PSpice models

We must now define the model for the diode. Click the LEFT mouse button on the diode graphic, —W—. The graphic should turn pink, indicating that it has been selected. Next, select Edit and then PSpice Model from the Capture menus ... 

The right screen is the PSpice model editor and it tells us that the model we create will be saved in a file named SECTION 3CJib. The model for the part we selected is displayed by the model editor in this case the model name is Dbreak. In this model, Rs is the series resistance of the diode and Qo is the junction capacitance. The only parameter that we will change for this example is the saturation current /S. Note in the screen capture above that the default value of /s is lxlO"14 amps. We can use the model editor to create a new model. Change the name of the model to DX and change ls to le-15 ... 

If the menu selection PSpice Model appears grayed out in the menu (PSpice Model), you will not be able to... 

The conversion between the two sets of equations is shown in Table 4-1. The PSpice model parameter names are close to the standard names used to represent MOSFET operation in many textbooks. One difference is that the PSpice model parameter Kp is twice the value of K. Thus, in our model we should set KP= 40 pA/V2. All other model parameters will be the same. 

In this part we will demonstrate how to modify existing PSpice models and how to create new models. We will assume that the user is familiar with PSpice models and knows how he or she would like to modify the models. A discussion of the various models requires too much detail to be given here. The user is referred to the PSpice Reference Manual available from Oread Corporation for model details. This manual is contained on the CD-ROM that accompanies this text. You will probably need to review the many references that Oread gives to understand the model parameters. Here, we will show how to make changes to existing models or create simple new models. Section 7.E contains simplified models for some of the commonly used parts. The model parameters given are for firsttime users. For more accurate models, you will need to refer to more detailed texts covering SPICE models. If you are more familiar with the models, you can use these procedures to modify all parameters in a model. 

DbreakZ Zener diode model. The PSpice models used to create a diode and a Zener diode are the same. The only difference is in the graphic symbols of the parts. 

If you have a PSpice library with models you would like to use, an easy way to use them is to change the model reference of a graphic symbol to use the name of the model in your library. In this section, we show how to change the model reference of a graphic symbol. We assume that you know the name of the PSpice model that you would like to use. 

This property is sometimes displayed on the schematic instead of the PSpice model name. 

There are two properties that display the name of the model, the Value property and the Implementation property. The Value property is not used by PSpice, but this property is sometimes displayed on the schematic instead of the PSpice model name. The Implementation property is the name of the PSpice model and it is the property used when creating the netlist. If you change the Value property to the name of your new model, nothing will change in the simulation. If you change the Implementation property to the name of your new model, the new model will be used. Always change the Implementation property. 

The PSpice model name (Implementation property) is displayed on the screen with breakout parts. When the model is changed, the changed model name appears on the schematic. This is because Capture assumes that you wish to change the breakout model to a different model, and that you wish to identify that model on the screen. Capture assumes that when you place a breakout part, you will change it. If you know you will be changing the model reference of a part, you should use the breakout parts. 

We will change the PSpice model of D3 back to Dbreak using a different method. Since, for breakout parts, the text shown on the screen is the PSpice model, we can double-click on the text to change the model. Double-click on the text D1H4734A for D3 ... 

The dialog box shows that we are changing the Implementation property, which is the PSpice model. Change the value to Dbreak and then click the OK button ... 

SQLUTIDI1 Select the graphic and then select Edit and PSpice Model to edit the resistor model R5patt ... 

We see that the file non Jib contains no PSpice models. Instead, all this file does is reference other libraries. Since non Jib is available to all projects, the libraries listed in HOnJIb are also available to all projects. Thus, libraries bteaHOUtJIb, evalJIb, and Class Jib are available to all projects. Close the Notepad when you are done. 

Many semiconductor manufacturers have data sheets and PSpice models available online for easy access by engineers. In this section we will show how to obtain those models so that we can use them in a simulation. The types of models we will show can be split into two types. The first type of models are primitives that use only a. model statement. Examples of these are diodes, bipolar junction transistors (BJT), and MOSFETs. The second type of models we will download are subcircuit models such as op-amps, IGBT s, Darlington transistors, and MOSFET subcircuit models. 

With the Dbreak part selected, select Edit and then PSpice Model from the Capture menus ... 

The parts contained in the Digikey database and the parts you can download from Activeparts do not have PSpice models, although this feature may be added in the future. Thus, the projects we create can only be used for documentation purposes or for PC board layouts. No simulations can be performed on a circuit we create from these parts. Here, we will only show how to add these parts and create bills of materials. 

The parts available in the database and the parts that can be downloaded from the Activeparts web site do not contain PSpice models, so we cannot use these parts to run a simulation. When you create a project, you should select either the Schematic or PC Board Wizard option. Run Capture CIS and then select File, New, and then Project to create a new project ... 

PSpice has a model for LM324, but the the UA741 op-amp model was used in its place. The operation amplifier does not play a critical role in this circuit because of its slow response. The limiting parameter of the delay time is the RC time constant and not the slew rate or drive capability of the operational amplifier. The PSpice model response to a step input is shown in Fig. 3.27, and the AC results are shown in Fig. 3.28. 

Figure 4.84 PSpice model of a two phase voltage-mode flyback converter.

In PSpice both a 7414 and a CD4093 were used. The 7414 is the digital model for the Schmitt trigger inverter. To use the digital device for an analog measurement, E sources (voltage-controlled voltage sources) were used as buffers. The schematic used for the PSpice model is shown in Fig. 8.59. The results are displayed in Fig. 8.60. 

In Fig. 10.19, the traces, from top to bottom, are Ron Kielkowski s model, the Micro-Cap model, the IsSpice model, the measured data from a 1N4002 from the quadrupler circuit, and the PSpice model. The measured data is the dotted line. All of the diode data is similar. The differences from the breadboard diode, as explained above, are largely due to manufacturing tolerances, different manufacturers, and lot-to-lot variations. Ron Kielkowski s model was taken from the data for an actual 1N4002 diode as well. Figure 10.19 is a good example of how differences in models do not indicate their correctness. It is easy to construct a SPICE-compatible diode model that will exactly trace the curve of the breadboard 1N4002 however it would still be valid only for the exact breadboard modeled with that diode. 

Hageman SC (1993) Simple PSpice models let you simulate common battery t3q>es. Electronic Design News 38 117-129... 

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