Your opamp works without negative feedback so now works like voltage comparator. Remember that open loop gain is around 100-120dB so very small difference between inputs causes saturation of opamp output.
@SunnySkyguy I have replaced the opamp with the new one.If you lower (+) input voltage with a pull down resistor to VEE and output drops, something else is wrong. If the Op Amp does not obey spec, replace it.
@SunnySkyguy I have replaced the opamp with the new one.
i checked the circuit by isolating output circuit, still i am getting 20 V at output.
You appear to have a fundamental misunderstanding of an op amp's operation. It responds to the difference voltage on the inputs, not the absolute value. If you tie the inputs together (both have the same voltage) than the intrinsic input offset voltage will drive the output to the rail, either high or low depending upon the polarity of the offset. To drive the output low the (-) input must be slightly more positive than the (+) input (by a value greater than the offset value as shown in the data sheet).
i have another unit with the same circuit and it works properly .
No. If the (+) input is more positive than the (-) input then the output will remain high. The (-) input must be more positive then the (+) input for the output to go low.Yes. i checked with it. whenever i give higher voltage to the (+) circuit works properly.
Many ordinary opamps like a 741 will not work.
The inputs of a 741 opamp have a useable common-mode voltage range of 3V more positive than VEE and 3V more negative than VDD. If they are closer to the supply voltages then the inputs are cutoff or are saturated, then they don't work properly. That is why they usually use a dual-polarity power supply and keep their input voltages away from its supply voltages.What does this mean (...will not work) ? Under which condition?
THen the fault is somewhere else in the circuit or in the design. WIthout details on the overall circuit, there is insufficient info.@SunnySkyguy I have replaced the opamp with the new one. i checked the circuit by isolating output circuit, still i am getting 20 V at output.
Just because one marginally designed circuit will work doesn't mean the second one you build will. If you can't change the circuit then I don't see how you can fix it. Reminds me of the tongue-in-cheek rule where I used to work "Fix it but don't change it"...............................
but the problem is i cant change the value of resistors, i have another unit with the same circuit and it works properly .
Just because one marginally designed circuit will work doesn't mean the second one you build will. If you can't change the circuit then I don't see how you can fix it. .
+1
I'm going to engrave your post in golden letters.
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