistor 37.

Note that although the operation is described with the configuration in which the capacitor 748 is charged here, it is needless to say that the circuit may be configured with the polarity to be discharged, and the effect of this embodiment can be achieved.

FIG. 10 is a waveform diagram showing the input voltage waveform information 92, the input current waveform information 91, the steady state determination signal 97, and the ON signal width information 94 of the mix circuit of the magnetron driving power supply according to the present embodiment. It is the wave form diagram which expanded the timing which changes to a steady state.

During the period when the cathode of the magnetron 50 is not heated to a sufficient temperature, the magnetron 50 exhibits an almost infinite impedance, so the input current waveform is substantially zero. For this reason, the signal amplitude reflecting the input voltage waveform information 92 is output from the output signal of the mix circuit 73. (Period T0 to T1) When the cathode 51 of the magnetron 50 is heated and ready to oscillate, the impedance decreases and the input current begins to flow. In the start-up control state of heating the cathode 51 of the magnetron 50, the amplitude of the input voltage waveform information 92 is adjusted so that the power supplied to the cathode 51 can be maximized. If this signal amplitude is large, Since the input voltage waveform information 92 is output from the mix circuit even in the steady oscillation state, a high power factor cannot be realized in the steady oscillation state. Therefore, in the present embodiment, the switching circuit 74 is provided so as to cut the input voltage waveform information 92 when it is detected that the magnetron 50 is in an oscillation state. Moreover, the mix circuit 73 as a selection part may provide the current injection part comprised by a voltage current conversion part. The current injection unit reduces the signal amplitude waveform selected by injecting current into the mix circuit 73. Furthermore, the amount of current injected by the current injection unit is preferably inversely proportional to the output voltage of the output setting unit 76.

With this configuration, when the magnetron 50 shifts to the oscillation state, the output of the mix circuit 73 can be determined by the input current waveform information 91. Therefore, even when the input current is small, a high power factor can always be maintained. It becomes possible. Further, when the input current waveform is small, the amplitude of the output signal of the mix circuit 73 is also small, so that the degree of modulation near the voltage peak point of the AC power supply 20 is also small. As a result, the ON time of the switching transistor 37 is set to be somewhat long. Will do. As a result, the energy accumulated in the resonance circuit 34 provided in the inverter circuit during the switching period can be secured, and the soft switching operation can be stably performed even when the conversion power of the inverter circuit is low. It is possible to prevent an excessive increase in loss of 37.

As described above, the magnetron driving power source according to the present invention performs pulse width modulation of the ON signal width of the switching transistor based on the input current waveform information and the input voltage waveform information, and performs pulse width modulation at the time of starting and steady oscillation of the magnetron, respectively. Can be designed independently.

For this reason, power conversion is performed while maintaining a high power factor, and stable switching operation can be realized even at low power, so a heating device or a garbage disposal machine using dielectric heating such as a microwave oven, or The present invention can also be applied to applications such as a microwave power source of a plasma power source that is a semiconductor manufacturing apparatus.

As described above, the magnetron driving power source according to the present invention performs pulse width modulation of the ON signal width of the switching element switching transistor based on the input current waveform information and the input voltage waveform information, and pulse width modulation at the time of starting and steady oscillation of the magnetron. Since each can be designed independently, power conversion can be performed while maintaining a high power factor, and stable switching operation can be realized even at low power. The present invention can also be applied to applications such as a garbage processing machine or a microwave power source of a plasma power source as a semiconductor manufacturing apparatus.

This application is based on a Japanese patent application filed on December 15, 2010 (Japanese Patent Application No. 2010-278787) and a Japanese patent application filed on October 26, 2011 (Japanese Patent Application No. 2011-234873). The contents are incorporated herein by reference.

DESCRIPTION OF SYMBOLS 20 AC power supply 30 Bridge type rectifier circuit 31, 75 Smoothing circuit 34 Resonant circuit 37 Switching transistor 40 High voltage transformer 47 Voltage doubler rectifier circuit 50 Magnetron 73 Mix circuit 74 Switching circuit 76 Output setting part 78 Sawtooth wave generation circuit 79 PWM comparator 80 Steady determination Circuit 91 Input current waveform information 92 Input voltage waveform information 93 Power control information 94 ON signal width information 95 Switching signal 96 Output setting signal 97 Steady state determination signal

Claims (15)

1. A magnetron drive power supply that controls an inverter circuit that rectifies the voltage of an AC power supply, modulates the on-time of high-frequency switching of the switching transistor, and converts it into high-frequency power,
   An input current detector that detects an input current from the AC power source to the inverter circuit and outputs input current waveform information;
   An input voltage detection unit that detects an input voltage input from the AC power source to the inverter circuit and outputs input voltage waveform information;
   A selection unit for selecting one of the input current waveform information and the input voltage waveform information;
   A switching converter that converts any of the input current waveform information and the input voltage waveform information selected by the selection unit into a drive signal of a switching transistor of the inverter circuit;
   The selection unit is a magnetron driving power source that selects the input voltage waveform information while the magnetron is in an activated state, and selects the input current waveform information when the magnetron is ready to oscillate.
2. The selection unit is connected between the input current detection unit and the input voltage detection unit and the switching conversion unit, and any one of the input current waveform information and the input voltage waveform information and an input current of the inverter circuit are Combining power control information for controlling to be a predetermined value, and composed of a combining circuit that generates an on-voltage signal of the switching transistor,
   2. The magnetron driving power source according to claim 1, wherein the switching converter converts the on-voltage signal into a driving signal for the switching transistor so that a peak voltage of the semiconductor switching element is suppressed.
3. A clock generation unit that generates a clock in synchronization with the cycle of the AC power supply,
   3. The magnetron driving power supply according to claim 1, wherein selection switching between the input current waveform information and the input voltage waveform information by the selection unit is synchronized with a clock output of the clock generation unit.
4. The clock generation unit generates a clock pulse at a timing when the absolute value of the AC power supply voltage starts to increase from a decrease,
   The magnetron driving power source according to claim 3, wherein the selection unit performs selection switching between the input current waveform information and the input voltage waveform information according to the clock pulse of the clock generation unit.
5. The clock generation unit generates a clock that divides the period of the AC power supply by two,
   The magnetron driving power source according to claim 3, wherein the selection unit synchronizes selection switching between the input current waveform information and the input voltage waveform information with a clock output of the clock generation unit.
6. 6. The magnetron driving power source according to claim 5, wherein the selection unit performs selection switching between the input current waveform information and the input voltage waveform information at a rising or falling edge of a clock output of the clock generation unit.
7. A magnetron drive power supply that controls an inverter circuit that rectifies the voltage of an AC power supply, modulates the on-time of high-frequency switching of the switching transistor, and converts it into high-frequency power,
   An input current detector that detects an input current from the AC power source to the inverter circuit and outputs input current waveform information;
   An input voltage detection unit that detects an input voltage input from the AC power source to the inverter circuit and outputs input voltage waveform information;
   A selection unit for selecting one of the input current waveform information and the input voltage waveform information;
   A switching converter that converts any one of the selected input current waveform information and the input voltage waveform information into a drive signal of a switching transistor of the inverter circuit;
   A clock generation unit that generates a clock in synchronization with the cycle of the AC power supply,
   The selection unit is configured to select a larger one of the output signals of the input current detection unit and the input voltage detection unit, and the output of the input voltage detection unit is gradually decreased by a predetermined number of steps. The power to drive the magnetron is synchronized with the clock output of the clock generator.
8. 8. The magnetron driving device according to claim 7, wherein the output of the input voltage detector decreases the output voltage to ½ amplitude in the first stage and gradually decreases so that the output voltage becomes 0 in the second stage. Power supply.
9. The magnetron driving power source according to claim 8, wherein a predetermined delay time is provided between the first stage and the second stage.
10. 10. The magnetron driving power source according to claim 9, wherein a clock count unit is provided, and the clock count unit counts the clock of the clock generation unit and shifts to the second stage when the clock is counted a predetermined number of times from the first stage.
11. 11. The magnetron driving power source according to claim 10, wherein the input voltage detection unit decreases the output voltage amplitude by a predetermined value each time the clock is counted by the clock counting unit.
12. A high-frequency heating apparatus comprising the magnetron driving power source according to any one of claims 1 to 11.
13. Magnetron drive that controls the inverter circuit that rectifies the voltage of the AC power supply, modulates the high-frequency switching on-time of the switching transistor and converts it into high-frequency power, and supplies power to the magnetron via the rectifier circuit that rectifies the high-frequency power Power supply,
    An input current detector that detects an input current from the AC power source to the inverter circuit and outputs input current waveform information;
    An input voltage detection unit that detects an input voltage input from the AC power source to the inverter circuit and outputs input voltage waveform information;
    A selection unit for selecting one of the input current waveform information and the input voltage waveform information;
    A switching converter that converts any of the input current waveform information and the input voltage waveform information selected by the selector into a drive signal of a switching transistor of the inverter circuit;
    A power command unit that commands the power supplied to the magnetron by the inverter circuit,
    The selection unit selects signal waveform information having a larger output amplitude from the input voltage detection unit and the input current detection unit,
    When the magnetron is ready to oscillate, the signal amplitude of the input voltage waveform information is reduced, and when the power commanded by the power command unit is a predetermined value or less, the signal amplitude obtained by the selection unit is reduced,
    The switching conversion unit is a magnetron driving power source that compares the signal waveform information selected by the selection unit with a triangular wave by a PWM comparator and uses the magnitude relationship as a driving signal for the switching transistor.
14. The magnetron driving device according to claim 13, wherein the selection unit includes a voltage-current conversion unit and a current injection unit, and the current injection unit reduces the selected signal amplitude waveform by injecting a current into the selection unit. Power supply.
15. The magnetron driving power source according to claim 14, wherein the amount of current injected by the current injection unit is inversely proportional to the output voltage of the power command unit.

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