JPH088144B2 - High frequency heating equipment - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high-frequency heating device configured to obtain a high-voltage power supply applied to a high-frequency oscillator by an inverter circuit, and more particularly to a power control system for this high-voltage power supply.

2. Description of the Related Art In a power control method of a high frequency heating device configured to apply a DC power source rectified from a commercial power source to a high frequency oscillator converted into a high voltage power source by an inverter circuit, an input current from the commercial power source has a predetermined value. The input current control method for controlling the current is used.

However, high frequency oscillator (hereinafter referred to as magnetron)
Current flows only to the heater part until it starts oscillating, and no current flows between the anode and cathode, so
When the input current is controlled to a steady value, an excessive voltage is applied between the anode and the cathode, 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.

However, the time required to start the oscillation is, for example, 4 seconds when the magnetron is cold and when the magnetron is warm.
Although there is a difference of 2 seconds, in such an input current control method, in such a case, the time for controlling the input current to a small value must be set to about 5 seconds.

Therefore, in the high-frequency heating device that controls the apparent high-frequency output by duty-controlling the period during which the magnetron operates, "the time difference (5-2 = 3 sec) X number of duty cycles" is a dead time.

Further, the change in voltage between the anode and the cathode with respect to the change in the input current and the degree of change in the heater current with respect to the change in the input current up to the start of the oscillation are several times larger than those during the oscillation. From the viewpoint, the input current setting before the oscillation is started cannot be increased so much.

Therefore, it is very difficult to shorten the rise time of the heater and cathode temperatures when the magnetron is cold, and the reduction of the dead time has its own limit.

Means for Solving the Problems In a high frequency heating apparatus according to the present invention, a rectifier circuit for converting a commercial power source into a DC power source, an inverter circuit for converting the DC power source into a high voltage power source, and a high voltage power source are applied to generate a high frequency wave. High-frequency oscillator that oscillates (hereinafter referred to as magnetron)
A current detector for detecting the current of the commercial power supply and a voltage detector for detecting the voltage of the high-voltage power supply, and the inverter circuit controls the output of the current detector to a predetermined value. An input current control unit, an output voltage control unit for controlling the output of the voltage detector to a predetermined value, and an input current control unit or an output voltage control unit, whichever has a smaller predetermined current of the commercial power supply, is automatically selected. And a selection circuit for selecting.

Action Until the magnetron develops oscillation by the means described above, the output voltage reaches a predetermined value even with a small input current as described above, so the output voltage control unit is selected to control the output voltage and cause the magnetron to oscillate. When started, the output voltage becomes lower than the predetermined value even at the predetermined input current, so the input current control unit is automatically selected to control the input current.

Therefore, regardless of whether the magnetron is cold or warm, the input current from the commercial power supply reaches the specified value in the shortest time (input power to the magnetron reaches the rated value) in each time, so dead time in the conventional method Becomes zero. Moreover, since no excessive voltage or excessive current is applied to the magnetron in the process, the life of the magnetron is not shortened.

Practical Example FIG. 1 is a circuit configuration diagram of a high-voltage power supply generation unit of a high-frequency heating apparatus according to the present invention.

The DC power supply 3 obtained by rectifying the commercial power supply 1 with a rectifier circuit is turned on / off by the power transistor 4, and the high voltage transformer 5
High voltage power supply 6
Is applied between the anode 7a and the cathode 7b of the magnetron 7 to operate the magnetron 7.

The input current detection unit 8 detects the input current Iin from the commercial power supply 1, amplifies the difference between the signal obtained by rectifying the output by the input current signal rectification circuit 9 and the current reference signal 10 by the current error amplification circuit 11, It is input to the comparator 13 via the selection circuit 12.
The comparator 13 and the sawtooth wave generation circuit 14 with this input signal
The power saw transistor 4 turns on due to the sawtooth wave
Create / OFF pulse 15. The input current detector 8 to the comparator 13 constitute the input current control unit 16, and when the input current Iin decreases, the output of the current error amplification circuit 11 rises, and
The ON time of the N / OFF pulse 15 becomes longer, and the input current Iin increases. Conversely, when the input current Iin increases, it operates so as to reduce the input current. In this way, the input current control unit 16
Is a part for controlling the input current Iin to be a predetermined value.

In addition, the output voltage detector 17 provided in the high voltage transformer 25
Is a signal that detects the voltage of the high-voltage power supply 6 and rectifies its output by the output voltage signal rectifier circuit 18, and the difference between the voltage reference signal 19 by the voltage error amplifier circuit 20 and inputs it to the selection circuit 12.
The ON / OFF pulse 15 is obtained from the comparator 13.

The output voltage detector 17 to the comparator 13 compose the output voltage control unit 21, and when the voltage of the high-voltage power supply 6 decreases, the output of the voltage error amplification circuit 20 rises, the ON time of the ON / OFF pulse becomes longer, and the high voltage The power supply 6 operates in the direction of increasing the voltage, and accordingly the input current Iin naturally increases.

Conversely, when the voltage of the high-voltage power supply 6 increases, it operates so as to reduce the voltage of the high-voltage power supply 6 and the input current Iin also decreases. In this way, the output voltage control unit 21 is a unit that controls the voltage of the high-voltage power supply 6 so that it becomes a predetermined value.

Here, the output of the current error amplification circuit 11 and the output of the voltage error amplification circuit 20 are input to the selection circuit 12, but as is clear from the figure, the one with the lower input voltage is selected and the comparator is selected.
It is configured to output to 13. This selection is ON / OFF
The shorter ON time required for pulse 15 is the commercial current 1
The smaller required input current Iin is selected.

As described above, the power transistor 4, the high voltage transistor 5, for obtaining the high voltage power source 6 from the current power source 3, the input current control unit 16 and the output voltage control unit 21 form the inverter circuit 22.

FIG. 2 shows the voltage waveform of the high-voltage power supply 6 when the magnetron 7 is oscillating and when it is not oscillating, and the difference between the two is clear. This negative voltage is the forward voltage that causes the magnetron 7 to oscillate, which is defined as V _AK ,
When the relationship with the input current Iin is obtained, the operation principle diagram as shown in FIG. 3 is obtained.

In FIG. 3, V is the allowable applied voltage of the magnetron 7,
I is an input current Iin from the commercial power supply 1 at the rated output of the magnetron 7, Iin is smaller than I when the magnetron 7 is not oscillating, and V _AK is smaller than V when the magnetron 7 is oscillating.

Therefore, in FIG. 1, the input current Iin is detected by the input current detector 8, the voltage of the high-voltage power supply 6 is detected by the output voltage detector 17, and the output voltage signal rectifier circuit 16 detects the voltage corresponding to V _AK. When the rectification direction is set so as to obtain, the current reference signal 10 is set to a value corresponding to I, and the voltage reference signal 19 is set to a value corresponding to V, the magnetron 7 is operated according to the above-described operating principle.
The output voltage control unit 21 operates until the start of oscillation, and the input current control 16 operates when the start of oscillation.

Fig. 4 shows V _AK and I after the circuit of Fig. 1 starts operation.
It is a starting characteristic diagram which shows the change of the value of in.

In Fig. 1, a transformer is used to detect the input current, and a dedicated winding is provided to detect the output voltage. The former inserts a resistor in the system to detect the current by the voltage drop, and the latter is high voltage. It is possible to change the method of detecting a voltage by providing a detection terminal on the secondary side winding of the transformer, and the input current control unit 16 and the output voltage control unit 21 are not limited to the illustrated circuit configuration. .

The same method can be applied to the case where a voltage doubler rectifier circuit is provided between the high voltage transformer 5 and the magnetron 7.

As described above, in the high-frequency heating apparatus according to the present invention, the input current Iin changes so that the rated output is automatically obtained when the magnetron starts oscillating regardless of whether the magnetron is cold or warm. The dead time, which is a problem in the conventional method, does not occur at all.

Further, since no excessive voltage or excessive current is applied to the magnetron, its life is not reduced.

[Brief description of drawings]

FIG. 1 is a circuit diagram of a high-voltage power generator of a high-frequency heating apparatus according to an embodiment of the present invention, FIG. 2 is a waveform diagram of the same high-voltage power source, FIG. 3 is the same operation principle diagram, and FIG. It is a figure. 1 ... Commercial power supply, 2 ... Rectifier circuit, 3 ... DC power supply, 6
...... High voltage power supply, 7 ...... Magntron, 8 …… Input current detector, 12 …… Selection circuit, 16 …… Input current control section, 17 ……
Output voltage detector, 21 ... Output voltage control unit, 22 ... Inverter circuit.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Kazuho Sakamoto 1006 Kadoma, Kadoma City, Osaka Prefecture Matsushita Electric Industrial Co., Ltd. (56) References JP-A-63-271886 (JP, A) JP-A-63-271885 (JP, A) JP 63-271884 (JP, A)

Claims (1)

[Claims] 1. A rectifier circuit for converting a commercial power supply into a DC power supply, an inverter circuit for converting the DC power supply into a high voltage power supply, a high frequency oscillator for applying a high voltage power supply to oscillate a high frequency, and a current of the commercial power supply. A current detector for detecting
The inverter circuit has a voltage detector that detects the voltage of the high-voltage power supply, the inverter circuit controls the output of the current detector to a predetermined value, and the output of the voltage detector has a predetermined value. A high-frequency heating apparatus comprising: an output voltage control unit that controls the above-described control, and a selection circuit that selects one of an input current control unit and an output voltage control unit that requires a smaller current from a commercial power supply.