plz tell the configuration of this opamp

[nikhil arora]

I have attached one ckt plz tell the working of this opamp

 

[dknguyen]

6.8 megaohms? Won't that make the circuit do nothing?

 

[Russlk]

If you are trying to make a comparator with hysterysis, swap the pos and neg inputs of the op amp. The feedback has to go to the positive input.

 

[nikhil arora]

i donot know much about the ckt it is right or wrong, but if we keep it still in this configuration then what this opam does.

 

[Russlk]

If the circuit is operating from a single 5 volt supply, it won't work due to offset. If it is operating from +- 12 volt supplies, the output will have 21 volts offset in the worst case. Here is how it is computed: 7 mV input offset multiplied by the gain of 680 = 4.76 volts output offset. 0.25 uA bias current multiplied by the 100K input resistor = 0.025 volts input voltage; multiplied by the gain of 680 = 17 volts output offset. Add this to the 4.76 volts = 21.76 volts offset. I neglected the current through the 6.8 meg, so the result is only approximate.

If you use the LT1006 it could work because the offset voltage is 50 uV max and the bias current is 0.5 nA max.

 

[Roff]

Russ, I think you were right about the inputs being swapped. The circuit is equivalent to an AC-coupled Schmitt trigger if this is the case.

 

[nikhil arora]

thank you very much russlk and ron
I also think that inputs are swapped.

what is the working of capacitors in this ckt