I’m trying to wrap my head around the emitter follower.

I’m currently using it to simulate a ~12V AC coming from a intercom ringer (about 700Hz).


simulate this circuit – Schematic created using CircuitLab

My input is a function generator and I would like my output to drive quite a bit of current. Right now the best I could do is drive a few mA but in the process I’m setting my \$R_E\$ on fire. Is there a way to improve the efficiency of this circuit? Or I’m better off using another buffer?

  • 1
    \$\begingroup\$ This circuit will not work as needed - use standard (two transistors) class a / ab amplifier \$\endgroup\$
    – fifi_22
    Nov 14, 2020 at 20:46
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    \$\begingroup\$ That's what a Class A amplifier does. Search "Class B" or "Class AB Amplifier" designs. \$\endgroup\$
    – user16324
    Nov 14, 2020 at 20:47
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    \$\begingroup\$ That \$R_E\$ just "pisses away" as much current as it can deliver to the output. What you need is an \$R_E\$ that varies its value depending on how much current is needed at the output. That's a job for another transistor. Like a class B (or AB) output stage. \$\endgroup\$ Nov 14, 2020 at 21:32
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    \$\begingroup\$ So the answer to my question is to add a second transistor? \$\endgroup\$
    – gurghet
    Nov 14, 2020 at 23:48
  • 2
    \$\begingroup\$ @gurghet At least one. And a few other parts, too. \$\endgroup\$
    – jonk
    Nov 15, 2020 at 6:59


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