JPS607359B2 - induction heating device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an induction heating device that is suitable for use in a cooking device, and particularly relates to an induction heating device that can appropriately drive a switching device when changing the output by varying the oscillation frequency of an oscillator that operates the switching device. It is composed of

That is, when a transistor or a GCS (gate controlled switch) is used as a switching element, the present invention controls the base current or gate current in the off state in accordance with the magnitude of the output, thereby controlling the switching element appropriately. It is designed to reduce loss and enable off-operation.

An embodiment of the present invention will be described below with reference to the drawings.

In the figure, 1 is a commercial AC power supply terminal, 2 is a rectifier circuit connected to the power supply terminal 1, 3 is an induction heating coil 4, a high frequency filter inserted between the rectifier circuit 2 and the induction heating coil 3; 5 is a switching element (hereinafter referred to as GCS) of the drive circuit, 6 is a damper diode, and 7 is a capacitor. Reference numeral 8 denotes a low-voltage DC power supply, which is composed of a step-down transformer 9, a rectifier circuit 10 and a capacitor 11 connected to the output side of the step-down transformer 9.

12 is a variable frequency oscillator whose output is passed through a driving transistor 13 to the primary coil 1 of a driving transformer 14.
4a, and the output of the secondary coil 14b is the above-mentioned G.
It is designed to be supplied to the gate of CS5.

Here, the drive signal from the variable frequency oscillator 12 is GCS5
A sawtooth wave current flows through the coil 3 while the current is in the normal state. The amplitude of this current increases in proportion to the length of the ON period of the drive signal, similar to the deflection yoke of a horizontal deflection circuit in a television receiver. In the present invention, a bias circuit 15 is inserted into the circuit that supplies the drive current to the GCS 5, and the oscillation frequency of the oscillator 12 -
The voltage obtained from the voltage conversion circuit 16 is used to bias the bias circuit 15.

In this example, the bias circuit 5 is configured by being grounded through the capacitor 15a and the resistor blade 5b on the side opposite to the GCS 6 of the secondary coil Kametsuru b of the drive transformer color 4, and the "conversion circuit a8' or switching element (hereinafter referred to as (called GCS)
The turtle also consists of a damper diode connected in parallel between its anode and cathode, a capacitor, and a coil 28a followed in series in a circuit through the anode and cathode of the GCS ~ television receiver. It uses the same circuit as the so-called horizontal deflection circuit in the circuit, and a driving transformer and a coil turtle c are provided so that the output from this is supplied to the gate of GCS turtle 7 of this circuit color S. There is.

The bias circuit 1 described above converts the voltage from the turtle fin of this conversion circuit into
In this example, coil 283 is coupled to coil 2b, and the output obtained from coil 2b is rectified by diode 2 to create a bias circuit 15. I try to give it to

According to this configuration, a voltage with a waveform shown in FIG. 2A is obtained in the secondary coil 14b of the drive transformer 14 by the pulse from the oscillator turtle 2, and a voltage with the waveform shown in FIG. It is well known that a high frequency current is supplied to the conductive heating coil 3 by a waveform current flowing and the GCS 5 performing a switching operation.

In the present invention, since the conversion circuit 16 is provided, the GCS1
A driving current as shown in FIG. 2C is also supplied to the gate of 7.

Figure 2D shows the anode current waveform of the GCS turtle.
This is a pulse generated at both ends of the coil 20a. This pulse voltage is transformed by the transformer 20', and a current as shown in Figure 2 flows through the bias circuit 15.
1, the current flows through the capacitor turtle 5a in the direction of the arrow, and when it reaches the negative polarity shown in the figure, the charging voltage of the capacitor 15,a is added to the voltage generated in the coil 14b, and based on this added voltage, the current is flows through the cathode gate of GCS5, turning it off. For example, if the oscillation frequency of oscillator group 2 is lowered in order to change the mother force of the heating device, the anode current of the GCS mother bone will also increase from period T to period T2 as shown in the diagram. As a result, the voltage of the pulse generated after the GCS voltage is turned off (see FIG. 2) similarly increases as shown from the period T to the period L, and accordingly, the charging voltage of the capacitor 5a also increases.

That is, according to the present invention, when an attempt is made to increase the output by lowering the oscillation frequency of the oscillator 2, the anode current increases accordingly. Since the voltage of a also increases, GCS
5 can be easily and reliably cut off.

The voltage charged to the capacitor a in this way is GC
The GC is used as a bias during off-operation of S5.
A complete off operation is performed. As described above, according to the present invention, even if the oscillation frequency of the oscillator package 2 is varied, the switching element of the drive circuit can be completely driven. The switching element 5 can be turned off immediately.

It is also possible to configure the switching element 5 so that a certain large current always flows in order to turn it off.In that case, the power loss due to the switching element becomes large. By making changes accordingly, such drawbacks can be avoided.

[Brief explanation of drawings]

Figure 2 is a circuit diagram of an example of an induction heating device according to the present invention. Figure 2 is a waveform diagram used to explain the operation of the present invention. The oscillator, 15 is a bias circuit, 15a is a capacitor, and 16 is an oscillation frequency-voltage conversion circuit.

Claims (1)

[Claims] 1. In an induction heating device in which a current flowing through an induction heating coil is generated intermittently by a switching element controlled by a variable frequency oscillator, and the output power is varied by controlling the conduction period of this switching element, the above-mentioned switching A bias circuit is inserted into a circuit that supplies drive current to the element, and the voltage generated by the bias circuit is related to the oscillation frequency of the variable frequency oscillator, and as the frequency decreases, the voltage changes and the switching element is shut off. An induction heating device that generates a voltage with a polarity such that the bias is applied to a control electrode of the switching element to facilitate shutoff of the switching element.