JPH01107491A - High frequency heating device - Google Patents

Abstract

PURPOSE:To make a current transformer compact and light and simplify a current value detecting circuit by providing a means to detect an AC output current of the secondary side high voltage coil of a transformer, clipping the positive side or negative side of the output of this means and controlling a current to a magnetron to be a desired value. CONSTITUTION:A current transformer 60 of a current detecting means for a high voltage circuit is connected at a position nearer to a transformer 20 than a diode 60 so as to make it possible to measure the AC output current of the secondary side high voltage coil of the transformer 20. This makes the current on the primary side of the current transformer 60 to be AC, so the need of considering saturation of the magnetic circuit of the current transformer is eliminated, and the current transformer 60 which is compact and light can be used. By connecting diodes D1, D2 to each end of the secondary coil to clip the positive or negative side of the output, the current value detecting circuit can be simplified.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention provides a high-frequency heating device suitable for microwave ovens, etc., in which the power supply unit is small and lightweight, and the output control unit is also small and simple, making the cost low. Regarding.

[Conventional technology]

In order to obtain the DC high voltage applied to the anode of the magnetron that generates the heating frequency of the high-frequency heating device, the method of boosting and rectifying the voltage at the commercial AC frequency using a transformer requires a large number of transformers, so in recent years commercial AC power is rectified to become DC, which is then turned on and off by switching elements.
The so-called inverter method converts (inverts) into high-frequency alternating current, which has a frequency much higher than that of commercial power, boosts the voltage using a small, lightweight transformer, and rectifies this alternating current again to apply the resulting high voltage direct current to the anode of the magnetron. High-frequency heating devices using a power source have been put into practical use. Inverter power supply is
Switching element on/off period ratio (duty ratio)
By controlling the output, output control can be easily and efficiently performed.

Regarding a conventional high-frequency heating device using an inverter-type IIl source, for example, Japanese Patent Application Laid-open No. 79345/1983 describes
an anode current detector that detects the anode current of the magnetron;
A device is disclosed that is provided with a duty control section that controls the duty of opening and closing of the switching element using the signal from the detector.

In the case of high-frequency heating devices conventionally used in microwave ovens,
In most cases, the secondary AC high-voltage output of the transformer is converted to DC by a half-wave or full-wave voltage doubler rectifier circuit that combines a diode and a capacitor, and is used as the anode power source for the magnetron. When detecting the magnetron anode current value of such a circuit using the conventional technology described above, the current value pulsates greatly over time, even though it is a direct current, so it is usually difficult to detect the high voltage circuit to be measured and the current value detection circuit. Use a current transformer with easy insulation between the two and low power loss.

However, the magnetron anode current that flows to the primary side of the current transformer is already rectified and flows only in one direction, so to prevent the core that forms the magnetic circuit of the current transformer from becoming saturated, the core cross section must be large enough,
This is especially serious when a full-wave rectifier circuit is used.

Furthermore, on the current value detection circuit side, since there is no DC component in the current transformer output, zero level adjustment must be performed with a DC regeneration circuit, which increases the number of parts.

Figure 2 is a schematic circuit diagram of an example of a conventional high-frequency heating device in which high-frequency waves from an inverter type power source are input to a transformer and a half-wave voltage doubler rectifier circuit is used on the secondary side of the transformer. 20 is a rectifier circuit, 20 is a transformer, 30 is a switching element, 31 is a drive circuit, 40 is a capacitor, 50 is a diode, 60 is a current transformer, and 70 is an output voltage of the current value detection circuit to the magnetron to a desired output in advance. A voltage comparator for comparing with a correspondingly set reference voltage value, 80 is a magnetron, 81 is a heater power supply for the magnetron, R1, R2
, R3, R4, R5 are resistors, Ol is a diode, Ql,
Port 2 is a transistor, and CI is a capacitor. Although the object to be measured is the rectified magnetron anode current (direct current), if a current transformer is used as the detection means, there will be no direct current component in its output, that is, the current of the current value detection circuit.

Therefore, the anode current must be detected by adjusting the zero level with a DC regeneration circuit and then clipping with the diode D1, resulting in a circuit with a large number of components including 1.02, R4, CI, etc.

In addition, since the current flowing through the primary side of a current transformer is a direct current that only flows in one direction, although it pulsates, the cross section of the current transformer's magnetic circuit must be made sufficiently thick (so that the magnetic flux does not become saturated). The amount of magnetic flux that intersects with the secondary winding must be changed sufficiently, so the core of the current transformer becomes large in proportion to the output, resulting in a large and heavy current transformer, and therefore a high cost. You will have to use something.

The output voltage of the current value detection circuit is compared with a reference value by a voltage comparator 70, which has been set in advance with a reference voltage value corresponding to a desired magnetron anode current value, and if a current exceeding the desired value is flowing, The output of the voltage comparator 70 is connected to the drive circuit 31
control is performed to lower the duty ratio of the switching element, and conversely to increase the duty ratio when the current value is less than a desired value. That is, the drive circuit 31 and the voltage comparator 7
0 forms a control circuit for the switching element 30.

[Problem that the invention seeks to solve]

The present invention is a conventional high-frequency heating device using an inverter type power supply, and the problem is that the current detection means for controlling the desired output is large and heavy, and the current value detection circuit has a large number of parts. It is an object of the present invention to provide a high-frequency heating device using a small and lightweight current detection means and a simple current value detection circuit with a small number of parts.

[Means for solving problems]

In order to solve the above problems, in the present invention, instead of detecting the anode current (after rectification) of the magnetron in order to control the output to the desired output, the alternating current output current of the secondary side high voltage sm of the transformer is detected. By providing a means and cliffing the positive side or negative side of the output of this means, the current value detection circuit can be made simple with a small number of parts.

[Effect]

In the present invention, a current transformer is used as a current detection means for a high-voltage circuit, since it is easy to insulate between the negative circuit and the secondary circuit, and the voltage reference point (e.g., ground point) on the secondary side can be arbitrarily determined. Since the current flowing through the primary side of the current transformer is alternating current, there is no need to consider the saturation of the current transformer's magnetic circuit, and a small and lightweight current transformer can be used.

In this case, an alternating voltage is naturally generated on the secondary side of the current transformer, but by connecting diodes to both ends of the secondary winding, the positive or negative side of the output can be clipped. Once this is done, the current value detection circuit will be simple.

〔Example〕

FIG. 1 shows an embodiment of the present invention, in which a current transformer 60 is connected closer to the transformer than the diode 50 so that the AC output current of the secondary high voltage winding of the transformer 20 can be measured. has been done. Therefore, the primary winding of the current transformer 60 (in the case of such a measurement transformer, the ampere turns on the - side are overwhelmingly larger than the secondary side, and the state of the magnetic flux in the magnetic circuit is Since there is an alternating current flowing through the current (determined by the ampere-turns on the Become something.

In the current value detection circuit, a diode DiSD2 is connected to both ends of the current transformer secondary winding to clip the negative side of the output voltage, and the DC regeneration circuit is eliminated, making the circuit simple.

The symbols other than those mentioned above and the functions of the parts are the same as in the case of FIG. 2.

FIG. 3 is an explanatory diagram of the operation of the embodiment shown in FIG. Figure (a) shows the on/off operation of the switching element 30. The off period is approximately constant depending on the inductance of the windings forming the circuit and the capacitance of a resonance capacitor (not shown) (however, the peak value is (the output increases as the output increases), and the output control is mainly performed by controlling the on period.

Figure (b) shows the secondary winding current of the current transformer, Figure (c) shows the current in the secondary winding of the current transformer.
indicates the detection voltage of the current value detection circuit.

〔Effect of the invention〕

As explained above, according to the present invention, the current transformer for detecting the input current to the magnetron can be small and lightweight, and the current value detection circuit connected to the secondary side of the current transformer can be simplified. , an inexpensive high-frequency heating device can be obtained.

[Brief explanation of the drawing]

FIG. 1 is a diagram of an embodiment of the present invention, and FIG. 2 is a schematic circuit diagram of an example of a conventional high-frequency heating device using an inverter type power source.
FIG. 3 is an explanatory diagram of the operation of the embodiment shown in FIG. 1 - Commercial AC power supply, 10 - Rectifier circuit, 20 - Transformer, 30 - Switching element, 31 - Drive circuit, 50 - Diode, 60 - Current transformer, 70
・-Voltage comparator, 80...-Magnetron, R1,
R2, R3, R5-・Resistance, DI, 02-・Diode, Ql-) transistor. Agent Patent Attorney Katsuma Ogawa r'

Claims (1)

[Scope of Claims] 1. Direct current obtained by rectifying a commercial AC power source is converted into alternating current with a frequency higher than that of the commercial power source by a switching element whose opening/closing operation is driven and controlled by a control circuit, and is used as the primary source of the transformer. In a high-frequency heating device in which the output of the secondary high-voltage winding of the transformer is rectified and applied to the anode of a magnetron that generates a heating high-frequency wave, the alternating current of the secondary high-voltage winding of the transformer A means for detecting an output current is provided, and a signal obtained by clipping the positive or negative side of the output of the means is provided to the control circuit to form a negative feedback loop, and the current to the magnetron is set to a desired value in advance. A high-frequency heating device characterized by controlling the heating value. 2. The high-frequency heating device according to claim 1, which uses a current transformer as a means for detecting the high-voltage AC output current of the transformer. 3. The high frequency heating device according to claim 2, wherein the positive side or negative side of the output is clipped by diodes connected to both ends of the output winding of the current transformer.