Analysis of noise absorption characteristics of ceramic chip varistor according to the equivalent circuit model.

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Recently, various motors are being controlled by a computer. Therefore, a countermeasure toward surge noise which occurs in the motor and the high frequency noise is important to prevent faulty operation of the machine and destruction. Varistor has a lot of advantages in comparison with zener diode, such as the symmetry of electric polarity in the voltage-current curve, the large electrostatic capacity and the high responsibility. Therefore, it is used as a protective component against not only the static electricity but also the surge noise for the portable telephone, video camera, CD-ROM, DVD-ROM and DC motor. Especially, ZnO varistor is available for the noise absorption, since it has a large non-linear coefficient between applied voltage and current at the region of a large current. However, the noise absorption characteristics have been hardly investigated.In this study, simulations were made to analyze it and to present the data for designing a ceramic varistor using the determin … More ed equivalent circuit of ceramic varistor. The equivalent circuit was determined as follows. In the variable resistor, the non-linearity of the voltage-current is being brought about by depletion layer in grain boundary layer, and comparatively small resistance value is shown in the grain. Therefore, the equivalent circuit of grain boundary was shown in parallel connection of resistance and condenser, and the equivalent circuit in the grain was shown at small resistance. In actual varistor, the ceramic crystal has been connected with braided. In this study, the equivalent circuit which showed in above-mentioned grain boundary and in the grain were connected braided.The decision procedure of the value of the resistance and the condenser which constitute equivalent circuit is shown in the following. At the first, values which is appropriate for the resistance and condenser were let in, and dielectric characteristic and voltage-current characteristic were calculated by the circuit simulator(PSpice). The values of resistance and condenser were decided so that the calculated dielectric characteristic and voltage-current characteristic were agree with experimental one. Less