PSpice Application Notes

APPLICATION NOTE 2 To specify the parameters, double-click on a coupling symbol (on the K-in-a-box, not the attributes), and enter the reference designators for the coupled inductor as the values for Li (i=1,2,...,5). Set the value of the COUPLING attribute to the value of the coupling factor, K. In this circuit, the COUPLING value is set as 1. The circuit describes the relationship between inductance, voltage, and current, that is V=L(di/dt) The curves in Figure 2 shows that as di/dt changes, the voltage changes. Figure 2: Inductor voltage and current To Use the Kbreak and K_Linear Symbols Besides the core library, magnetic.olb, you can also use the inductor coupling parts, Kbreak and K_linear, to represent transformer cores. The K_linear part from the analog.olb library, is used to represent a linear or an air core. When using K_linear part, you specify the coupling coffecient and the reference designator values of the tranformer windings (inductors) to be coupled. With K_linear cores, the inductances values of the tranformer windings must be specified in Henry (H). The Kbreak part from the breakout.olb library, is a generic symbol that can be used represent nonlinear cores. Kbreak has a pre-assigned model attribute, but its corresponding model in the breakout.lib library will not have a pre defined model parameters and it will simulate a core with default simulator model parameters. In this section, we will cover three example circuits that will help in understanding the usage of Kbreak and K_Linear symbols. These are the following: Simple two winding Transformer How to model a Transformer with different dot convention Centre-tapped Full Wave Rectifier Transformer Example 1: Simple two winding Transformer Top-right circuit in Figure 1, represents a simple sine wave step-up transformer with step up ratio of 2. This step up ratio is define by (Ls/Lp) 1/2 , where Ls is inductance of secondary coil and Lp is inductance of primary coil. In this case step up ratio is (L2/L1) 1/2 , which is (4m/1m) 1/2 =2. Therefore, in figure 3, voltage of the secondary coil is 2 times of the voltage of the primary winding.

• Cover