Hello all, I'm having an issue with my Tesla Coil's logic board - I'm the rankest of amateurs so I'm hoping someone can point out to me what I'm doing wrong.
Specifically, my board's design is based on this one which is very popular:
https://www.loneoceans.com/labs/ud27/My board is at
https://github.com/bmboucher/drsstcI basically borrowed the schematic wholesale, dropped the extra MOSFETs that boost the driver output, and replaced the external fiber optic interrupter with an Arduino on the board so the whole thing is self-contained. I also added some ICM7216 frequency counter chips because.... I'm not gonna lie, I thought they were cool
It's a traveling science exhibit that a local museum uses for outreach.
Anyhow, the part of the board that's giving me the problem is the TL3116 comparator; the role of this circuit is to convert the incoming feedback signal (sine wave) and convert it to a 5V logic square wave via zero-crossing detection. The UD2.7 website says to test it by hooking up a frequency generator to the inputs and probing the drive output, but no matter what I do the output doesn't look right. At some point I realized I had gotten the pinout wrong in the PCB, and corrected that with a new chip and some minor surgery, but still no dice. Eventually I built a breakout circuit on a breadboard (yes, I know that should have been step one but PCBs are so cheap these days I got cocky).
The test circuit schematic is attached below - I dropped everything except the input voltage clamp to 1.6V, the 1.6V divider for the reference and the hysteresis feedback. The INPUT is connected to a frequency generator producing a roughly +/-3V sine wave (with AC coupling). When I scope the two inputs to the TL3116 I get exactly what I expect (see test A below), which is a clamped sine wave on the inverting input and a flat line on the non-inverting.
I would expect the output then to be a 5V square wave at the same 250kHz frequency I'm driving the frequency generator, but instead I get.... a 1V square wave at ~60
hertz? The test B images below are taken with different time scales to show that but note that the voltage scales are aligned and the same as the test A images.
I'm sure its possible I just damaged the chip somehow, I originally tested this circuit without the 1.6V clamp. But this chip was otherwise just used for this circuit and the one on the board has also been replaced once without showing any changes. Is there something I just don't understand here? The circuit I'm attempting to copy is very widely used but I don't see any discussion of problems like what I'm having.
BTW, here's the chip I bought:
https://www.digikey.com/product-detail/en/texas-instruments/TL3116CD/296-6626-5-ND/372679