JPS6316596A - induction heating device - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a drive circuit for a semiconductor switching element used in an inverter circuit for an induction heating cooker.

Conventional technology In recent years, induction heating devices have been used as heating devices.
In the future, we must continue to satisfy the requirements of high efficiency, miniaturization, and high reliability.

Various systems have been adopted as driving means for the inverter transistor in the conventional induction heating apparatus having the above-mentioned problem. For example, as shown in FIG. 4, the voltage of the AC power source 1 is lowered by a power transformer 21, etc., rectified by a diode 28 from the secondary winding, smoothed by a capacitor 22, etc., and controlled via a resistor 23. There is a method in which the transistor 9 is driven according to a signal from the circuit 24. This transistor 9 switches an inverter circuit having a heating coil 6 and a capacitor 7, and causes a high frequency current to flow through the heating coil. Further, as shown in FIG. 5, the electromotive current generated in the pickup coil 10 due to electromagnetic coupling with the current flowing in the heating coil 6 is once smoothed by a capacitor 25, and then used as a DC power source via a resistor 27. There is a method in which the transistor 9 is driven according to a control circuit 28 signal.

Problems to be Solved by the Invention However, a common problem with conventional transistor driving means is that the pace current to drive the inverter transistors is approximately 2A, and the DC power supply and pace current limiting resistor are required to supply it. , a high capacity smoothing capacitor is required. As a result, the parts themselves have become larger and the printed circuit board has also become larger, making it difficult to achieve a compact design, and the energy loss caused by the parts has also increased.

In addition, a magnetic field generated by a strong external current other than the current flowing through the heating coil 6 causes the pickup coil 1o to
There is also a problem in that an induced voltage is generated, the semiconductor switching element 9 malfunctions, and stable inverter operation cannot be ensured. The cause of this problem is, for example, when an induction heating cooker has multiple burners and heating coils are placed adjacent to each other.

When a current is passed through one heating coil, an induced voltage may also be generated in a pickup coil installed near another heating coil due to electromagnetic coupling.

In view of the above problems, the present invention enables miniaturization, low loss,
It is also an object of the present invention to provide an induction heating device that does not malfunction even in response to external noise.

Means for Solving the Problems In order to achieve the above object, the induction heating device of the present invention has the following features:
an inverter circuit having a switching element; a pickup coil that is electromagnetically coupled to the heating coil and supplies a drive current to the first switching element; and a second switching element that controls supply of drive current to the pickup;
a control circuit that controls the conduction time of the first switching element, a third switching element is provided between the pickup coil and the drive terminal of the second switching element, and a signal from the control circuit is connected to the second switching element; The switching element and the third switching element are configured to be driven simultaneously.

According to the above configuration, the third switching element is in an off state when there is no signal from the control circuit, so even if an induced voltage is generated in the pickup coil due to a change in an external magnetic field, the inverter semiconductor switching element doesn't work,
Malfunctions can be prevented. In addition, when there is a signal from the control circuit, the pickup coil and the inverter semiconductor switching element become conductive, but the current induced in the pickup coil is due to the current flowing through the heating coil in its own impulse circuit. What is determined is to provide the heating coil and the pickup coil as close to each other as possible so that the ratio does not pose a problem compared to the externally supplied one.

EXAMPLE Hereinafter, an example of the present invention will be described with reference to the accompanying drawings. In FIG. 1, an AC power supply 1 applies voltage to an inverter circuit 2 that converts low frequency AC into high frequency power.

A control circuit 16 for controlling the inverter circuit 2, and a transistor 13 that performs switching operation by the control circuit 16.
, the thyristor 1 is triggered by the transistor 13.
1. When the transistor 13 is switched on, the resistor 12 that limits the gate current of the thyristor 11, the resistor 14 that limits the pace current of the transistor 9, and the pickup coil 1° provided near the heating coil 6. Become.

The inverter circuit 2 is connected via a rectifier bridge circuit 3,
A choke coil 4 and a capacitor 6 are connected, and a parallel circuit of a heating coil 6 and a resonance capacitor 7 is connected in series with a parallel circuit of a transistor 9 and a diode 8 from an input terminal of a DC power source.

A cooking pot 16 is placed near the heating coil 6 and used for cooking.

FIG. 2 shows current waveforms at various parts of the inverter circuit 2 with the above configuration under normal load. 4 is the waveform of the current flowing through the heating coil 6, (B) is the collector current waveform of the transistor 13, and (q is the base current waveform of the transistor 9).

When the transistor 13 is switched on by the control circuit 15, the current flowing through the resistor 12 turns on the thyristor 11, and the current flowing through the resistor 14 turns on the transistor 9.
flows into the base of the transistor 9 and drives the transistor 9. At this time, at the same time that current begins to flow through the heating coil 6, an induced voltage is generated in the pickup coil 10.If the winding polarity is set so that the current flows to the anode side of the thyristor 11 as shown in FIG. The current generated in the coil 1o can directly serve as a base current for driving the transistor 9, and even if the current flowing through the transistor 13 is small, a large current drive is possible.

Note that even if a triac is used in place of the thyristor 11, the above description does not change in any way.

Furthermore, as shown in FIG. 3, when turning on the transistor 9, the terminal a is set to ■ and the terminal C is set to e between terminals a and 0 of the control circuit 15, which is the same as the operation shown in FIG. 1. However, when turning off the transistor 9, between the terminals b and c of the control circuit 16, the terminals e1 and terminal C are set to the polarity ■, and a reverse bias current flows from the emitter of the transistor 9 toward the base, thereby speeding up the turn-off of the transistor 9. There are means.

Effects of the Invention As mentioned above, when the transistor in the inverter circuit is stopped, even if external induced voltage is generated in the pickup coil, the connection between the pink-up coil and the base of the transistor is cut off. , it is possible to prevent malfunctions. Furthermore, we were able to provide a low-loss drive circuit that enables large current drive simply by holding a small current drive trigger.

[Brief explanation of the drawing]

Fig. 1 is a circuit diagram of an induction heating device according to an embodiment of the present invention, Fig. 2 is a current waveform diagram of each part of the inverter circuit in the same normal state, and Fig. 3 is a circuit diagram of an embodiment of the present invention when bias driving is performed. Figure 4 is a circuit diagram showing a conventional example. 2... Inverter circuit, 6... Heating coil, 9... First semiconductor switching element. , 11...Third semiconductor switching element, 1
3...Second semiconductor switching element, 16.
...Control circuit. Name of agent: Patent attorney Toshio Nakao and 1 other person2-
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Claims (1)

[Claims] an inverter circuit having a first switching element that causes a resonant circuit of a heating coil and a resonant capacitor to oscillate; a pickup coil that supplies a drive current for the first switching element through electromagnetic coupling with a current flowing through the heating coil; a second switching element that controls the supply of drive current from the pickup coil to the first switching element; and a control circuit that controls the conduction time of the first switching element, the pickup coil and the first
A third switching element is provided between drive terminals of the switching element, and the control circuit makes the third semiconductor switching element conductive when the second switching element is conductive.