Poor Man's Electronics Web Page

One Transistor Audio Amp

Exploring transistor design:

If you haven't installed the interpreter software yet, go back to the main page and do so. Unzip all the files to a directory of your choice on your hard drive.

Run the FLIP.EXE program (double click on its icon). When the program comes up and gives you the little triangle prompt, enter LOAD QA1AMP and press enter. Follow the instructions on the screen.

Amp screen shot

The upper part of the screen shows a schematic of a class A bipolar transistor NPN audio amplifier with simple biasing. What does all that mean? The lower part of the screen is where you will supply the parameters of the design so that the program can compute performance. Here are the questions and answers (the answers shown in bold) for this project: The transistor data is taken from a spec sheet of the 2N2222A that you can download from Data Sheets.

Below is a portion of the spec sheet for the small signal characteristics. Outlined in yellow are the parameters needed for the program. These values have a range because of the variations in manufacturing the device, so I have put the average value next to them. You'll need to do the same for your designs. Of course, you can run the program several times using combinations within the range of parameter values to see how your design will hold up under the wide tolerances that exist in transistors.

2N2222A Spec
small signal characteristics

The program computes the following output using the values in bold above:
Ibe (DC bias base current), uA =     3.773
Ice (DC collector current), mA =     0.660
Vbe (DC base voltage) =              0.700
Vce (DC collector voltage) =         6.821
Rin (Input resistance), K ohms =     1668.
Rout (Output resistance), K ohms =    3.10
Overall voltage gain =               115.5
Low frequency 3db roll-off, hertz =  821.3
The output is also sent to a file called OUTPUT.ASC in the same directory as the FLIP interpreter. You must open it with WordPad or DOS Edit; it will look funny if opened with Notepad or Microsoft Word.

Run the program with different values of the parameters. (At the triangle prompt, type REPARSE to re-execute it or just type LOAD QA1AMP which will load and run it all over again.) Try designs using other transistors; download their spec sheet from the link above. For instance, try the 2N3904 transistor, another popular transistor for experimenters.

I've added another FLIP program called QCURVES which is in the download package. Run it for an analysis of a Class A amplifier using a 2N3904 NPN transistor with a slightly different approach.

Copyright © 2007 - Prof. W.S. Walker, West Virginia State University - All Rights Reserved.
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