# How to Create a DC Source SPICE Model

How to Create a DC Source SPICE Model

Modeling designs helps engineers verify whether their circuit will function as intended. Modeling programs simulate circuit behavior under different conditions and in accordance with the design requirements, allowing engineers to better plan and build circuits.

Every SPICE simulation needs to have a source or input signal. To analyze how the circuit will behave in real life, this input must be modeled accurately. If not modeled accurately, functionality issues can go undetected until far later in the design process, wasting time and money. To efficiently and accurately model a source, the intended input signal must be interpreted by identifying the type and signal values for replication.

What is a DC Source

A DC source is a constant level of voltage or current. If the analog portion of the circuit requires DC power, then a DC source must be included in the design and simulation. A DC power supply can be constructed as an ideal DC or non-ideal DC source which contains an internal resistance.

What is needed to Model a DC Source

To create the required DC source for simulation, there are three items that must be defined:

● Type

○ Which type of signal will be the input for the circuit: voltage or current?

● Ideal vs. Non-Ideal

○ Does the source contain an internal resistance?

● Data Points

○ What is the required voltage or current level?

This information must be incorporated into the SPICE simulation model which can be achieved by manually creating or editing a text file. Keep in mind if the source signal created is not the intended outcome, values will need to be edited manually. This manual process to produce the desired source signal is time consuming and increases the likelihood of errors; however, the PSpice Modeling App provides a fast, easily-configurable, and fully-integrated method to create DC sources for simulation.

PSpice Modeling App

The DC source modeling application quickly creates various DC source models with a wizard-based approach. The necessary source specifications are pre-defined and users can easily input desired parameters required for all DC sources such as:

● Type: Select either a Voltage or Current

● Ideal vs. Non-Ideal Easily select from an ideal or non-ideal DC source. The PSpice Modeling Application automatically defines the required parameters based on the source type.

● DC Value: Define the constant level of voltage or current required for the simulation.

● Source Resistance: Easily incorporate an internal resistance to create a non-ideal DC source and a more realistic simulation.

Using the inputted information above, the PSpice Modeling App generates a schematic symbol and automatically associates the newly created DC source SPICE model without leaving the OrCAD Capture environment. The PSpice Modeling App also automatically manages the simulation profile configuration, eliminating any library set up for simulation. To try this yourself, be sure to download the Free Trial of OrCAD and check back for more SPICE model how-tos in this series.

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