Category | Varistors

3% import tax for power electronics modules to China

Posted on 07 January 2020

  Based on a recent publication (in Chinese) released on the 16th of December 2013, it seems that the Chinese government has introduced to its tariff policies a 3% customs duty for importing power electronics modules into China. There is a general tariff of 10% applied, e.g. on drivers, and a temporary, or provisional, tariff [...]

Calculation Example: Ensuring EMC of Equipment Connected to 230V Lines

Posted on 17 July 2020

              The following calculation example describes the selection procedure for a varistor in order to ensure that the electromagnetic compatibility (EMC) of a device is met in accordance with IEC 62020-4-5  for 230 V operating voltage and a test voltage of 4 kV. Figure 1. EMC test in accordance [...]

Protection of Automotive Electrical Systems Using Varistors

Posted on 13 July 2020

              Requirements for Automotive Electrical Systems Electronic equipment must work reliably in its electromagnetic environment without, in turn, unduly influencing this environment. This requirement, known as electromagnetic compatibility (EMC), is especially important in automotive electrical systems, where energy of mJ levels is sufficient to disturb or destroy devices that [...]

Preventing Overvoltages with Varistors

Posted on 12 July 2020

              Industrial and commercial systems, as well as building, automation, and household appliances, are often destroyed by overvoltages, necessitating their repair or replacement. To avoid this damage, variable resistors, known as varistors, are incorporated into the electrical network or circuit. Varistors are voltage dependent resistors whose resistance decreases with [...]

Introduction to Metal Oxide Varistors

Posted on 05 June 2020

                Despite its many benefits, semiconductor technology also has a few drawbacks, one of which is the vulnerability of solid state devices to overvoltages. Even voltage pulses of very low energy can produce interference and damage, sometimes with severe consequences. Optimum overvoltage or transient suppression is a crucial [...]

Varistor Operation - Derating, Temperature, Overload

Posted on 29 May 2020

              Below is a description of several factors that limit the operational life of a varistor. Derating Derating is the intentional reduction of maximum ratings in the application of a device. With metal oxide varistors, derating is of particular interest under the following conditions: Derating for repetitive surge current [...]

Design Notes - Varistors

Posted on 17 May 2020

              Below are several important design considerations regarding the use of varistors in power electronics applications. Physical protection - fuses Due to the unpredictable nature of transients a varistor may be overloaded although it was carefully selected to begin with. An Overload may result in package rupture and expulsion [...]

Terms and Descriptions - Varistors

Posted on 10 May 2020

              Below is a guide to terms commonly found in product tables and data sheets for varistors. Varistor operating voltage Product tables generally specify maximum AC and DC operating voltages. These figures should only be exceeded by transients. Automotive types, however, are rated to withstand excessive voltage (jump start) [...]

V-I Characteristics - Varistors

Posted on 04 May 2020

              Varistor V-I characteristic forms of representation When selecting metal oxide varistors for specific applications, it is often convenient to use a mathematical representation of the V-I characteristics of the varistors being considered. Generally, a suitable approximation to the V-I behavior of a varistor can be accomplished by use [...]

PSpice Simulation Model

Posted on 19 April 2020

  Varistor model The development of a varistor model for the “PSpice Design Center” circuit simulation program allows varistors to be integrated into computer assisted development of modern electronic circuitry. In the PSpice modeling concept, a varistor is represented by its V/I characteristic curve, a parallel capacitance, and a series inductance. The structure of this [...]