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LM833 As A comparator

Dear friends

I used lm833 as a comparator because of it's high slew rate but the problem is one of the inputs comes from a detector- an analog signal which amplitude is 0 to

9V-. The minimum is 0 but when I connect it to the input pin of opamp it comes up about 0.5V -DC is added by opamp-and the operation of comparing with about 0.5V intrfaces big problems .My circuit is a very primary one with no resistances in the output. Any idea how can I remove the DC from the opamp pin?

Thanks in advance Sara

Reply to
Sara
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Any comparator configuration (inverting or noninverting) require input resistors, one to the signal to be compared and the other to the reference voltage. Also you must have a positive feedback resistor to increase the switching speed and add a small hysteris on the input.

Vasile

Reply to
vasile

The input common range of the LM833 typically only goes down to about

1V above the negative rail. They don't guarantee it below 3V above the neagtive rail.

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If you must use an op amp as a comparator - a very bad idea if you don't know what you are doing - use a single supply op amp. For single supply op amps the input voltage range usually includes the negative rail.

Have a look at the LM393 dual comparator.

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Bill Sloman, Nijmegen
Reply to
bill.sloman

Sara, If an op-amp saturates, its input offset voltage is not gauaranteed. When using an op-amp as a comparator, it's best to do the following: . Connect a reference voltage to the reference input (Inv or Non inv, depending on which input the input signal is connected to.) This reference must be higher than the minimum allowable common mode input. I suspect that this is where your 0.5 VDC is coming from. . Use a smal amount of positive feedback to guarantee that the op-amp does not try to stay in its linear range. . Regards, Jon

Reply to
Jon

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