抄録
According to increase a use of DC motor for various electronic instruments together with a large-scale integrated (LSI) circuit, measures against a high frequency noise and a surge voltage have been very important to protect semiconductor device from miss operation and destruction. Ceramic varistor has a large electrostatic capacity and a large non-linear coefficient between applied voltage and current at the region of a large current. Therefore, it is often used to prevent these noise and surge. However, the large electrostatic capacity often causes a series resonance together with a inductance and a resistance of a motor. It is necessary to design a ceramic varistor suitably with considering characteristics of a motor.
In the present paper, the authors replaced a ceramic varistor with a simple equivalent circuit from the experimental results for frequency characteristics of capacity and dissipation factor and DC characteristics. After then analyse a noise reduction mechanism of ceramic varistor by using simulation program with integrated circuit emphasis (SPICE). In this method, it is easy to measure current which is conducted in a each part of ceramic varistor and motor. It is expected for the present method to design a ceramic varistor theoretically.
