JPH01235185A - Inverter for cooking utensil - Google Patents

Abstract

PURPOSE:To decrease the rating of a switching element and reduce its cost by detecting the phase of the power voltage and shorten the on-time of the switching element near the peak value of the power voltage. CONSTITUTION:A control circuit 7 controlling the on or off of a switching element 5 by the voltage or current of a heating coil 4 and the signal of a phase compensating circuit shortens the on-time of the switching element 5 near the peak of the power voltage and controls the switching element current. The phase of the power voltage is detected and the on-time of the switching element 5 near the peak value of the power voltage is shortened, thereby the peak value of the current of the switching element 5 has a flat wave-form near the peek of the power voltage. The increased quantity of the peak value from the average value of the current of the switching element 5 is made small, the rating of the switching element is decreased, its cost can be reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to an inverter for a cooking device such as an electromagnetic cooking device for general household use.

2. Description of the Related Art FIG. 3 shows a high frequency power source conventionally used in a general household electromagnetic cooker. In Fig. 3, 1 is an AC power supply;
2 is a rectifier for rectifying the AC power supply 1, 3 is a smoothing capacitor, 4 is a heating coil, and 6 is a switching element, which is shown here as a transistor and a diode connected in antiparallel. Reference numeral 6 denotes a resonant capacitor, and 7 denotes a control unit that detects the voltage or current of V4 (heating coil) and turns on and off the switching element 6 at an appropriate timing. In this conventional device, constant frequency control is performed regardless of the phase of the power supply voltage, and therefore the switching element current is proportional to the power supply voltage as shown in FIG.

Problems to be Solved by the Invention However, this conventional method has the disadvantages that there is a large difference between the average value and the peak value of the switching element current, and that the switching element has a high rating and is required to be expensive. The present invention was made in view of this point, and the average '1 and peak current of the switching element are
The purpose of the present invention is to provide an inverter for a cooking appliance in which the rating of the switching element is reduced and the cost is reduced by reducing the difference of 10 to /1\.

Means for Solving the Problems In order to solve the above problems, the present invention provides a power supply circuit including an AC power supply, a rectifier for rectifying the AC power supply, and a smoothing capacitor connected in parallel to the rectification output side thereof, and a power supply circuit connected to the power supply circuit. a series circuit of a heating coil and a switching element, a resonant capacitor connected in parallel to the switching element, a control circuit for controlling on/off of the switching element, and an output of the power supply circuit. In the above configuration, the power supply voltage By detecting the phase of the switching element and shortening the ON time of the switching element near the peak value of the power supply voltage, the peak value of the switching element current becomes a flat waveform near the peak value of the power supply voltage. As a result, the increase in the peak value of the switching element current relative to the average value can be made smaller than in the conventional method.

Embodiment Hereinafter, an embodiment of the present invention will be described with reference to the accompanying drawings.

In FIG. 1, 1 is an AC power supply, 2 is a rectifier for rectifying the AC power supply 1, and 3 is a smoothing capacitor connected in parallel to the rectified output side of the rectifier, forming a power supply circuit. 4 is a heating coil connected to the power supply circuit, and 5 is a switching element forming a series circuit with the heating coil 4, which is shown here as a transistor and a diode connected in antiparallel. 6 is a resonant capacitor connected to the heating coil 4 or the switching element 6; 7 is a control circuit that controls ON/OFF of the switching element 5 according to the voltage or current of the heating coil 4 and a signal from a phase compensation circuit described later; The ON time of the switching element 5 is shortened near the peak of the voltage, and the switching element current is controlled as shown in FIG. 8 is a phase compensation circuit that detects the output voltage of the power supply circuit and performs phase compensation.

In the above embodiment, by detecting the phase of the power supply voltage and shortening the ON time of the switching element 6 near the peak value of the power supply voltage, the peak value of the current of the switching element 6 near the peak of the power supply voltage is adjusted as shown in FIG. The waveform becomes flat. As a result, it is possible to reduce the increase in the peak value of the current of the switching element 6 with respect to the average value.

Effects of the Invention As described above, according to the inverter for cooking appliances of the present invention, it is possible to reduce the difference between the average value and the peak value of the switching element current, and to make the rating of the switching element small and inexpensive. The practical effect of this is great.0

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram of an inverter for a cooking device according to an embodiment of the present invention, FIG. 2 is a time chart showing the operation of the present invention, and FIG.
The figure is a circuit diagram of a conventional inverter for a cooking device, and FIG. 4 is a time chart showing the operation of the conventional example. 1... AC power supply, 2... Rectifier, 3.
... Smoothing capacitor, 4 ... Heating coil, 6 ... Switching element, 6 ... Resonance capacitor, 7 ... Control section, 8 ... ...Phase compensation circuit.

Claims (1)

[Claims] a power supply circuit including an AC power source, a rectifier that rectifies the AC power source, and a smoothing capacitor connected in parallel to the rectified output side;
a series circuit of a heating coil and a switching element connected to the power supply circuit; a resonant capacitor connected in parallel to the heating coil or the switching element; a control circuit that controls turning on and off of the switching element; and the power supply. An inverter for a cooking appliance, comprising a phase compensation circuit that detects an output voltage of the circuit and performs phase compensation, and changes the on/off period of the switching element depending on the phase of the output voltage of the power supply circuit.