Small singal amplifer. How to calculate

Thread Starter

Maintenance Man

Joined May 12, 2010
25
Hi to all
Could someone please help me figure VE, IE, VRL and VCE of a small common emitter amplifier using a voltage divider as the input on base. I just would like to know the formuals. Thank you very much for your help.
 

Jony130

Joined Feb 17, 2009
5,183
For this diagram



Base current is equal to :

\(Ib = \frac{Vth - Vbe}{ Rth + (\beta+1)*Re}\)


\(Vth = Vcc*\frac{R2}{R1+R2}\)

\(Rth = *\frac{R1+R2}{R1*R2}\)

And emitter current

\(Ie = Ib*(\beta+1)\)

\(Ve = Ie * Re\)

Collector current

\(Ic = Ib*\beta\)

\(Vc = Vcc - Ic * Rc\)

\(Vce = Vc - Ve\)


VRL ??

The voltage gain is equal

\(Av = \frac{Rc||RL}{re} = gm * Rc||RL \approx 40 *Ic *(Rc||RL)\)

\( re = \frac{Vt}{Ic} \approx \frac{26mV}{Ic}\)

\( gm = \frac{1}{re} = \frac{Ic}{26mV} \approx 40 *Ic\)
 

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