Hi!

I have been looking into RC Low Pass filters a wee bit more than I possibly should. whilst I'm ok with the math to get to the cutoff frequency, and build up an RC filter that performs as I need it to, I am somewhat confused as to how the current flows in a filter.

I simulated the filter as per the attached image.

As Vin increases, current flows through the resistor and the capacitor. As the voltage increases, more current is pushed into the capacitor and the voltage across the capacitor increases. As long as Vin > Vc, the capacitor will continue to charge. At some point, Vin < Vc, and the capacitor will discharge. This will produce a negative current, which has no where to go but back into the source - this appears to be correct according to my simulation. This is what I am not quite grasping - Vin is still positive and trying to push current into the circuit, but the higher voltage capacitor is pushing current back into the source - is this correct? what are the real world implications of this?

i have looked into this for a few days, read all my text books, but I have yet to find any great discussion on this - most texts jump straight to the equations. I have discussed this with a few people but have yet to find a good answer. Hoping someone can clear my misunderstanding!

To be clear, I get how a filter works, and why it works. The math makes sense - the response over a full cycle; but this detail is messing with me for some reason.

I have been looking into RC Low Pass filters a wee bit more than I possibly should. whilst I'm ok with the math to get to the cutoff frequency, and build up an RC filter that performs as I need it to, I am somewhat confused as to how the current flows in a filter.

I simulated the filter as per the attached image.

As Vin increases, current flows through the resistor and the capacitor. As the voltage increases, more current is pushed into the capacitor and the voltage across the capacitor increases. As long as Vin > Vc, the capacitor will continue to charge. At some point, Vin < Vc, and the capacitor will discharge. This will produce a negative current, which has no where to go but back into the source - this appears to be correct according to my simulation. This is what I am not quite grasping - Vin is still positive and trying to push current into the circuit, but the higher voltage capacitor is pushing current back into the source - is this correct? what are the real world implications of this?

i have looked into this for a few days, read all my text books, but I have yet to find any great discussion on this - most texts jump straight to the equations. I have discussed this with a few people but have yet to find a good answer. Hoping someone can clear my misunderstanding!

To be clear, I get how a filter works, and why it works. The math makes sense - the response over a full cycle; but this detail is messing with me for some reason.

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