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Old May 17th 2010, 05:20 AM   #1
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Question Operational Amplifier Basics

This is the basic diagram of an op-amp. The saturation voltage is equal to the voltage of one of the power supply either neagative or positive. My question is that why isn't it equal to the combined effect of both and if it depends saturation voltage depends on one of the voltage supply then what is the need for the other battery?
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Old May 18th 2010, 06:11 AM   #2
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In an ideal op-amp if both non-inverting and inverting inputs are equal the output should be zero. In the real world however a small differential voltage appears across these two terminals due to various reasons like difference in input currents etc. Since there is no feedback resistor connected between the output and inv input, this is equivalent to a very high or infinite resistance. The gain thus becomes very high and even for a small differential input voltage (DIV), the output swings into saturation . If the DIV is +ve it goes into +ve saturation and vice versa.
If we were to just add the + and- supply voltages, the output would be zero would'nt it? And the op-amp depends on both supplies.
Commercially there are op-amps available which need only a +ve supply and ground. However these cannot give you a -ve output voltage which may be required in D.C. applications,
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Old May 23rd 2010, 08:52 PM   #3
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Thanks for the lovely explanation.
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Old May 30th 2010, 12:37 AM   #4
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Glad i could be of help.

Most of the properties of op-amps can be easily understood by remembering that the inv input tries to achieve the same voltage as the non-inv input
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