In a recent conversation with Gary N3GO he suggested that I might benefit and gain further insights into electronic circuit characteristics through the use of the well known circuit simulator LTspice. Indeed Gary was correct. Thank you!

EMRFD Chapter 2.2 is a study in Amplifier Basics. The schematic below is the EMRFD study example of a single transistor audio amplifier.

I performed the 'manual' calculations using the classic common emitter simplified model with the aid of a spreadsheet. The results are shown in the value(rms) column. I then converted the small signal voltages and currents into pk-pk values as shown in the value (pk-pk) column so that I could compare them with the LTspice DC operating point simulator and the AC linear analysis simulator results.

The LTspice simulation uses a 2N2222 transistor while the manual calculations assume a generic transistor with a beta value of 100 and a base-emitter voltage drop of 0.6V. The manual calculations also use the diode equation derived formula to re=26/Ie.

Comparing the results are interesting. Some observations as follows:

- The emitter bias voltages show a difference of 90mV. Why?
- The base bias currents show a difference of 10uA. Almost double in the manual calculation.
- The small signal analysis shows reasonable correlation between the two models although there is some difference between the collector voltage calculation.

As a next step I plan to build and measure a similar circuit on the bench.

It will be very interesting to compare those results.

Good work Dick -- base current will vary with beta -- SPICE ran a higher beta than you

ReplyDeleteNoted Vasily. Yes I tried varying the beta but then other measurements then do not correlate. So there are a number of variances between the models beyond beta of course.

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