• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2002.05c
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• pp.15-17
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• 2002

Leakage inductance and temperature rise are two of the more impotent problems facing the magnetic core technology of today's high frequency transformers. Excessive leakage inductance increases the stress on the switching transistors and limits the duty-cycle, and excessive temperature rise can lead the design limitation of high frequency transformer with high current. The flat transformer technology provides a very good solution to the problems of leakage inductance and thermal management for high frequency power. The critical magnetic components and windings are optimized and packaged within a completely assembled module. The turns ratio in a flat transformer is determined as the product of the number of elements or modules times the number of primary turns. The leakage inductance increase proportionately to the number of elements, but since it is reduced as the square of the turns, the net reduction can be very significant. The flat transformer modules use cores which have no gap. This eliminates fringing fluxes and stray flux outside of the core. The secondary windings are formed of flat metal and are bonded to the inside surface of the core. The secondary winding thus surrounds the primary winding, so nearly all of the flux is captured.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2003.11a
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• pp.587-590
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• 2003

The first attention in designing a transformer for low temperature rise should be to reduce losses. Leakage inductance and temperature rise are two of the more impotent problems facing the magnetic core technology of today's high frequency transformers. Excessive leakage inductance increases the stress on the switching transistors and limits the duty-cycle, and excessive temperature rise can lead the design limitation of high frequency transformer with high current. The flat transformer technology provides a very good solution to the problems of leakage inductance and thermal management for high frequency power. The critical magnetic components and windings are optimized and packaged within a completely assembled module. The turns ratio in a flat transformer is determined as the product of the number of elements or modules times the number of primary turns. The leakage inductance increase proportionately to the number of elements, but since it is reduced as the square of the turns, the net reduction can be very significant. The flat transformer modules use cores which have no gap. This eliminates fringing fluxes and stray flux outside of the core. The secondary windings are formed of flat metal and are bonded to the inside surface of the core. The secondary winding thus surrounds the primary winding, so nearly all of the flux is captured.

• Journal of IKEEE
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• v.26 no.3
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• pp.445-455
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• 2022

This paper presents the optimal design of flyback transformer with the flat copper winding method of injection type suitable for the small-size and winding method of automatic type used in 90W DC to DC converter for LED-TV. This paper also proposes the flyback transformer with the flat copper winding method of injection type capable of the winding method of automatic type and the reduction of transformer size and enhanced uniformity in electrical characteristics compared to the conventional mass-production flyback transformer with the winding method of manual type. In particular, the flat copper winding transformer of injection type proposed in this paper is constructed in a vertical winding method of its transformer to realize the winding method of automatic type. The primary and secondary windings of flyback transformer with the flat copper winding method of injection type used the conventional winding, triple insulated winding and the flat copper winding method of injection type, respectively. The optimal design of flyback transformer with the flat copper winding transformer of injection type proposed in this paper suitable for small-size and winding method of automatic type was carried out based on the simulation results using Maxwell 2D and 3D tool.

• The Transactions of the Korean Institute of Power Electronics
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• v.10 no.3
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• pp.248-256
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• 2005

This paper presents the design method of the DC/DC converter using flat transformer which is suitable for midium or large capacity and high density power supply. Flat transformer module is composed and manufactured of multi-transformers in parallel and has a number of parallel single turn secondary windings. Therefore, its leakage inductance is highly decreased and it is more suitable for high frequency operation than conventional one. In this paper, we manufactured and tested 750W AC/DC converter with variable output powers to verify the performance of the flat transformer.

• Proceedings of the KIPE Conference
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• 1999.07a
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• pp.577-580
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• 1999

High power density on-board power supply is implemented by using flat transformer. In the high frequency switching converters, large leakage inductance increases the switching stress and duty cycle loss, which sometimes limits maximum switching frequency. The flat transformer is designed by using special core structure, which has very low profile and low temperature rise since the thermal loading is spread evenly over a larger area. 100W, 3.3V output on board supply is built and tested and 50.7W/$\textrm{inch}^{3}$ power density is achieved.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2002.07b
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• pp.638-641
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• 2002

This paper presents design and construct of flat type step-down piezoelectric transformer for the application to AC-adapters. This piezoelectric transformer operated in resonance vibration mode. In this paper, Finite element method(FEM) was used for analysis piezoelectric transformers. Vibration mode and electric field of piezoelectric transformer at resonance frequency were simulated. Using this simulation, we manufactured flat type piezoelecric transformer and measured its output characteristics. As results, output power was linearly increased by increasing input power at resonance frequency. And it was found that the transformer exhibited an output power of 11.4[W] at 60[V] input voltage. From these results, we expect that this piezoelecric transformer can be applied to AC adapters.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2003.07b
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• pp.1168-1171
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• 2003

In contrast to a conventional transformer, the flat transformer is made using a number of small ferrite cores. Two cores for transformer and one core for inductor, which composed one module. Many modules can be connected together to form a flat matrix transformer. This structural arrangement eliminates the single hot spot problem in conventional transformers and permits high current density pertains at high frequency. In this study, the ferrite magnetic cores of Mn-Zn system for the Flat transformer were manufactured and the electrical and magnetic characteristics of its tested. The power loss of sample FO2(Mn-Zn ferrite) sintered at $1350^{\circ}C$ was $350kW/m^3$ in test conditions of 250kHz, 200mT and $100^{\circ}C$, which showed the good power loss property in high frequency. The power loss of FO2 samples has been studied as a function of magnetic flux density and frequency. Steinmetz exponent was 2.82 at 250kHz and 2.73 at 500kHz. These results illustrated the switching of power loss mechanism in ferrite core from hysteresis losses to eddy current losses or others.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2003.05e
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• pp.23-26
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• 2003

The flat transformer, typically, has a number of parallel single turn secondary windings. Each secondary winding is coupled to the same primary winding. Therefore, the current in each secondary winding is equal to the ampere-turns in the primary winding, and to each other. These characteristics are particularly advantageous where parallel rectifiers are used. The windings share the current equally, with no need for ballast resistors or other added components. In this study, the ferrite magnetic core samples of Mn-Zn system for the Flat transformer are manufactured and the electrical and magnetic characteristics of its tested. The density of sample FO2-2 sintered at $1350^{\circ}C$ is $4.00kg/m^3$, which shows the good microstructural state. The initial permeability and saturation flux density of FO2 at room temperature is 2700 and 510mT, individually. The power loss of FO2 samples at 250kHz have been ranged $350kW/m^3$ to $80kW/m^3$ with temperature. And the minimum power loss of sample FO2-2 showed at $70^{\circ}C$, which property seems very positive to apply for a flat transformer.

• Proceedings of the KIPE Conference
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• 2004.07b
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• pp.709-712
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• 2004

본 논문에서는 고밀도 전원 장치에 적합한 플랫 트랜스포머(Flat Transformer)를 사용하여 다양한 출력을 갖는 AC/DC 변환장치의 설계 예를 제시하였다. 기존의 트랜스포머에 비해 플랫 트랜스포머는 다수의 트랜스포머를 병렬로 구성하여 제작하고, 이차 권선이 항상 1턴으로 구성되므로 누설 인덕턴스가 크게 감소하게 되어 고주파 스위칭에 적합한 형태를 가지고 있다. 일차측 AC/DC 변환기는 고조파 규제를 만족시키기 위해 경계 모드 (Boundary Mode)에서 동작하는 역률 보상회로로 구성하여 설계하였으며, 이차측 DC/DC 변환기는 플랫 트랜스포머에 적당한 하프 브리지(Half-Bridge) 컨버터를 적용하였다. 본 논문에서는 500W급 AC/]DC 변환기를 구성하여 다양한 출력을 갖는 전원 장치를 설계/제작하였다.

• Proceedings of the KIEE Conference
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• 2008.07a
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• pp.1297-1300
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• 2008

A conventional linear accelerator system requires a flat-topped pulse with less than ${\pm}$ 0.5% ripple to meet the beam energy spread requirements and to improve pulse efficiency of RF systems. A pulse transformer is one of main determinants on the output pulse voltage shape. The pulse transformer was investigated and analyzed with the pulse response characteristics using a simplified equivalent circuit model. The damping factor ${\sigma}$ must be >0.86 to limit the overshoot to less than 0.5% during the flat-top phase. The low leakage inductance and distributed capacitance are often limiting factors to obtain a fast rise time. These parameters are largely controlled by the physical geometry and winding configuration of the transformer. A rise time can be improved by reducing the number of turns, but it produces larger pulse droop and requires a larger core size. By tradeoffs among these parameters, the high-voltage pulse transformer with a pulse width of 10 ${\mu}s$, a rise time of 0.84 ${\mu}s$, and a pulse droop of 2.9% has been designed and fabricated to drive a klystron which has an output voltage of 284 kV, 30-MW peak and 60-kW average RF output power. This paper describes design optimization of a high-voltage pulse transformer for high-power pulsed applications. The experimental results were analyzed and compared with the design. The design and optimal tuning parameter of the system was identified using the model simulation.