# DC Amplifier

Discussion in 'General Electronics Chat' started by cruise7777, Mar 17, 2012.

1. ### cruise7777 Thread Starter New Member

Mar 17, 2012
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Hello, I have a project at the university, I should design a DC amplifier (0-3khz) input voltage 1mv,output 2.5V,max supply(single) 5V.
So I'm going to use two operational amplifiers everyone with gain 50(33DB). Max offset voltage 10mikro. So I decided to use opa2334 (texas instruments).
I have one qustion... I'm new here, and i don't know what does output voltage swing mean... my ouput voltage swing from rail is 10mV(I get this from the datasheet), so can I get 2.5V output? :?

I'm going to input 1mV in the first amplifier, which will become 50mV, and then input 50mV in the second to get 2.5V, it is possible to do this with opa2334

Thank you, and sorry for my English

2. ### Audioguru New Member

Dec 20, 2007
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896
1mV and 2.5V are they peak, peak to peak or RMS voltages?

The OPA2334 is in tiny surface-mount packages that are difficult to solder.
With a 5V supply, the output swing into a 10k load is plus and minus 2.4V peak or 1.7V RMS.

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3. ### cruise7777 Thread Starter New Member

Mar 17, 2012
6
0
It's a DC amplifier, 1mv and 2.5V are peak, so can I use this amplifier to get 2.5V output voltage with 5V supply, and if don't can you help me with choosing amplifier (input offset voltage less than 10mikro,and supply less than +5V(single))
Can I know how you calculate, that the max output of this amplifier is 2.4V

Last edited: Mar 17, 2012
4. ### cruise7777 Thread Starter New Member

Mar 17, 2012
6
0
Can I input 1mV in opa2381, to amplify it to 50mv,then to input these 50mV in another opa2381, and get 2.5V at the output, it is possible ?

5. ### Audioguru New Member

Dec 20, 2007
9,411
896
The output might get close to the rails with no load. You did not say what is your load.
The datasheet says the output gets to 2.4V (not 2.5V) when it has a 10k load.

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6. ### cruise7777 Thread Starter New Member

Mar 17, 2012
6
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I think that I can use 25k, the professor didn't say anything about Rl, I think that I can choose it

7. ### Audioguru New Member

Dec 20, 2007
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896
An opamp is not available without a voltage drop when it has a load.
The datasheet for the OPA2335 shows a max voltage drop of 50mV when its load is 100k.
You must guess (or measure) the voltage drop with a 25k load.

8. ### cruise7777 Thread Starter New Member

Mar 17, 2012
6
0
It's really hard to understand this things.... Ok can you help me with choosing op amplifier that can get 2.5V on it's output, with 5V supply (single) and input offset voltage less than 10mikro

9. ### Audioguru New Member

Dec 20, 2007
9,411
896
When it has a load, the output of any opamp will have some voltage drop so its output will not swing the entire supply voltage.

10. ### cruise7777 Thread Starter New Member

Mar 17, 2012
6
0
Ok.... can you give me name of a model, than can provide 2.5V on it's output, with 5V supply and offset less than 10mikro volts :S

11. ### Audioguru New Member

Dec 20, 2007
9,411
896
I have never seen or used an opamp with extremely low input offset voltage.