Electrical FE /EIT Exam Prep - Electronics 5: BJT Transconductance

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[@chriskiesler5892]

Thanks for making these videos, I am very rusty on semiconductors. What is meant by "Icq = dc collector current at the Qpoint"? I can't remember what the Qpoint is..

[@EngineeringEducation]

@Chris Kiesler : The "Q-point" is also known as the "operating" point or the "bias" point of the BJT. When performing small-signal analysis on a BJT, we first solve the circuit in DC (open circuit all capacitors and solve for all DC currents/voltages). Using those DC values, we then apply a small-signal model (usually the hybrid-pi model) to solve the circuit in AC. We do this because all small-signal parameters (gm, re, ro, r_pi) depend on the DC parameters (I_C, I_B, I_E, V_CE). The Q-point current is the collector current found in the DC analysis. It is the output current when no AC input signal is applied. Here is a helpful video: kzbin.info/www/bejne/j5OrlqOAnrlripo

[@natemac8473]

When it comes to semiconductors, you can call me rusty trombone

[@cryora]

It's a deep subject rooted in solid state physics, with literature dating as far back as the 19th century. A good read is the chapter on Semiconductors in Ashcroft and Mermin.