JPH01276589A - High-frequency heating device - Google Patents

Abstract

PURPOSE:To reduce the dispersion of the working time of a power relay and decrease the rush current value by providing a voltage controller controlling the coil application voltage in series to the operating coil of the power relay turning on or off the power source of a high-voltage transformer. CONSTITUTION:A voltage controller 17 is provided in series to the operating coil of a power relay 9 so that the operating coil voltage becomes the rated value or above as soon as the power relay is turned on. A resistor is used here, but a switch means or the like may be used. As the coil application voltage is increased, the operating time is accelerated, the dispersion of the relay operating time is reduced. When the relay coil application voltage becomes 200% of the rated value, the dispersion is decreased to about a half of the rated value. When the overvoltage is fed to the operating coil of the power relay, the dispersion of the operating time of the power relay can be suppressed small, the rush current of the high-voltage transformer can be suppressed small.

Description

DETAILED DESCRIPTION OF THE INVENTION A major invention in the field of industrial application relates to phase control of a power relay used as a means for turning on and off the power of a high frequency oscillator of a high frequency heating device.

BACKGROUND ART High-frequency heating apparatuses generally provide high-frequency output at an appropriate level depending on the type, quality, and finished product of the food to be cooked, and this is useful for improving cooking performance. In this way, as a means of changing the high frequency output to an appropriate level, there are two methods: one method is to intermittent the high voltage power supply on the secondary side 1 of the high voltage transformer that supplies power to the high frequency oscillator that irradiates the high frequency output, and the other is to intermittent the high voltage power source on the secondary side 1 of the high voltage transformer. A method has been developed to do this. In particular, from the viewpoint of cost, insulation performance, and configuration, a method in which the primary side of the high-voltage transformer is disconnected has become mainstream.

Conventional circuit diagrams are shown in FIGS. 5 and 6.

A triac or a power relay is used as a high-power electronic component as a means for disconnecting the primary side of a high-voltage transformer 8 that supplies power to the high-frequency oscillator 7. In the method using a triac shown in FIG. 5, the power-on phase angle when powering on the high-voltage transformer 8 can be precisely controlled;
Although it has the advantage of being able to keep the inrush current of the high-voltage transformer low, there is a high risk that the triac will be easily damaged by static electricity coming in from outside the main unit, lightning induced by falling snow, and surge voltage generated inside the main unit. The damage mode becomes a short-circuit mode, and power is constantly supplied to the high-voltage transformer 8, creating a dangerous state in which high-frequency oscillation occurs. To prevent this, it is necessary to improve the protection circuit. Additionally, auxiliary parts such as photocouplers are required to insulate between the power supply circuit and the control circuit, which complicates the configuration.

FIG. 6 shows a conventional example using a system in which the primary side of a high voltage transformer is switched on and off using a power relay. The main circuit 6 includes a high-voltage transformer 8 that supplies power, and a power relay 9 installed in the primary line of the high-voltage transformer to switch on and off the high-frequency oscillator 7. Further, this power relay 9 has a control circuit 10.
Based on the phase of the commercial power source, the ON state of the operating coil of the power relay 9 is determined and controlled at a constant level. The low-voltage transformer 11 steps down the voltage of the commercial power source to approximately 30 V AC, and supplies power to the control circuit. The relay supply power circuit 12 is
The AC power supply is half-wave rectified to create the power supply for the power relay. 13 is a microcomputer supply power circuit to the microcomputer. This microcomputer 14 performs a series of operations based on a predetermined sequence including phase control of the power relay 9, and the control section 10 is the central part. The power supply clock circuit 15 is a waveform shaping circuit that converts a commercial power supply waveform to a level that can be recognized by a microcomputer, and is a reference for determining the phase angle of the power relay 9. The power relay drive circuit 16 is a drive circuit that connects and disconnects the power supply to the primary side of the above-mentioned high voltage transformer.

FIG. 7 is a timing chart showing the control timing of the power relay 9 by the control section 10.

(a) is a voltage waveform of the low-voltage transformer 11 obtained by stepping down the commercial power supply. (b) shows a commercial power source whose waveform has been shaped by the power source clock circuit 15.

The microcomputer recognizes the rise or fall of the waveform read from the INT board, and determines the phase angle of the power relay based on the rise. (cl indicates the phase timing to the operating coil of the power relay 9 that connects the high voltage transformer 8 to 0N10FFL.) The ON signal is output from port 80 after a predetermined hour from the rising waveform in (b).

Also, this timing is set so that the inrush current flowing through the primary side of the high voltage transformer is minimized when the voltage is at its maximum.
T is set so that N. (dl shows the current waveform flowing through the primary side of the high-voltage transformer.
The phase timing for N is T ( ) N = T + T d (T d : power relay operation time) from the reference (zero crossing point of commercial power supply), and T is adjusted so that the low voltage transformer voltage is maximum. The N time is determined.

Problems to be Solved by the Invention However, the above-mentioned system has the following problems. As shown in Figure 7 (dl), the phase timing at which the power relay turns on depends on the operating time of the power relay.-
The operating time of the power relay has a variation of about ±4 ms, and if this variation l is τ and τ2, a phase angle deviation of about 90' occurs. At this time, the current flowing through the primary side of the high-voltage transformer reaches its maximum, resulting in a waveform like the broken line. The current value can reach about 10 times the steady current, which is more than 100 A.

The present invention is intended to solve such conventional problems, and aims to suppress variations in operating time of power relays and suppress inrush current values to a low level.

Means for Solving the Problems In order to solve the above problems, the high frequency heating device of the present invention has the following features:
A heating chamber that heats food, a high-frequency oscillator that supplies high-frequency output to the heating chamber, a high-voltage transformer that supplies power to the high-frequency oscillator, a power relay that switches on and off the power of this high-voltage transformer, and an operating coil of this power relay. The structure includes a voltage control section that controls the voltage applied to the coil in series.

Operation The present invention can control the voltage applied to the operating coil of the power relay and suppress variations in power relay operating time to a small level by using the above-described configuration.

Therefore, the power relay can always be operated at optimal phase timing, and the inrush current value can be kept low.

Embodiments Hereinafter, embodiments of the present invention will be described based on the accompanying drawings. FIG. 2 shows an external view of one embodiment.

Reference numeral 1 denotes a high-frequency heating device main body, and a heating chamber 2 made of a ferromagnetic material is provided inside this main body.

A fan 3 that can be opened and closed to take food in and out of the heating chamber 2
A keyboard 4 for operating cooking time, output, cooking start, stop, etc., and a display tube 5 for displaying the status are provided on the front of the main body 1.

FIG. 1 shows a circuit diagram of one embodiment. Reference numeral 6 denotes a main circuit, which is provided with a high-frequency oscillator 7 that irradiates high-frequency output into the heating chamber 2, and a high-voltage transformer 8 that supplies power to the high-frequency oscillator 7.

The contacts of a power relay 9 are connected to the primary side of the high voltage transformer 8, and the high frequency output is made variable by opening and closing the contacts. 1
0 indicates a control circuit that controls the power relay 9. The low voltage transformer 11 steps down the voltage of the commercial power supply to about 30V and supplies power to the control circuit. The power relay supply voltage circuit 12 performs half-wave rectification of the AC power supply to create a voltage sufficiently higher than the rated voltage of the operating coil of the power relay 9. The microcomputer supply power circuit 13 generates power to be supplied to the microcomputer. This microcomputer 14 performs a series of operations based on phase control of the power relay 9 and a predetermined sequence, and is the core of the control circuit. The power supply clock circuit 15 is a waveform shaping circuit that converts a commercial power supply waveform into a voltage waveform that can be recognized by the microcomputer, and serves as a reference for determining the phase angle of the power relay 9. The power relay drive circuit 16 is a drive circuit that connects and disconnects the power supply to the primary side of the high voltage transformer 8 . A voltage control section 17 is provided in series with the operating coil, and the operating coil voltage is configured to exceed the rated value at the moment the power relay is turned on. Although a resistor is used in the embodiment, a switch means or the like may also be used. Another method is to use the regulation of a low voltage transformer.

Figure 3 shows the operating time characteristics of the power relay, and the control method will be described. The horizontal axis shows the voltage applied to the coil, and the vertical axis shows the operating time and variation. Increase the voltage applied to the coil (
As a result, the operating time becomes faster and the variation in relay operating time becomes smaller.

When the voltage applied to the relay coil is 200% of the rated value, the variation is reduced to about half of the rated value. In the embodiment shown in FIG. 2, the voltage applied to the coil has a waveform as shown in FIG. 4.

Overvoltage is applied only when the power relay operates, and in steady state, a voltage below the coil rating is supplied.

Therefore, according to this configuration, by supplying an overvoltage to the operating coil of the power relay, it is possible to suppress variations in the operation time of the power relay to a small level, and it is possible to suppress the inrush current of the high voltage transformer to a small level.

Effect of the invention As described above, the present invention has the following effects.

(1) The inrush current can be suppressed to a low level, the durability of the contacts of the power relay can be significantly improved, and the unpleasant vibration noise of the heating chamber or the like can be eliminated.

(2) Overvoltage is applied to the operating coil only when the power relay operates, and after operation, the voltage is below the rated voltage, so there is no deterioration such as temperature rise of the operating coil, and the life of the power relay can be extended. It is.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram of an embodiment of the present invention, and FIG. 2 is a circuit diagram of an embodiment of the present invention.
An external view of the present invention, FIG. 3 is a power relay characteristic diagram, FIG. 4 is a circuit characteristic diagram of the present invention, and FIGS. 5 and 6 are:
An example of a conventional circuit, FIG. 7 is a timing chart of the same. 2... Heating chamber, 7... High frequency oscillator, 8
...High voltage transformer, 9...Power relay,
17...Voltage suppression section. Name of agent: Patent attorney Toshio Nakao and 1 other person/-
11 square shoulders 1 hot water tank 2--1 Kaxing room? ---Bird Figure 2 Figure 3 Wasi Koinomu $ Electricity V5 (2) Figure 4 N Makimon Figure 5 Figure 6 Figure 7

Claims (2)

[Claims] (1) A heating chamber that stores food, a high-frequency oscillator that supplies high-frequency output to the heating chamber, a high-voltage transformer that supplies power to the high-frequency oscillator, a power relay that connects the power to the high-voltage transformer, and this power A high-frequency heating device configured to include a voltage control section that controls the voltage applied to the coil in series with the operating coil of the relay. (2) The high-frequency heating device according to claim 1, wherein the voltage control section supplies an overvoltage to the operation coil when the power relay is operated, and supplies a voltage equal to or lower than the rated voltage after the operation.