JPH02280716A - Automatic rice boiler - Google Patents

Abstract

PURPOSE:To enable satisfactory rice boiling irrespective of the fluctuation of voltage by detecting the line voltage of the external power supply so as to adjust the frequency of AC voltage applied to an induction heating coil and to maintain the heating output constant. CONSTITUTION:When a drive circuit 8 outputs a switching signal, a switching transistor 5 is switched to supply AC current to an induction heating coil 3 for heating a rice boiling pot. When voltage of a power supply 1 is divided through resistances R1, R2 and inputted to a microcomputer MC, the corresponding signal is outputted from the microcomputer MC through a drive signal generating circuit 7 to a drive circuit 6. When heating of 1000W output is carried out with 100V line voltage and 28kHz switching frequency (f) and the line voltage may be reduced to 90V, the microcomputer MC reduces the switching frequency of the transistor 5 to 18kHz. When the line voltage of the power supply is raised to 110V, said computer MC increases the switching frequency (f) to 38kHz for maintaining the heating output at 1000W.

Description

DETAILED DESCRIPTION OF THE INVENTION (a) Field of Industrial Application This invention relates to an automatic rice cooker mainly used in general households, and more particularly, to an automatic rice cooker that heats a rice pot by induction.

(B) Conventional technology Conventionally, in this type of automatic rice cooker, an induction heating coil is attached to an electric pot made of a magnetic material, and an alternating current is supplied to the electromagnetic heating coil to create an eddy current in the rice cooker by induction. is generated and heated.

(c) Problems to be Solved by the Invention However, when the input power supply voltage of the automatic rice cooker changes, the heating output changes proportionally as shown in FIG. Therefore, for example, if you set the rice cooking time when the input voltage is toov, if the power supply voltage drops to 90V, the heating will be insufficient, and if the power supply voltage rises to ttov, the heating will be excessive and the rice will not be cooked satisfactorily. The problem was that it was not carried out.

This invention was made taking these circumstances into consideration, so
The present invention provides an automatic rice cooker that automatically adjusts the frequency of the voltage applied to an induction heating coil in accordance with fluctuations in power supply voltage to maintain a constant heating output.

(d) Means for Solving the Problems This invention provides an automatic rice cooker configured to heat a rice cooker using an induction heating coil, in which an AC voltage is applied to the induction heating coil in response to input from an external power source. a voltage generating means, a frequency variable means for adjusting the heating output of the induction heating coil by changing the output frequency of the AC voltage generating means, a detecting means for detecting the power supply voltage of the external power supply, and a voltage generating means corresponding to the output of the detecting means. control means for adjusting the frequency of the alternating current voltage outputted to the frequency variable means and applied to the induction heating coil to maintain a constant heating output against fluctuations in external power supply voltage. It is a vessel.

(e) Operation When the voltage of the external power source fluctuates, the detection means detects it and inputs it to the control means. Accordingly, the control means outputs an output to the frequency variable means to adjust the output frequency of the AC voltage generating means to maintain the heating output constant. Therefore, even if the external power supply voltage fluctuates, proper rice cooking is always performed with a constant output.

(f) Examples Hereinafter, the present invention will be described in detail based on examples shown in the drawings. This invention is not limited by this.

FIG. 1 is a block diagram showing a control circuit according to an embodiment of the present invention, in which ① is an AC toov commercial power source, 2 is a rectifying and smoothing circuit for rectifying and smoothing the output of the power source 1, and 3 is a rice cooker (not shown). Electric! ! 4 is a resonant capacitor; 5 is a switching transistor that performs switching at a frequency of 20 to 35 kHz; 6 is an induction heating coil that heats by induction;
7 is a drive circuit that supplies a switching signal to the switching transistor 5; 7 is a drive signal generation circuit that supplies a drive signal to the drive circuit 6 to set the switching frequency of the switching transistor 5; 8 is a power supply 1;
This control circuit controls the switching frequency of the switching transistor 5 so that the heating output of the induction heating coil 3 is constant by outputting it to the drive signal generation circuit in accordance with the voltage of the induction heating coil 3.

FIG. 2 is a detailed explanatory diagram of the control circuit 8 shown in FIG.
T is a step-down transistor, B is a rectifier bridge, C is a smoothing capacitor, R1 and R2 are voltage dividing resistors, and VR is a DC constant voltage circuit. The IC is a microcomputer, which is driven by the output of a DC constant voltage circuit VR as a power source, and voltage dividing resistors R1 and R2.
It receives the divided voltage and outputs it to the drive signal generation circuit 7.

In such a configuration, when the drive circuit 8 outputs a switching signal, the switching transistor 5 switches and a resonant current is passed from the rectifying and smoothing circuit 2 to the series resonant circuit of the induction heating coil 3 and the resonant capacitor 4. An alternating current flows through the induction heating coil 3 to heat the rice cooker.

FIG. 3 shows that in the embodiment shown in FIG. 1, the switching frequency f of the switching transistor 5 is 18 kHz,
It is a graph showing the relationship between the heating output and the power supply voltage when the frequency is maintained at 28 kHz or 38 kHz.

Figure 4 is a graph showing the relationship between the power supply voltage preset in the memory of the microcomputer MC and the switching frequency. The voltage of voltage dividing resistor R1,
When the voltage is divided and inputted to the microcomputer MC via R2, a corresponding signal is outputted from the microcomputer MC to the drive circuit 6 via the drive signal generation circuit 7. In other words, the switching transistor 5
As shown in FIG. 4, switching is performed at a low frequency when the power supply voltage decreases, and at a high frequency when the power supply voltage increases. Therefore, as shown in FIG.
v, when heating the output tooow at a switching frequency of f-28ktlz, the power supply voltage is 90
When the voltage drops to V, the heating output stops there and tries to drop, but the microcomputer MC detects the drop in the power supply voltage and lowers the switching frequency of the switching transistor 5 to 18 kHz to maintain the heating output at too low. Furthermore, when the power supply voltage rises to ttov, the heating output tends to increase, but the switching frequency f is 3.
Increase to 8 kHz to maintain heating power too low.

In either case, the heating output is 1 as shown by the broken line in Figure 3.
00OW is maintained constant.

In this way, the microcomputer MC adjusts the switching cycle number r in accordance with the power supply voltage and maintains the heating output constant against changes in the input power supply voltage, so that rice is always cooked satisfactorily. .

(G) Effects of the Invention According to the present invention, the heating output is maintained constant without fluctuations in response to fluctuations in power supply voltage, so the cooked state is not affected by fluctuations in power supply voltage and is good. You can cook rice.

[Brief explanation of drawings]

Fig. 1 is a block diagram showing a control circuit of an embodiment of the present invention, Fig. 2 is a partial detailed electrical circuit diagram of Fig. 1, and Figs. 3 and 4 show characteristics of the embodiment shown in Fig. 1. Graphs to explain,
FIG. 5 is a graph showing the characteristics of heating output with respect to power supply voltage in a conventional example. l...Power supply, 2...Rectifier smoothing circuit, 3
...Induction heating coil, 4.Group resonance capacitor, 5.....Switching transistor, 6..
...Drive circuit, 7...Drive signal generation circuit, 8...
control circuit. Figure 1 *3 IgF 2nd m /I source pressure (V) R2R3

Claims (1)

[Scope of Claims] 1. An automatic rice cooker configured to heat a rice cooker using an induction heating coil, comprising an AC voltage generating means for applying an AC voltage to the induction heating coil in response to input from an external power source; a frequency variable means for adjusting the heating output of the induction heating coil by changing the output frequency of the voltage generating means; a detection means for detecting the power supply voltage of the external power source; and an output to the frequency variable means corresponding to the output of the detection means. An automatic rice cooker characterized by comprising: control means for adjusting the frequency of an alternating current voltage applied to an induction heating coil to maintain a constant heating output against fluctuations in external power supply voltage.