[SOLVED] Op amp in open loop - sine to square wave

[Y.li]

Hello,

Can Op amp in open loop be used to generate a square wave from sine wave. I am giving a sine wave (10 mV p-p) to an op amp (LM324) in open loop and trying to get a square/rectangular wave. But no luck. In concept, the open loop op amp should saturate/ unsaturate and there should be a dc pulse of nearly the same period as of sine wave (50 Hz).

Any ideas pls.

Thanks,
Y Li

 

[madhusuthanan]

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[FvM]

LM324 is supposed to work as a comparator for 50 Hz, even with only 10 mVpp input. There's a apparently a problem in your circuit.

 

[goldsmith]

Can Op amp in open loop be used to generate a square wave from sine wave

Hi Y Li
FvM has replied your question , but i want notice a thing : don't use the word generate for this case . it is not correct ! you want convert a sine wave to a square wave . ( generate means create from DC signal or perhaps create from a system without supply ( magnetic system ) )
Best Wishes
Goldsmith

 

[Y.li]

LM324 is supposed to work as a comparator for 50 Hz, even with only 10 mVpp input. There's a apparently a problem in your circuit.

Well I was able to convert the sine to square finally. One of the sr. engg. told me that I needed to give the input through a potential divider, ie each of the input pins of op amp is to receive signal through a resistor and the pins are to be connected to gnd with a resistor as well. This solved the problem. Though i dont know why this was required. Direct coupling of the sine signal simply saturated the output.

Thanks,
Y. Li

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Hi Y Li
FvM has replied your question , but i want notice a thing : don't use the word generate for this case . it is not correct ! you want convert a sine wave to a square wave . ( generate means create from DC signal or perhaps create from a system without supply ( magnetic system ) )
Best Wishes
Goldsmith

OK. Thanks

Y.Li

 

[Y.li]

I have one more query pls. In LM 324, when both the inputs of op amp are shorted to gnd, the output saturates to 4.6v (in open loop). Is it because the offset voltage is getting amplified or something else...?

Thanks,
Y.Li

 

[FvM]

In LM 324, when both the inputs of op amp are shorted to gnd, the output saturates to 4.6v (in open loop).

Only by chance, could be ground as well.

 

[Y.li]

Hello FvM,

I powered up an LM 324 IC and checked the o/p to find it saturated at 4 v. This was true for all op amps in the package and for another IC as well.

Thanks & Regards,
Y. Li