JPS59226670A - Transistor inverter - Google Patents

Abstract

PURPOSE:To enable to readily match the impedance by providing taps at the arbitrary middle positions of a coil which forms a parallel resonance circuit, and controlling the voltages of the taps by a transistor switching circuit. CONSTITUTION:Switching transistors QA1-AAn form the first switching circuit, and switching transistors QB1-BBn form the second switching circuit. A capacitor C1 and a coil L1 forms a parallel resonance circuit. A capacitor C2 is connected across a coil L1, and taps A, B provided at the arbitrary positions of the coil L1 are connected to the switching circuit. The switching circuits respectively control the tap voltages.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides high power FFT, SIT (Static
This article deals with transistor inverters using MucNon Transistor (MucNon Transistor) etc. as switching elements.

As an inverter used for high frequency induction heating,
Conventionally, large power generators using vacuum tubes have been used. However, in this device using vacuum tubes, transformers, coils, capacitors, etc., are required to have high withstand voltages, resulting in a problem that the device becomes larger and more expensive. For this reason, with the recent increase in voltage resistance of transistors,
A so-called transistor inverter using a transistor as a switching element has come into practical use. For this transistor inverter, a parallel resonant circuit in which a coil and a capacitor are connected in parallel is usually used due to the oscillation circuit configuration and power matching requirements.

The transistor inverter using the above-mentioned parallel resonant circuit directly rectifies the commercial alternating current voltage and receives the direct current voltage. Further, a voltage transformer is used as a means for increasing high frequency power. In order to supply a large amount of power to the load side with this transistor inverter, it is necessary to increase the output voltage or output current. However, since the breakdown voltage of the switching element (transistor) is limited to a certain value, there is a limit to its maximum output voltage. On the other hand, regarding the output current, the impedance Z of the parallel resonant circuit.

There are ways to make it smaller. Here, the impedance Zo of the parallel resonant circuit is the inductance of the circuit 1-
1 capacitance is C1 resistance is R, then the following formula % formula % 7o = 1-10R< 1) Therefore, in order to reduce the impedance Zo, the capacitance C
If J is increased or the inductance L is decreased, J:
stomach. However, if the inductance L is λ, for example, 1 tll-
When the value is less than 1, the high frequency distribution of the coil decreases, the power transfer rate becomes extremely small, and the power transmission device becomes unusable. Therefore, an apparatus having a configuration as shown in FIG. 1 is currently used.

In FIG. 1, OA I to QA n (n is an integer) are switching transistors (FETs) whose trains and sources are commonly connected to form a first switching circuit. On the other hand, QB1 to Qen are also switching transistors (FETs), and their drains and sources are commonly connected to form a second switching circuit. These switching circuits are driven in a complementary manner by driving pulses applied to transistors QA1 to QAn and QB+ to QBn. C1 is a capacitor, L+ and L2 are coils, and the capacitor C+ and the coil 1-1°L2 constitute a parallel resonant circuit. - A DC voltage obtained by rectifying the commercial voltage, for example, is applied between the intermediate tap of the secondary coil L1 and the connection part of the first and second switching circuits, and this voltage is applied to the first and second switching circuits. The switching circuit alternately turns on and off, and power is transmitted to the secondary coil 1-2. A load (not shown) is connected to the secondary coil L2 and receives the necessary power.The reason why a plurality of transistors are commonly connected to the first and second switching circuits is as follows. This is because a single transistor does not have enough current capacity for a device that needs to supply high-frequency high power to a secondary load.Therefore, several to several dozen transistors with matching characteristics are connected in parallel. This covers the lack of capacity.

By the way, in order to efficiently transmit power through a switching circuit, it is necessary to perform impedance matching according to the law of maximum power supply. In other words, 15. It is necessary to make the resistance of the parallel resonant circuit equal to the resistance of the switching circuit, and to select the reactance components so that their absolute values are equal and the poles f1 are opposite. In the circuit shown in FIG. 1, how this situation is handled will be explained using FIG. 2. FIG. 2 is an equivalent circuit diagram of the circuit of FIG. 1. The switching circuit is equivalent to n resistors having a resistance value r connected in parallel. Here, r is the output resistance of a single transistor (eg, OAI and QBl). Also, as in the above case, C is the capacitance of the parallel resonant circuit, R is the resistance of the parallel resonant circuit, and inductance of the coil. Now, if we ignore the reactance, the combined resistance of each switching circuit is r/n, which is 1
- It can be seen that as the number n of connected transistors increases, the combined resistance r/n becomes smaller, and it becomes difficult to match it with the resistance R of the parallel resonant circuit. As a result, it becomes difficult to transmit large amounts of power to the secondary side.

The present invention has been made in view of these points, and an object thereof is to provide a transistor inverter that outputs a large power as described above and can easily achieve impedance matching.

4- The present invention achieves this objective by using parallel resonant circuits to
The transistor inverter is characterized in that a tap is provided at an arbitrary position between the coils constituting the parallel resonant circuit, and the voltage of the tap is controlled by a transistor switching circuit.

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

FIG. 3 is an electrical configuration diagram showing an embodiment of the present invention.

In this figure, the same parts as in FIG. 1 are designated by the same reference numerals, and their explanation will be omitted. As is clear from FIG. 3, in this embodiment, a capacitor C2 is connected to both ends of the coil L1, and taps A and B provided at arbitrary positions on the coil L1 are connected to the switching circuit. Each switching circuit is adapted to control the voltages of these taps. To simplify the explanation of the operation of the above circuit,
FIG. 4 shows an equivalent circuit of one of the switching circuits (for example, the first switching circuit). Note that the output resistance r of each transistor and the constant of the parallel resonant circuit are the same as those of the equivalent circuit shown in FIG. 2. Fourth
In the figure, the total number of turns of the coil (the number of turns between 0 points in Figure 4) is N2, and the number of turns up to the intermediate tap (the number of turns between 0 points in Figure 4) is
If the number of turns between the point and the 0 point is N1, then the relationship between the impedance Xo' which is 1 no. from both sides of the coil and the impedance X○ connected between the intermediate tap (the 0 point and the 0 point) is as follows. holds true.

Xo'=(N?/N+>2・Xo (2> Obviously N2:・N1 here, so the impedance Xo' at both ends of the coil is (N2/ N1) becomes twice as large.Conversely speaking, by increasing the connection as shown in FIG.

Therefore, since the above-mentioned combined resistance r/n of a circuit in which h transistors are connected in parallel columns can be considered in correspondence with the above-mentioned XO,
The combined resistance r/n is determined by using the center tap (N2/N1
) This means that it has doubled.

Therefore, if the coil turns ratio N2/Nl is appropriately selected, (
r/n ) ・(N2/N+ > 2 can be matched with the impedance of the resonant circuit, previous)! This makes it possible to eliminate the problem (impedance drop) caused by connecting a plurality of IS transistors in parallel. Incidentally, if the impedance ZO of the resonant circuit is the inductance L' of the center tap, it is expressed by the following formula (3) The characteristics of the above configuration are as follows.

(1) High output can be achieved by increasing the current without lowering the impedance of the parallel resonant circuit.

(2) The output can be adjusted without changing the inductance 1- and capacitance C of the parallel resonant circuit.

(3) Since the Q of the resonant coil is proportional to the equivalent resistance of the transistor switching circuit, in the above configuration where the equivalent resistance can be increased, the Q can be increased. Therefore, efficiency is improved.

(4) Even with high impedance loads, matching can be achieved because the high frequency distribution of the coil is good.

Note that when SIT is used as a transistor, the power amplification method is voltage proportional type, similar to vacuum tubes, but in the method of directly converting commercial AC voltage (3 phase 220V) to DC, the voltage is constant and the current is increased. The invention is economical. Furthermore, by combining the two and operating the switching element near its maximum breakdown voltage, even greater power transmission becomes possible.

As explained below, according to the present invention, a tap is provided at an arbitrary position in the middle of the coil constituting the resonant circuit, and this tap voltage is controlled by a transistor switching circuit, so that the tap position can be changed. By adjusting, impedance matching between the switching circuit and the resonant circuit can be easily achieved. Therefore, high frequency high power can be efficiently transmitted to the tQ load.

[Brief explanation of drawings]

-9-J8.8- Fig. 1 is an electrical configuration diagram showing a conventional device, Fig. 2 is an equivalent circuit diagram of the circuit in Fig. 1, and Fig. 3 is an electrical diagram showing an embodiment of the present invention. The configuration diagram, FIG. 4, is an equivalent circuit diagram of the circuit shown in FIG. 3. OA1~QAnlQBl~QBn...Transistor C1, C2...Capacitor Ll, l-2...Coil Patent applicant JEOL Co., Ltd. Agent Patent attorney Fujiji Ijima 10-

Claims (1)

[Claims] A transistor inverter using a parallel resonant circuit, characterized in that a tap is provided at an arbitrary position between the coils constituting the parallel resonant circuit, and the voltage of the tap is controlled by a transistor switching circuit. inverter.