JPH0513159A - Induction heating cooker - Google Patents

Abstract

PURPOSE:To prevent the overheat and breakage of a switching element by the load of an inverter circuit and the fluctuation of a power source voltage without complicating the circuit scale. CONSTITUTION:An input current detecting circuit 4 for detecting the input current of an inverter circuit 3, a voltage detecting circuit 5 for detecting the voltage of a commercial power source 1, a microcomputer 6 for controlling the whole body, and an oscillating circuit 7 for changing pulse width according to the output signal from the microcomputer 6 are provided. According to the fluctuations of the input current and the power source voltage, an operation is conducted to form a proper oscillating pulse width.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an induction heating cooker which determines the suitability of a load to be induction-heated and controls the pulse width of an oscillation signal of an inverter circuit.

[0002]

2. Description of the Related Art In an induction heating cooker in which a high frequency current is applied to a heating coil to generate a high frequency magnetic flux to induce an eddy current in a load magnetically coupled to the heating coil and the Joule heat heats the load, Depending on the characteristics and size of the load, there is a drawback that a large load is applied to the switching element and the temperature rises or the switching element is destroyed due to increased loss.

Conventionally, in order to solve this problem, an input current detection circuit for detecting the input current of the inverter circuit and an input voltage detection circuit for detecting the input voltage of the inverter circuit are provided, and a known example is disclosed (Japanese Patent Laid-Open No. 57-57). No. 878), the pulse width of the output of the oscillation circuit is controlled by passing the output of the input current detection circuit and the output of the input voltage detection circuit through a comparison operation circuit, an OR circuit, an amplification circuit, or the like. Alternatively, another known example (Japanese Patent Laid-Open No. 61-126794)
As shown in (1), a microcomputer that detects and calculates the input current of the rectifier circuit and the high frequency current of the inverter circuit is used to control the pulse width of the output of the oscillator circuit.

[0004]

However, in the above means, the circuit scale is increased, the complexity is increased, and the cost is increased.

An object of the present invention is to realize proper oscillation according to the load of an inverter circuit without increasing the circuit scale.

[0006]

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and includes an rectifier circuit, an inverter circuit including a smoothing circuit, and an input current detection circuit for detecting an input current of the inverter circuit. A voltage detection circuit for detecting the voltage of a commercial power source, a microcomputer for performing overall control including pulse width control of an oscillation signal of the inverter circuit, and an oscillation circuit for changing the pulse width according to an output signal from the microcomputer And the microcomputer determines the signal level to be output to the oscillation circuit, prioritizing overall control.

[0007]

With the above configuration, when the load or the power supply voltage fluctuates, a proper signal is output and proper power is input to the inverter circuit.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to FIGS. FIG. 1 is a circuit diagram of an induction heating cooker according to an embodiment of the present invention. FIG. 2 is a flowchart of the same arithmetic processing.

In FIG. 1, 1 is a commercial power supply, 2 is a rectifying circuit for rectifying the commercial power supply 1, 3 is a smoothing circuit 31 for smoothing the output of the rectifying circuit 2 into a direct current, a heating coil 32, a resonance capacitor 33, An inverter circuit having a switching element and a switching element 34 having an antiparallel diode, 4 is an input current detection circuit of the inverter circuit 3, 5 is a voltage detection circuit of the commercial power supply 1, 6 is a microcomputer for controlling the whole, 7 is a microcomputer 6 Is an oscillation circuit that changes the pulse width according to the output of.

The microcomputer 6 performs the operation shown in FIG.

The microcomputer 6 uses the voltage detection circuit 5 or
When the output of the current detection circuit 4 has not changed, the overall control, for example, the control of the display device is sequentially performed, and the oscillation circuit 7
To the pulse width control signal (Process → → →
→). When there is a change in the output of the heating coil 32 or the voltage of the commercial power supply 1, the microcomputer 6 calculates the level of the signal output to the oscillation circuit 7 such that appropriate power is input to the inverter circuit 3, A signal that gives an appropriate pulse is output to the oscillation circuit 7. (Processing → Computation A, B → Processing →→) In the case of the above-described embodiment, one cycle of processing performed in synchronization with the power supply cycle is 10 ms, and the processing may be delayed by 10 ms such as control of the display device. Is. As a result, the time from the calculation to the proper output to the heating coil 32 can be shortened.

[0012]

According to the present invention, the oscillation pulse width is calculated by a complicated calculation according to the load fluctuation and the power supply voltage fluctuation in a short processing time without increasing the circuit scale, and the switching element is appropriately oscillated. It can be driven, and destruction of the switching element and temperature rise can be prevented.

[Brief description of drawings]

FIG. 1 is a circuit diagram of an induction heating cooker showing an embodiment of the present invention.

FIG. 2 is a flowchart of the same operation.

[Explanation of symbols] 1 commercial power supply 2 rectifier circuit 3 inverter circuit 4 input current detection circuit 5 voltage detection circuit 6 microcomputer 7 oscillation circuit 31 smoothing circuit 32 heating coil 33 resonant capacitor 34 switching element

Claims (1)

Claims: 1. A rectifier circuit (2) for rectifying a commercial power supply (1),
A smoothing circuit (31) for smoothing the rectified output to obtain a DC voltage, a heating coil (32) for converting this DC voltage into an AC, an inverter circuit (3) including a resonance capacitor (33) and a switching element (34), and An input current detection circuit (4) for detecting the input current of the inverter circuit (3), a voltage detection circuit (5) for detecting the voltage of the commercial power supply (1), and an oscillation signal of the inverter circuit (3) The microcomputer (6) for performing the entire control including the pulse width control, and the oscillator circuit (7) for changing the pulse width according to the output signal from the microcomputer (6),
(6) The induction heating cooker characterized in that the signal level to be output to the oscillation circuit (7) is determined in preference to the overall control.