I have designed a class A amplifier ( its my assignment, note that im student). My problem is that the output ain't amplified instead it is smaller that the input. Whats the problem ? It is a Common Emitter btw.

 

Hello,

Is there a connection between the resistors and the base?
I do not see the connection dot.

Bertus

 

@bertus There is. My simulator look that way, Sorry sir. its Voltage divider sir. A common emitter configuration

 

Get a voltmeter and measure the voltage at the base, emitter and collector,

 

...There is. My simulator look that way, Sorry sir. its Voltage divider sir. A common emitter configuration

Since your simulator correctly put connection dots at the other nodes, I suspect there is no connection to the base of the transistor except the input coupling capacitor, hence no bias.

At what frequency? You need to use .AC analysis (not .DC) and determine the gain vs. frequency (Bode Plot).[/user]

 

300Hz to 30kHz Sirs! Okay my bad, so clumsy thanks sirs

 

Sirs? What if im going to make this a 2 stage. Can i just attached same amp to it with a cap between them ? And btw thanks it works now.

 

Yebbut...you might want to place about a nanofarad in parallel with R1 to limit the gain above 30KHz.

 

Oh okay.

 

Which cap actually is controlling my highest freq sirs?

 

Which cap actually is controlling my highest freq sirs?

The one that isn't installed in parallel with R1.

 

@#12 Sir? C = 1/(2pifR), then f= 30kHz ( highest freq) and R will be R1 only?

 

@bertus How to do it ?

 

Hello,

Perhaps the following page might give you an idea:
http://www.rason.org/Projects/bipolamp/bipolamp.htm

This is one of the links of this EDUCYPEDIA page on ampifiers:
http://educypedia.karadimov.info/electronics/amplifiers.htm

Bertus

 

Sorry for the rush ! Lel. Well Thanks a lot tho, admin @bertus

 

Can someone show/tell me how and why Bypass capacitor is a high pass filter?

 

What type of cap are being used in amplifiers? Some schematics have non-electrolytic, and some are using electrolytic. Can someone clarify this?

 

It will depend on the capacitor value. If C is > 1μF we are going to use electrolytic capacitor. But if C < 1μF we can easily use non-electrolytic cap for example a metal film capacitors. And in general we are trying to avoid the ceramic capacitors in the signal path unless the cap is < 1nF and we are gonna to use Class 1 ceramic capacitors.

As for your amp:

C1 > 0.16/(300Hz * R3||R4||(hfe+1)*26mV/Ic) ≈ 0.16/(300Hz * 3kΩ) = 177nF, so we need to use 220nF.
C3 > 0.16/(300Hz * 26mV/Ic) = 0.16/(300Hz * 26Ω) = 22μF
C2 > 0.16/(300Hz * (R1 + Rload))

 

I handed you the answer (and now I regret doing that). What kind of component, where to place it, and a fair estimate of the size. This being the Homework Forum, why don't you use the formula that you already know (post #12) and find out if using only R1 results in about a nanofarad of capacitance being the right size? Is it easier to ask 6 times over the course of 4 days than to do one line of math?

 

I actually did it sir, @#12 . I just asked for clarifications since i learned that inorder to control my highest freq, all i need to do is put a capacitor in parallel with Vce( goin to ground) . That's why doubts are coming.