Question about differential amplifier(isolated input signal)

In summary, if you want to use an op amp as a differential amplifier, you need to use it with caution, as there is the potential for shorts to power supplies or other parts of the circuit.
  • #1
samaaa
48
0
Hi:

when using op amp as differential amplifier,
can it used for input signal isolated from power supply of that op amp?
as this figure:

http://uploadpic.org/storage/2011/k9bEue1EtqkWGlH5yTDN3198.jpg

so if the input signal is sinewave 5 Vp.p,
will be the output of this op amp sinewave 5 Vp.p also ??
 
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  • #2
Yes...with condition.

If you look at the data sheet, given the + and - supply, the input range is usually about 1V below the either supply voltage. Look at the data sheet under "input range". There are so called rail to rail input op amp that can accept input up to the supply voltages. I would put some protection diode at the input of the amp to protect from over voltage.
 
Last edited:
  • #3
yungman said:
Yes...with condition.

If you look at the data sheet, given the + and - supply, the input range is usually about 1V below the either supply voltage. Look at the data sheet under "input range". There are so called rail to rail input op amp that can accept input up to the supply voltages..

yes that right,i know that

i not ask about the range of input signal,
i ask if op amp(as differential amplifier) can or can't ,work with input signal isolated from power supply(the signal come from other circuit) ??
 
  • #4
Yes, that's what I said the first time. As long as you conform to the input range.
 
  • #5
Yes samaaa, there is no need to shout at someone trying to help.

We can see that you have put significant effort into your work.

And yes the differential configuration will work with a non ground referenced signal ( ie floating) as you have drawn.

However your circuit does not isolate the signal from the op amp circuitry and therefore there is the opportunity for an electrical short to the power supply or other parts of the circuit.

To properly isolate the signal you would need to interpose an optoisolator or other device between the signal source and the differential amp input.

Please note this is unlikely to be necessary at the voltages you have here, I am just being pedantic for you to see correct use of terminology.

Please also note that your implementation of a differential amp using a single op amp is a poor one. A better circuit would use three (from the same package)
 
Last edited:
  • #6
thank you (Studiot & yungman) for help
 

1. What is a differential amplifier?

A differential amplifier is an electronic circuit that amplifies the difference between two input signals while rejecting any common signal that is present in both inputs. It is commonly used to amplify small signals in the presence of a large common-mode signal.

2. What is the purpose of isolation in a differential amplifier?

The purpose of isolation in a differential amplifier is to prevent any common-mode signal from affecting the output. This is important in applications where the input signals may have a common ground or reference point, which can introduce noise and inaccuracies in the amplified signal.

3. How does a differential amplifier work?

A differential amplifier works by taking two input signals and amplifying the difference between them. It uses two amplifying devices, such as transistors, with their inputs connected in opposite polarity. The amplified difference signal is then taken from the collector or drain of the devices.

4. What are the advantages of using a differential amplifier?

There are several advantages of using a differential amplifier, including high accuracy and linearity, low noise and distortion, and high common-mode rejection ratio (CMRR). It can also be used to amplify small signals in the presence of a large common-mode signal, making it useful in many electronic applications.

5. What are some common applications of a differential amplifier?

Differential amplifiers are commonly used in instrumentation and measurement systems, audio amplifiers, and signal processing circuits. They are also used in communication systems to amplify and filter signals, as well as in control systems for accurate measurement and control of signals.

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