LMV721 op-amp behaviour

[Kinshoro]

help please... I am using an opamp lmv721.... the opamp is being used for a mic preamp.... the problem is when I connect nothing to the positive or negative terminal of the opamp I should get 0v as output... but I am always getting the supply voltage as output... is there anything wrong with the opamp......

 

[Resqueline]

No, that's perfectly normal for those conditions. If not for the input offset current it might behave ideally, like your statement would require.
You'll have to connect the positive input to 0V and the output to the negative input to see if it's ok. Output should then differ no more than a few mV from the positive input.

 

[Kinshoro]

ok..... but shouldn't there be a output if there is a change or difference in the negative or positive terminal..... now when I connect the positive terminal with 1.1v ac source I dont get any output... my opamp is being used as a non-inverting amplifier.... so the positive and negative terminal of the opamp should have equal voltages.... but the negative end of my opamp has 0V while the postive end has 1.1V.. is the opamp not working as it should???

 

[Resqueline]

Are you refering to this diagram in your other thread?
What kind of power supply are you using, what impedance is your 1.1V AC source, and what kind of bias are you applying to the positive input?

 

[neon]

when you disconnect the inputs there is no more feedback so it will take the input offset polarity and slew to the rails