JPH0740465B2 - Inverter circuit transformer for magnetron - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to the configuration of a transformer in a method of driving a magnetron using an inverter.

2. Description of the Related Art As shown in FIG.
A method of providing a high frequency choke 27 in series with the primary winding 22 of 28 is often used.

In this type of conventional example, not only the transformer 28 but also the high frequency choke 27 is added to efficiently supply electric power to the magnetron 15 without imposing a heavy burden on the switching transistor 10 (for example, the outlet). "Design of inverter circuit for magnetron by CAD").

Problems to be Solved by the Invention Although such a conventional circuit has an advantage that the anode current flowing in the magnetron 15 can be limited by providing the high frequency choke 27, as described in the above document, the inductance L _{S of the} high frequency choke is reduced. Is 25 μH, the primary inductance of the transformer is 30 μH, the secondary inductance is 15 mH, and the primary and secondary coupling coefficients are 0.98. Therefore, a high frequency choke with an inductance that is approximately equal to the primary inductance is required.

Further, the coupling coefficient is as dense as about 0.98, and it is necessary to adopt a configuration in which the primary winding and the secondary winding are wound in a concentric circle. The limiting condition of these configurations is that a high frequency choke with almost the same size as the transformer is indispensable and the power supply section becomes large. In addition, since the primary winding and the secondary winding cannot be spatially separated from each other, it is difficult to ensure insulation, which causes a problem.

The present invention has been made in view of the above points, and an object thereof is to provide an inverter transformer for a magnetron having a simple structure that does not require a high frequency choke, by devising the structure of the transformer.

Means for Solving the Problems In order to solve the above problems, the present invention provides a primary winding so as to surround a gap between a pair of U-shaped cross-section cores instead of a high frequency choke, and A secondary winding is provided adjacent to the primary winding and the coupling coefficient between the primary and secondary windings is set to 0.
The inverter circuit is configured by adopting a configuration that allows loose coupling in the range of 6 to 0.8.

Effect The present invention is capable of configuring a simple inverter circuit without excessively increasing the anode current flowing through the magnetron, and without excessively increasing the resonance voltage of the switching transistor in particular, by the above configuration. is there.

Practical Example FIG. 1 is a diagram showing an example of an inverter circuit of the present invention. In FIG. 1, the commercial power supply 1 is rectified and smoothed by a diode 2, a choke coil 3 and a smoothing capacitor 4. A transformer 9 including a primary winding 6, a secondary winding 7, and a heater winding is connected in parallel with the capacitor 5 to the DC power supply formed in this way. This LC resonant circuit is a switch circuit consisting of transistor 10 and diode 11
The inverter circuit is constructed by switching at KHz or higher. The transistors are switching-controlled by an oscillation circuit 12 having a DC power supply terminal a, a transistor V _CE (collector-emitter voltage V _CE ) detection terminal b, a ground terminal c, and a transistor drive terminal d. Trance
9a The secondary winding 7 is connected to the magnetron 15 through a voltage doubler rectifying circuit consisting of a high voltage capacitor 13 and a high voltage diode 14 and an average current of 200 to 300 mA (power of 800 to
1200W) DC high voltage is supplied.

On the other hand, the heater winding wound on the same core is a magnetron.
The heater power of about 50 to 100 W is supplied to 15. Figure 2,
FIG. 3 shows a voltage waveform (a) and a current waveform (b) applied to the transistor 10 and the diode 11 of this kind of inverter circuit. When the transistor 10 is closed by detecting that the voltage applied to the transistor has decreased, a gradually increasing current flows through the transistor 10 (T _ON ) during this period as shown in FIG. When 10 is opened, the LC resonance voltage (T _OFF ) is applied between the collector and emitter of the transistor during that time (T _OFF ). The dotted line shows the voltage waveform applied to the transistor 10 when the transistor 10 is opened and then the transistor 10 is not closed. Voltage responsibility here D _V
To Define in. In the inverter circuit as shown in FIG. 2, the current does not flow when a voltage is applied to the transistor 10 and the voltage is not applied when a current is flowing to the transistor 10, so that the heat generation loss of the transistor 10 is small and the efficiency is high. Inverter can be configured. On the other hand, depending on the constant of the LC resonance circuit, the circuit waveform is as shown in FIG. That is, the voltage resonance circuit may be in an overdamping state and the voltage waveform may not be zero. In this case, there is no choice but to close the transistor 10 when a voltage is applied to the transistor 10, and a large short circuit current flows as shown in FIG. 3 (b). In this case, the transistor 10 bears a large current load and the generated loss becomes large. Therefore, it is necessary to avoid the state of FIG. 3 when selecting the inverter circuit constant.

FIG. 4 shows the coupling coefficient k of the primary winding and the secondary winding under the condition of avoiding the overdamping state as shown in FIG.
_{FIG. 12} is a diagram showing the results of measurement of the relationship between the DC voltage and the resonance voltage ratio K _V with respect to ₁₂ and the voltage duty D _V as a parameter. Actually, switching frequency is 20KHz to 100KHz, commercial power supply voltage is 50V to 2
I changed it to 20V.

As is clear from the figure, the coupling coefficient k ₁₂ rapidly increases when it exceeds 0.8, and in this case, the transistor 10 having a high breakdown voltage is required. It is very difficult to make a transistor with high switching speed and high breakdown voltage. In particular, a transistor having a large voltage burden has a large chip size and a high cost. On the other hand, although the current burden for securing a constant power is not shown, it sharply increases when k ₁₂ = 0.6 or less. Further, a transformer with k ₁₂ <0.6 has a large leakage magnetic flux from the transformer and is strongly affected by the arrangement of magnetic materials such as an iron plate around the transformer, which makes it difficult to obtain stable inverter operation during mounting.

In the conventional example, in order to solve these problems, an inverter was constructed without increasing voltage burden and current burden by combining with a high frequency choke under the condition of k ₁₂ ≧ 0.9.

FIG. 5 shows a specific configuration example of the transformer of the present invention.
Coupling coefficient k _{12 is} obtained by arranging ferrites 16 and 17 having a U-shaped cross section so as to face each other through a gap 18 and arranging primary winding 6, secondary winding 7 and heater winding 8 in contact with each other as shown in the figure. Is 0.6 to 0.
A transformer of 8 can be realized, and the magnetic flux between the primary winding 6 and the secondary winding 7 is coupled even in the air, so the core
It is possible to obtain a transformer having desired characteristics while making 16 and 17 smaller.

A concrete example of the result of operating at a frequency of 20 to 30 KHz D ≈ 0.3 is a transformer with dimensions l ₁ = 55 mm, l ₂ = 74 mm, and G = 2 mm, the primary inductance is 58 μH, the secondary inductance is 22 mH, and the coupling coefficient is
By operating under winding conditions of k ₁₂ = 0.65 to 0.7, the peak voltage of the transistor is about 600V with a commercial power supply of 100V (peak voltage of 141V) (that is, K _V = 600 / 141≈4.26), as shown in Fig. 2. Efficient operation with a waveform like
The power of 00W is supplied. FIG. 6 and FIG. 7 show examples of conventional transformer and inverter circuits. Sixth
As shown in the figure, the transformer cores 20 and 21 face each other with a gap in between, and the primary winding 22 and the secondary winding 23 are concentrically arranged with respect to the core in order to increase the coupling coefficient k ₁₂ . 24 is a heater winding. In FIG. 7, 25 is a choke coil, 26 is a resonance capacitor, 27 is a high frequency choke, and 28 is a conventional transformer. In the conventional example, as shown in FIG. 6, the primary winding and the secondary winding need to be spatially densely arranged. This means that when the magnetron is a load, the secondary winding voltage needs to be increased. Therefore, there are problems that it is difficult to ensure insulation between the windings and that it is difficult to cool the secondary winding, whereas the present invention can solve these problems.

EFFECTS OF THE INVENTION As described above, according to the present invention, there is provided a transformer of an inverter circuit for a magnetron, which has an extremely simple structure, a small size, a light weight, and a simple structure, and which performs stable and highly efficient inverter operation. it can.

[Brief description of drawings]

FIG. 1 is a circuit diagram of one embodiment of the present invention, FIGS. 2 and 3 are waveform diagrams of an inverter circuit, FIG. 4 is a characteristic diagram of relevant parts, FIG. 5 is a configuration diagram of a transformer of the present invention, and FIG. , FIG. 7 is a transformer configuration diagram and a circuit diagram of a conventional example. 5 ... Resonance capacitor, 6 ... Primary winding, 7 ... Secondary winding, 8 ... Heater winding, 9 ... Transformer, 10 ... Transistor, 12 ... Oscillation circuit, b ... Transistor Applied voltage detection terminal, 15 ... Magnetron, 16, 17 ... Core, 18
……gap.

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Takahiro Matsumoto 1006 Kadoma, Kadoma City, Osaka Prefecture Matsushita Electric Industrial Co., Ltd. (72) Inventor Villa Daisuke 1006 Kadoma, Kadoma City, Osaka Prefecture Matsushita Electric Industrial Co., Ltd. 56) References JP-A 64-14846 (JP, A)

Claims (1)

[Claims] 1. An oscillation circuit having a magnetron, a resonance capacitor, a switching transistor, a transformer and an applied voltage detecting element for the transistor, and the transformer is composed of a pair of U-shaped cross-section cores. A primary winding is provided so as to surround a gap provided between cores, and a secondary winding and a heater winding are provided adjacent to the primary winding, and the primary winding and the secondary winding are provided. A transformer for a magnetron inverter circuit, characterized in that the coupling coefficient of is set to a value between 0.6 and 0.8.