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op amp question

mechtronics

Aug 7, 2011
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Aug 7, 2011
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if i have a 6 volt supply to a 741 op amp can i amplify (invert) a 1 volt signal or any, voltage to get a 12 volt output? havent used op amps in years and was just wondering can u amplify a voltage thats more than the supply voltage.? diagram would be cool by any 1 if it can be done thanks
 

duke37

Jan 9, 2011
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You cannot find voltage where there is non. With a 6V supply, you would be lucky to get 4V maximum output.

You could use some kind of voltage multiplier (boost converter) to generate a 15V supply. It all depends on the currents involved.
 

KrisBlueNZ

Sadly passed away in 2015
Nov 28, 2011
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As duke37 says, an op-amp cannot produce an output voltage that is outside the voltages supplied to it. If you look up the data sheet on an op-amp, the output voltage swing will be specified.
For example, the Fairchild data sheet for the old 741 op-amp, at
http://media.digikey.com/pdf/Data Sheets/Fairchild PDFs/LM741.pdf
says that if the device is powered from +15V and -15V supplies and is operating into a load resistance of 10K or more, it can produce an output voltage swing of +/- 14V typically, and +/- 12V guaranteed. In other words, the output is only guaranteed to be able to swing to within 3V of the supply rails.
If you want to boost a supply voltage, you need a boost converter, which typically uses an inductor to store energy and release it at a higher voltage and lower current (like a transformer).
If you want to boost a variable signal, you need to use an amplifier that is supplied from voltage rails that are wider than the maximum required output swing by a small amount. The amount depends on how close to the supply rails the output can swing, which is determined by the design of the op-amp's output stage and is also affected by load current, or load resistance. Some op-amps have outputs that can swing very close to one or both supply rails, assuming the load current is low.
 
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