JPS6116621Y2 - - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to an induction heating cooker and aims to prevent the propagation of noise caused by an oscillation signal of a high frequency inverter.

The induction heating cooker uses a high frequency inverter to produce approx.
It generates a high frequency alternating current of 25KHz to about 50KHz and supplies it to an induction heating coil to heat a cooking pot placed close to it. In such a cooker, the fundamental wave and high frequency of the high frequency inverter oscillation frequency are returned to the power source (commercial AC power source),
There is a problem in that noise signals enter other electrical devices connected to the same power source and interfere with their normal operation. FIG. 1 is a diagram for explaining this, in which 1 is a high frequency inverter, 2 is an induction heating coil, and both are housed in a metal case 3. The metal case 3 can be made of aluminum or a copper-plated insulating resin plate, and is used to prevent noise caused by electromagnetic waves emitted from the inverter from leaking to the outside of the cooker. Among the above-mentioned noises, symmetrical wave components having a constant frequency close to the oscillation frequency can be prevented from leaking by providing a filter circuit, but asymmetrical components cannot be easily removed. In other words, among the asymmetric components, the noise component v induced into the power supply line a
_R also occurs in power plugs, etc. that are not protected by a filter circuit, so the filter circuit is not effective.
Further, a noise component v _c is also generated in the metal case 3 . If the oscillation frequency of high-frequency inverter 1 is approximately 25KHz, the asymmetric components of these noises will be approximately 25KHz.
Hz to about 100MHz, and if the oscillation frequency is about 50KHz, it will be about 50KHz to about 100MHz. 4 is
100V or 200V AC power supply, and 5 is a noise measurement circuit to be described later. Normally, the metal case 3 is required to be grounded in order to prevent electrical leakage due to contact between a live part inside the metal case 3 and a non-live part such as the case, or an accident in which the user touches the case 3 and receives an electric shock. However, if the metal case 3 is grounded, there is a risk that the aforementioned high frequency noise components v _R and v _c may be input to the AC power supply 4 which is also grounded through the metal case 3 and the ground.

On the other hand, in order to test the product's suitability as a product, it is necessary to interpose a noise measuring circuit 5 between the power supply lines a and a to measure the noise. As this measuring circuit 5, resistors R ₁ and R ₂ and capacitors C ₁ and C ₂ are usually connected in series as shown in the figure, the connection point of the capacitors C ₁ and C ₂ is grounded, and the measurement signal is connected to both ends 6 of the resistor R ₂ , 6, and a circuit for measuring with a noise level meter or the like is used. Resistors R ₁ and R ₂ are approximately 1 KΩ, and capacitors C ₁ and C ₂ are approximately 0.1 μF. Capacitors C ₁ and C ₂ are 50Hz,
It blocks low frequency signals such as 60Hz. However, in such a circuit, the noise component v _c induced in the metal case 3 mixes into the measurement signal through the ground, appears in the voltage between the terminals 6 and 6, and increases the noise voltage, making the product unsuitable. There is a risk of being judged.

The present invention was devised in consideration of such circumstances, and one embodiment will be described below with reference to FIGS. 2 and 3. Note that the example shown in the figure is a two-burner heating cooker. 1 ₁ , 1 ₂ are high frequency inverters corresponding to each heating port, 7 are each high frequency inverters 1 ₁ , 1 ₂
Plugs 8 and 9 serving as common power supply terminals are plugs serving as power supply terminals for the high frequency inverters 1 ₁ and 1 ₂ individually. 3 is a metal case that houses the high frequency inverters 1 ₁ and 1 ₂ ; 10 is a ground pin; 11 is a
A ground coil connected between the metal case 3 and the ground pin 10 exhibits high impedance characteristics for high frequency currents and low impedance characteristics for low frequency currents. As this earth coil 11,
If one of about 700 μH is used, asymmetric noise components of about 1 MHz or more can be blocked. 12
is a top plate on which a cooking pot made of ferrous metal is placed, and is made of a heat-resistant insulating board such as a ceramic board. 13 is a support portion fixed to the metal case 3. The illustrated example shows a built-in type that is installed in a microwave oven incorporating other heating means such as a gas burner, together with or in place of the burner, and a recess provided at a suitable position in the microwave oven in the supporting part 13. is placed and mated. At this time, the plugs 7, 8, 9 and the ground pin 10 are inserted into an outlet provided in the range and electrically connected. Furthermore, when the metal case 3 of the cooker is assembled into a range, it maintains electrical insulation with respect to the range, and is grounded to the range only through the earth pin 10. Such insulation can be achieved by forming a space between the metal case 3 and the microwave oven and interposing an insulator such as rubber on the contact surface between the support portion 13 and the microwave oven.

With the above-described configuration, electromagnetic waves generated from the induction heating coils and the switching elements constituting the high-frequency inverters 1 ₁ , 1 ₂ are transmitted to the metal case 3 .
Even if high-frequency noise v _c is induced in the AC power source 4 , since this is prevented from leaking to the outside by the earth coil 11 , there is no risk that the high-frequency noise will flow into the AC power supply 4 . In addition, the above-mentioned noise v _c passes through the ground of the measuring circuit 5 and becomes a noise voltage at the measuring terminal 6,
There is no danger that it will appear within the next 6 days.

Furthermore, even if a live part of the cooker comes into contact with the metal case due to an accident and a current leakage occurs, the low frequency current flows through the ground coil 11, so there is no danger of electric shock when the user touches it. Note that although the high frequency noise is confined within the metal case, this does not have any effect even if the user touches it and does not pose a practical problem.

[Brief explanation of the drawing]

Fig. 1 is a schematic diagram for explaining the generation of high frequency noise, Fig. 2 is a circuit diagram of an embodiment of the present invention, and Fig. 3 is a schematic diagram for explaining the generation of high frequency noise.
The figure is a perspective view of the same line. 1,1 _{1,1 2} ...High frequency inverter, 2...
Induction heating coil, 3... Metal case, 5... Noise measurement circuit, 7, 8, 9... Plug, 10... Earth pin, 11... Earth coil.

Claims (1)

[Scope of utility model registration request] In an induction heating cooker in which an induction heating coil and a high-frequency inverter, etc. that supply a high-frequency alternating current to the coil are housed in a metal case, an earth pin is provided to ground the metal case, and a high-frequency An induction heating cooker characterized by interposing a grounding coil having high impedance characteristics against current and low impedance characteristics against low frequency current.