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How could I get only positive pulses at opamp output?

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epp

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OpAmp help

Hello!
How could I get only positive pulses at opamp output? I mean Look at the picture attached. Supply of opamp are: +5V and -0 gnd.
At input V+ is sinus 18*sin(2pi*50*t) and at V- is DC 10V. I want positive output of opamp only when positive sinus i greater than 10VDC.
Thanks.
 

Re: OpAmp help

You are driving the amplifier beyond its allowable input range. You should use a comparator and then a resistive voltage divider to cut the input signal level to the allowable range specified for the comparator.
 

OpAmp help

You can use 'half-wave' rectifier or a diode before the V+. So, only POSITIVE Sinewave will go into your opamp.
 

OpAmp help

I guess the DC input and the sinewave are the
two input of your opamp and the small square
wave is the output. The unexpected behavior
in the plot is that the opamp output goes to high
when the input pass through ground level (normally it shouldnt). This suggest that when you go below ground level, something going on within the opamp.
Is the input pair MOSFET?
 

Re: OpAmp help

Thank you guys!
Finally, I used opamp TL082 and my problems disappeared. :))
After this I think that I would'n use AD opamps anymore.
 

OpAmp help

I have a question here, his Vcc is +5V and Vee is 0V, how come is he expecting a negative output? His rails is only postive and returns to ground, therefore the ouput is only the difference of the two inputs of course amplified by the OP AMP's gain.
 

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