AC23: From Oscillations to Shocking High-Voltage: Analysis of Resonant Circuits!

In this video, we explore parallel and series resonant circuits, considering how they can be used to form band pass and band stop filters. We also consider the case of a Tesla coil, a device that uses a resonant transformer to create exceptionally high voltages! Using SPICE we explore the behaviour of a series resonant circuit designed to generate 100's of kV!
This is the last video in my series on AC circuits, I hope you found it useful! I'll be uploading several tutorial-like videos in the coming weeks... thanks for watching!

[@simonyoungglostog]

Thank you. The blue colour on the plts is hard to see. Try Pink and lime green :) at 19:34, the time domain plot looks like there is another sine wavw, almost a carrier signal. You can see it more clearly later in the video the 'Tesla" coil.

[@thecircuithelper]

Hi Simon, the blue colour on black background is super annoying. For lectures I always had to change the colour (and line thickness) as nobody could see them at the back of the theatre, I thought it would be ok on the recorded version, but just checked now and it’s pretty hard to see still! Not a good choice from the designers of LTSpice to have that scheme as the default! Regarding the time domain plot ~19 mins, there’s definitely some harmonics included. Probably because it’s been driven ever so slightly off resonance. I should have done an FFT of the waveform to check what’s going on…

[@simonyoungglostog]

Will you be looking at Semiconductors? I'm keen to see how you approach Transistors.

[@thecircuithelper]

I’m in two minds what to do next… first I will put out quite a few worked example videos that I have already made. I’ve also bought quite a few components to do a few project-type videos in the lab. After this I’ll prepare another course, it could either be semiconductor devices, e.g., diodes, transistors, fets etc; or, something on instrumentation, sensors etc. I was toying with the idea of something on digital electronics (it’s years since I even looked at digital stuff, so it would be a good way to refresh). Recording new material is a little tricky at the moment as I don’t really have any space to film in at the moment, I need to find a new place asap! Thanks for watching!

[@johnnywintery8608]

If you make a band-pass filter with a resonant circuit, wouldn't the gain be so massive it would damage your equipment?

[@thecircuithelper]

Well, typically you would design the filter with the application in mind, making sure that the voltage at resonance isn’t going to damage whatever you connect to your filter to. For example, thinking about a simple AM radio, we exploit both the filtering and gain of a resonant circuit. We tune the variable capacitor so the circuit has a resonant frequency that matches that of the received signal, this basically amplifiers all but the received frequency by the circuits Q value, this signal is then de modulated using a simple diode and RC filter. In this example we’re expecting (10’s) uV levels and hopefully we might get mV’s out that can then be further amplified. If we suddenly received more than the expected voltage there would be trouble, but it’s very unlikely!