JPS6247354B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an electromagnetic induction heating device suitable for use as a cooking device, and in particular to prevent elements from being destroyed when the voltage of the commercial power source, which is the input power, drops below a normal value. It was designed to do so.

An electromagnetic induction cooking device as shown in FIG. 1 has been previously proposed. That is, in FIG. 1, 1 indicates a plug connected to a commercial power source, and the commercial power supplied to this plug 1 is connected to a fuse 2 and a power switch 3.
a, 3b to the input side of a rectifier circuit 4 composed of a diode bridge, and the positive voltage output terminal 4a of this rectifier circuit 4 is connected to a high frequency blocking coil 5, a work coil 6, and a resonance capacitor 7. It is grounded through a series circuit, the connection point of this chiyoke coil 5 and work coil 6 is connected to the cathode of the damper diode 8, the anode of this damper diode 8 is grounded, and the connection point of this chiyoke coil 5 and work coil 6 is connected to the cathode of the damper diode 8. The point is connected to the anode of the GCS9 constituting the switching element, and the cathode of this GCS9 is grounded. Further, in FIG. 1, numeral 10 indicates a top plate disposed on the work coil 6, and numeral 11 indicates a pot made of magnetic material. Also, the negative voltage output terminal 4 of the rectifier circuit 4
b is grounded via a resistor 12 with a low resistance value, for example, 30 mΩ, for detecting the current flowing through the work coil 6. In Figure 1, 13 is, for example, 19kHz~
A voltage-controlled variable frequency oscillator that oscillates in a frequency band of 33 kHz is shown, and the oscillation output signal of this voltage-controlled variable frequency oscillator 13 is transmitted through a drive circuit 14.
Supplies to the gate of GCS9. In this case, the GCS 9 is turned on and off according to this oscillation output signal, and the work coil 6 cooperates with the resonance capacitor 7 and the damper diode 8 to perform an electromagnetic induction heating operation. In this case, as the oscillation frequency of the oscillation output signal of the variable frequency oscillator 13 increases, the current flowing through the work coil 6 increases, and the output power increases. That is, in the example shown in FIG. 1, the oscillation frequency of this variable frequency oscillator 13 is controlled to control the output power.

Further, the connection point between the negative voltage output terminal 4b of the rectifier circuit 4 and the current detection resistor 12 is grounded through a series circuit of a resistor 15 and a capacitor 16 constituting a low-pass filter. Connect the connection point to diode 1 for temperature characteristic correction.
The anode of this diode 17 is connected to the base of an npn transistor 18 constituting an amplifier circuit, the emitter of this transistor 18 is grounded, and the collector of this transistor 18 is connected to the positive side through a resistor 19. This transistor 1 is connected to a power supply terminal 20 to which a DC voltage of
8 is connected to the base of this transistor 18 via a resistor 21. The collector of this transistor 18 is connected to the anode of a diode 23 via a resistor 22, and the connection point of this resistor 22 and diode 23 is connected to capacitors 24 and 25.
This resistor 2 is grounded through a series circuit of
The connection point between the capacitors 24 and 25 is connected to the connection point between the resistors 26 and 27. In this case resistors 22, 26, 2
7 and capacitors 24 and 25 constitute an average value detection circuit. Further, an operational amplifier circuit 2 is connected to the cathode of the diode 23 via a resistor 28 to form a comparator circuit.
The connection point between the diode 23 and the resistor 28 is grounded through a parallel circuit of a resistor 30 and a capacitor 31. In addition, the power terminal 20 is connected to a resistor 32 and a volume adjuster 33 for adjusting the output power.
The movable contact 33a of the output power adjusting volume 33 is connected to the negative input terminal of the operational amplifier circuit 29 through the resistor 35, and The output terminal is connected to the negative input terminal of this operational amplifier circuit 29 via a feedback resistor 36, and this operational amplifier circuit 29
The output terminal of the comparator circuit is connected to the oscillation frequency control signal input terminal of the voltage controlled variable frequency oscillator 13. In this case, the voltage supplied to the positive input terminal of the operational amplifier circuit 29 and the movable contact 33a of the output power adjusting volume 33 obtained at the negative input terminal
An error signal is obtained at the output terminal of this operational amplifier circuit 29 such that the reference voltage corresponding to the set value of the output power obtained in control. In this case, when the output power adjusting volume 33 is adjusted from the minimum point to the maximum point of the movable element 33a, the output power of the work coil 6 is, for example, 300W.
~1.2KW. Further, the connection point between the power switches 3a, 3b and the rectifier circuit 4 is connected to the input side of a rectifier circuit 37 for detecting the voltage of the commercial power source. This voltage detection rectifier circuit 37 is designed to be able to obtain on its output side a DC voltage of a level corresponding to the voltage of the commercial power supply supplied to its input side. The output terminal of this voltage detection rectifier circuit 37 is grounded through a series circuit of resistors 38, 39 and 40, and the connection point of these resistors 39 and 40 is connected to the ground.
The collector of this transistor 41 is connected to the power supply terminal 20, the emitter of this transistor 41 is connected to the connection point of resistors 26 and 27, and the emitter of this transistor 41 is connected to the resistor 42. The connection point of resistors 38 and 39 is connected to the power supply terminal 20 through a capacitor 43 and grounded. In this case, a current corresponding to the voltage of the commercial power supply, that is, the input voltage flows through the transistor 41, and this current is transferred to the resistor 27.
pour it into Therefore resistor 26 and diode 2
The voltage at the connection point a of No. 3 is the sum of the voltage Va based on the current flowing through the resistor 12 that detects the current flowing through the work coil 6 and the voltage Vb based on the input voltage. Further, the values of the resistors 38, 39, 40, 42, etc. are selected so that the transistor 41 operates when the voltage of the commercial power supply becomes, for example, 85 VAC or higher.

In FIG. 1, the comparison voltage Vo supplied to the positive input terminal of the operational amplifier circuit 29 is the same as that of the work coil 6.
This corresponds to the voltage obtained by adding the voltage Va based on the current flowing through the resistor 12 that detects the current flowing through the resistor 12 and the voltage Vb based on the input voltage, and this comparison voltage Vo is the voltage at the negative input terminal of this operational amplifier circuit. Movable contact 33 of output power adjustment volume 33 supplied to
Voltage controlled variable frequency oscillator 1 so that the reference voltage Vs corresponds to the set value of output power obtained in a.
Since the oscillation frequency of 3 is controlled, the output power of the work coil 6 can be automatically controlled to the value set by the output power adjustment volume 33. However, in this case, this induction heating cooker is designed based on the input voltage, that is, the voltage of the commercial power supply, which is the rated voltage of AC100V, but in general, the voltage of the commercial power supply is
Varies from AC85V to AC115V. For this reason, in the case where a feedback circuit is provided as shown in FIG. 1 to keep the output power of the work coil 6 constant, when the voltage of this commercial power supply decreases, the work coil 6
This increases the current flowing through the output circuit, and there is a risk that the elements constituting the output circuit may be destroyed due to this increase in current.

In view of this, the present invention is designed to prevent the elements of the output circuit from being destroyed when the input power drops below a normal value.

An embodiment of the electromagnetic induction heating device of the present invention will be described below with reference to FIG. In FIG. 2, parts corresponding to those in FIG. 1 are designated by the same reference numerals, and detailed explanation thereof will be omitted.

In the example in Figure 2, the resistor 3 in Figure 1 is
The connection point of 8 and 39 is connected to the base of a pnp transistor 44, the collector of this transistor 44 is connected to the connection point of resistors 26 and 27, and the emitter of this transistor 44 is connected to the power supply terminal 20 through a resistor 45. and the emitter of this transistor 44 is grounded via a resistor 46. The values of the resistors 45, 46, etc. are selected so that the transistor 44 operates when the input voltage, that is, the voltage of the commercial power supply, falls below a predetermined value, for example, 90 VAC. That is, when this commercial power supply becomes AC90V or less, this transistor 44 operates, and a current corresponding to the decrease in the voltage of this commercial power supply flows into the resistor 27 through this transistor 44, increasing the voltage at point a by that much. . The rest of the structure is the same as in FIG. 1.

Since the present invention is configured as described above, the voltage of the commercial power supply supplied to the plug 1 is set to a predetermined value, for example.
When the voltage is 90 VAC or more, the operation is similar to that shown in FIG. 1, and the output power of the work coil 6 can be automatically controlled to the value set by the output power adjustment volume 33. In addition, in the present invention, when the voltage of the commercial power supply supplied to the plug 1 falls below a predetermined value, for example, 90 VAC, the transistor 44 also operates, and the current corresponding to the low voltage of the commercial power supply is supplied to the plug 1. The current flows into the resistor 27 through the transistor 44, and the potential across the resistor 27 increases accordingly, and the potential at the connection point a between the resistor 26 and the diode 23 increases. The comparison voltage Vo supplied to the work coil 6 increases to limit the increase in the current flowing through the work coil 6. Therefore, when the voltage of the commercial power supply, that is, the input voltage of the electromagnetic induction cooking device, decreases, the feedback circuit operates to increase the current flowing through the work coil 6 by the amount that the voltage has decreased. A current corresponding to the decrease in the current flows through the transistor 44 and into the resistor 27. Therefore, the comparison voltage Vo supplied to the positive input terminal of the operational amplifier circuit 29 is increased to limit the increase in the current flowing through the work coil 6, and the electromagnetic induction It is possible to prevent the elements constituting the heating cooker from being destroyed.

In addition, in this example, the transistor 41 operates to make the electromagnetic induction heating cooker less susceptible to the influence of the ambient temperature, and to prevent the temperature of the components used in the device from rising excessively due to a rise in ambient temperature, thereby preventing a decrease in reliability. do. That is, in general, the base-emitter voltage V _BE of the npn transistor 41 has a temperature characteristic of about -2 mV/°C. Therefore, as the ambient temperature rises, the base-emitter voltage V _BE of the transistor 41 increases.
When V becomes smaller, even if the voltage of the commercial power supply is at the rated voltage (for example, 100 VAC), the base-emitter voltage V _BE of this transistor 41 becomes correspondingly smaller, and the current flowing through the transistor 41 increases. At this time, this transistor 4
1, a current corresponding to the ambient temperature flows into the resistor 27, thereby increasing the voltage across the resistor 27, thereby increasing the potential at point a, and increasing the voltage at the positive input terminal of the operational amplifier circuit 29. Since the comparison voltage Vo to be supplied is increased, the feedback circuit operates in the direction of reducing the current flowing through the work coil 6, that is, in the direction of reducing the output power of the work coil 6.
In other words, when the ambient temperature rises due to the action of the transistor 41, the output power of the work coil 6 is reduced accordingly, making the electromagnetic induction cooking device less susceptible to the effects of the ambient temperature and preventing internal use due to the rise in ambient temperature. Prevents excessive temperature rise of parts and reduces reliability.

As described above, according to the present invention, even when the input voltage, for example, the voltage of the commercial power supply, drops below a predetermined value, it is possible to prevent the elements of the output circuit from being destroyed.

In the above-mentioned embodiments, an example in which the present invention is used in an electromagnetic induction heating cooker has been described, but it goes without saying that the present invention can be used in other electromagnetic induction heating devices. Furthermore, it goes without saying that the present invention is not limited to the above-described embodiments, and can take various other configurations without departing from the gist of the present invention.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an example of an electromagnetic induction heating cooker, and FIG. 2 is a block diagram showing an embodiment of the electromagnetic induction heating device of the present invention. 6 is a work coil, 7 is a resonance capacitor, 8 is a
is the damper diode, 9 is GCS, 12,2
6, 27, 38, 39, 40, 42, 45 and 4
6 is a resistor, 13 is a voltage controlled variable frequency oscillator, 29 is an operational amplifier circuit constituting a comparison circuit, 3
3 is a volume for adjusting output power, 37 is a rectifier circuit for detecting input voltage, and 41 and 44 are transistors, respectively.

Claims (1)

[Claims] 1. A first detection circuit that detects a current flowing through a load, a second detection circuit that detects a voltage of a commercial power source that is input power, and a set value that sets the output power of the load. An output power adjustment volume that generates a corresponding reference signal, and a detection signal formed based on the respective output signals of the first and second detection circuits and a reference signal from the output power adjustment volume are compared. a variable frequency oscillator that is varied by the output signal of the comparison circuit; a drive circuit that is controlled by the output signal of the oscillator; and a switching element to which the output of the drive circuit is supplied. In the electromagnetic induction heating device, which is configured to control the current flowing through the load by controlling the switching element, detecting that the effective value of the commercial power supply voltage has decreased from a normal value, An electromagnetic induction heating device characterized in that the current flowing through the load is limited by a detection output signal.