Creating a symbol for a part In my PSpice books, there are a few symbols that did not come with the evaluation

version (and indeed the full version too), and had to be created. Also, in a final year

project (what prompted the production of this document), there will be occasions

when your design uses a component not in existing libraries. The following procedure

is a little bit tedious but well worth the effort in the end. We need to download the

model, LM386.LIB, and the default symbol, LM386.OLB. I found the two LM386

power amplifier files at the site shown in Figure 1.

Figure 1: Download the models

Save these files into a directory of your choice, and then open the .OLB file as shown

in Figure 2.

Figure 2: Go to the directory where you saved the symbol and model information

To display the downloaded default symbol-a rectangle with pins, select the symbol

name from the Design Resources as in Figure 3.

1

Figure 3: Double left click as shown

We should make the grid visible as it helps in constructing a new symbol. This is

done from the Options/Preferences/Grid Display, shown in Figure 4. In the Part

and Symbol Grid on the right hand side, set Pointer snap to grid to off.

Figure 4: Setting the grid parameters

The default symbol should appear as in Figure 5.

Figure 5: Default symbol

Remove the names on the inside of the symbol by selecting Options/Part Properties,

as shown in Figure 6.

2

Figure 6: Remove the pin names-Options/Part Preferences

The pin names inside the box are made invisible by setting the Pin Names Visible to

False as shown in Figure 7.

Figure 7: Set Pin Names Visible to False

Next, remove the boundary box as shown in Figure 8 to leave a dotted outline.

Figure 8: Make a triangle

We can make the outline rectangle into a triangle for the power amplifier using the

line tool from the right toolbar, but first move the outline box into a 6 x 6 grid by

grabbing the dotted rectangular corners. Select a pin and move it to the desired

location (use the downloaded IC data sheet-LM386.PDF as a guide). Select pin 6, and

change the Pin Properties as shown in Figure 9. In this case, pin 6 is a power pin (get

the pin information from the model, i.e. LM386.lib). You may also shorten the pin

length from the Shape: box.

3

Figure 9: Changing pin parameters

Use the Place line tool from the right hand toolbar to connect the pin to the triangle

(make sure the snap to grid is off-see Figure 4).

Figure 10: Draw the fill in line using the Line tool

Note: Do not change the pin names. These names have to be the same pin names as in

the model. You may rotate pin numbers using the keyboard, R. Use Notepad to look

at the model LM386.lib. Using the text tool, add the negative (-) and positive symbols

(+) to the inputs. The final symbol can be incorporated into the schematic shown in

Figure 11.

+

-U1

LM386

12

34

5

7

8

6

Rload8

R210

V1 15Vdc

C1

220uF

C210u

0

Vin

FREQ = 1kHzVAMPL = 20mVVOFF = 0

C3 10uF

C40.05u

0

I

W

V

Figure 11: Final circuit

4

Time

0s 1ms 2ms 3ms 4ms 5ms 6ms 7ms 8ms 9ms 10msV(C1:2)

-5.0V

0V

5.0VW(R1)

0W

2.0W

4.0W

SEL>>

Output Power in Watts

I(R1)-1.0A

0A

1.0A

Figure 12: Output waveforms

You may wish to use a model for a speaker instead of the 8 resistance. In that case, use the schematic in Figure 13.

Importing a .LIB file for an existing symbol There are many symbols that have no model attached to them (right click, and if Edit

PSpice Model is greyed out, then no model is attached). To download the model and

symbol libraries, select the following Texas Instruments site and search for THS4131 http://focus.ti.com/docs/prod/folders/print/ths4131.html There is a zipped file containing the 4131.lib, the model file, and ths4131.olb, the

symbol file at this location,. To add the downloaded symbol file in PSpice, start a new

project by selecting NEW/ Library, as shown in Figure 1.

Figure 13: Opening a library

Double left click on the selected THS4131.olb as shown highlighted in Figure 14

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Figure 14: The symbol library

In this case, the proper symbol is supplied so there is no need to carry out the

procedure outlined in the first section. To add the model library, THS4131.lib, select

the Edit Simulation Settings icon and then select Configuration Files as shown in

Figure 15. Press the Browse icon and locate the downloaded files. Then Add as

Global, if you wish this symbol to be available for all schematics, or Add as Local,

for the schematic under investigation.

Figure 15

Create the following schematic in Figure 16.

6

-+Vocm

U2

THS4131

8

1

36

4

52

R1

44k2

R2

44k2

R3

44k2

R4

44k2

C1360pF

C2

360pF

V15Vdc

V25Vdc 0

neg

pos

V31Vac0Vdc 0

pos

neg

Figure 16

Carry out an AC analysis to observe the frequency response.

Frequency

1.0Hz 10Hz 100Hz 1.0KHz 10KHz 100KHz 1.0MHzDB(V(OUT2)-V(OUT1))

-50

-40

-30

-20

-10

0

Figure 17

Note the differential output is plotted as DB(V(OUT2)-V(OUT1), using the dB()

operator.

Importing a .LIB file The file contains the model information and can also be named .MOD, or .CIR, as

well. Open the library as shown in Figure 18.

7

Figure 18:

Select the PSpice Model Editor from the main Windows menu. Using the Model

Import Wizard, is the easiest way of importing a library.

Figure 19: The Model Import Wizard

Figure 20

8

Figure 21: The .lib contents

9

Creating a symbol for a partImporting a .LIB file for an existing symbolImporting a .LIB file