Voltage amplifier with 2N3904

Alec_t

Joined Sep 17, 2013
10,901
My input signal have a range between 0.5v and 1v
Are you talking about a DC signal or an AC one. If AC, do you mean a) it has an amplitude within the 0.5v to 1V range or b) it has a positive peak of 1V and a negative peak of 0.5V? If AC, what frequency?
Here's the result using your circuit with a 1V amplitude 1kHz AC signal. Do you see the problem and know the cure?
SimpleAmp.PNG
 

Thread Starter

yoannwyffels

Joined Mar 23, 2016
16
Are you talking about a DC signal or an AC one. If AC, do you mean a) it has an amplitude within the 0.5v to 1V range or b) it has a positive peak of 1V and a negative peak of 0.5V? If AC, what frequency?
Here's the result using your circuit with a 1V amplitude 1kHz AC signal. Do you see the problem and know the cure?
View attachment 104240
Hello Alec_t,

I'm talking about a DC signal which go from +0.5v to +1v. Maybe this amplifier (with 2n3904) only work with AC signal ?
 

Alec_t

Joined Sep 17, 2013
10,901
Even if you remove the capacitor the circuit shown won't work as you want with a ground-referenced 0.5V-1V input.
a) 0.5V would switch the transistor off,
b) taking the output at the transistor emitter gives no gain at all.
c) if you take the output from the transistor collector you get gain, but there is inversion, i.e. as the input voltage rises the output voltage falls.
When the input goes from 0.5V to 1V do you want an output going from 1.5V to 3V?
I will use any LM741 opamp to do what I want to do !
Good luck with that :D
 

dl324

Joined Mar 30, 2015
9,981
lm741 opamp isn't a good choice ?
Read the datasheet. Input and output voltage are only guaranteed to within 3V of the supplies and minimum supply voltage is spec'ed at 10V. It will likely operate at a lower supply voltage and, if you're lucky, you'll be able to find a unit that gives better than typical voltage swings.
 

Alec_t

Joined Sep 17, 2013
10,901
Can't get your link to work. You can upload files direct to this site using the 'Upload a File' button next to the 'Post Reply' button.
 

AnalogKid

Joined Aug 1, 2013
8,302
For what I'm trying to do, I'm on a +5V DC Power supply (not a +15V), and need to have a gain x3
My input signal have a range between 0.5v and 1v
Does this schematic will be working well ?
No, for two reasons. First, this is not a voltage amplifier, it is an emitter follower. This is a circuit configuration that has current gain but no voltage gain.

Second, while R1 and R2 might be the correct ratio of values for biasing the circuit, their absolute values are way too small and will load down the input signal.

ak
 
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