JPS62147689A - Induction heating cooker source abnormality detecting circuit - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a power supply abnormality detection circuit for an induction heating cooker used in a general household.

Conventional technology In induction heating cookers, in order to protect the high frequency inverter that supplies high frequency current to the induction heating coil, it is generally done to detect excessive or insufficient power supply voltage and stop the above-mentioned in/parter. There is.

As shown in Figure 5, the conventional power supply abnormality detection circuit
After full-wave rectification of voltage a with rectifier 3, voltage dividing resistors 4 and 6
A method has been adopted in which the voltage is divided by , and compared with a reference voltage 6 by a comparator 7. In this method, the induction heating circuit 2 is stopped in response to excessive power supply voltage by setting the reference voltage 6 to generate a detection output when the power supply voltage reaches 120% or more of the rated power supply voltage, for example. to protect the induction heating circuit from destruction. Conventionally, as shown in FIG. 7, the voltage a of the power supply 1 is full-wave rectified by a rectifier 3, then divided by voltage dividing resistors 8 and 9, and the divided voltage output is passed through a diode 10. Another method has been to hold the peak with a peak hold circuit including a capacitor 11 and a resistor 12, and compare it with a reference voltage 13 with a comparator 14. In this method, for example, by setting the reference voltage 13 to generate a detection output when the power supply voltage reaches 80% or less of the rated power supply voltage, the induction heating circuit 2 can be stopped in response to an excessively low power supply voltage. This protects the induction heating circuit from being destroyed due to malfunction of the control circuit included in the induction heating circuit due to insufficient power supply voltage or the like.

Problems to be Solved by the Invention In the conventional example shown in Fig. 6, when a momentary power outage t or lightning surge application t2 occurs in the power supply voltage a as shown in Fig. 6 a), As shown in FIG. 6b), the partial pressure output of a cannot be detected because only a proportional output of a is obtained. Figure 6 b) and c) are the voltages of Figure 5, respectively.
, and vr in FIG. 6b) represents the reference voltage 6 in FIG.

In addition, in the conventional example shown in FIG. 7, the power supply voltages a and d shown in FIG.
As can be seen from the peak hold output d of ) and the detection output e of
It cannot be detected because it never reaches Vr, which represents 3.

However, even for power supply abnormalities that do not reach such a detection level, high voltages are often generated in the switching elements that constitute the induction heating circuit due to malfunction of the control circuit, leading to destruction of the switching elements. . Conventionally, this has been prevented by, for example, increasing the breakdown voltage of the switching element sufficiently. Increasing the breakdown voltage of a switching element generally results in a decrease in performance other than breakdown voltage, such as switching speed and on-voltage, and a decrease in yield.
This causes problems such as increased costs due to an increase in chip size, etc.

The present invention solves the above-mentioned conventional problems, and aims to protect an induction heating circuit in the event of a power failure with a simple configuration.

In order to solve the above problems, the present invention provides a voltage dividing means that outputs a voltage obtained by dividing the power supply voltage of an induction heating cooker, and a voltage that compares the output voltage with a reference voltage. The voltage dividing means has a bypass characteristic in which the output voltage becomes larger with respect to high frequencies.

According to the above-described structure, the output voltage of the voltage dividing means increases when the power supply voltage suddenly changes, so that sudden changes in the power supply voltage, which could not be detected in the past, can be detected at the same time as the power supply voltage is too high or too low. be able to. Therefore, by stopping the induction heating circuit or reducing the heating output based on the detection output, the induction heating circuit can be reliably protected in the event of a power failure.

Embodiment FIG. 1 is a circuit diagram showing an embodiment of a power supply abnormality detection circuit for an induction heating cooker according to the present invention. In FIG. 1, 21 is the voltage of an AC power source a, 22 is an induction heating circuit, and 4o is voltage dividing means, which is composed of a rectifier 23, resistors 24, 25, 2, and a capacitor 26. b is the output of the voltage dividing means 40, which is connected to a voltage comparing means 41 composed of a voltage comparator 29 and a reference voltage 28. The induction heating circuit 22 is controlled by the output of the voltage comparison means 41. C is the output of the voltage comparison means 41 and is connected to the induction heating circuit 22. The AC power supply voltage a becomes a pulsating voltage by the rectifier 23, and is divided by the resistors 24, 25, and 27.

A sudden change in the power supply voltage a is largely transmitted to the output by the capacitor 26. That is, the voltage dividing means 4o has bypass characteristics. FIG. 2 is a waveform diagram showing the operation of FIG.
)l b) and C) show the waveforms of FIG. 1 a, b, and c, respectively, and Vr in b) shows the voltage of the reference voltage 28.

In Figure 2, as in a), there is a momentary power outage at tl, t2
When a lightning surge or the like occurs in the voltage dividing means 4 as shown in b)
Since a large change is obtained in the output of 0 and reaches the detection level vr, a detection output C is obtained as shown in FIG. 2C), and the induction heating circuit 22 is stopped or the heating output is reduced. With the configuration shown in FIG. 1, excessive voltage can be detected simultaneously with sudden changes in the power supply voltage.

FIG. 3 is a circuit diagram showing another embodiment of the present invention. Third
In the figure, 21 is an AC power supply, a is its voltage, and voltage dividing means 4o
It is connected to the. The voltage dividing means 4o includes a rectifier 23, resistors 30, 31, 32, 35, 39, and capacitors 34, 38.
, and a diode 33. Reference numeral 41 denotes voltage comparison means, which is composed of a voltage comparator 37 and a reference voltage 36, and is connected to the output of the voltage dividing means 4o. C is the output of the voltage comparison means 41 and is connected to the induction heating circuit 22.

The AC power supply voltage a becomes a pulsating voltage by the rectifier 23, and is divided by the resistors 30, 31, and 32. The divided voltage is turned into a DC voltage by a peak hold circuit including a diode 33, a capacitor 34, and a resistor 36. Sudden fluctuations in the power supply voltage a are added to this DC voltage by a capacitor 38 and a resistor 39 to output it.

Therefore, the output of the voltage dividing means 4o shows a large change when the power supply voltage a suddenly changes. That is, the voltage dividing means 40 has bypass characteristics. FIG. 4 is a waveform diagram showing operating waveforms of the embodiment of FIG. 3. Figure 4 a) + b) +
C) shows a, b, and c of FIG. 3, respectively. Further, vr in b) indicates the voltage of the reference voltage 36. t in a.

K Momentary power outage, a lightning surge is applied at t2, but this sudden change is transmitted through the capacitor 38, and the output changes greatly as shown in b) and reaches the reference voltage vr, so it is detected as shown in C) The output C is obtained and the induction heating circuit 22
Stop or reduce heating output. With the configuration shown in FIG. 3, it is possible to detect an undervoltage at the same time as sudden fluctuations in the power supply voltage.

Above, an embodiment has been described in which the voltage dividing means 4o is provided with bypass characteristics using the Re differentiating circuit.
A configuration using a combination of LC, etc. can be easily considered, and the point is that the output of the voltage dividing means changes greatly when the input changes suddenly.
It is sufficient if the voltage dividing means 40 has bypass characteristics.

Effects of the Invention As described above, according to the present invention, with an extremely simple configuration, it is possible to detect sudden fluctuations in the power supply voltage in the event of a power failure, and to stop the induction heating circuit or reduce the heating output in the event of a power failure. Since the induction heating circuit can be reduced, etc., the induction heating circuit can be reliably protected, which is extremely useful in practice.

[Brief explanation of drawings]

Fig. 1 is a circuit diagram showing one embodiment of the present invention, and Fig. 2 is a circuit diagram showing an embodiment of the present invention.
3 is a circuit diagram showing another embodiment of the present invention, FIG. 4 is a waveform diagram explaining the operation of another embodiment of the present invention, and FIGS. FIG. 6 is a circuit diagram and waveform diagram of one conventional example, and FIGS. 7 and 8 are circuit diagrams and waveform diagrams of other conventional examples. 21...Power supply, 4o...Voltage dividing means, 4
1... Voltage comparison means. Name of agent: Patent attorney Toshio Nakao and 1 other person t7
tt 21-11 Electric 5 Field Figure 4 6, tz Figure 5? Figure 6 Figure 7? r (d-nt, rf-2 Procedural amendment 1 vehicle ('1-' display 1985 1.S' Patent application No. 288683 2 Name of invention Relationship to incident Patent application
Address: 1006 Oazama J', Kadoma City, Osaka Name (582) Matsushita Electric Industrial Co., Ltd.
Akira Tanii Kiji 4 Agent 571 Address 1006 Oaza Kadoma, Kadoma City, Osaka Prefecture Matsushita Electric Industrial Co., Ltd. Name (5971) Patent attorney Toshio Nakao (and 1 other person) (Ren I3 phone number (mkyo) 437 -1121 j11ml
Jin branch) 6. Contents of amendment (1) The scope of claims section of the specification will be amended in a separate document. (2) “Power supply voltage” in line 19 of page 1 of the same page is changed to “power supply voltage.”
will be corrected. (3) On page 5, line 9, "AC power source a is" will be corrected to "AC power source, a is." (4) In the same page, page 7, line 12, "a de" will be corrected to "ra) de". 2. Claims Voltage dividing means for outputting a voltage obtained by dividing the power supply voltage of the induction heating cooker, voltage comparison means for comparing the output voltage with a reference voltage, and controlled by the output of the voltage comparison means An induction heating circuit, wherein the voltage dividing means has a high-pass characteristic in which the output voltage increases with respect to high frequencies, and the power supply abnormality detection circuit for an induction heating cooker detects sudden fluctuations in the power supply voltage.

Claims (1)

[Claims] It has a voltage dividing means for outputting a voltage obtained by dividing the power supply voltage of the induction heating cooker, a voltage comparing means for comparing the output voltage with a reference voltage, and an induction heating circuit controlled by the output of the voltage comparing means. A power supply abnormality detection circuit for an induction heating cooker, wherein the voltage dividing means has a high-pass characteristic in which the output voltage increases with respect to high frequencies, and detects sudden fluctuations in the power supply voltage.