JPS6113356B2 - - Google Patents

Description

[Detailed description of the invention] The present invention relates to an induction heating cooker.

Induction heating cookers use commercial alternating current as a power source, rectify it, and add it to a high-frequency inverter.
A 40KHz high-frequency current is generated and applied to the induction heating coil, and a corresponding high-frequency alternating magnetic field is generated. In such cooking appliances, it is known that the high frequency current generated by the high frequency inverter flows back to the AC power source, and at the same time has an adverse effect on the operation of other electrical equipment that uses this AC as a power source. For example, the above-mentioned high frequency noise causes noise in a radio, and also causes noise on the screen of a television. Therefore, in such a cooking device, it is desirable to provide a filter circuit between the AC power source and the inverter to prevent high frequency current from leaking into the AC power source. However, simply providing a filter circuit cannot achieve the intended purpose. In other words, the magnetic field generated by the induction heating coil is applied to the line that makes up the filter circuit, and it becomes a noise signal that appears on the AC side, and when the power is turned on, the capacitor that makes up the filter circuit is charged with an AC peak voltage of approximately 140V. This has disadvantages such as the possibility that a voltage higher than the withstand voltage will be applied to the semiconductor switching elements constituting the inverter, causing them to be destroyed.

The present invention solves these drawbacks, and one embodiment of the present invention will be described in detail below with reference to the drawings.

Fig. 1 shows an induction heating cooker 1, 2 is a plug that is inserted into an AC power outlet, and 3 is a top plate that constitutes the upper surface of the cooker, and is made of a hard insulating plate such as a ceramic plate. A cooking pot (not shown) is placed there. 4 is an induction heating coil disposed close to the bottom surface of the top plate 3;
Reference numeral denotes an electrical equipment case that houses electrical components constituting an inverter circuit, a rectifier circuit, etc., 6 an electrical component constituting a filter circuit, and 7 a power switch.

Figure 2 shows the implementation circuit, 8 is a commercial AC power supply, 9 is a filter circuit, and two capacitors.
Including C ₁ , C ₂ and inductor L. Here, capacitors C ₁ and C ₂ are high frequency bypass capacitors with a capacity of about 10 μF, and inductor L
acts to increase the impedance of the power supply when viewed from the load side, and at commercial AC frequency of 50Hz,
Impedance is small for 60Hz. 10
1 is a rectifier circuit to which an AC power source 8 is applied via a filter circuit 9, and is composed of a diode bridge circuit. S ₁ is a first switch provided on one power supply line on the input side of the filter circuit 9, S ₂ is a second switch provided on another power supply line on the output side of the filter circuit 9, and both switches S ₁ and _S2 are interlocked, and the first switch _S1 is configured to operate in advance of the second switch _S2 . 11 is a high frequency inverter to which the output of the rectifier circuit 10 is supplied as a power source, and includes an induction heating coil 4, a resonant capacitor 12,
Diode 13 and semiconductor switching element 1
Contains 4. As this semiconductor switching element 14, a large capacity transistor, a gate turn-off thyristor GTO, or the like is used. 15 is
This is a gate drive circuit that applies an on/off signal to the gate of the switching element 14 to control the oscillation of the inverter. 16 is a cooking pot to which a high frequency alternating magnetic field generated by the induction heating coil 4 is applied.

Next, the operation will be explained. 1st and 2nd switch S ₁ ,
Closing S ₂ first closes switch S ₁ and then closes switch S ₂ . Therefore, AC power source 8 is supplied to rectifier circuit 10 via filter circuit 9, rectified, and provided to inverter 11. The inverter 11 oscillates at a frequency corresponding to the on/off period of the switching element 14 and passes a high frequency alternating current to the induction heating coil 4 . The frequency is set to about 20 to 40 KHz. The high frequency component generated by the inverter 11 passes through the rectifier circuit 10 and flows back to the filter circuit 9, but this high frequency component is returned to the inverter ₁₁ side through the capacitor C2. Also, inductor L is connected from the inverter 11 side.
Even if a high frequency component is added to the inductor L, the impedance of the inductor L for the high frequency component is set to be large, so that almost all of the high frequency component is prevented from passing through to the AC power source 8 side. Even if a high frequency component were to appear on the AC power supply 8 side via this inductor L, it would be returned to the inductor 11 side by the capacitor _C1 , and would be almost completely blocked by the capacitor _C1 .

Here, the positional relationship between the first and second switches S ₁ and S ₂ will be described. Traditionally, in induction heating cookers, the power switch 7 has been placed on the front (on the left side in the figure) as shown in Figure 1, for reasons of design or ease of operation, as with general electrical equipment, and a power switch 7 on the back. The power plug 2 is often installed on the right side of the figure.
In such a case, the power supply plug 2 is first led to the front operation section via the power line a, and then introduced into the electrical equipment case 5 via the power switch 7 disposed there. However, in such a configuration, if the filter circuit 9 is provided in the electrical case 5, the high frequency components in the inverter 11 will be prevented from flowing out by the filter circuit 9, but will not reach the power switch 7 to the power plug 2 on the rear panel. The magnetic field from the induction heating coil 4 is applied to the line a, which becomes a noise signal and flows out to the AC power supply side, making the filter effect incomplete. Therefore, in the present invention, the capacitors C ₁ and C ₂ are arranged near the outlet of the power plug 2 at the rear of the cooker, and the capacitors C ₁ and C ₂ and the power supply 8
A line a between the two is constructed so that it is not affected by the magnetic field. In this way, noise leakage to the power supply 8 side can be almost completely prevented.

The first and second switches S ₁ and S ₂ are both interlocked,
And when the power is turned on, the first switch S ₁ switches to the second switch S ₂
is configured to operate in advance of the The antecedent and subsequent relationship of this operation will be explained. Assuming that the second switch S ₂ closes before the first switch S ₁ , the two capacitors C ₁ , C ₁ and
C ₂ and the inductor L resonate, thereby generating a maximum voltage of about 140 V on the output side of the filter circuit 9, which is equal to the maximum value of the AC power supply voltage of about 140 V.
140V is added and a high voltage of approximately 280V is applied to inverter 1.
1, and in that case, there is a risk that the switching element 14 may be destroyed. In other words, this cooker is designed so that the normal power supply voltage is 140V, and the maximum voltage generated in the inverter 11 at this time is approximately 600V, and the withstand voltage of the switching element 14 is set to approximately 800V. . However, when the power supply voltage reaches about 280V, a high voltage of about 1200V is generated in the inverter 11, which destroys the switching element 14. For this reason, in the present invention, the operation of the first switch _S1 is made to precede the operation of the _second switch S2, so that chattering occurs in the first switch _S1 and high voltage is applied to the filter circuit 9. Even if a high voltage occurs, the second switch _S2 is turned on after the high voltage becomes a normal voltage.

3A and 3B show the specific structure of the first and second switches S ₁ and S ₂ constituting the power switch 7, both switches S ₁ and S ₂ are composed of micro switches, and the support frame 16 are fixed in parallel. 17
is a hollow frame body provided in the support frame 16, and holds the slide body 18 inside. This slide body 1
8 presses buttons s ₁ and s ₂ of switches S ₁ and S ₂ by the movement.
The contact surfaces for the push buttons s ₁ and s ₂ are formed at different levels, and the push button s ₁ of the first switch S ₁
The surface facing _the push button _s2 of the second switch S2 is formed low. Therefore, by pressing and moving the slide body 18, first the push button s1 of the _first switch S1 is pressed, and then the push button _s2 of the second switch S2 _{is pressed} .
will be pressed. Reference numeral 19 denotes an operating lever, which is rotatably supported by the frame 17 via a support shaft 20. Reference numeral 21 denotes an engaging body provided on the lever 19, which engages with the hole 22 of the slide body 18 and moves the slide body 18 in accordance with the rotation of the lever 19. 23 is a spring whose one end is fixed to the frame 17;
Elasticity is imparted to the rotation of the lever 19 via a sphere 25 provided in the lever recess 24. 26 is a stopper that limits the rotation angle of the lever 19.
When the operating lever 19 is rotated in the direction of the arrow in the figure against the elasticity of the spring 23, the slide body 18 moves upward in the figure, and first the first switch S ₁
, and then the second switch S ₂ is closed with a slight time difference. In this way, the power is turned on and heating operation is started. In the above power-on state,
The sphere 25 comes out of the lever recess 24 and moves into the adjacent recess 2.
7, even if the finger is released from the lever 19, the lever 19 is fixed at this position by the elasticity of the spring 23, and the first and second switches S ₁ and S ₂ remain in the on state. On the other hand, in order to turn these off, the lever 19 can be turned in the opposite direction of the arrow to move the sphere 25 into the lever recess 24.

As explained above, the induction heating cooker of the present invention has the following features:
It is equipped with a filter circuit that prevents high-frequency noise from leaking to the power supply side, and the electrical components that make up this filter circuit, especially the capacitor, are placed in a position that is not affected by the magnetic field generated by the induction heating coil. It is possible to prevent the generation of noise caused by a magnetic field in the case where a filter circuit is simply provided, and it is possible to almost completely block noise flowing to the AC power source side. Furthermore, the present invention provides two switches operated by one operating lever, and these are arranged on the input side and output side of the filter circuit, so that the operation of the switch provided on the input side precedes the operation of the other switch. Therefore, even if high voltage is generated in the filter circuit due to the chatter of the input switch,
Since the output side switch is turned on after the high voltage of the filter circuit reaches normal voltage, damage to the inverter components can be prevented and the safety of the cooker can be ensured.

[Brief explanation of the drawing]

FIG. 1 is a sectional view of one embodiment of the present invention, FIG. 2 is a circuit diagram, FIG. 3A is a front view showing the switch portion, and FIG. 3B is a partially cutaway side view of the switch. 1...Induction heating cooker, 2...Power plug, 3
...Top plate, 4...Induction heating coil, 5
...Electrical case, 9...Filter circuit, 11...
...High frequency inverter, S ₁ , S ₂ ... First and second switches, 18 ... Slide body, 19 ... Operation lever.

Claims (1)

[Claims] 1. An AC power source, a high-frequency inverter, a filter circuit interposed between the AC power source and the high-frequency inverter to prevent a high-frequency signal from flowing back to the AC power source, and an input side of the filter circuit. A first switch provided on the power supply line and a second switch provided on another power supply line on the output side of the filter circuit are provided, and the first switch and the second switch are interlocked and the operation of the first switch is controlled. An induction heating cooker characterized in that the operation of the second switch is preceded. 2. At least a part of the electrical components constituting the filter circuit is arranged near the AC power supply introduction part of the cooker, and the magnetic field generated by the induction heating coil is not applied to the cord between the electrical components and the AC power supply. An induction heating cooker according to claim 1.