JPH0547465A - Electromagnetic induction heating cooking device - Google Patents

Abstract

PURPOSE:To provide an inexpensive electromagnetic induction heating cooking device having a simplified circuit and a function to prevent the fracture of components. CONSTITUTION:There is provided a drive circuit 3 to actuate a switching element 2 for turning on and off a current flow to the coil 1 for an electromagnetic induction heating. In addition, values detected with a temperature sensor 5, an input current transformer 6, a switching current transformer 7 and an input voltage dividing resistor 8 are inputted to a microcomputer 13 in a control section 4. Then, the switching element 2 is turned on and off via the drive circuit 3, on the basis of control output from calculation or the like in the control section 4. High frequency current thereby caused to flow through the coil 1 is used to heat a cooking ingredient in a heated vessel placed on the coil 1 via a hot plate.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high frequency switching circuit such as an electromagnetic induction heating cooker (hereinafter referred to as an electromagnetic cooker).

[0002]

2. Description of the Related Art A high frequency switching circuit used in an electromagnetic cooker or the like is a PWM (pulse width modulation) system as disclosed in Japanese Patent Laid-Open No. 3-88293.
That is, the separately excited method and the self-excited oscillation method as disclosed in Japanese Patent Publication No. 3-29147 are used. FIG. 5 is a high-frequency switching circuit diagram of a self-excited oscillation system used in a conventional electromagnetic cooker. In FIG. 5, 1 is a heating coil, 3 is a drive circuit for the switching element 2, 70 is a CR circuit, 71 is a synchronous circuit, 72 is a control unit, 73 is a PWM control unit, 74 is an error amplifier, and 75 is current detection. , 76 is an output setting unit, 77 is a full-wave rectifying and smoothing circuit, and 79 is a resonance capacitor.

In the conventional electromagnetic cooker as described above,
The control unit 72 of FIG. 5 constantly oscillates at the free-running frequency by the CR circuit 70 formed by the external resistance and the capacitor.
The waveform indicated by Vc in FIG. 6 shows the oscillation waveform, the gate of the switching element 2 is configured to generate the on-time of Tmax with the waveform of Vgo, and the switching element 2 cuts off the switching current Ic. , An ON pulse is again generated at T2 at a timing when the Vce waveform generated as a reverse current crosses zero (point a of Vg), and the ON pulse is driven with an ON width of Tp corresponding to a predetermined output.

This ON width is determined by the PWM of the control unit 72.
It operates by the output of the error amplifier 74 by the control unit 73.
The error amplifier 74 has a voltage obtained by converting the energizing current by the current detecting section 75 and an output setting section 75 for setting a predetermined output by the voltage.
The output obtained as a result of comparison with the voltage of
3, the ON width is sequentially determined.

[0005]

A conventional drive circuit for an electromagnetic cooker includes an IC for a switching power supply and a standard logic I.
Since it is composed of a circuit in which C is combined, there are problems that the operation is complicated, the reliability is low, and the cost is high.

The present invention has been made in order to solve the above-mentioned problems, and simplifies the circuit and adds a function of preventing damage to the constituent parts, thereby achieving high reliability and low cost, and The purpose is to obtain a user-friendly electromagnetic cooker.

[0007]

An electromagnetic cooker according to the present invention includes a coil for electromagnetic induction heating, a switching element for interrupting a current flowing through the coil, a drive circuit for the switching element, and a heated plate. Equipped with a temperature detection element,
A control means for detecting and controlling the input current, the input voltage, the switching element current, and the temperature of the heated plate is provided.

Further, the drive circuit is provided with a self-drive prohibiting circuit which operates simultaneously with power-on, and a control means for outputting a prohibiting circuit blocking signal at the start of operation to start heating.

Further, an overcurrent stop circuit is provided in the drive circuit, and the control means for stopping the countdown of the timer by the operation signal of the overcurrent stop circuit and outputting a signal for resetting the overcurrent stop circuit at the time of re-driving. It is provided.

Further, the overcurrent stopping function is also provided in the switching circuit, and the control means having the overcurrent stopping threshold value lower than the threshold value of the switching circuit is provided.

Further, there is provided control means for performing re-driving a plurality of times when the driving of the device is stopped due to a failure or the like and the input current becomes a predetermined value or less.

Furthermore, when the hot plate temperature detecting element detects a predetermined temperature rise rate or more, the input current is controlled to a predetermined current value, and when the temperature detected value of the hot plate temperature detecting element becomes a predetermined value or more. A control means for stopping driving is provided.

[0013]

In the present invention, the power supply is self-stopped when the power is turned on, so that no erroneous oscillation occurs. Further, since the control side knows the overcurrent stop state of the drive circuit, it can be reset from the control side during driving and easily re-driven even if the drive circuit is overcurrent stopped. Normally, the overcurrent stop function of the control side operates, but when the control side has a failure, the overcurrent stop of the drive circuit operates, so that the safety is improved. Further, even if the input current becomes low due to a circuit abnormality and the oscillation is temporarily stopped, the oscillation is not stopped due to the temporary abnormality because the re-driving is performed several times. Furthermore, the temperature is lowered so that it does not overheat due to an increase in the bottom temperature of the heated container having a small heat capacity, and when abnormal heating occurs, driving is stopped to prevent damage.

[0014]

1 is a circuit diagram of an electromagnetic cooker according to an embodiment of the present invention. In FIG. 1, reference numeral 1 is a coil for electromagnetic induction heating, 2 is a switching element for connecting and disconnecting a high frequency current to the coil 1, 3 is a drive circuit for the switching element 2, 4 is a control unit for controlling the drive circuit 3, and 5 is a heated object. A temperature sensor for detecting the temperature of the bottom of the container, 6 is an input current transformer, 7 is a switching current transformer, 8 is a voltage dividing resistor for input voltage, and 9 is a voltage dividing resistor.
Is a power plug, 10 and 11 are transistors operated by a voltage between terminals of a resistor 12, 13 is a microcomputer (hereinafter referred to as a microcomputer) in the control unit 4, 14 is an output port for outputting start and stop of driving, and 15 is A transistor 16 which receives the output and blocks the operation of the transistors 10 and 11 is a rectifying / smoothing circuit of the current transformers 6 and 7.

Reference numerals 17 to 20 are analog input ports of the microcomputer 13, 17 is a switching current value, 18 is an input current value, 19 is an input voltage value, and 20 is a voltage value of the temperature sensor 5. Reference numeral 21 is a switch key group arranged on the operation unit, and 22 is a display unit group. An input / output port 23 is connected to the overcurrent stop circuit of the drive circuit 3. 24 is a D / A converter, 25 is a first voltage comparator that outputs a synchronizing signal, 26 is a second voltage comparator, which outputs the ON width of the switching element 2, and the value thereof is input to the non-inverting input 27. It depends on the applied potential. 28 is a third voltage comparator that shapes the waveform, 29 is a fourth voltage comparator for stopping overcurrent, 30 is a transistor for holding the operation of the fourth voltage comparator 29, 31 is also for canceling the inverting operation It is a transistor.

FIG. 2 is a sectional view of the cooker main body, in which 32 is a container to be heated, 33 is a substrate on which the drive circuit 3 is arranged,
34 is a substrate on which the control unit 4 is arranged, 35 is an operation unit,

FIG. 3 is a block diagram showing the details of the input / output port 23. Reference numeral 37 is an input buffer, 38 and 39 are transistors forming an earth state output, 40 is a data line, and 41 is an output inhibit line.

FIG. 4 is an input / output timing chart.
42 is the output of the fourth voltage comparator 29, 43 is the output of the input / output port 23, and 44 is the output waveform of the output port 14.

In the electromagnetic cooker according to the present invention having the above-described structure, when the power plug 9 of FIG. 1 is connected to the commercial power source, the dropper resistor 12 is released and the transistors 10 and 1 are connected.
1 is conducted, the output of the first voltage comparator 25 and the output of the third voltage comparator 28 are short-circuited, and the drive circuit 3 does not generate a signal for connecting and disconnecting the switching element 2. This prevents the voltage comparators 25 and 28 from malfunctioning when the power is turned on.

To start driving, when the start key 21a in the switch key group 21 is operated, an "H" signal is output from the output port 14 and the transistor 15 becomes conductive, so that a circuit including the transistors 10 and 11 is formed. Is started, a predetermined output code is output from the microcomputer 13, converted into a voltage command by the D / A converter 24, and applied to the non-inverting input 27 of the second voltage converter 26. The ON width of the switching element 2 becomes wider as the voltage command is higher.
That is, the output is increased. This ON signal has a waveform formed by the third voltage converter 28 and is applied to the switching element 2 via the drive transistor.
The input voltage at this time is converted into a voltage by the input current transformer 6, and rectified and smoothed by the rectifying and smoothing circuit 16.

This input information is applied to the analog input port 18 of the microcomputer 13, and the divided voltage value of the input voltage is applied to the analog input port 19 to multiply the current value and the voltage value. Then, the output code calculated by comparison with the electric power set on the operation panel 35 is converted into the D / A conversion unit 24.
And the command voltage is feedback controlled. The switching current information obtained from the switching current converter 7 is applied to the analog input port 17 of the microcomputer 13,
It is controlled so that the allowable current of the switching element 2 is not exceeded, but when the value equivalent to 14 A is exceeded, the device is stopped. That is, the output of the output port 14 is set to "L", the internal counter is suspended, and the next start input is awaited.

The same signal as that of the analog input port 17 of the microcomputer 13 is applied to the inverting input of the fourth voltage converter 29, and the non-inverting input is set to a threshold value equivalent to 15A. Therefore, it operates only when the microcomputer 13 fails to make the determination. When this operation is performed,
The output of the voltage converter 29 of 1 becomes "L", the transistor 15 is blocked, the transistors 10 and 11 become conductive, and the driving is stopped. At the same time, the transistor 30 is turned on and the third
Since a high potential is applied to the inverting input of the voltage converter 28, the inverting operation is held and the driving is stopped. Therefore, “L” is input to the input / output port 23, and the microcomputer 13 knows that the overcurrent has stopped.

Next, the microcomputer 13 enters a stop process, sets the output of the output port 14 to "L", temporarily stops the internal timer, and switches the input / output port 23 to the output at the time of restart, and outputs "H" of 10 mS. A signal is output to cause the transistor 31 to perform one-shot operation by capacitor coupling, and the inversion of the fourth voltage converter 29 is released. That is, the output is stopped at the output inhibit line 41 in FIG. 3, the transistors 38 and 39 are in the blocking state, the signal from the input / output port 23 is read through the input buffer 37, and the data line 40 is output at the time of output. More pulses are generated to turn on the transistor 38.

In FIG. 4, when the input / output port 23 processes a signal of “H” to “L” as an input like the output 42 of the fourth voltage converter 29, the output port 14 also has an output waveform 44. When the system is stopped and restarted, the input / output port 23 outputs a 10 mS pulse as indicated by the output 43, and the output port 14 outputs “H” indicated by the waveform 44.

On the other hand, when the driving is stopped due to some failure, information on the input current from the input current transformer 6 is monitored and 3
If it is A or less, the operation of repeating the restart three times every 100 mS is performed.

The potential change in the temperature sensor element 5 is read by the analog input port 20, and the input current is reduced by judging the temperature rise rate to reduce the thickness of the heated container 32.
To prevent abnormal temperature rise. In this example, 1
The power value is reduced from 300 W to 800 W to prevent it. In this case, the rate of temperature rise is determined at 1 ° C per second,
Baking temperature of container is 200 ℃, abnormal heating temperature is 250
It was set to ° C.

[0027]

As described above, according to the present invention, the input current, the input voltage, the switching element current and the hot plate temperature are comprehensively processed and controlled as listed below. An electromagnetic cooker with high operability and good operability can be obtained.

Since the driving is stopped when the power is applied, there is no malfunction during driving and the controllability is good.

Since the switching drive circuit is provided with an overcurrent stopping function, the operation of the switching drive circuit can be judged by the control unit, and the operation can be reset at the time of restart, so that the reliability is enhanced.

The control section is also provided with an overcurrent stop function, and the operation threshold value is set lower in the control section so that the drive circuit itself can stop the overcurrent even if a failure occurs in the control section. As a result, it became a highly reliable system.

Even if the oscillation is stopped due to some failure, the restart is repeated a plurality of times to continue the operation, so that the reliability is improved.

The rate of temperature rise of the plate to be heated is calculated, and if the value is high, it is determined that an abnormally heated container having a small heat capacity is placed, and the input is reduced to maintain a predetermined temperature. At the same time, the driving is stopped at a temperature slightly higher than this temperature, so that the device can be prevented from being damaged.

[Brief description of drawings]

FIG. 1 is a control circuit diagram of an electromagnetic cooker according to an embodiment of the present invention.

FIG. 2 is a sectional view showing a configuration of an electromagnetic cooker according to an embodiment of the present invention.

FIG. 3 is a block diagram showing a configuration of an input / output port in FIG.

FIG. 4 is an input / output timing chart for explaining the operation of the present invention.

FIG. 5 is a block diagram showing a circuit configuration of a conventional electromagnetic cooker.

FIG. 6 is a waveform diagram for explaining the operation of the conventional electromagnetic cooker.

[Explanation of symbols]

 1 coil 2 switching element 3 drive circuit 4 controller 5 temperature sensor 6 input current transformer 7 switching current transformer

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Tetsumasa Kubota 1728 Omaeda, Hanazono-cho, Osato-gun, Saitama 1 Mitsubishi Electric Home Equipment Co., Ltd. Within Mitsubishi Electric Home Equipment Co., Ltd.

Claims (6)

[Claims] 1. An electromagnetic induction heating coil, a switching element for connecting and disconnecting a current flowing through the coil, a drive circuit for the switching element, and a temperature detection element for a heated plate, and an input current and an input voltage. An electromagnetic induction heating cooker comprising a control means for detecting and controlling the switching element current and the temperature of the heated plate. 2. The drive circuit is provided with a self-drive inhibiting circuit which operates at the same time when the power is turned on, and a control means for outputting a inhibit circuit blocking signal at the start of operation to start heating. The electromagnetic induction heating cooker described. 3. An overcurrent stop circuit is provided in the drive circuit,
3. The electromagnetic induction according to claim 1, further comprising control means for stopping the countdown of the timer by the operation signal of the overcurrent stop circuit and outputting a signal for resetting the overcurrent stop circuit at the time of re-driving. Heating cooker. 4. The overcurrent stop function is also provided in the switching circuit, and the control means is provided having an overcurrent stop threshold value lower than the threshold value of the switching circuit. ~ 3 electromagnetic induction heating cooker. 5. The electromagnetic induction heating according to claim 1, further comprising a control means for performing re-driving a plurality of times when the driving of the apparatus is stopped due to a failure or the like and the input current becomes a predetermined value or less. Cooking device. 6. The hot plate temperature detecting element controls an input current to a predetermined current value when the hot plate temperature detecting element detects a temperature rising rate or more, and drives when the temperature detected value of the hot plate temperature detecting element becomes a predetermined value or more. The electromagnetic induction heating cooker according to any one of claims 1 to 5, further comprising a control means for stopping the operation.