Multisim common collector confusion

Thread Starter

jaydnul

Joined Apr 2, 2015
151
I am trying to do a basic current gain amplifier. Everything works until I place the capacitor in series with the 10 ohm load to remove the DC offset:

I have no clue what's going on here. I tried playing with C1 value but it didn't do much. Shouldn't the output just be the input at the origin? What am I doing wrong?

Thanks

Edit: the transistor is an ideal NPN
 
Last edited:

crutschow

Joined Mar 14, 2008
23,531
So for this circuit to drive a 4 ohm speaker I would need a giant capacitor? Like .1 Farads?
Guessing at part values does not generally work well for electronic design. :rolleyes:
If you do the math for the -3dB point [C = 1/(2πRf)] it requires nearly a 2,000μF capacitor to give a -3dB rolloff into a 4 ohm load at f = 20Hz.
 
Last edited:

Picbuster

Joined Dec 2, 2013
979
Well your problem is simple to explain.
the current (Emit + Basis) goes via 10 ohm.
open then sw then it goes via 1K so Ue goes up and when above 0,6V The xtor is switched off.
adive: measure Ue when sw is open and alter the 1K resistor
 

Thread Starter

jaydnul

Joined Apr 2, 2015
151
Haha ya, .1F was an exaggerated estimation. I'm still thinking about this problem though; if I have a DC biased audio signal and I want to send it into a 4 ohm speaker, is the only simple option a giant capacitor or is there some technique that I am missing?
 
Top