Tapeshnik Pt.3: troubleshooting 50% duty cycle

[@tntube23]

Awesome-3! I was also a bit worried of BW for the opamps used

[@svofski]

I'll see if it makes a difference when I get a hold of faster opamps.

[@mightwilder]

is that fastest opamps around?

[@svofski]

lm358 (actually lp2904 here) has 0.3V/uS slew rate so not very fast. do you think opamp speed may be critical in this application?

[@mightwilder]

@@svofski it seems modern op amps have much high slew rate specified (lt1818), you could try one to see if there would be any difference, but most likely the issue with breadboard wiring interference and long wires because signal looks asymmetrical

[@svofski]

@@mightwilder what I have here is essentially an analog PWM modulator: there is a triangle input and a const value at an input of a comparator. As long as the const value is perfectly centered, we get 50% duty cycle. Move it lower, get 45%, etc.. Note that I got it centered by changing the positive input offset by a tiny bit. If the slew rate is 0.3V/uS and the signal is 5Vp-p, our limiting frequency would be about 30kHz. So at 10 and even 20 kHz we're well within the specs. We'll see how it goes. I'm afraid the mechanical factors like the flutter will be the real bottleneck here.

[@tntube23]

Also are they rail to rail opamps?

[@svofski]

@@tntube23 they are not. check out the schematic btw :) the link to written notes is in the description, they are up to date