# Clarification on a common emitter amplifier circuit

Discussion in 'Homework Help' started by majawahar, Feb 20, 2016.

1. ### majawahar Thread Starter New Member

Jan 28, 2016
15
0
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

2. ### shteii01 AAC Fanatic!

Feb 19, 2010
3,514
514
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.

vol_ likes this.
3. ### majawahar Thread Starter New Member

Jan 28, 2016
15
0
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

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4. ### Jony130 AAC Fanatic!

Feb 17, 2009
3,993
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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.

5. ### #12 Expert

Nov 30, 2010
16,704
7,354
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.