JPS6155881A - Electromagnetic cooking device - 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] (a) Purpose [Field of Industrial Application] The present invention relates to an electromagnetic cooker that utilizes induction heating, and particularly relates to improvements in its control circuit.

[Prior art]

In an electromagnetic cooker, an induction heating coil and a switching element are connected in series to a DC power supply, and an inverter circuit, which has a resonant capacitor connected in parallel to the switching element, drives the induction heating coil and heats a pan, etc. It is prepared by cooking. By the way, among the components of this inverter circuit, the switching elements are relatively easily destroyed. If a voltage exceeding the rating is applied to the switching element, it will be destroyed in a short period of time, and the electromagnetic cooker will completely lose its function. Therefore, conventionally, the voltage applied to the switching element is detected and suppressed to below the rated value.
If the rating is exceeded, the inverter circuit should be driven by fγ.
The function of protecting the switching element by controlling the stop or conduction period of the switching element has been regarded as one of the important functions that should be provided in the control circuit of the electromagnetic cooker.

However, in conventional electromagnetic cookers, the voltage applied to the switching element is detected by a voltage dividing resistor inserted in parallel between both ends of the switching element.

(Problem to be solved by the invention) By the way, the voltage dividing parallel resistors inserted at both ends of the switching element cannot be expected to have much mechanical strength, and breakage is often seen. Conventional voltage detection means have had problems, such as when the resistor is disconnected, the high terminal voltage of the switching element is directly applied to the control circuit, destroying the electronic components of the control circuit and leading to destruction of the switching element.

In view of these circumstances, the present invention provides a durable electromagnetic cooker having a 1Xlt mechanically and electrically robust voltage detection means.

(Example) Structure of the Invention The present invention includes a DC power source, an induction heating coil connected in series to both ends thereof, a switching element, a detection coil that induces a voltage by magnetic flux of the induction heating coil,
It includes a resonant capacitor connected in parallel to the switching element, and a control circuit that opens and closes the switching element, and the control circuit detects the output voltage of the detection coil and controls the conduction period of the detection switching element. This is an electromagnetic cooker that is characterized by:

〔Example〕

The present invention will be described in detail below based on embodiments shown in the drawings.

Note that this invention is not limited to J:.

In the electrical circuit diagram of the electromagnetic cooker shown in Figure 1, (1)
is a DC power supply that receives an AC power supply (8) as an input and outputs DC, and is composed of a rectifier (14), a choke coil 05), and a smoothing capacitor 06). (2) is an induction heating coil, (3) is a switching element, (4) is an induction heating coil (a detection coil installed near the 2J and detects its magnetic flux, (5) is a resonant capacitor, and (6) is a control circuit. , ('/) is a comparison circuit, (9) is an output regulator that divides and varies the voltage of the DC power supply and inputs it to the control circuit (6).
(11) is a rectification and smoothing circuit that rectifies and smoothes the output of the detection coil (4) and inputs it to the control circuit, and az is a current transformer provided to detect whether the AC input current is within a predetermined range. , 03) is a rectifying and smoothing circuit that rectifies and smoothes the output of the current transformer 02) and inputs it to the control circuit.

Next, the configuration of the detection coil (4) will be explained. In Fig. 2, the detection coil (4) is composed of one turn of conductive wire with an insulating coating applied to the upper center of the II heating coil (2).
It was shown to. The ribs protect the heating coil (a, and add 95'f
The top plate (18) is a coil base on which a heating coil (2) is fixed. Figure 3 is the second
A case is shown in which the detection coil +2 shown in the figure is installed in the central hole of the heating coil (4). Further, the detection coil (4) may be embedded inside the coil base 08) as in the fortieth example. Furthermore, although the shape of the detection coil (4) is shown as round,
It may be triangular or polygonal, and the number of turns is not limited to one turn, but may be 2 to 3 turns or more. As the detection coil, it is preferable to use a wire or band material with good electrical conductivity, such as copper, aluminum, or brass. Note that the detection coil (4) needs to be covered with an insulator (such as a silicon tube) that can withstand the heat generated by the heating coil [21].

Next, the operation of the embodiment will be explained. FIG. 5 shows the waveforms of the output (VA) (VB) of the control circuit (6) and the output (VC) of the comparator (7) in FIG. 1.

The DC level voltage (VA), which varies according to the voltage of the output regulator (9), and the triangular wave voltage (VB) are compared, and the VA
>VB, the rectangular wave voltage (V
C) is output from the comparator (7). This voltage (VC)
conducts the switching element (3) periodically for a time (tw), and the current (Ic) from the DC power supply (1) is supplied to the heating coil (2. In this way, the DC level voltage (V
When A) is increased or decreased, the conduction period ('tw) changes, the drive current to the heating coil (2) is varied, and the output of the electromagnetic cooker is adjusted.

On the other hand, when heating coil (20,000 energized) like this, the 2nd to 4th
As shown in the figure, a voltage is induced in the sensing coil (4) installed near the heating coil (2) by the magnetic flux. This induced voltage is naturally proportional to the terminal voltage of the heating coil (2). Also, during the closing period of the switching element (3), the energy of the heating coil (2) is transferred to the resonant capacitor (5).
Therefore, the terminal voltage of this capacitor, that is, the terminal voltage (VT) of the switching element (3) is qualitatively proportional to the detection voltage (VD) of the heating coil (2) or the detection coil (4). can be explained. FIG. 6 shows an example of the results of experimentally measuring this and determining the relationship between the switching element applied voltage (VT) and the detection coil voltage (VD).

It is confirmed from FIG. 6 that the voltage applied to the switching element (VT) and the detection coil voltage (VD) are in a proportional relationship. Therefore, by using this relationship, the applied voltage (VT) of the switching element can be detected by the detection coil voltage.

By inputting this voltage (VD) and controlling the conduction period (Y) of the switching element, the control circuit (6) can control the applied voltage (VT) to a predetermined value fi+I.

(C) Effect According to this statement 1!13, since it is possible to detect a voltage proportional to the voltage applied to the switching element by the detection coil installed near the heating coil, this can be used to detect the voltage applied to the switching element. Provided is an electromagnetic cooker that can control voltage and is robust and durable.

[Brief explanation of drawings]

FIG. 1 is an electric circuit diagram of an embodiment of the present invention, and in FIGS. 2 and 3 (ω is the detection coil J5 in FIG. Fig. 4 is a sectional view showing another example of the configuration of the detection coil and heating coil, Fig. 5 is an explanatory diagram of the output waveform of each part in Fig. 1, Fig. 6 is a graph showing the relationship between the applied voltage of the switching element and the voltage of the detection coil. (1)...DC power supply, (2J...Induction heating coil, (3)・・・・・・Switching element, (
4)...Detection coil, (5)...Resonance capacitor, (6)...Control circuit. Figure 1 Figure 2 Figure 3 18″

Claims (1)

[Claims] 1. A DC power supply, an induction heating coil and a switching element connected in series to both ends thereof, a detection coil that induces a voltage by the magnetic flux of the induction heating coil, and a detection coil parallel to the switching element. a resonant capacitor connected to
An electromagnetic cooker comprising: a control circuit that opens and closes the switching element, wherein the control circuit detects an output voltage of the detection coil and controls a conduction period of the switching element.