Abstract-Recently, we proposed a new high frequency transformer that could allow the manufacture of small power supplies. In this paper, we propose a thin film transformer for small electronic devices, and apply the integral equation method to analyze this transformer. Both the primary and secondary coils of the film transformer are arranged coaxially on one layer and multiply laminated. The operation principal of the transformer is based on the skin effect and the mutual effect between the coils at high frequency. Because of the coaxially arranged coils, the magnetic field of the transformer can be modeled with an axisymmetric assumption. Using the model, we evaluate the electromagnetic field and calculate the lumped circuit parameters, i.e., inductance and resistance, which are compared with experimental values. A fairly good agreement is obtained. Thus, the applied method is quite useful for design and investigation of the thin film transformer.

Previously, we have proposed a thin film transformer. The operating principle of this transformer is based on the skin effect. Thereby, its weight and size are extremely small but its operating frequency having high efficiency is limited only to high frequency region. In order to remove this fault, we employ the thin ferrite tiles which have been sandwiched between the film conductors. As a result, we succeeded in widening the operating frequency range about 100 times compared with those of original one. I .INTRODUCTIONIn order to develop a small size and light weight high frequency transformer for DC to DC converter use, we have previously proposed a coreless transformer utilizing the skin effect of the adjacent current carrying conductors [l]. 15W output power was obtained by the coreless transformer having only 7g weight [2]. Satisfactory result of the coreless transformer spurred to exploit a film transformer, which was fabricated by the photo etching technique. When we installed our film transformer to a push-pull type DC to DC converter, l l w output power was obtained with 72% overall efficiency [3]. This record is fairly good comparing with those of the other similar type of converters [4,5]. However, we have found that magnetizing inductance of the film transformer is too small to use the DC to DC converters instead of the conventional core type transformers. In the other words, the coreless film transformer is light and small so that it is possible to realize a light weight DC to DC power supply. However, it is difficult to replace the conventional core type transformers because of the film transformer's peak frequency characteristics, i.e., useful operating frequency range of the film transformer is extremely narrow for practical use.In the present paper, it is revealed that the f i l m transformer sandwiched by the ferrite tiles yields about 70 times larger self inductance and gives about 100 times wider usefbl operating frequency range comparing with those of the original coreless film transformer. Thus, we have succeeded in improving the characteristics of film transformer by means of a simple sandwich structure. II .EXPERIMENTAL A. Basic principle and structureFigure l(a) shows a typical core type conventional transformer which utilizes the magnetic flux linking the conductors wound around the magnetic core. The proposal coreless transformer utilizes the magnetic flux enclosing the current carrying conductors as shown in Fig. 1 (b) [ 1,2]. Because of this, the internal inductances of the primary and secondary coils should be small in order to obtain higher coupling. This can be accomplished by the skin effect at high frequency. Thus, the coreless transformer should be operated only in the higher frequency range. To utilize the same operating principle in a flat surface, the primal and secondary conductors are arranged alternatively on a film base surface. Figure 2(a) shows a coaxial circular shape film transformer. The connection of the coils are shown in Fig. 2(b). Further details of the film tra...

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A pulsed power supply has been developed for exciting a copper vapor laser with a bore diameter of 80 mm and a discharge length of 2890 mm. The pulsed power supply has two thyratrons, an LC-inversion circuit and a two-staged magnetic pulse compression circuit. An efficiency of 82% has been obtained which is defined as the ratio of energy stored in the storage capacitor to the output energy of the magnetic pulse compression circuit, with a voltage greater than 40 kV, averaged output power of 24 kW, and voltage rise time of 70 ns. The pulsed power supply was successfully operated for more than 2000 h and an optical output power of 272 W was obtained.