JPH0241838Y2 - - Google Patents

Description

[Detailed description of the invention] (a) Industrial application field This invention relates to an induction heating cooker that cooks by induction heating.

(B) Prior Art In general, induction heating cookers contain heat-generating parts such as heating coils and high-frequency switching elements, and are therefore equipped with a fan motor for forced air cooling of these parts.

In conventional induction heating cookers, power is supplied to the fan motor from a power transformer for the drive circuit of the high frequency switching element.

(c) Problems to be solved by the invention There are the following problems to be solved in such an induction heating cooker.

(1) When the output of the cooking device is on, current flows through the drive circuit of the switching element, so the power supply voltage of the cooling fan motor decreases, and when it is off, it increases. Therefore, the number of revolutions of the fan motor changes in response to the on/off of the output, and the cooling fan rotation sound increases and decreases repeatedly, giving the user a feeling of discomfort and anxiety.

(2) A regulator to compensate for voltage fluctuations may be provided, or a power transformer exclusively for the fan motor may be provided, but the regulator and transformer are expensive and undesirable.

The present invention was made to solve these problems, and provides an inexpensive induction heating cooker in which the rotation speed of the fan motor does not fluctuate.

(d) Means for solving the problem This invention includes an LC resonant circuit composed of an induction heating coil and a capacitor, and a switching element that switches the current supplied to this LC resonant circuit at high speed. In the induction heating cooker, an inductance element electromagnetically coupled to the induction heating coil, and a step-down transformer that supplies power from a commercial power source to a drive circuit of the switching element;
The induction heating cooker includes a fan motor that air-cools heat-generating components, and the fan motor is driven by the output of the transformer and the inductance element.

(E) Effect According to the above-described configuration, when the cooker is turned on, a high frequency current flows through the induction heating coil and a voltage is induced in the inductance element.

This induced voltage is supplied to the fan motor to compensate for the voltage drop across the transformer caused by the current supplied to the switching element drive circuit.
Therefore, a substantially constant voltage is supplied to the fan motor regardless of whether the cooker is on or off, and its rotational speed is kept substantially constant.

(f) Examples This invention will be described in detail below based on examples shown in the drawings. Note that this invention is not limited to this.

In FIG. 1, 1 is an LC resonant circuit consisting of an induction heating coil 2 and a capacitor 3, 4 is a switching element consisting of a transistor 5 and a diode 6,
7 is an inductance element electromagnetically coupled to the induction heating coil 2; 8 is a drive circuit for the switching element 4;
9 is a step-down transformer to which power is supplied from a commercial power supply via a plug 10 and a switch 11; 12 is a fan motor that air-cools heat-generating components; 13 is a diode that rectifies the output of the transformer 9 and supplies it to the fan motor 12; 14 is a diode that rectifies the output of the inductance element 7 and supplies it to the fan motor;
15 is a smoothing capacitor, and 16 is a power conversion circuit that receives power from a commercial power supply, rectifies and smoothes it, and supplies power to the LC resonant circuit.

Here, when the plug 10 is inserted into an AC power outlet and the switch 11 is closed, the transformer 9
The voltage V stepped down by the diode 13 is rectified by the diode 13, smoothed by the capacitor 15, and applied to the fan motor 12. A load current IM is supplied to the motor 12, and the motor 12 rotates. next,
The drive circuit 8 is controlled by a cooking start sensor (not shown).
starts turning on and off its output, and when it is on, a current IC is supplied from the transformer 9 to the drive circuit 8, and a high frequency current is supplied from the power converter 16 to the LC resonant circuit 1 by the switching element 4. As a result, magnetic flux is generated in the induction heating coil 2. Voltage V' induced in inductance element 7 by the magnetic flux is rectified by diode 14, smoothed by capacitor 15, and applied to fan motor 12, and current IM' is supplied as part of motor current IM. . Furthermore, when the drive circuit 8 is off, the current IC becomes almost zero, and no high-frequency current is supplied to the LC resonant circuit 1, so the voltage
V' is not induced, the supply of current IM' to the motor 12 is stopped, and the load current IM of the motor 12 is again
are all supplied from transformer 9. Figure 2a,
b and c are graphs showing these relationships. In other words, Fig. 2a shows the transformer 9 in a conventional cooker.
The characteristic A of the output current I and voltage V of is shown.

When the motor current IM is output, the output voltage V of the transformer 9 first drops to _V1 . Next, when cooking is started, the current IC is further output when the drive circuit 8 is turned on, so that the output voltage V drops to _V2 . Then, when it is turned off, it rises to V ₁ again. Therefore, different voltages V ₁ and V ₂ are applied to the motor 12 depending on whether the drive circuit 8 is turned on or off, so that the rotation speed of the motor 12 fluctuates. In contrast, FIGS. 2b and 2c show the effect of this embodiment. The characteristics of the output current I' and voltage V' of the inductance element 7 can be varied as B1, B2, and B3 depending on the degree of electromagnetic coupling with the induction heating coil 2, as shown in FIG. 2b. Thereby, the current IM' supplied from the inductance element 7 to the motor 12 can be arbitrarily adjusted and set while maintaining the voltage _V1 .

As mentioned above, when the drive circuit 8 is turned on, the current IC,
When IM′ flows, the output current of transformer 9 is IC+
(IM−IM′). Therefore, by adjusting the current IM', the output voltage V of the transformer 9 shown in FIG. 2c can be set to _V1 .

Therefore, the current IM' is determined so that the output voltage V of the transformer 9 becomes _V1 when the drive circuit 8 is turned on, and the current IM' is supplied from the inductance element 7 at the voltage _V1 as shown in FIG. By adjusting the output characteristics of b, the voltage V ₁ will always be applied to the motor 12 regardless of whether the drive circuit 8 is on or off. Note that the above is a case where the current IC of the drive circuit 8 is smaller than or equal to the motor current IM, and the IC is smaller than or equal to the motor current IM.
When the voltage is larger, all of the motor current IM is supplied from the inductance element 7 when the drive circuit 8 is turned on, and the inductance element 7 is adjusted so that the output voltage V' of the inductance element 7 at that time becomes _V1 .
All you have to do is select the output characteristics of

(G) Effect of the invention According to this invention, the cooling fan motor is supplied with its load current from the power transformer for the driving circuit of the switching element and the inductance element electromagnetically coupled to the induction heating coil, and when the driving circuit is turned on, Since the load current of the power transformer whose voltage drops is shared and supplied by the inductance element, a substantially constant voltage is applied to the motor regardless of whether the drive circuit is on or off, eliminating fluctuations in the rotational speed. Therefore, fluctuations in the fan rotation noise generated during operation are eliminated, and the user's discomfort and anxiety are eliminated.

[Brief explanation of the drawing]

FIG. 1 is an electric circuit diagram showing one embodiment of this invention, and FIGS. 2a, b, and c are graphs explaining the operation of FIG. 1. 1...LC oscillation circuit, 2...Induction heating coil,
3... Capacitor, 4... Switching element, 7
...Inductance element, 8...Drive circuit, 9...
...transformer, 12...fan motor.

Claims (1)

[Scope of utility model registration request] In an induction heating cooker equipped with an LC resonant circuit composed of an induction heating coil and a capacitor, and a switching element that switches the current supplied to the LC resonant circuit at high speed, the LC resonant circuit is electromagnetically coupled to the induction heating coil. an inductance element,
The switching element includes a step-down transformer that supplies power from a commercial power supply to the driving circuit of the switching element, and a fan motor that air-cools heat-generating components, and the fan motor is driven by the output of the transformer and the inductance element. An induction heating cooker.