# Clarification on a common emitter amplifier circuit

#### majawahar

Joined Jan 28, 2016
15
Dear friends,

Can some one clarify my doubt

In a 12V single stage common emitter amplifier circuit, i assume that when the circuit is on with a steady +12 DC, the voltage and current accross the transistor collector,base and emitter will be constant and will vary only when a sino sidal wave or anny other wave is appled at the input (base) of the transistor

If i am wrong then can some one explain ?

Regards

M.A.Jawahar

#### shteii01

Joined Feb 19, 2010
4,644
I think you need to separate DC and AC components.

The AC components will influence the DC components (voltages and currents), but the influence should be very very very small. I am thinking in uV and nA.

Remember, DC is there to setup the level around which the AC will oscillate.

#### majawahar

Joined Jan 28, 2016
15
Ok thanks shteiio1 .I will look into it.However i am posting as attachment the circuit diagram also so that you can see it and enlighten me

#### Attachments

• 181.2 KB Views: 7

#### Jony130

Joined Feb 17, 2009
5,211
Notice that if voltage at the emitter resistor is slightly larger than 1V and Re is 180Ω, this will give us Ie = Ic > 1V/180Ω > 5.6mA. Therefore VRc = VR1 = 5.6mA*1.2kΩ > 6.8V. Also capacitor across emitter resistor do not increases the transistor hfe. This capacitor increases voltage gain not the current gain.

#### #12

Joined Nov 30, 2010
18,216
I've been answering this Duplicate Thread in the Projects Forum. majawahar has not stated that there is any signal connected to the base, but he did say his problem is with the Simulation showing changes in the collector current with no mention of any input signal.