JPH0815115B2 - Magnetron power supply - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetron power feeding device configured to obtain a high voltage power source applied to a magnetron with an inverter circuit.

2. Description of the Related Art In a power control method of a magnetron power supply device configured to convert a DC power source rectified from a commercial power source to a high voltage power source with an inverter circuit and apply it to a magnetron, an input current from the commercial power source has a predetermined value. An input current control method for controlling is used.

However, in the magnetron, current flows only in the heater section until it starts oscillating, and no current flows between the anode and the cathode, so if the input current is controlled to a steady value, an excessive voltage will occur between the anode and the cathode. Is applied and an excessive current flows through the heater, shortening the life of the magnetron.

Therefore, the problem is solved by initially adopting a method of setting the input current smaller than that in the steady state and switching the input current to a steady value after a lapse of a time sufficient to start the oscillation.

FIG. 7 shows a circuit diagram of a conventional magnetron power feeding device. In FIG. 7, the power of the commercial power source 1 is rectified by the diode bridge 2 to form a unidirectional power source. Reference numeral 3 is an inductor, and 4 is a capacitor, which serves as a filter for the high frequency switching operation of the inverter.

The inverter is composed of a resonance capacitor 5, a step-up transformer 6, a transistor 7, a diode 8 and a drive circuit 9. The transistor 7 performs a switching operation at a predetermined cycle and a duty (that is, an on / off time ratio) by the base current supplied from the drive circuit 9. As a result, the current Ic / d as shown in FIG. 8A, that is, the collector current Ic of the transistor 7 and the current Id of the diode 8 flow. On the other hand, when the transistor 7 is off, the resonance of the capacitor 5 and the primary winding 10 causes a voltage Vc as shown in FIG. 8 (b).
e is generated between C and E of the transistor 7. Therefore 1
A current as shown in FIG. 8C flows through the secondary winding 10, and high frequency power is generated at both ends of the primary winding 10. Therefore, high frequency voltage power and high frequency low voltage power are generated in the secondary winding 11 and the tertiary winding 12, respectively. This high frequency high voltage power is a capacitor
It is rectified by the diode 13 and the diode 14 and supplied between the anode and cathode of the magnetron 15, while the high-frequency low-voltage power is supplied to the cathode heater. Therefore magnetron 15
Oscillates to permit dielectric heating. The magnetron 15 is composed of a magnetron main body 15 ', capacitors 16, 17, 18 and choke coils 19, 20 constituting a filter. In such a configuration, the core cross-sectional area of the step-up transformer 6 becomes smaller as the frequency of the electric power supplied to both ends of the primary winding 10 becomes higher. Therefore, for example, when the inverter is operated at a frequency of about 20 kHz to 100 kHz, Compared with the case where the voltage is boosted at the power supply frequency as it is, the weight and the weight of the step-up transformer can be reduced to several tenth to tenth, and the cost of the power supply unit can be reduced.

Reference numeral 21 is an input current detection unit, which is a current Ii from the commercial power supply 1.
A signal is transmitted to a drive circuit that detects n and controls so that the value becomes a predetermined value. The signal from the input current detector 21 controls the input current to be small until the magnetron 15 starts to oscillate, and then controls to a predetermined current.

However, since the high frequency does not oscillate at all until the magnetron 15 starts to oscillate, it becomes an unnecessary time for heating and cooking. The longer this time is, the longer the heating time is, which is a big problem for a magnetron power feeding device such as a microwave oven characterized by high-speed cooking with high frequency.

In order to shorten the time required to start the magnetron oscillation, it is sufficient to increase the input current.
As shown in the figure, when the magnetron is not oscillating,
Even if the input current is small, the anode-cathode voltage V _A becomes large, and an excessive voltage is applied to the magnetron. Therefore, there is a limit to the reduction of the time required to start oscillation.

Figure 10 shows the voltage between the anode and cathode of the magnetron.
The waveform of V _AK is shown. Since the peak value of V _AK when the magnetron is not oscillating is large, the time required for oscillation could not be shortened.

Means for Solving the Problems In the magnetron power feeding device according to the present invention, a unidirectional power source is used.
And at least the amount of strain that converts the unidirectional power supply to high frequency
Also one switching element and the switching element
Inverter circuit with drive circuit and food and fluid
A magnetron for generating high frequency for heating,
Boosts the output of the inverter circuit to a high-frequency high-voltage power supply.
Voltage transformer and primary inductance of the boost transformer
A resonant capacitor that resonates with the secondary of the step-up transformer
The high voltage for rectifying the high frequency high voltage power supply
Pressure capacitor and high voltage diode, and the magnetro
Capacitor C between the anode and cathode of the With and
The primary inductance of the step-up transformer and the resonance capacitor
Resonant frequency of the capacitor₁In contrast, the secondary a
Conductance, the capacitor, the anode / caso
Capacitor C between terminals Resonance frequency due to₂Is₁Noho
The frequency is set to be an odd multiple.

Functions The present invention has the following functions due to the above-mentioned configuration.

Conventionally, there was a problem that a high voltage was generated on the secondary side of the step-up transformer while the magnetron was not oscillating.
When the magnetron to the step-up transformer primary side resonance frequency ₁ is not oscillating the resonance frequency ₂ of the secondary side of the step-up transformer (when the open-load) are substantially odd multiple, secondary i.e. magnetron waveform of the voltage V _AK between the anode and cathode of _two to _one frequency of the waveform
The waveform of the frequency is superimposed on the waveform, and the voltage peak is suppressed.

Therefore, the input current can be increased even with the same peak value of V _{AK, and} the time required to start oscillation of the magnetron can be shortened.

 Also, the capacitor C between the anode and the cathode By
Resonant frequency on the secondary side₂Since we have decided
When Ron starts oscillating, capacitor C Mug in parallel with
The netron load is connected in parallel, and the secondary side
Since the resonance frequency of the
The voltage peak can be suppressed only in

EXAMPLES Examples of the present invention will be described below with reference to the accompanying drawings.

FIG. 1 shows a circuit diagram of the magnetron power feeding device of the present invention. The same components as those in FIG. 6 are designated by the same reference numerals. The commercial power supply 1 is rectified by a diode bridge 2 and has a filter circuit composed of an inductance 3 and a capacitor 4 on the output side to form a unidirectional power supply 22. The inverter unit 23 including the switching element 7, the regenerative diode 8 and the drive circuit converts the electric power from the unidirectional power source 3 into a high frequency,
It is applied to the step-up transformer 6. The primary resonance frequency ₁ is determined by the primary inductance 24 formed by the primary winding of the step-up transformer and the resonant capacitor 5. The switching element 7 performs a switching operation by an ON / OFF signal from the drive circuit 9 synchronized with this resonance circuit. The high voltage generated across the secondary inductor 25 formed on the secondary side of the step-up transformer is double-voltage rectified by the high voltage capacitor 13 and the high voltage diode 14 and applied to the magnetron 15. At the same time, a heater current is supplied to the cathode from the heater winding 12 of the step-up transformer 6, the cathode heater generates heat, emits electrons, and the magnetron 15 oscillates.

 Fig. 2 shows the cathode heater of the magnetron 15 at startup.
Is not heating enough and the magnetron is not oscillating
When the magnetron has an infinite load
Shows the equivalent circuit diagram of the primary and secondary resonant circuits of the step-up transformer 6.
You. In Fig. 2, the magnetron's anode casing
C is the conductance component between And anode
・ Cathode voltage V_AKBecomes large when not oscillating,
Is smaller than that, so V_AKPee
The key is to keep the value low. In Figure 2
When the switching element 7 is off, the arrow
Current flows in the opposite direction and forward current flows in the high voltage diode.
Flow, V_AKIs almost 0V. Switching element 7
When turned on, current flows in the direction of the arrow and
V when the netron is not oscillating_AKOccurs. This voltage waveform is
Resonance frequency due to vibration capacitor 5 and primary inductance 24
number₁Voltage waveform by (Fig. 3₁Waveform) and high voltage conde
Sensor 13 and conductance component between anode and cathode
C And resonance frequency due to secondary inductance 25₂By
Voltage waveform (Fig. 3₂Waveform)
It At this time₂To₁Since it is three times larger than V_AKWaveform
Peak V_AKP′ Is suppressed V_AKPBecomes₂But₁of
The peak can be suppressed if it is almost an odd multiple.

 Generally, the maximum applied voltage of magnetron is about 10 kV.
Therefore, considering the safety factor, V_AKPWill be about 7kV
As described above, the input current Iin during non-oscillation is adjusted. Kondak
Closet component C Change the capacity of₁Twice the₂To
V when set and tripled_AKThe waveform is shown in Fig. 4.
You. As shown in Fig. 4 (a)₂≒ 2₁Time and fourth
As shown in Figure (b)₂≒ 3₁Peak voltage at
Setting the input current so that both are set to 7 kV,
₂≒ 3₁At the time of₂≒ 2₁Almost 1.3 times
The input current Iin of can be made to flow. Of the power at this time
Most of the mug is through the heater winding 12 of the boost transformer 6.
As it is supplied to the cathode of the Netron 15,
The electric current supplied to the
The cathode heater is sufficiently heated until it can start oscillating.
The time spent can be shortened.

 Fig. 5 shows the boosting tiger when the magnetron 15 is oscillating.
An equivalent circuit diagram of the primary / secondary resonance circuit of the sensor 6 is shown. Fifth
In the figure, the resonance frequency of the primary side₁′ Is a resonant capacitor
5 and primary inductance 24. Meanwhile, Magnetro
When the load characteristics of the oscillator are oscillating, as shown in Fig. 6, the nonlinear characteristics are
And the anode current flows to some extent,
Is the voltage V between the anode and cathode_AKThe fluctuation of
Anode-cathode conductor because of its quality
C There is not much current flowing in. Therefore, the secondary
Side resonance frequency₂′ Is high voltage condenser 13 and secondary side
Determined by the inductance 25.₁′ ≒₂If set to ‘
The switching operation of the inverter circuit should be stable.
It

 With the above configuration, the magnetron will start oscillating.
It shortens the time required and stabilizes the oscillation operation of the magnetron.
A magnetron power feeding device can be realized. Also, magneto
Ron anode-cathode conductance component C Is
Also serves as a magnetron feedthrough capacitor for noise prevention.
Since it can be done, there is almost no cost increase due to it.
Yes.

Effects of the Invention As described above, the magnetron power feeding device of the present invention has the following effects.

(1) Since the secondary resonance frequency ₂ of the step-up transformer is set to approximately an odd multiple of the primary resonance frequency when the magnetron is not oscillating, the peak of the voltage between the anode and the cathode is suppressed. And the power supply to the cathode heater can be increased, so that the time required for the magnetron to oscillate can be shortened. Therefore, a magnetron power feeding device suitable for high-speed cooking can be realized.

(2) Since the secondary side voltage of the magnetron is suppressed during non-oscillation, it is possible to realize a magnetron power supply device with high safety and reliability.

[Brief description of drawings]

 FIG. 1 is a circuit diagram of a magnetron power feeding device of the present invention, and FIG.
The figure shows the booster transformer of the same device when the magnetron is not oscillating.
Figure 3 is an equivalent circuit diagram of the primary and secondary resonance circuits of the device.
Magnetron Anode-Cathode Voltage V_AKWaveform
FIGS. 4 (a) and 4 (b) show the conventional example and the anode of the present invention.
・ Cathode voltage V_AKFig.5 shows the magnetron
Primary / secondary equivalent circuit diagram of step-up transformer during oscillation,
FIG. 6 is a load characteristic diagram of the magnetron, and FIG. 7 is a conventional example.
Circuit diagram of magnetron feeding device, Fig. 8 shows each part of the device
Waveform diagram, Fig. 9 shows magnetron oscillation and non-oscillation of the device
Input current Iin, anode-cathode voltage V_AKCharacteristic
Figures and 10 show V of the device_AKIt is a waveform diagram of. 5 ... Resonant capacitor, 6 ... Step-up transformer, 7 ...
Itching element, 9 ... Driving circuit, 13 ... High voltage capacitor
14 ... High voltage diode, 15 ... Magntron, 16,1
7 ... Anode-cathode capacitor C , 22 …… single
Directional power supply, 23 ... Inverter circuit, 24 ... Primary inductor
Tansu, 25 …… Secondary inductance.

Front page continued (72) Inventor Naoyoshi Maehara 1006 Kadoma, Kadoma, Osaka Prefecture Matsushita Electric Industrial Co., Ltd. Inventor Takashi Niwa 1006 Kadoma, Kadoma City, Osaka Prefecture Matsushita Electric Industrial Co., Ltd. (72) Inventor Villa Daisuke 1006 Kadoma, Kadoma City, Osaka Prefecture Matsushita Electric Industrial Co., Ltd.

Claims (2)

[Claims] 1. A unidirectional power supply and a high frequency for the unidirectional power supply.
At least one switching element for converting,
Inverter circuit having a drive circuit for the switching element
Path and mug that generates high frequency to heat the object to be heated
High frequency by boosting the output of the netron and the inverter circuit
Step-up transformer for high-voltage power supply and one of the step-up transformers
Resonant capacitor that resonates with the secondary inductance and the boost
The high-frequency high-voltage power supply is provided on the secondary side of the transformer and doubles the voltage.
High-voltage capacitor and high-voltage diode for flowing,
A capacitor provided between the anode and cathode of the magnetron.
Densa C And a primary inductor of the step-up transformer
And the resonant frequency of the resonant capacitor₁In front of
Secondary inductance of transformer and high-voltage capacitor
And a capacitor C between the anode and the cathode Due to
Swing frequency₂Is₁Frequency that is almost an odd multiple of
Magnetron power supply device. 2. A magnetron cathode-anode coil
Indexer C Also serves as a feedthrough capacitor for the magnetron
The magnetron power feeding device according to claim 1, which is used.