JPH0577159B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION A. Field of Industrial Application The present invention relates to an induction heating device used as an induction heating cooker.

B. Prior Art An induction heating device used as an induction heating cooker is connected to a full-wave rectifier circuit 2, which is formed by full-wave rectifying a commercial alternating current 1, via a chiyoke coil 3 and a bypass capacitor 4, as shown in FIG. induction heating coil 5
, a resonant capacitor 6 that forms a resonant circuit together with the induction heating coil, and the induction heating coil 5
switching element 7 for generating excitation current in
and a diode 8 connected in antiparallel to this switching element 7. Turning the switching element 7 ON and OFF generates a resonant current in the resonant circuit, and generates a high frequency alternating magnetic field in the induction heating coil 5. In this way, a cooking utensil for a heated object placed close to the heating coil 5 is heated by induction.

In such an induction heating cooker, the input power is controlled by detecting the AC input current with the current transformer CT ₁ , and controlling the switching element with the control circuit 9 so that the current is equal to a preset level.
I was trying to control the ON time. Such an induction heating device is disclosed in, for example, Japanese Patent Laid-Open No. 54-48346.

C. Problems to be Solved by the Invention In such an input-controlled induction heating device, a current transformer for detecting the input current must be provided on the primary side of the full-wave rectifier circuit. For this reason,
In an induction heating cooker having a plurality of induction heating devices, a full-wave rectifier circuit must be provided for each heating port, which hinders miniaturization of the cooker.

The present invention enables input current control to be performed even in a multi-port induction heating cooker without providing a full-wave rectifier circuit for each heating port. Furthermore, this input current control can be performed stably.

D. Means for Solving the Problems The present invention has been made in view of the above points, and includes a current detecting means for detecting the current flowing in the switching element, a level setting means for setting the level, and a current detecting means for detecting the current flowing in the switching element, a level setting means for setting the level, and an ON time control circuit that adjusts the ON time of the switching element so that the detection level of the detection means is equal to the setting of the level setting means;
A correction circuit detects the OFF time length of the switching element and corrects the ON time.

E. Effect The input power input to the heated object load changes in proportion to the ON time of the switching element, but the rate of change varies depending on the shape and material of the load. Such differences in shape and material appear as the equivalent inductance of the heating coil. In the present invention, while adjusting the ON time of the switching element so that the switching element current is equal to the set level,
Detects the OFF period of the switching element corresponding to the resonance period of the induction heating coil and resonant capacitor,
Extracts information on the equivalent inductance of the induction heating coil and turns on the switching element accordingly.
Time is corrected to correct input power differences due to load differences.

F. Example Fig. 2 is a circuit block diagram of the induction heating device of the present invention, and Fig. 1 is a circuit diagram of the control circuit of the induction heating device of the present invention, in which the same parts as in Fig. 9 are given the same reference numerals. . In these figures, 10 indicates a rectifying and smoothing means for rectifying and smoothing the detection signal from the current transformer CT ₂ , and 11 indicates a level setting means for setting the current level of the switching element 7, and the level is adjusted by a variable resistor VR ₂ . be adjusted. A comparator 12 compares the level of the level setting means 11 with the output level of the rectifying and smoothing circuit 10, and its output is integrated by an integrating circuit comprising resistors 13, 14, and a capacitor 15. Reference numeral 16 indicates an ON timing detection circuit that detects that the collector of the switching element 7 has fallen sufficiently and its output falls, and thereafter the output rises with time. 1
A comparator 7 compares the level of the capacitor 15 with the output of the ON timing detection circuit 16, and its output becomes an ON/OFF signal for the switching element 7. 8 is an inverter that inverts the output of the comparator 17, and 19 is a capacitor that constitutes an integrating circuit together with resistors 20 and 21. When the output from the comparator 17 is "L" level, that is, the switching element 7 is OFF. At this time, the capacitor 19 is charged. 22 indicates a comparator that compares the level of the capacitor 19 with a predetermined voltage level set by resistors 23 and 24, and its output is connected to the capacitor 15 via a resistor 25 to adjust the voltage level of the capacitor 15. I'm starting to do that.
26 is a peak detection circuit that detects the peak of the current flowing through the switching element 7; 27 is a comparator that compares the signal of this peak detection circuit 26 with a predetermined level determined by resistors 28 and 29; the output thereof is a diode 30 is connected to the capacitor 15 through a resistor 31, and the level of the capacitor 15 is adjusted.

In such an induction heating device, the switching element 7 is turned on and off by comparing the outputs of the capacitor 15 and the ON timing detection circuit 16. This is done by the following operations.
When the ON timing detection circuit 16 detects the timing, its output is temporarily lowered and the comparator 1
7 output becomes "H" and switching element 7
Turned on. Then ON timing detection circuit 16
gradually rises, and when it exceeds the level of the capacitor 15, the output of the comparator circuit 17 becomes "L", the switching element 7 is turned off, and resonance between the heating coil 5 and the resonant capacitor 6 begins. Due to this resonance, the voltage between the terminals of the switching element 7 once rises and then falls. This switching element 7
Upon detecting the falling voltage between the terminals, the ON timing detection circuit 16 lowers its output, and the comparison circuit 1
7 output becomes "H" level, switching element 7 is turned ON again, and ON/OFF operation continues.
As can be seen from this, the switching element 7
The ON time is determined by the voltage held by the capacitor 15.

By the way, the current flowing through the switching element 7 is detected by the current transformer CT ₂ , rectified and smoothed by the rectification and smoothing circuit 10, and then supplied to the comparator 12. The comparator 12 compares the output of the level setting means 11 and the output of the rectifying and smoothing circuit 10, and adjusts the charging voltage of the capacitor 15 so that the output of the level setting means 11 becomes equal to the output of the rectifying and smoothing circuit 10.
Incidentally, the output Wf ₁ of the current transformer CT ₂ , the output Wf ₂ of the rectifying and smoothing circuit 10, and the output Wf ₃ of the inverter 18 are shown in FIG.

In addition, in such an induction heating device, the ON/OFF signal from the resistor 17 is inverted by the inverter 18, as shown in Wf ₃ in Fig. 3 above, and the level corresponding to the OFF period of the switching element 7 is maintained by the capacitor 19. When this voltage becomes lower than a predetermined value, an "L" level signal is outputted from the comparator 22, and the capacitor 15 is pulled to the negative side, thereby acting to reduce the ON time of the switching element 7.

On the other hand, the peak of the signal from the current transformer CT ₂ is detected by the peak detection circuit 26, and the peak of the signal from the current transformer CT 2 is detected by the peak detection circuit 26.
When the output of the peak detection circuit 26 exceeds a predetermined level, the voltage of the capacitor 15 is discharged via the diode 30 and the resistor 31. Incidentally, the output Wf ₄ of the peak detection circuit 26, the output of the comparator 27, and Wf ₅ at this time are shown in FIG.

FIG. 5 is a circuit diagram showing another embodiment of the control circuit for the induction heating apparatus of the present invention, in which the same parts as in FIG. 1 are given the same reference numerals. That is, in this circuit, a signal synchronized with the fall of the ON/OFF signal from the comparator 17 is generated by the differentiating circuit 35 consisting of the capacitor 32 and resistors 33 and 34.
This is inverted via inverter 36 to increase the level of capacitor 37.
The level of this capacitor 37 is compared with the level set by the level setting means 11 by a comparator 38, and the level of the capacitor 15, which determines the ON period, is adjusted based on the output thereof.

Therefore, when the switching element 7 is controlled to flow a predetermined current, when the load is iron-based, the equivalent inductance and equivalent resistance of the heating coil 5 are relatively large, and its ON time becomes long, resulting in a decrease in the output of the comparator 17. As shown in Fig. 6, Wf ₆ has longer ON and OFF signal times, and is connected to differentiating circuit 35 and inverter 36.
charging signal given to capacitor 37 via
The occurrence of Wf ₇ is low. Therefore, the charge level of the capacitor 37 is lower than the level of the level setting means 11, as shown by the solid line in FIG. 8, and the output of the comparator 38 is kept at the "H" level.

On the other hand, when the load is made of stainless steel, the equivalent inductance and equivalent resistance of the heating coil 5 are relatively small, its ON time is shorter than that of the iron load, and the output Wf' ₆ of the comparator 17 is 7
As shown by the dotted line in the figure, the ON signal and OFF signal times become shorter, and the charging signal Wf' ₇ applied to the capacitor 37 via the differentiating circuit 35 and the inverter 36 increases. Therefore, the charge level of the capacitor 37 tends to become higher than the output of the level setting means 11 as shown by the one-dot chain line in FIG. 7, and the output of the comparator 38 becomes "L" level. As a result, the charge level of the capacitor 15 decreases, and the period of the ON and OFF signals tends to become even higher. However, if the charge level of the capacitor 15 becomes low and the current of the switching element 7 decreases, the current transformer CT ₂
The current detected by the comparator 12 becomes "H". That is, the level of the capacitor 15 is maintained at a level that balances the output of the comparator 12 and the output of the comparator 38.

(G) Effects of the Invention According to the induction heating device of the present invention, the current flowing through the switching element is detected, and the switching element is controlled so that the detected current becomes equal to the set level.
The ON time is adjusted, and even when configuring a multi-port induction heating cooker, input current control for each port can be performed without providing a full-wave rectifier circuit or the like for each port.

Furthermore, the OFF time length of the switching element is detected and the ON time is corrected, so that the input current control can be performed stably.

[Brief explanation of the drawing]

FIG. 1 is a control circuit diagram of the induction heating device of the present invention, FIG. 2 is a circuit block diagram of the induction heating device of the present invention, FIGS. 3 and 4 are operational waveform diagrams showing the operation of the induction heating device of the present invention, and FIG. FIG. 5 is a circuit diagram showing another embodiment of the control circuit of the induction heating device of the present invention, and FIGS.
The figure is an operation waveform diagram showing the operation of the circuit in Figure 5.
The figure is a block diagram of a conventional induction heating device. 1...Commercial AC, 2...Full wave rectifier circuit, 3...
Chiyoke coil, 4... Bypass capacitor, 5
...Induction heating coil, 6...Resonance capacitor, 7
...Switching element, 9...Control circuit, 10...
... Rectification and smoothing means, 11 ... Level setting means, 1
2, 17, 18, 27, 38... comparator, 15,
19, 32, 37...Capacitor, 16...ON
Timing detection circuit, 18, 36...Inverter, 26...Peak detection circuit, 30...Diode, 35...Differentiating circuit, _CT1 , _CT2 ...Current transformer.

Claims (1)

[Claims] 1 Consists of an induction heating coil connected to a DC power supply, a resonant capacitor that forms a resonant circuit together with this induction heating coil, and a switching element for generating a resonant current in the induction heating coil, and when the switching element is turned ON, In an induction heating device that generates a resonant current in the resonant circuit by turning off the switching element, a current detection means detects the current flowing through the switching element, a level setting means sets the level, and the detection level of the current detection means is set to a level. an ON time control circuit that adjusts the ON time of the switching element to be equal to the setting by the setting means;
An induction heating device comprising: a correction circuit that detects the OFF time length of the switching element and corrects the ON time in the ON time control circuit.