JP2006040789A - Electromagnetic cooker - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electromagnetic cooker capable of determining whether there is a pan or not while controlling an output power at a constant level, even when the output power is low. <P>SOLUTION: In the electromagnetic cooker composed of a current transformer 4 to detect a power supply electric current Is, conversion resistances 6, 7 to convert an output electric current It of the current transformer 4 to a voltage signal Vs, and a control device 9 to carry out an electric power control based on the voltage signal Vs and the determination whether or not there is the pan, when the power supply electric current Is is large, a resistance value of the conversion resistances 6, 7 is reduced, and when the power supply electric current Is is small, the resistance value of the conversion resistance 6 is increased. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an electromagnetic cooker.

In an electromagnetic cooker, as described in Patent Document 1, a control device such as a microcomputer determines whether a pan is placed based on a power supply current or keeps the output constant. It is carried out.
Japanese Patent Laid-Open No. 11-76049

  FIG. 4 shows a circuit diagram of a conventional electromagnetic cooker. A conventional electromagnetic cooker includes an inverter circuit 22 to which a current Is is supplied from a power source 21, a heating coil 23 to which a drive current is supplied from the inverter circuit 22, a current transformer 24 for detecting the power source current Is, and a current transformer 24. The diode bridge 25 that rectifies the output current of the diode bridge 25, the conversion resistor 26 that converts the output current It of the diode bridge 25 into the voltage signal Vs, the smoothing capacitor 27 that averages the voltage signal Vs, and the inverter circuit 22 are controlled. The voltage signal Vs is input to the input terminal 29 of the control device 28.

  FIG. 5 shows the relationship between the power supply current Is and the voltage signal Vs input to the control device 28. The output current It (A) obtained by rectifying the output current of the current transformer 24 by the diode bridge 25 has a current value proportional to the power supply current Is, and is grounded via the conversion resistor 26 having a resistance value R (Ω). Yes. For this reason, the voltage of the voltage signal Vs applied to the input terminal 29 of the control device 28 becomes It × R (V) according to Ohm's law.

In this electromagnetic cooker, if the power supply current Is proportional to the output of the heating coil 23 is a set current value Ix (A), it can be evaluated that the electromagnetic cooker is operated at a predetermined output. Therefore, the control device 28 controls the inverter circuit 22 so that the voltage signal Vs becomes the operation voltage Vx (V) corresponding to the predetermined current value Ix. Further, the control device 28 determines that the voltage signal Vs is equal to or less than the no-load voltage V ₀ (A) corresponding to the no-load current I ₀ (A) that is the power source current Is when the heating coil 23 has no load. It is determined that the pan is not placed on the heating coil 23. Further, since the control device 28 can recognize the voltage signal Vs only within the range of the maximum voltage Vmax (V) or less, the voltage signal Vs corresponding to the power supply current Is at the maximum output exceeds Vmax (V). Therefore, it is necessary to determine the resistance value R (Ω) of the conversion resistor 26 so as not to occur.

However, if the appropriate operating voltage Vx at the maximum output is set to a value close to Vmax, the difference between the appropriate operating voltage Vx ′ at the low output and the no-load voltage V ₀ becomes very small, and the operation is being performed at a low output. Even if the pan is picked up, the control device 28 has a problem that it cannot detect that there is no pan.

  In view of the above problems, an object of the present invention is to provide an electromagnetic cooker that can determine the presence or absence of a pan while controlling the output constant even when the output is low.

  In order to solve the above problems, an electromagnetic cooker according to the present invention includes a current transformer that detects a power supply current, a conversion resistor that converts an output current of the current transformer into a voltage signal, and power control and A control device for determining the presence or absence of a pan, when the power supply current is large, reduce the resistance value of the conversion resistor, and when the power supply current is small, increase the resistance value of the conversion resistor; To do.

  According to this configuration, even when the output is low, the difference between the voltage input to the control device at a predetermined output and the voltage input to the control device when there is no pan is large, and the output is controlled to be constant. It is possible to accurately determine the presence or absence of a pan.

  Moreover, the electromagnetic cooker of this invention WHEREIN: The said conversion resistance consists of at least 2 resistance, The resistance value of the said conversion resistance may be changed by connecting or disconnecting at least 1 said resistance.

  According to this structure, the electromagnetic cooker which can discriminate | determine the presence or absence of a pan, controlling output uniformly with a simple structure is realizable.

  In the electromagnetic cooker of the present invention, power control may not be performed for a predetermined time after the resistance value of the conversion resistor is changed.

  According to this configuration, since an unstable voltage immediately after changing the value of the conversion resistor is not reflected in the control, the output is not unstable, and the presence or absence of the pan is not erroneously determined.

  In the electromagnetic cooking device of the present invention, the power control may be performed after detecting the pan by increasing the resistance value of the conversion resistor.

  According to this configuration, since the presence or absence of the pan is first determined accurately, useless energy is not consumed to increase the output without the pan.

  As described above, according to the present invention, it is possible to provide an electromagnetic cooker that can determine the presence or absence of a pan while controlling the output to be constant even when the output is low.

Hereinafter, an electromagnetic cooker according to an embodiment of the present invention will be described with reference to the accompanying drawings.
In FIG. 1, the circuit diagram of the electromagnetic cooker of 1st Embodiment of this invention is shown. The electromagnetic cooker of this embodiment includes an inverter circuit 2 to which a current Is is supplied from a power source 1, a heating coil 3 to which a drive current is supplied from the inverter circuit 2, a current transformer 4 that detects the power source current Is, and a current A diode bridge 5 that rectifies the output current of the transformer 4 to direct current, and a first conversion of a resistance value R1 (Ω) that converts the output current It of the diode bridge 5 to a voltage signal Vs having a voltage proportional to the current It. It comprises a resistor 6 and a second conversion resistor 7 having a resistance value R2 (Ω), a smoothing capacitor 8 for averaging the voltage signal Vs, and a control device 9 for controlling the inverter circuit 2. The voltage signal Vs is input to the input terminal 10 of the control device 9. Although the first conversion resistor 6 is directly grounded, the second conversion resistor 7 is connected to the control terminal 11 of the control device 9 and is grounded via the internal contact 12 of the control device 9.

FIG. 2 shows the relationship between the power supply current Is and the voltage signal Vs input to the control device 9 in the electromagnetic cooker having the above configuration, and the control by the control device 9 will be described. When the electromagnetic cooker is activated, the internal contact 12 is opened, and all the output current It proportional to the power supply current Is flows through the first conversion resistor 6 and is grounded. Then, the voltage of the voltage signal Vs applied to the input terminal 10 of the control device 9 becomes It × R1 (V) according to Ohm's law. When the voltage signal Vs is equal to or lower than the no-load voltage V ₀ generated by the no-load power source current I _0, which is the no-load power source current Is, the control device 9 places the pan at a predetermined position on the heating coil 3. The output of the inverter circuit 2 is stopped.

When the pan is placed at a predetermined position, the inverter circuit 2 is controlled so that the voltage signal Vs becomes the predetermined operating voltage Vx (V), and the pan is heated by the heating coil 3. That is, based on the voltage signal Vs, the inverter circuit 2 is controlled so as to maintain a predetermined operating current Ix (A) that can obtain an output set by the power supply current Is. At this time, if the voltage signal Vs input to the control device 9 is equal to or higher than the upper limit voltage V _H (V), the internal contact 12 of the control device 9 is closed. Then, the second conversion resistor 7 is connected to the first conversion resistor 6 in parallel, and the same result is obtained as when the resistance value of the first conversion resistor 6 is changed to R1 × R2 / (R1 + R2). That is, the voltage signal Vs applied to the input terminal 10 of the control device 9 becomes It × R1 × R2 / (R1 + R2) (V), and therefore is lower than when the internal contact 12 is opened as shown in FIG. Become a voltage. Thus, the control device 9 is input to the control device 9 corresponding to the operation current Ix ′ (A) that can obtain the set output so as to maintain the operation voltage Vx ′ (obtained when the internal contact 12 is closed). The inverter circuit 2 is controlled. Conversely, when the internal contact 12 is closed and the voltage of the voltage signal Vs decreases and falls below the lower limit voltage V _L (V), the internal contact 12 is opened and the second conversion resistor 7 is disconnected from the circuit. (Or, the electric current does not flow and the device does not substantially function).

According to the above control, when the power supply current Is is small, a large voltage drop is generated by the first conversion resistor 6 having a large resistance, and the voltage of the voltage signal Vs input to the control device 9 is increased. As a result, the difference between the operating voltage Vx and the no-load voltage V ₀ is controlled even when the power supply current value Ix for obtaining the set output is a small value close to the power supply current value I ₀ when there is no pan. It becomes sufficiently larger than the resolution of the device 9. Therefore, while being controlled to maintain the power source current Is driving current Ix (A), even if the pot is taken up reliably that the power current Is drops to no-load supply current I ₀ It can be detected to avoid wasting energy. When the power supply current Is is large, the second conversion resistor 7 is connected in parallel to the first conversion resistor 6 to reduce the resistance value as a whole to reduce the voltage drop, and the voltage signal Vs input to the control device 9 is reduced. The voltage is lowered. As a result, even when the appropriate operating current Ix ′ of the power supply current Is for obtaining the set output is large, the operating voltage Vx ′ to be input to the control device 9 is the maximum voltage Vmax at which the control device 9 can recognize the voltage. It is possible not to exceed this, and appropriate control can be performed so as to maintain the set output.

  The electromagnetic cooker according to the present embodiment connects or disconnects the second conversion resistor 7 to / from the circuit by opening and closing the internal contact 12 according to the value of the voltage signal Vs input to the control device 9. Immediately after connecting the conversion resistor 7 to the circuit and immediately after disconnecting it from the circuit, the voltage of the voltage signal Vs input to the control device 9 becomes transiently unstable. The signal Vs is ignored and not reflected in the control.

Next, the circuit diagram of the electromagnetic cooker of 2nd Embodiment of this invention is shown in FIG. In the present embodiment, the same components as those in the first embodiment are denoted by the same reference numerals and description thereof is omitted.
The second conversion resistor 7 of the present embodiment is grounded via the transistor 13, and the internal contact 12 of the control device 9 is connected to the power supply of the control device, and outputs a voltage signal from the control terminal 11, Can be switched. Thereby, the control apparatus 9 can isolate | separate the 2nd conversion resistance 7 from a circuit, or can connect it in parallel with a 1st conversion resistance.

  The electromagnetic cooker of this embodiment is also controlled in exactly the same way as in the first embodiment. However, in this embodiment, the current flowing through the second conversion resistor 7 is grounded by the transistor 13 without flowing through the control device 9. For this reason, even if a large current is generated in the current transformer 4, a large current does not flow through the control device 9, and there is no fear of the control device 9 being damaged.

  The second conversion resistor 7 may be connected or bypassed in series with the first conversion resistor 6, and all other circuit configurations that change the ground fault resistance are applicable to the present invention.

The circuit diagram of the electromagnetic cooker of 1st Embodiment of this invention. The graph which shows the relationship between the power supply current and control apparatus input voltage of the electromagnetic cooker of FIG. The circuit diagram of the electromagnetic cooker of 2nd Embodiment of this invention. The circuit diagram of the conventional electromagnetic cooker. The graph which shows the relationship between the power supply current of a conventional electromagnetic cooker, and a control apparatus input voltage.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Power supply 4 Current transformer 6 1st conversion resistance 7 2nd conversion resistance 9 Control apparatus

Claims (4)

A current transformer for detecting the power supply current;
A conversion resistor for converting the output current of the current transformer into a voltage signal;
It consists of a control device that performs power control and determination of the presence or absence of a pan based on the voltage signal,
When the power supply current is large, the resistance value of the conversion resistor is decreased, and when the power supply current is small, the resistance value of the conversion resistor is increased.   The electromagnetic cooker according to claim 1, wherein the conversion resistor includes at least two resistors, and the resistance value of the conversion resistor is changed by connecting or disconnecting at least one of the resistors.   The electromagnetic cooker according to claim 1 or 2, wherein power control is not performed for a predetermined time after changing the resistance value of the conversion resistor.   The electromagnetic cooker according to any one of claims 1 to 3, wherein the power control is performed after detecting the pan by increasing the resistance value of the conversion resistor.

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