JPS58198888A - High frequency induction heater - 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 high-frequency induction heating device using an electrostatic induction thyristor that can heat a desired object to be heated with high efficiency using high-frequency power.

High-frequency induction heating is generally a method of heating the conductor of the heated object by generating heat using eddy currents induced by a high-frequency magnetic field, and utilizes the skin effect, edge effect, proximity effect, etc. obtained by high oscillation frequencies. This is what we are doing.

High-frequency induction heating equipment is used in semiconductor manufacturing processes, for example, to heat the floating zone in order to improve the purity of semiconductor materials, to heat the crucible in single crystal growth equipment, or to heat the crucible in single crystal growth equipment. It is used for a variety of purposes, including as a power source for high-frequency power generation, and as a source of other heating energy.

Conventional high-frequency induction heating devices used vacuum tube type oscillation elements, but these are gradually being replaced by high-power transistors that are turned on and off by base current.

Since this high-power transistor is composed of many cells, it is difficult to operate all cells uniformly.
Moreover, it has not been possible to make large-sized devices.

Furthermore, it is not possible to output high frequency output, and since excess carriers accumulate in the base region of this transistor, it takes a long time to extract excess carriers at turn-off, that is, the accumulation time is long.In addition, the transistor has the following disadvantages: It also has

(1) Switching time is slow because the base resistance is large.

(2) In the case of large area transistors, there is a delay time for the entire device to turn on.

(3) It is difficult to make products with high voltage resistance.

(4) Due to poor efficiency, temperature rise due to loss is large.
Current concentration tends to occur and the element is destroyed.

(5) During switching, the base current must continue to flow during turn-on, and the drive power of the base is large and efficiency decreases in the case of large current switching.

(6) The voltage drop at turn-on is large.

For the above reasons, the conversion efficiency of the oscillation and amplification of the transistor is approximately 40 to 50%, and is only 70% at most.

On the other hand, although the conversion efficiency of an oscillator using a conventional pnpn-structured thyristor is better than that of a bipolar transistor, the operating frequency is at most 1 KHz or less. pnpn structure gate
Even if a turn-off thyristor is used, the operating frequency limit is only about several tens of kilohertz.

As described above, conventional high frequency induction heating has many major drawbacks.

The present invention is intended to eliminate the above-mentioned conventional drawbacks, and its purpose is to provide a high-frequency induction heating device that can efficiently heat an object to be heated even in a frequency range exceeding approximately 100 KHz to MHz. be.

The present invention will be described in detail below with reference to the drawings.

The high frequency induction heating device of the present invention has an electrostatic induction thyristor and heats an object to be heated with high frequency through a heating coil.

The electrostatic induction thyristor has already been developed by the inventor of the present invention in Japanese Patent Publication No. 57-
No. 9226 (Japanese Patent Application No. 1982-56002) ``Thyristor'' and others have proposed it, and it can be turned on simply by reducing the gate voltage to zero volts, and can be placed in a forward blocking state by applying a voltage between the gate and cathode in the opposite direction. In addition to its advantages, it can be used as a switching element for high-frequency induction heating equipment, has a fast response speed, is easy to apply electronic control, and does not generate heat inside the element, and even if it does, it is less heat-generating than that of conventional high-power transistors. It has the advantage of being able to perform high-frequency switching extremely efficiently and with an order of magnitude less frequency.

FIGS. 1(a) to 1(d) are diagrams for explaining an embodiment of the high-frequency induction heating device of the present invention, and FIG.
) is a specific circuit example.

The high frequency induction heating device in this embodiment has two electrostatic induction thyristors A and B. In the figure, 1 is a DC power supply, 2 is a choke coil, 3 is a transformer with an intermediate tap,
4 is a driving circuit of transistors Q1 to Q4 that drive the gates of the electrostatic induction thyristors A and B, Q1 and Q3 are p-channel MOS transistors that turn on the electrostatic induction thyristors A and B, respectively, and Q2 and Q4 are Turn off the electrostatic induction thyristors A and B, respectively.
Channel MOS transistors, VG1 and VG3 are current power supplies that turn on static induction thyristors A and B, VG2 and VG4 are DC power supplies that turn off static induction thyristors A and B, 5 is a heating coil, and 6 is a current power supply that turns on static induction thyristors A and B. The objects to be heated, C2 and R2, are a capacitor and a resistor for surge absorption.

By alternately energizing the electrostatic induction thyristors A and B, an alternating current flows through the heating coil 5 and the object to be heated 6 is heated.

FIG. 1(b) is a diagram showing a pulse train generated by the drive circuit 4 shown in FIG. 1(a).

Transistor Q1 becomes conductive due to φ1, and VG1 is applied between the gate and cathode of static induction thyristor A, turning the
Turn on. In the half cycle, transistor Q2 becomes conductive due to φ2, and VG2 is applied between the gate and cathode of static induction thyristor A, turning it off.

With the same phase as φ2, φ3 makes transistor Q3 conductive, and VG3 turns on static induction thyristor B. In the first cycle, transistor Q4 is made conductive by φ4, VG4 is applied to static induction transistor B, and static induction thyristor B is turned off. φ1 is added in the same phase as φ4, and the electrostatic induction thyristor A turns as before.
Turn on.

FIG. 1(C) is a diagram showing changes in the current on the primary side of the transformer 3 explained in FIGS. 1(a) and 1(b).

The heating coil 5 is driven by the alternating current flowing through the primary side of the transformer 3, and the object to be heated 6 is heated with high frequency.

The choke coil 2 is provided to prevent alternating current from flowing to the DC power supply 1 side. The DC power supply 1 is composed of a DC power supply obtained by rectifying a commercial power supply using a diode or by rectifying a commercial power supply via a transformer. The DC power supply voltage can be made variable by adjusting the voltage using an electrostatic induction thyristor on the primary side of the transformer.

Static induction thyristors turn on and turn off very quickly, and with a turn-off time of about 0.1 μsec, high-frequency induction heating of approximately 100 KHz or more can be achieved.
It can be obtained with an efficiency of 90% or more.

Both of FIGS. 1(a) and 1(d) can be easily implemented by changing the period of the drive circuit 4, or by changing the values of L1 and C1 to change the resonance frequency, or by changing both at the same time. In the case of FIG. 1(d), the operating frequency f is approximately given by f=1/2π■. Note that here, L1 is the inductance of the transformer 3, and C1 is the capacitance of the capacitor.

FIG. 2 shows another embodiment of the invention. The difference from the embodiment shown in FIG. 1 is that there are two DC power supplies, but the other main parts are the same as in FIG. 1(d).

In addition, the same parts in the figure as in FIG. 1 are indicated by the same reference numerals.

This also applies to the following drawings. The DC power supply 10 is alternately made conductive by the electrostatic induction thyristor A, and the DC power supply 11 is made conductive by the electrostatic induction thyristor B, and an alternating current flows through the resonators L1 and C1.

The gate driving method can be performed in the same manner as shown in FIG. The voltages of the DC power supplies 10 and 11 may have the same value.

FIG. 3 shows yet another embodiment of the invention. The high frequency induction heating device in this embodiment has four electrostatic induction thyristors A, B, C, and D. By simultaneously turning on and turning off the electrostatic induction thyristors A and C, and then turning on the electrostatic induction thyristors B and D simultaneously, an alternating current can be caused to flow through the resonators L1 and C1.

Q1, Q5, VG1, and VG5 are conduction transistors for turning on static induction thyristors A and C, respectively, and DC power supplies for turning on, Q2, Q6, VG2, and VG6 are transistors for turning off static induction thyristors A and C, respectively. Conduction transistor, turn-off DC power supply Q3, Q7, VG3
, VG7 are conduction transistors for turn-on of static induction thyristors B and D, respectively, and DC power supplies for turn-on, Q4, Q8, VG4, and VG8 are conduction transistors for turn-off of static induction thyristors B and D, respectively, and turn-off. It is a DC power supply for

The embodiment shown in FIGS. 2 and 3, unlike the embodiment shown in FIG. 1, has the advantage that a center-tapped transformer is not required. When the voltage of the DC power supply 1 is V, the forward blocking voltage of the electrostatic induction thyristor is ZV in the embodiment shown in FIG. 1(a), and V in the embodiments shown in FIGS. 2 and 3. . The electrostatic induction thyristor used in the high-frequency induction heating apparatus shown in FIGS. 1 to 3 is a normally-on type element that is turned off by applying a reverse bias between the gate and cathode and becomes conductive at 0 gate bias. Either a normally-off type element which is in a blocking state when no gate bias is applied, or an element having characteristics intermediate between a normally-on type and a normally-off type may be used. It is desirable to use a static induction thyristor that has a large forward blocking gain and a large current gain during turn-off.

FIG. 4 shows another embodiment of the invention.

E is a reverse conducting electrostatic induction thyristor Q10 and VG10 are transistors for turn-on conduction of the gate and a power source for turn-on. C1, L1 are resonant circuits, C2,
R2 is a capacitor and resistor for surge absorption.

φ10 is a pulse voltage for turning on Q10, which turns on electrostatic induction thyristor E and connects resonant circuits C1 and L1.
conduction. In this example, L1 also serves as a heating coil.

When the resonant circuit C1 is discharged, the electrostatic induction thyristor E is reversely conductive, so that the charge charged to the opposite polarity of the capacitor C1 is discharged. Upon discharging, the electrostatic induction thyristor E becomes blocked again and the capacitor C1 charges. φ10 is applied to turn on the electrostatic induction thyristor E again.

By repeating the above, an alternating current flows through the heating coil L1, and the object to be heated 6 is heated.

In the embodiments described above, transistors Q1 to Q10 are used as gate drive circuits. The gate driving transistor must have self-erasing capability. Although an example using MOS transistors has been explained here, it is not limited to MOS transistors, but also static induction transistors,
A bipolar transistor may also be used. In addition, in the embodiment, the circuit applies DC power when turning on and off the gates of the electrostatic induction thyristors A to E.
Suitable for high frequencies. The gate turn-off circuit may be a capacitor charging method, a reactor method, a pulse transformer method, or a capacitor and pulse transformer method.

An embodiment for simplifying the switching of electrostatic induction thyristors for high currents is described below.

FIG. 5 shows an embodiment using normally-off type electrostatic induction thyristors F and G that are turned on by a light pulse.

Reference numerals 20 and 21 are pin photodiodes, phototransistors, photostatic induction transistors, etc. that are turned on by light pulses, and VG11 and VG12 are DC power supplies for turn-off. The other circuits are the same as in FIG. 1(a). 1
5 is an optical fiber line, 16 is an electrostatic induction thyristor F, G
, 20, 21, and is composed of a pulse circuit, a laser diode or a light emitting diode, and a power source. 31 and 33 are light pulses that turn on F and G, and 32 and 34 are light pulses that make 20 and 21 conductive. Figure 5(b) and Figure 5(a)
) shows the operation of the embodiment shown in FIG. The electrostatic induction thyristor F is made conductive by the light pulse 31, and then the light pulses 32, 3
3 turns off the electrostatic induction thyristor F and turns on the electrostatic induction thyristor G, and then the light pulse 3
4 makes 21 conductive and turns the electrostatic induction thyristor G.
Turn it off. At the same time as the electrostatic induction thyristor G is turned off, the electrostatic induction thyristor F is made conductive again by the optical pulse 31. By passing current alternately through the electrostatic induction thyristors F and G, an alternating current flows to the heating coil 5,
The object to be heated 6 is heated.

When F and G are normally-on type electrostatic induction thyristors, the optical pulses 31 and 32 are unnecessary, and as shown in FIG.
) can be operated with light pulses such as

FIG. 5(d) shows an example in which elements 22 and 23, such as photodiodes and phototransistors, which conduct with a light pulse that turns on the gate, are connected to electrostatic induction thyristors F and G, respectively. VG13 and VG14 are This is the voltage source for turning on the gate. The method of operation is shown in Figure 5 (
Same as b). In a normally-on type electrostatic induction thyristor, VG12 may be omitted. Further, 20 and 21 may be replaced with large resistances Rg. In that case, 2
It will be turned on at 2 and 23, and the light pulse 32
, 34 are not necessary, and it is sufficient to apply the optical pulses 31 and 33 as shown in FIG. 5(e).

It goes without saying that the gate drive circuit of the high-frequency induction heating apparatus described above can also be made into a circuit using light, as shown in FIG. Further, as a protection circuit, it is desirable to provide a reset circuit that turns off all the electrostatic induction thyristors when the fuse and pulse drive circuit are powered on.

Although the industrial high-frequency induction heating device of the present invention has been described above with reference to several embodiments, the present invention is not limited to the above embodiments, and may be configured to include at least an electrostatic induction thyristor. It doesn't matter what you have.

For example, the heating coil that heats the object to be heated using high frequency waves may be a wire-wound coil or a flat plate coil, or may be a single set or a plurality of sets of these coils. When wire-wound coils are used in parallel, the magnetic east may be oriented in the same direction.

As explained above, the high frequency induction heating device of the present invention has many advantages as described below by being configured with at least an electrostatic induction thyristor, and has extremely high industrial value. It is something.

(1) Faster switching is possible than conventional thyristors.

(2) It is possible to generate a continuous output of large power in a frequency range exceeding approximately 100 KHz to MHz band, and it can also be used as a substitute for a high-frequency induction oscillator using a transistor or thyristor in a frequency range below this band.

(3) Conversion efficiency can be increased to 90% or more, resulting in energy savings.

(4) High stability and reliability, with no element destruction.

(5) During switching, it is only necessary to flow a small pulse voltage current during turn-on and turn-off, so the power required for switching can be reduced.

(6) Since it can be easily turned off, it requires fewer parts and is small in size, making it compact as a whole and requiring only a small amount of installation space.

[Brief explanation of drawings]

FIGS. 1(a) to (d) show one embodiment of the high-frequency induction heating device of the present invention and diagrams for explaining it, and FIGS. 2 to 4 show another embodiment of the present invention, and FIGS. Figure 5 (a) to (d)
These are still other embodiments of the present invention and diagrams for explaining them. Electrostatic induction thyristor...A, B, C, D, E, F, G Patent applicant Jun Nishizawa■

Claims (1)

[Claims] A high-frequency induction heating device characterized by having an electrostatic induction thyristor.