JPS6161503B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a high frequency induction heating device, and more particularly to an improvement in an output matching circuit using a parallel resonant circuit.

High-frequency induction heating uses the alternating magnetic field of a heating coil (work coil) to generate eddy current loss in the heated object and generates heat, and is widely used in various fields such as heat treatment, heat processing, and bonding. It is being

Generally, in high-frequency induction heating devices, a parallel resonant circuit is used as an output matching circuit.

FIG. 1 is a circuit diagram showing an example of a conventional parallel resonant circuit of this type. In FIG. 1, field effect transistors Q ₁ , used as switching elements,
The source of _Q2 is connected to the power supply terminal -Vc, and the drain is connected to the capacitor _C0 and to the switching tap of the primary coil _L1 of the matching transformer T. Primary coil of matching transformer T
The power supply terminal +Vc is connected to the middle tap of _L1 ,
A work coil _L3 is connected to the secondary coil _L2 . The resonant frequency f ₀ of such a circuit is determined by using the sign itself as the capacitance of the capacitor C ₀ and calculating the inductance seen from the primary side of the matching transformer T by L
Then, it can be expressed as f ₀ =1/(2π√ ₀ ), and the output impedance Z ₀ can be expressed as Z ₀ =L/(C ₀ R), where R is the resistance component. That is, by changing the connection of the switching tap of the primary coil _L1 of the matching transformer T, the resonant frequency can be adjusted.
f ₀ and output impedance Z ₀ can be varied. For example, in order to obtain a larger output signal, change the connection of the switching tap of the primary coil L ₁ of the matching transformer T so that the inductance L becomes smaller, thereby reducing the output impedance Z ₀ and allowing the signal to flow to the work coil L ₃ . All you have to do is increase the current.

However, according to such a conventional configuration, if the connection of the switching tap of the primary coil L ₁ of the matching transformer T is changed, the resonant frequency f ₀ will also change significantly, so in order to reduce the change in the resonant frequency f ₀ , the capacitance of capacitor C ₀ must also be adjusted. Also, when focusing on the matching transformer T, the connection of the switching tap of the primary coil _L1 prevents current from flowing through a part of the primary coil _L1 , and the high-frequency signal distribution applied to the secondary coil _L2 is uneven. As the loss becomes uniform, the loss increases. Alternatively, the connection of the secondary coil L ₂ may be changed in order to match with the work coil L ₃ , but if there is such an uneven distribution of high frequency signals, the connection position of the switching tap of the primary coil L ₁ may be changed. The problem is that it is subject to restrictions.

The present invention has been made in view of these points, and its purpose is to solve each of the above-mentioned problems and provide a high-frequency induction heating device that is excellent in various characteristics.

The present invention achieves this object in a high-frequency induction heating device that supplies a high-frequency signal to a work coil through a matching transformer in which the primary coil is provided with a plurality of switching taps. The feature is that a matching capacitor is connected between both ends of the primary coil so that the current flows.

Hereinafter, the present invention will be explained in detail with reference to the drawings.

FIG. 2 is a circuit diagram showing a main part of an embodiment of the present invention, in which a matching capacitor C ₁ is connected between both ends of a primary coil L ₁ of a matching transformer T similar to that in FIG. 1. There is. As shown in Figure 1, C ₀ is a capacitor necessary for stable operation of transistors Q ₁ and Q ₂ , and is connected near transistors Q ₁ and Q ₂ , forming part of a parallel resonant circuit. It is something to do. FIG. 3 shows an equivalent circuit diagram focusing on these capacitors C ₀ and C ₁ and the matching transformer T. Here, let n ₁ be the number of turns of the coil where capacitor C ₀ is connected, and capacitor C ₁
Assuming that the number of turns of the entire primary coil L ₁ to which the capacitor (its capacitance is C ₁ as well as its sign) is connected is n ₂ (n ₁ ≪ n ₂ ), the effective capacitance C ₁ ′ of the capacitor C ₁ is: C ₁ ′=(n ₂ /n ₁ ) ²・C ₁ , and the effect of capacitor C ₁ is ^twice that of capacitor C ₀ (n ₂ /n ₁ ). That is, capacitor C ₁
will dominate the parallel resonant circuit. Therefore,
The resonant frequency f ₀ can be set mainly by the capacitance of the capacitor C ₁ , and the output impedance Z ₀ can be set by the primary coil L ₁
By changing the connection of the switching tap, any value can be set without making a large change to the resonance frequency _f0 .

According to such a configuration, the distribution of the high frequency signal of the primary coil L ₁ of the matching transformer T does not become uneven as in the conventional case, and the distribution of the high frequency signal applied to the secondary coil L ₂ also becomes uniform. Secondary coil L ₂
can be freely connected in parallel or in series.
Further, by integrating the capacitor _C1 and the matching transformer T, output current processing can be easily performed. Furthermore, the Q of the matching transformer T can be increased, and the efficiency can be improved. Furthermore, one type of matching transformer can be used over a wide range of frequencies. In addition, matching between the primary coil L ₁ , L secondary coil L ₂ and work coil L ₃ becomes easier, and matching can be easily achieved even for a wide range of loads. Furthermore, in order to obtain the same capacitance as the conventional one, a capacitor with a smaller capacitance than the conventional capacitance is required, resulting in a significant cost reduction.

As described above, according to the present invention, it is possible to realize a high-frequency induction heating device including an output matching circuit with a relatively simple configuration and excellent various characteristics, and its practical effects are extremely large.

[Brief explanation of the drawing]

Fig. 1 is a circuit diagram showing an example of a conventional parallel resonant circuit, Fig. 2 is a circuit diagram showing a main part of an embodiment of the present invention, and Fig. 3 is a part of an equivalent circuit of the circuit shown in Fig. 2. It is a circuit diagram. Q ₁ , Q ₂ ... field effect transistor, C ₀ , C ₁ ...
...Capacitor, T...Matching transformer, _L1 ...Primary coil, _L2 ...Secondary coil, _L3 ...Work coil.

Claims (1)

[Claims] 1. In a high-frequency induction heating device that supplies a high-frequency signal to a work coil through a matching transformer in which the primary coil is provided with a plurality of switching taps, a A high-frequency induction heating device characterized by connecting a matching capacitor.