# help in projet with amplifiers

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#### simos9584

##### New Member
hello there
i have to do a project at my school and i need some help.the project is that i should design a circuit with amplifiers,converter dc to dc,sine signal from 2,5-5 volts and should convert it to the output in sine signal from 0-6 volts and it should be in the same phase as the input signal.i was thinging to do it with operational amplifier,but how i will take the output 0 volts when i give in the input 2,5 volts should i use voltage divider?i am confused any help will be apreciatable

You do not make sense when you say "convert it to the output in sine signal from 0-6 volts". Do you want the output to be from 0V to 6V peak-to-peak?

What is the DC to DC converter for? What is the supply voltage?

sorry about my bad english,actually i input a signal as i told u from 2,5 to 5 volts and i need to be the output 0 volts to 6 volts peak to peak as u told,it will be like when i have 2,5 volts input the output should be 0 volts when iinput 3 volts input the output should be 1,2 volts when i put 3,5 volts peak to peak the output should be 2,4 volts peak to peak and so on so on.i just need to design this converter the use doesnt matter its not for connecting with some other circuit or other use,the supply voltage as i know dependes on the amplifier that we will use (and i do not have limitations,its in my choise)we usallly use the LM741 OR TLC271 in our lessons.so as i remember in the tlc271 the suply voltage is 10 volts and in lm741 +- 15 volts

I think you described an "expander" circuit.
When the input is 2.5V RMS then the output is nothing. When the input is 3V RMS then the output becomes 1.2V peak-to-peak. When the input is 3.5V RMS then the output is 2.4V peak-to-peak. When the input is 5V RMS then the output is 6V peak-to-peak.

An expander uses a voltage controlled variable gain amplifier like an old NE572 compander IC or you can make the circuit with opamps and a Jfet.

But what will the DC to DC converter be used for?

Simos, your English is good but the way your post is written makes it VERY difficult to read.

There are no spaces after punctuation marks, no capitals at the start of sentences, decimal points should be shown as 2.5 not 2,5.
There are a few spelling mistakes, but the meaning is not lost.

hello there
i have to do a project at my school and i need some help.the project is that i should design a circuit with amplifiers,converter dc to dc,sine signal from 2,5-5 volts and should convert it to the output in sine signal from 0-6 volts and it should be in the same phase as the input signal.i was thinging to do it with operational amplifier,but how i will take the output 0 volts when i give in the input 2,5 volts should i use voltage divider?i am confused any help will be apreciatable
Would be much better written as:

Hello there
I have to do a project at my school and i need some help.
The project is that I should design a circuit with amplifiers, converter dc to dc.
The input is a sine signal from 2.5 to 5 volts (peak to peak).
The output should be sine signal from 0 to 6 volts (peak to peak), and it should be in the same phase as the input signal.
I was thinking to do it with operational amplifier, how will I take the output to 0 volts when I give in the input 2.5 volts should I use voltage divider?
I am confused, any help will be appreciated.
There are one or two bits with "awkward English", but it is much more readable and understandable than the original.

JimB

Last edited:
sorry but u confused me,why u use the rms?i give my input from the frequency generator (a signal(that is sine wave))so we should measure it on v peak to peak right?or i am wrong?so it should be 2,5 volts peak to peak the input and the output nothing,then 3 volts input peak to peak and then 1,2 volts output peak to peak and so on and at last 5 volts input peak to peak and output 6 volts peak to peak output.and the output should be in the same phase as the input phase.i am in the idea of opamps,but what is confusing is the input 2,5 volts and the output nothing.until now we used amps with gain 1 volt or when the input is 10 mv the output to be 10 times more,or 2,5 times more.do u have any good i dea how i should start?

ok jimB
I will correct it in my next reply
thank u vey much

audioguru
as for the question for what is the use of this dc to dc converter?
As i told u its a project and the question is to design that and only that,
its not for be used for something.

The output of my signal generator is scaled in volts RMS and my oscilloscope shows volts peak-to-peak.
When the input is 2.5V RMS or less you want the output to be zero then we say that the output is muted. A "noise gate" or "voice gate" circuit mutes when the input level is low.
Then you need an "expander" circuit that increases the gain as the input signal rises.

There is no DC to DC converter in this circuit. A DC to DC converter can be made with a ICL7660 charge-pump IC. It can convert a positive voltage to a negative voltage or almost double a positive voltage. Another DC to DC circuit uses a power oscillator to drive a stepup transformer. The output of the transformer is rectified and filtered into a higher DC voltage.

AG
I cant help but think that you have mis-understood the requirements here.
I think that the OP is looking for a simple scaling and offset process, so that when he inputs a signal which varies between 2.5 and 5.0 volts (a swing of 2.5 volts) it is amplified to have a swing of 6.0 volts, and, offset so that the swing is from 0.0 to 6.0 volts.

JimB

AG
I cant help but think that you have mis-understood the requirements here.
Nobody knows what he wants because he is in Greece and he "no speeky zee English".
Why doesn't he ask in Greek in a forum in Greece??

Why is he talking about a DC to DC converter??

audioguru
i am sorry i made a mistake using dc to dc converter,i want a V/V converter.
as u know the procesion of signals at the output of a transducer is either V or I (usually very small size).therefore it needs amplfie from a suitable preamplifier that it will have a suitable output to the size(V OR I) and to the width,so to lead a system of data acquisition.
So we have 4 types of amplifiers depending the signal of input and the signal of output that they convert.
1)V/V
2)I/I
3)V/I Transresistance
4)I/V Transconductance
i want the V/V converter

You do not want a V/V converter. You just need a preamplifier with enough voltage gain. 