JPS63271886A - High-frequency heating device - Google Patents

Abstract

PURPOSE:To enable a rated output to be automatically retained by providing an output voltage detection tap in a input transformer secondary winding of a magnetron oscillator, detecting oscillation starting of the oscillator by variations of the output voltage, and immediately controlling a power source input current. CONSTITUTION:An output voltage detection tap is provided in an input transformer secondary side 13 of a magnetron oscillator 15 driven with an inverter 8. And a detected current of an input current detection part 16 of the power source is compared with a current base 18 with a comparator 19. Then the output is made to an on/off pulse 22 with a comparator 20 and saw-tooth-wave generator 21, and the input current is retained at a given value with a turned on electricity time of the inverter 8 controlled. The output of the output tap of the winding 13, in the condition, is compared to the base voltage with a comparator 27, and a value of the base 18 is made to change with a transistor 29 controlled by the output. This enables the rated output of magnetron to be produced concurrent with its oscillation starting with the input current controlled.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a high-frequency heating device configured to obtain a high-voltage power source of nanometers to a magnetron using an inverter circuit, and particularly relates to a power control system for this high-voltage power source.

Conventional technologyThe power control method of a high-frequency one-thermal device configured to convert a unidirectional power source obtained by rectifying a commercial power source into a high-voltage power source using an inverter circuit and supplying it to a magnetron requires that the input current from the commercial power source be a predetermined value. An input current control method is used to control the current so that

However, with magnetrons, until the oscillation starts, current flows only through the heater section and no current flows between the anode and canode, so if the input current is controlled to the steady state value, the current flows between the anode and canode. Excessive voltage is generated, and excessive current flows through the heater, shortening the life of the magnetron.

Therefore, the above-mentioned problem is solved by adopting a method in which the input current is initially set smaller than the steady state value, and after a sufficient time has elapsed to start the oscillation, the input current is switched to the steady state value.

Problems to be Solved by the Invention However, the time required to start the oscillation differs, for example, when the magnetron is cold, 4SeC1 and 2 seconds when it is hot, but with the input current control method, this is not possible. In this case, the time for controlling the input current to a small value must be set to about 5 seconds.

Therefore, in a high-frequency thermal device that controls the apparent high-frequency output by duty-controlling the operating period of the magnetron, the wasted time is (time difference (: 5-2-3 seconds) x number of duty cycles).

In addition, the voltage change between the anode and cathode in response to the input current change and the heater current change in response to the input current change until oscillation starts are several times larger than those during oscillation, so the above-mentioned lifespan etc. From this point of view, the input current setting until the oscillation starts cannot be made too large.

Therefore, it is very difficult to shorten the time it takes to raise the temperature of the heater and cathode when the magnetron is cold, and there is a limit to the reduction of the dead time.

Means for Solving the Problems A high frequency thermal device according to the present invention comprises: a unidirectional power source; an inverter circuit having at least one switching element for converting the output of the unidirectional power source into a high frequency wave; and a driving circuit thereof; The inverter circuit includes a current detector that detects the current of a power source, a magnetron that generates high frequency waves for heating food, fluids, etc., and a transformer that boosts the output of the inverter circuit and supplies power to the magnetron. The transformer includes an input current control section that controls the output of the current detector to a predetermined value, and the transformer supplies high voltage, high frequency power to the primary winding connected to the inverter circuit and the magnetron, and adjusts the output voltage thereof. The magnetron includes a secondary winding having a detection terminal for detecting the magnetron, and a tertiary winding for supplying low-voltage high-frequency power to the cathode heater of the magnetron.

action The above-mentioned means have the following effects.

During the period until the magnetron starts oscillating, the output voltage reaches a predetermined value even with a small input current, as described above. When the output voltage exceeds a predetermined value, the output voltage is suppressed by switching so as to gradually decrease the reference signal of the input current control section. The output voltage gradually decreases in response to the input current, and when it falls below a predetermined value, the reference signal is switched to gradually increase. While the output voltage is being suppressed repeatedly, the magnetron starts oscillating, and the output voltage becomes lower than the predetermined value even at a predetermined input current, so the input current gradually increases to the predetermined value and is then stabilized. do.

Therefore, regardless of whether the magnetron is cold or hot, the input current from the commercial power supply reaches the specified value in the shortest possible time (the input power to the magnetron reaches the rated value), so there is no waste in the conventional method. time becomes zero. Also, excessive voltage to the magnetron in the process,
Since there is no overcurrent mark 1, the service life will not be shortened.

Embodiments Hereinafter, embodiments of the present invention will be described based on the accompanying drawings.

FIG. 1 is a circuit diagram of a high-voltage power generation section of a high-frequency heating device according to the present invention. In Fig. 1, the power from a commercial power supply 1 is rectified by a diode bridge 2, and the power from a unidirectional power supply 3 is rectified by a diode bridge 2.
is formed. 4 is an inductor, and 6 is a capacitor, which serves as a filter for the high frequency switching operation of the inverter circuit 6.

The inverter circuit 6 includes a resonant capacitor 7, a switching power transistor 8, a diode 9, and a drive circuit 10. The power transistor 8 performs a switching operation at a predetermined cycle and duty (ie, on/off time ratio) by a base current supplied from the drive circuit 1o.

The resulting high frequency power is transferred to the primary winding 1 of the transformer 110.
2 and appears in the secondary winding 13 as a high frequency high voltage output 14, which is supplied between the cathode 151L and anode 1sb of the magnetron 15, and low voltage high frequency power is generated in the tertiary winding 16 of the transformer 11, and the low voltage high frequency power is generated in the magnetron 16. The cathode 161L is heated and the magnetron 16 is operated.

The input current detector 16 detects the input current Iin from the commercial power supply 1.
is detected, and the difference between the signal whose output is rectified by the input current signal rectifier circuit 17 and the current reference signal 18 is amplified by the current error amplification circuit 19 and inputted to the comparator 2o. The comparator 2o creates an on/off pulse 22 of the power transistor 8 using this input signal and the sawtooth wave from the sawtooth wave generation circuit 21. The input current detector 16 to the comparator 20 constitute an input current control section 23,
When the input current Iin decreases, the output of the current error amplification circuit 19 increases, and the on-off pulse 22 operates in the direction of increasing the input current 1in as the on-time of the on-off pulse 22 becomes longer. Conversely, input current I
When in increases, it operates to reduce the input current. In this way, the input current control section 23 performs control so that the input current Iin becomes a predetermined value.

Further, a voltage similar to the high voltage 14 is generated at a detection terminal 24 provided on the secondary winding 13 of the transformer 11 . The signal rectified by the output voltage signal rectifier circuit is compared with the voltage reference signal 26 by the comparator 27, and the output logic is inputted to the current reference signal switching circuit 28, and the current reference signal 18 is changed according to the high voltage 14. Switch. That is, until the magnetron 16 starts oscillating, the high voltage 14 is maintained with a small input current Iin.
increases, so the current reference signal 18 is kept low, and the voltage reference signal 26 is set to switch the current reference signal 18 so that the input current Iin increases when the magnetron 16 starts oscillating and the high voltage 14 drops. In other words, the start of oscillation of the magnetron 15 is detected by the decrease in the output voltage of the detection terminal 24, and the input current I
In will be adjusted to the rating. In the current reference signal switching circuit section, a photocoupler 29 is used to transmit the output logic of the comparator 27 to the input current control section 23 because the reference potentials are different between the primary side and the secondary side of the transformer 11.

FIG. 2 shows the waveform of the high voltage 14 when the magnetron 16 is oscillating and when it is not, and the difference between the two is clear. This negative voltage is the head voltage that causes the magnetron 16 to oscillate, and if we define it as YAK and find its relationship with the input current, we get a diagram of the principle of operation as shown in FIG.

FIG. 4 is a start-up characteristic diagram showing changes in the values of Vm and Iin after the circuit of FIG. 1 starts operating.

In Figure 1, a transformer is used to detect the input current, but in the former case, a resistor is inserted into the system and the current is detected by the voltage drop, and a detection terminal is provided to detect the voltage. However, the input current control section 16 is not limited to the illustrated circuit configuration.

Furthermore, a similar method can be applied to the case where a voltage doubler rectifier circuit is provided between the high voltage transformer 6 and the magnetron 7.

Furthermore, since the output voltage of the detection terminal 24 is completely similar to the voltage of the secondary winding 13 of the transformer 11, it can also be used to detect abnormalities such as stopping operation when abnormal voltage occurs in the high voltage transformer due to some kind of failure. .

Effects of the Invention As described above, the high frequency door heating device of the present invention provides the following effects.

(1) Regardless of whether the magnetron is cold or hot, when the magnetron starts oscillating, the input current Iin changes automatically to obtain the rated output, which eliminates the wasted time that is a problem with conventional methods. It doesn't happen at all.

(2) Since there is no need to apply excessive voltage or excessive current to the magnetron, its life will not be reduced.

[Brief explanation of the drawing]

Fig. 1 is a circuit configuration diagram of the high-voltage power generation part of the high-frequency thermal device according to the present invention, Fig. 2 is a waveform diagram of the secondary winding of the transformer, Fig. 3 is a diagram of the same principle of operation, and Fig. 4 is the same. It is an excitation characteristic diagram. 3... Unidirectional power supply, 6... Inverter circuit, 8... Switching element (power transistor), 10... Drive circuit, 11...・
・Transformer, 12...Primary winding, 13...
...Secondary winding, 16...Magnetron, 16.
... Tertiary winding, 23 ... Input current control section, 24 ... Detection terminal. Name of agent: Patent attorney Toshio Nakao and 1 other person 2nd
Fig. 3. υ, 1 Fig. 4. In VA.

Claims (1)

[Claims] a unidirectional power source, an inverter circuit having at least one switching element that converts the output of the unidirectional power source into a high frequency and a drive circuit thereof, a current detector that detects the current of the unidirectional power source, and heating food, fluid, etc. The inverter circuit includes an input current that controls the output of the current detector to a predetermined value, and a transformer that boosts the output of the inverter circuit and supplies power to the magnetron. the transformer has a controller, the transformer is connected to the inverter circuit;
a secondary winding having a detection terminal for supplying high-voltage high-frequency power to the magnetron and detecting its output voltage; and a tertiary winding for supplying low-voltage high-frequency power to the cathode heater of the magnetron. Equipped with a high frequency heating device.