I just started learning about electronics and decided to quickly sketch a circuit. When it comes to OP and changing the said circuit into an Ac equivalent, I got stuck. Sorry in advance if this is considered a basic question.

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  • 1
    \$\begingroup\$ Where did you get stuck? What have you tried so far? \$\endgroup\$
    – John D
    Sep 2, 2020 at 17:03
  • \$\begingroup\$ Can you put any voltages on to any nodes? \$\endgroup\$
    – Andy aka
    Sep 2, 2020 at 17:04
  • \$\begingroup\$ This diagram is all i have to work with \$\endgroup\$ Sep 2, 2020 at 17:06
  • \$\begingroup\$ Right at the beginning. I am not really sure what to do since the source i was learning from is poorly done. \$\endgroup\$ Sep 2, 2020 at 17:08
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    \$\begingroup\$ Sorry, but we have seen this circuit or at least a transistor biased with 4 resistors so many times in questions from people who seem to try nothing by themselves that probably you will not get a full tutorial written specifically for you. You can think to start to begin to consider if you possibly could try to work the case by yourself for example by applying this electronics-tutorials.ws/amplifier/amp_2.html or some other of the numerous tutorials in the web. \$\endgroup\$
    – user136077
    Sep 3, 2020 at 8:34

1 Answer 1


For the DC analysis, remove all capacitors (they act as open-circuit devices at DC) and calculate the DC emitter current (Ie), with which you calculate r_e=vt/Ie.

For the AC analysis, short all capacitors (if you're thinking of ideal analysis for very large frequencies), calculate r_pi by r_pi=r_e(Beta+1) and then draw the common emitter ac equivalent model, which is likely the one you'll be using in your analysis.

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    \$\begingroup\$ Understanding this needs so much knowledge that with it the whole question would be never born. The questioner can see us quite conceited. \$\endgroup\$
    – user136077
    Sep 3, 2020 at 8:45
  • \$\begingroup\$ I think that this answer is correct however pretty useless to OP. What OP needs to learn is circuit analysis followed up by small signal analysis. There are many, many books and courses explaining this, OP needs to study these. \$\endgroup\$ Sep 3, 2020 at 9:00

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