Automatic current sharing circuit for connecting common mode choke in series on primary side of parallel transformers

Abstract

The invention discloses an automatic current sharing circuit for connecting a common mode choke in series on a primary side of a parallel transformer. The automatic current sharing circuit comprises an external first inverter input alternating current pulse circuit, an external second inverter input alternating current pulse circuit, an external first MOS tube power module, an external second MOStube power module, an external first LC resonant cavity, an external second LC resonant cavity, an external rectifying circuit and an external load resistor. After external MCU signals are received bya first driving circuit and a second driving circuit, the signals are amplified and isolated, the first MOS tube power module and the second MOS tube power module are driven to alternately conduct MOS tubes in the first MOS tube power module and the second MOS tube power module, alternating current signals are output, the alternating current signals are output to the primary sides of a transformer T1 and a transformer T2 through the first LC resonant cavity and the second LC resonant cavity, and the same phases of inverse output are connected in parallel and are rectified by a rectifier bridge D1 and a rectifier bridge D2 to supply power to the load resistor.

Description

technical field [0001] The invention relates to the technical field of high-voltage power supplies, and more specifically, relates to the problem of parallel current sharing of two transformers in a high-frequency high-voltage generator. Background technique [0002] In the digital imaging technology of medical imaging equipment, the breast machine for breast disease detection requires a strong electric field to excite the electron cloud and generate X-rays, in which the breast high-frequency and high-voltage generator is used to provide the required electric field. The main function of the breast high-frequency high-voltage generator is to convert the 220V AC power input by the power frequency into a high-voltage DC power of 20KV-40KV. We generally rectify the 220V AC power into DC 311V, and then perform high-frequency inverter on the DC voltage. The transformed AC pulse is boosted and rectified by the step-up transformer, and finally output to the load by the high-voltage ...

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Problems solved by technology

[0003] In order to reduce the volume of the generator, we need to increase the switching frequency. At present, we achieve 100KHZ-200KHZ frequency conversion control, the maximum power is 16KW, the highest frequency is 200KHZ, and the output voltage is between 20KV-40KV. Due to the high output voltage, if Use a step-up transformer to boost the voltage, and remove the voltage drop of the LC resonant cavity of the main circuit. The amplitude of the input voltage pulse on the primary side of the transformer is about 200V. To boost the AC pulse with an amplitude of 200V to 40KV, the boost ratio must be 100. If the primary side is wound with 10 turns, the secondary side needs 1000 turns. If it is wound on a wire package, the interlayer withstand voltage of these wire packages must reach up to 40KV. The middle insulating layer requires a large thickness and sufficient space. The volume of the transformer has also become larger correspondingly, and the processing technology is complicated, which is not conducive to mass production

[0004] For this reason, we divide the step-up transformer into two groups, namely +KV and -KV, and then short-circuit +KV and -KV in series. Figure 1 In the LC resonant cavity, in order to output high voltage, the transformer turns ratio is usually very large, reaching a single 1:60 or more, and the number of secondary coil turns is more than 500. Due to the large number of turns, the distributed capacitance between winding layers and the distributed capacitance between turns become Very large, in high-frequency circuits, interlayer distributed capacitance becomes a parameter with great influence, especially for the resonant frequency of the LC / LCC / LLC resonant cavity on the primary side of the transformer, and the non-absolute uniformity of the winding process, There is a certain difference in the distributed capacitance between different windings, which will form a certain circulating current between the transformer winding and the capacitor, intercepting a part of the energy that should be output to the load, which is equivalent to adding an additional load. When it is large, it will cause asymmetry of +KV and -KV in the two windings. The whole system uses the absolute value sum of positive and negative KV for closed-loop processing. When +KV and -KV are asymmetrical, it will cause a high voltage , a low voltage, high voltage may cause ignition to the rectifier diode and the load, or high voltage breakdown, causing irreversible losses

[0005] Therefore, it is necessary to provide a method that can correspondingly solve the problem of +KV and -KV asymmetry caused by the above-mentioned uneven distributed capacitance.

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