Micro-Cap v7.1.6 / RM

from these values. The B field (in Gauss) and the H field (in Oersteds) are available as output variables in transient analysis.

To place a single core in a circuit, use this procedure:

1. Place an inductor in the circuit with these attributes: PART L1

VALUE 1

The value 1 represents the number of turns.

2. Place a K device in the circuit with these attributes:

Step 2 changes the inductor L1 from a standard linear model to a nonlinear core whose properties are controlled by the model statement. See the circuit file CORE for an example of a single core device and how to do BH loop plots.

To place two magnetically coupled cores in a circuit, use this procedure:

1. Place the first inductor in the circuit with these attributes:

This procedure creates two coupled cores whose magnetic properties are controlled by the KCORE model statement. See the sample circuit file CORE3 for an example of multiple, coupled core devices.

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Doing it manually requires this procedure:

1.Many data sheets provide the value of Bsat in Gauss. To calculate the required value of MS in units of Amps/meter, multiply the Bsat value in Gauss by 79.577. This yields the required model value for MS in Amps/meter.

2.Run the sample circuit CORE.CIR and adjust the values of A, K, C, and Alpha, to fit the data sheet BH curve. The effect of increasing each parameter is as follows:

where µ is the slope or permeability, HC is the coercive force value, and BR is the remanence.

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Laplace sources are characterized by a linear transfer function. The two basic types are distinguished by the way the transfer function is calculated. The Formula type uses an algebraic expression to describe the transfer function in terms of the complex frequency variable, S. The Table type uses a table of ordered data triplets which describe the transfer function. Each data triplet comprises the frequency, magnitude, and phase of the transfer function.

In AC analysis, the value of the transfer function is computed from the algebraic expression involving S, where S = 2•π •frequency•j, or obtained by interpolation from the given table.

For DC analysis, the value of the transfer function is computed from the given algebraic expression involving S, where S = 0, or obtained from the table, using the lowest frequency data point supplied.

For transient analysis, it is necessary to first determine the impulse response of the function. The impulse response is obtained by performing an inverse Fourier transform on the transfer function. Then, during the transient run, the output of the source is obtained from the convolution of the waveform at the source input nodes and the impulse response waveform. This allows the source to accurately respond to any input waveform, not just simple, predefined waveforms.

The accuracy of this procedure is limited by the number of time points in the impulse response, or alternatively, by the bandwidth of the function. As a practical matter, no more than 8192 time points should be computed for the impulse response, due to memory and time limitations. The actual number of time points, N, is a logarithmic function of the value of RELTOL.

N = 26 –log10 (RELTOL)

For example, for RELTOL= .001, 512 time points are computed.

As a general rule, Laplace sources will give the best transient analysis results on narrow band functions. Wide band functions, such as the differentiator, f(s)=s, and the integrator, f(s)=1/s, are best modeled by using discrete components. See the sample circuits INT (integrator macro) and DIF(differentiator macro).

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5.The function is logarithmically interpolated for frequencies values between the table values.

6.The table should contain one data point at DC or zero frequency.

The table may be entered directly as the parameter string or indirectly using the

.define statement. For illustration, see the circuit P1.

The input variable and output variables and definition names are as follows:

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To use a macro:

Select the macro from the Component library. Place it in the circuit that will use it and edit its parameters, if it has any. You can also use an alias which, using a .macro statement, substitutes a short name like 2N5168 for the macro FILE name and a corresponding set of parameters.

The format of the macro command is:

.MACRO <alias> <macro circuit name(parameter list)>

This statement lets you store the parameters that turn a general macro for, say an SCR, into a specific model for a specific part like the 2N5168 SCR, and to access the part with a simple meaningful name, like 2N5168. For more information on the

.MACRO statement see Chapter 20, "Command Statements".

When a macro is placed in a circuit, the program reads the macro circuit file, determines if it has parameters from the .PARAMETERS statement in the macro circuit file and shows these parameters and their default values in the Attribute dialog box. Edit the parameter values from their default values to the those you want.

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