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In an emitter follower Vbe should be around 0.7 volts. Instead the simulation shows 2.7 volts.

Thanks for any comment or help.

Hi @lsears, interesting problem!

The TIP31 model that CircuitLab is using has a series $R_B = 172.309 \ \Omega$. The roughly 10mA into the base, when multiplied by this base resistance, is causing an extra 1.7 V drop as you're seeing.

This $R_B$ value is quite large (and perhaps erroneous). Can you check your other simulation package models to see what value they're using for that parameter?

If you double-click on Q1 and change R_B to 0 you'll probably find a result closer to what you're expecting.

Hi @lsears, I've investigated further and found that our TIP31 parameters were a bit off. I've fixed these now, and made a circuit here:

to allow me to match Figure 7 (Base-emitter on voltage) of the datasheet https://www.st.com/resource/en/datasheet/tip31c.pdf

The TIP31 model within CircuitLab has been updated, but this only applies to new insertions. To apply it to your circuit, you'll need to delete Q1 and re-add it.

Thanks for reporting this. Glad we were able to get it corrected.

Thank you so much for your prompt and helpful reply. The updated model for the TIP31 does, indeed, provide an answer that is much more reasonable. To answer your earlier question, running the circuit in LTSpice using a very similar part gives a value of 0.802 mV and PartSim gives a similar answer. Thanks again!