JPH0665136B2 - Frequency converter - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a frequency conversion device that supplies a high frequency current to a heating coil of an electromagnetic induction heating device.

2. Description of the Related Art An electromagnetic induction heating device generally uses a frequency converter to convert a commercial power source into a high frequency power source and supplies a current to a heating coil. A conventional frequency converter will be described with reference to FIG.

In the figure, 1 is a commercial power supply, and 2 is a rectifying bridge, which turns on and off the transistor 8 by a drive signal of the control circuit 9 to generate a high-frequency current in the resonance capacitor 5 and the resonance coil 6. . Then, the resonance coil 6 is formed into a flat plate shape, and a pot 10 for heating is installed in the vicinity thereof. 3 is a choke coil, 4 is a high frequency bypass capacitor, and 7 is a commutation diode.

There are power supply means for driving the transistor 8 as shown in FIGS. 5 and 6.

FIG. 5 shows a system using the power transformer 11, and FIG. 6 shows a coil system. In this system, as shown in FIG. 7, two auxiliary coils 12 are provided in a substantially concentric shape at the center of the flat coil 6. The directions of the induced currents are the same so that the two auxiliary coils do not interfere with each other. The auxiliary coil 12 makes it possible to utilize the current induced in the auxiliary coil 12 when a high frequency current flows through the flat coil 6.

Problems to be Solved by the Invention However, since a transistor that generates a high-frequency current needs to perform a high-speed switching operation, a reverse bias current must flow from the emitter in the pace direction at the time of turn-off. Two types of power sources, a negative power source and a negative power source, were required. Therefore, since the direction of the induced current is the same in the above-mentioned coil system configuration, there is a problem that a smoothing circuit for each of the positive and negative power supplies and a base current limiting resistor are required, resulting in an increase in the number of parts. The power transformer method requires a relatively large power transformer, which makes it difficult to reduce the size and thickness of the frequency converter.

The present invention has been made in consideration of the above problems, and it is an object of the present invention to provide a frequency conversion device in which a power transformer is omitted and the number of parts is reduced to reduce the size and thickness.

Means for Solving the Problems Two auxiliary coils each wound around a rod-shaped ferrite core provided below the heating coil are provided diagonally below the surface of the heating coil, and among the auxiliary coils One is used for the transistor forward bias, and the other is used for the reverse bias power supply.

Action Two auxiliary coils, each wound around a rod-shaped ferrite core provided under the heating coil, are provided at positions facing each other below the heating coil surface to prevent mutual magnetic field interference between the auxiliary coils and ensure stable transistor drive. It ensures the current waveform.

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

In FIG. 1 and FIG. 2a, a ferrite core 13A provided below the flat coil 6 which is a heating coil,
Auxiliary coils 14A and 14B are wound around 13B. The two auxiliary coils 14A and 14B are arranged diagonally.

FIG. 2b shows the connection between the two auxiliary coils 14A and 14B and the transistor 8 in the frequency converter. In the figure, the winding direction of the auxiliary coils 14A and 14B is such that when the collector current Ic of the transistor 8 increases,
Is set in the forward direction of the diode 15, and the auxiliary coil 14B is set in the forward direction of the diode 16 in the direction of current flow. Further, the capacitor 17 forms a closed loop with the auxiliary coil 14B. When the transistor 18 is turned on, the charge voltage of the capacitor 17 is
The configuration is such that a reverse bias is applied between the emitters, and a forward bias current can be made to flow from the small-capacity DC power supply 20 to the base of the transistor 8 via the resistor 19.

In the above structure, when the transistor 8 starts to turn on, its collector current has a small value, and the base current for driving it may be as small as I _B1 shown in FIG. 3c. Therefore, a DC power supply with a small capacity can be used.

Next, when the collector current Ic shown in FIG. 3a flows through the transistor 8, the induced current shown in FIG.
I _B ′ is generated and can be used as it is as the base current of the transistor 8. The base current value at this time is adjusted by adjusting the number of turns of the auxiliary coil 14A and the mounting distance to the flat coil 6. It can be set arbitrarily. Although an induced current is also generated in the auxiliary coil 14B, when the transistor 8 is on, the base voltages of the other transistors 18 are zero and in the off state as shown in FIG. 3d. Therefore, the induced current is stored in the capacitor 17 as it is as a charge voltage.

Next, when the transistor 8 is turned off,
The other transistors 18 are turned on at the same time, and the charge voltage of the capacitor 17 changes to the base of the transistor 8.
It is applied in the reverse bias direction of the emitter. At this time, a current also flows from the resistor 19 and the auxiliary coil 14A in the forward direction, but if the number of turns of the other auxiliary coil 14B is set so that the voltage can flow a reverse bias current higher than that,
The forward base current is canceled and a reverse bias current I _B2 flows as shown in FIG. 3c. By causing the reverse bias current to flow in this manner, the loss when the transistor 8 is switched off can be reduced.

As described above, according to this embodiment, the two auxiliary coils are
Since it is installed in the radial direction of the flat coil and is installed at a position opposite to the diagonal, interference due to mutual electromagnetic coupling can be prevented, and the forward bias current waveform is approximately similar to the current waveform flowing in the flat coil. It can be taken out in the state.

This means that the forward bias current value can be easily designed and stable operation can be guaranteed only by adjusting the distance between the auxiliary coil and the flat coil or the number of turns of the auxiliary coil.

EFFECTS OF THE INVENTION As is clear from the above description of the embodiments, according to the present invention, two auxiliary coils each wound around a rod-shaped ferrite core provided in the lower part of the heating coil are diagonally arranged below the surface of the heating coil. Since the auxiliary coil is wound around the ferrite core because it is provided at a position opposite to the above, the electromagnetic coupling with the heating coil is dense, the number of coil turns can be reduced, and an efficient configuration can be achieved. Mutual interference due to electromagnetic coupling between the auxiliary coils can be reduced, and highly reliable operation can be performed. Furthermore, the ferrite core wound with the auxiliary coil can also function as a magnetic shield. Therefore, the number of ferrite cores for magnetic shield can be reduced, and the directions of the induced currents of the two auxiliary coils can be changed, so that a smoothing circuit for each of the positive and negative power supplies. Can be simplified and the driving power supply of the transistor can be realized with a simple structure, and a stable driving signal can be obtained by providing the transistor at a position diagonally below the surface of the heating coil.

[Brief description of drawings]

FIG. 1 is an exploded perspective view of a flat coil and an auxiliary coil.
FIG. A is a sectional view of a flat coil and an auxiliary coil, FIG. 2b is a circuit diagram of a frequency conversion device, FIG. 3 is a waveform diagram of each part in FIG. 2b, and FIG. 4 is a configuration diagram of the frequency conversion device. FIG. 5 is a configuration diagram of a conventional frequency conversion device for obtaining a transistor driving power supply, FIG. 6a is a configuration diagram of another conventional frequency conversion device for obtaining a transistor driving power supply, and FIG. 6a is a sectional view of the flat coil and the auxiliary coil, and FIG. 7 is an exploded perspective view of the flat coil and the auxiliary coil of FIG. 6a. 6 ... Flat coil, 8 ... Transistor, 13A, 1
3B ... Ferrite core, 14A, 14B ... Auxiliary coil.

Claims (1)

[Claims] 1. A switching element for supplying a high frequency current to a heating coil, a rod-shaped ferrite core provided under the heating coil, and a magnetic flux wound around the ferrite core to generate an induced current in the heating coil. A frequency conversion device comprising: two auxiliary coils that are generated, the auxiliary coil supplies an induced current as a trigger current source of the switching element, and is provided in a diagonally opposite position below the heating coil surface.