Question:
what maximum input can be applied to op-amp?
Kousar
2013-07-13 09:30:22 UTC
like DC input limitation of op-amp as+-15 or +-30Volts for 741?
also what is the difference between DC and AC amplification for op-amp??? what mostly op-amp used for AC amplification or dc amplification?
Four answers:
Steven
2013-07-13 10:10:52 UTC
Any amplifier, including an op-amp meters out a voltage that is derived from it's power supply, based on some controlling input. Just as a horse pulling a cart can never be stronger than a horse no mater how hard you beat it, an amplifier can only output it's power supply no mater how hard you drive it's input. It does not actually amplify the input, rather the input controls the output from the power supply to the load.

uA741 and similar op-amps have a power supply maximum that is typically +/- 18V and a minimum output saturation of about 3V from either rail. Any input beyond the supply rail will cause the device to behave badly and possibly self destruct. Newer "rail to rail" op-amps have very little input and output saturation voltage so they can operate almost to the rail voltage. It is possible for inputs to operate slightly beyond the rails, but this is essential by attenuating the input. If there is any danger of an input voltage exceeding the rail voltage, that input should be diode clamped to the rail with a series resistance to limit clamping current.

AC signals are simply a voltage that varies rapidly, so an amplifier's AC ability is mostly about how fast it can follow an input. This is called the slew rate. Older op-amps like the uA741 were quite slow and not well suitable even for audio frequencies.

DC amplification usually requires precession so the input offset error and thermal drift are critical. One design that provides excellent DC operation is called chopper amplifier, but has a very limited frequency response.

In all cases, an engineer must chose a device that provides the required performance at a good price and reliable source. A device with better performance but at a higher price or single source is probably a poor choice.
Steve-o
2013-07-13 10:21:41 UTC
Maximum input is the same for AC or DC and is detrermined by the OpAmp's design - Steven's answer is good.



Steven left out the "mostly AC or DC" answer. That's hard to say since any one person may only be away of *some* of the uses in practice today. However, I'd venture a guess that most are AC applications used in the filtering of audio and audio-like signals... My guess, but I did mostly analog design.
Sampada
2016-04-06 12:13:41 UTC
Whatever the input applied to op-amp...the output is always limited to 90% of power supply voltage..for eg if we apply a input of 20V to an op-amp with a power supply of 15V then the output will saturate to 13.8V(90% of 15V) this property of op amp is called as saturating property..and the output voltage is limited to maximum and minimum value close to 90% of power supply
John
2013-07-13 09:54:20 UTC
18V


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