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current-sense amplifier

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pona

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I am using this current-sense amplifier. When i change the load resistance, the output of amplifier increases and decreases in the form of ramp. I want it to change in the form of square wave. I am using Lm139 opamp.
 

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LvW

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There is no "squarewave" at all. Each waveform that is called "squarewave" is - more or less - a ramp.
Therefore, it is important to tell us something about the rise time in comparison to the pulse length.
 

chuckey

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Over what period does your "ramp" increase in voltage. Its just that every sharp step is actually a ramp, its just whether it takes 2nS or 1mS. If the change of state is too slow for your application, then its most likely that the amplifier has an insufficient slew rate which is ability to quickly charge and discharge stray circuit capacitance and tends to mean that it is incapable of driving high enough currents into this capacitance.
Frank
 

FreeMAn0110

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It might also depend on how fast he is changing his load as well. It's impossible to jus increase the load instantly. So if you can help us with that it would be good.
 

pona

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The delay is 150 us approx and its slow for my application. Is it possible that this slow output is the result of slowly varying input?
 

FvM

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I am using Lm139 opamp
In what function do you use it? Do you mean the two OPs drawn in the rectangle? LM139 is an open collector comparator (uncompensated, unstable as amplifier), not an OP.
 

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