When we analyze textbooks, we tend to ignore real-world concerns for the sake of learning. So, a typical theoretical voltage divider is simply two resistors. But if you examine an RC low-pass filter, you’ll see a single resistor and a capacitor. What if you combine them ? That’s what [Old Hack EE] did in a recent video, and you can check it out below.
It helps if you’re familiar with teunin equivalents and, of course, Ohm’s law. There’s also a bit of algebra, but nothing too complicated. The example design has a lossy filter at 100 Hz.
Obviously, RC filters are easy to understand if you think of them as voltage dividers with a frequency-varying resistance, which is what the math is essentially saying. The load impedance, in this case, is R2 in parallel with XC at a given frequency.
He mentions that you might find a circuit like this in a power supply. However, it’s also common to see this circuit whenever a divider drives a load with capacitance or even parasitic capacitance in cables or circuit boards.
We’ve discussed tennin equivalence modeling before. If you want really good filters, you’ll probably need operational amplifiers.
