April/May 2023
www.us-tech.com Powerful Filter Simulation with SPICE
Continued from page 60 The Choke Figure 1 shows the equivalent circuit of
an inductor, the basic element of a choke, which is identified by the international abbreviation L. In addition to the nominal inductance (L), two other elements are added in parallel to better characterize it: the stray capacitance of the winding (marked C) and a resistance contribution (R) proportional to the core losses. By adding new parameters, it is possible
to take into account parasitic effects associat- ed with the choke. This allows fine tuning of the simulated impedance curve and improves its match with the
evaluating the performance of a choke before even testing a sample. Access to the SCHURTER choke SPICE library helps them to make the best choice for their own development. SCHURTER chokes are devel- oped to offer chokes for a wide range of end- use applications in various electrical fields: from frequency converters to charging sta- tions and switching power supplies (SMPS). This, combined with the widely used SPICE software, makes SCHURTER SPICE models a versatile and useful tool for development purposes.
Figure 2 (next page) is a simplified rep-
resentation of a buck converter simulated with LTSpice at an input voltage of 10V con- taining an artificial mains network (LISN) and a MOS transistor.
The components are modeled taking into account real parasitic effects, which lead to noise contributions superimposed on the expected signals. In particular, the input voltage is affected by some noise, as can be seen when examining the node.
In the given example, the customer may choose to install a choke between the LISN and the switching power supply to reduce the
Continued on next page
Page 65
Figure 1: Equivalent circuit diagram of the first approximation of an inductance.
measured impedance curve. In the case of a single-phase choke (e.g. DKIH-1, DKIV-1), the com- plete model consists of two equal inductance models, one for each winding of the choke. In the case of a three-phase choke (e.g. DKIH-3), the three windings are modeled with three equal imped- ance models. Models for all cur- rent ratings have been modeled (ferrite core version), and these are now available on the SCHURTER website upon request.
The impedance curves for all chokes of the DKIH-1, DKIV-1 and DKIH-3 families were meas- ured with a vector network ana- lyzer. The measurements were performed in the frequency range from 10 kHz to 10 MHz, with input and output impedances of 50. The parameter values used in the simulation model were previously extrapolated by direct measurements and subsequently modified to improve the results, i.e., the matching between simu- lated and measured impedance curves was increased.
In particular, L is propor- tional to the impedance slope at low frequency, i.e., before reso- nance, while C and R are propor- tional to the resonant frequency and the impedance magnitude at the resonant frequency, respec- tively.
Using the models
During the design phase of an electronic device, the cus- tomer is usually interested in
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