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ArcticMyst Security by Avery

Is a 75 KHz 12V peak signal suitable for LM324N?

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Jul 5, 2017
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The LM324n has a gain-bandwidth product of 1 MHz, so I guess it works from 0 Hz to 1 MHz, is what I understand true?

Here is the datesheet of lm324n

Its slew rate is 0.5V/us which means that it can generate a 500 kHz output signal, is that true too?

If the above are both true, why when I apply a 75 kHz 12V peak signal to Vin+ with +12V DC supplies and Vin- is connected to Vout so it should work as a buffer, is the output signal destroyed?
 





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The Slew rate of 0.5v/ uS needs to be scaled to suit your supply voltage. That means the output can move 0.5 volts for every microsecond. If you want the output to move 12 Volts you will need 24 Microseconds.

Don't forget there is a positive slew and a negative slew for one complete cycle. Really it comes down to 48 uS on a 12 Volt Supply. Which gives you a max frequency for a full 12v signal will be 20.8 kHz with a triangle wave output.

You can get a 75 kHz signal thru it. But the voltage swing will be much less than 12 Volts.

These Op Amps with internal compensation were aimed at Audio Freqencies.
 
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Why do you need an audio quad OP amp? What are you trying to accomplish?
 

Benm

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Both are actually very well defined parameters.

First off, the gain-bandwidth product. This is exactly what it says. If you have an opamp with a 1 MHz gain-bandwidth product, that means it can achieve a unity gain (i.e. same output voltage as input voltage at 1 MHz). It also means you can get a voltage gain of up to 10 times out of it at 100 kHz, or 100 times at 10 kHz etc.

The slew rate is another factor. Provided that the gain-bandwidth product is not limiting, it determines how fast the output volage can change. As Mosc explained it is the limit on how large the output singal can be depending on frequency. If the slew rate was 1 V/uS, the maximum signal amplitude fromt the opamp would be 1 volt at 1 MHz, or 2 volts at 500 kHz and so on.

And yes, the slew rate does not have to be identical going up and down. If you read a datasheet and just find a minimum defined, presume this is under worst case conditions. It could be far faster pulling down than up, but unless otherwise specified the slew rate is that measured in the least favourable direction unless otherwise indicated.
 
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