Tuesday, 16 January 2018

analog - what is Rail to Rail supply?




I am new to analog electronics and I have been hearing this word from my seniors they always talk about Rail-Rail supply while working on some amplifiers and Opamp,also while calculating and designing a suitable pull-up network ,can anyone please explain what are significance of rail-rail supply.
All I know that is has to do something with the +ve supply and -ve supply,Can we just ground the other end ,
Why do we need this rail like structure?



Answer



Rail-to-rail means that the output of the op-amp can go all the way from V- to V+. Usually the output of non rail-to-rail op-amps can't reach negative or positive supply. For example if you apply a 5Vp-p sine wave to the AC-coupled input of a non rail-to-rail op-amp in unity gain configuration powered from +-2.5V, the output will be distorted (top and bottom of the waveform will be cut off). Some op-amps like LM358 are rated for "single supply operation". In practice this simply means that it's output can reach 0V when the negative supply is grounded.


Note that even if you ground the negative supply of the op-amp you might need to provide a virtual ground for the op-amp to operate correctly.


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