LC and LR filter Help

The last type of filter you can’t remember the name or is a notch filter. It blocks out only a very narrow range of frequencies letting the rest pass. It’s useful for measuring harmonics since you can use it to remove the core signal but keep the harmonics in pristine condition. The RL filter is quite similar too an RC filter, only if you change the capacitors to inductors then any low pass filters will become high pass and any high pass filters will become low pass. The equations for RL are probably similar if not identical to those for RC, only you have to swap the resistors and and inductors to keep it as low pass and high pass. Also, what you said about inductors acting as resistors at high frequencies isn’t quite right. They do block high frequencies the same way a capacitor blocks low frequencies, and they let in low frequencies the same way capacitors let in high frequencies, but they don’t block them like resistors in the same way capacitors don’t block low frequencies quite like resistors. Imagine an inductor as a long tube full of water with electricity being water, and if the voltage raises (pressure builds up) the water in the long tube will take a moment to gain momentum, and when the pressure is released, it’ll take a moment to lose that momentum. So it’ll block high frequencies since their cycle length is too short for the momentum to build up and come back down, but with low frequencies theirs plenty of time for the momentum to build up and go back down. To get a feel for this momentum business, make a circuit with a 5V source connected in series with a 150ohm resistor connected in series with a normal open button connected in series with an inductor. Then take two LEDs and connect them in parallel to the inductor, with one reverse biased. When you push the button, the forward biased LED should light up only briefly. If it doesn’t, increase the inductance. When you press the button, the electricity will go through the LED since the inductor hasn’t had enough time to build up momentum yet, but once it does build up momentum, it is a much lower resistance path for the electricity than the LED, so the LED goes dark. Once you let go of the button, the inductor has built up some momentum which has to go somewhere. So it pulls on the wire where it had gotten it’s electricity from creating a negative voltage lighting up the reverse biased LED which absorbs and converts into light all that momentum energy. If there were no LED, then the inductor would lose it’s momentum instantly, but it would take an infinite amount of voltage to stop it instantly, so the end result is a very large but equally brief voltage spike which can damage components such as a diode biased the wrong way to let the voltage spike through or turned off transistors and can even arc between wires or windings of the inductor if the inductor had enough energy in it. So that’s how an inductor works. LC filters are indeed used for band pass, notch, low-pass, and high-pass filters. If there is no damping resistor, it will have a theoretical infinite Q, but of course in reality everything has some resistance, especially the inductor because it’s a coil of wire instead of a short strip of it. That’s why you should see my circuit on underdamped vs critically damped vs over damped. I’ll make a tutorial on LC filters.

I made the tutorials.

Thanks Jason, I'll check out your tutorial