Hi Everyone

I am working in a 0 to 20 amp non contact measurement device.

Before a Delta Sigma converter I would like to insert a passive low pass filter for anti alias

followed by a OP amp as unity gain buffer to drive the converter. The cutoff frequency is around 1.592 kHz.

I am using LM358 with 3.3 v single supply and from a Function generator I am injecting a sine wave of

0.5 Vpp / 60Hz to simulate the output of a CT.

I am attaching the simulation schematic I did and the scope screenshot.

As you can see there is a clipping in spite of there is a virtual ground to refer the low pass filter

and the Function generator signal.

My question is why there is clipping if the virtual ground is at 1.65 v and the signal has 0.5 Vpp.

Thank you in advance







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The output of the '358 will not go very close to the positive rail but it will go very close to the negative rail (a few mV). Try reducing the virtual ground voltage to, perhaps, 1V.

 

Welcome to AAC!

LM358 output can only get to within 1.5V of the positive rail (typical).



Schematic for the convenience of others:

 

Welcome to AAC!

LM358 output can only get to within 1.5V of the positive rail (typical).
View attachment 121499
View attachment 121500

Schematic for the convenience of others:
View attachment 121497

Hi Dennis
Thank you very much for your help I was forgetting this point, thank you again.
Best regards.
Challenger.

 

The output of the '358 will not go very close to the positive rail but it will go very close to the negative rail (a few mV). Try reducing the virtual ground voltage to, perhaps, 1V.

I did that and the filter is working.
Thank so much