on page connectors supplying op amp power produces odd result

[Pauly007]

The attached circuit produces a voltage at pin 3 of U1A whether the power supply switch is closed or open. This was confusing the hell out of me and I discovered that if I connect U1A pin 11 directly to Net0 instead of using the on page connector U1_NEG then the voltage will only rise significantly when the switch S1 is closed - exactly what I would expect to happen. Can you help me understand why this is? Many many thanks!

[J_Oneill]

Hi,

I simulated your circuit and found I got the same results - voltage across pin 3 even when S1 was open.

I started investigating if the op-amps were grounded correctly, I grounded them by dropping a ground pin from the components list instead of the U1_NEG, this solved the issue.

I think you have a problem with your U1_NEG and U1_POS on page connectors whereby they were not connected correctly. When I deleted them and dropped them again, it solved the issue and the circuit behaved as desired.

Kind regards,

James O'Neill - Applications Engineer - National Instruments