ChipMar 5

This mess is a LM3748-based SEPIC converter. The idea is this will be the power supply for the pulse welder. All it needs to do is charge up the caps, so it doesn’t need to be particularly beefy or, y’know, good.

I had it working, blew up the MOSFET, and dropped in (I think) a 2N7002 (which is of course a bad choice). It didn’t work after that, I got frustrated, went to bed, and forgot about it.

Show threadChipMar 5

Today I came back to it. I pulled up the datasheet, checked all the connections, and everything looked fine until I got to this bit on the FA/SD pin. I thought, “Huh. That’s weird. That’s hooked up to VCC. It’ll never run like that!”

Then I remember this little bit in the datasheet about the FA/SD pin. Apparently I had designed this so that you have to short the middle of those two resistors to ground before it will even turn on. I’m the problem. 😆

With a jumper in place, it runs fine. (Well, not fine, it runs like crap. But it runs.)

Show threadChipMar 5
Oh wonderful. It makes terrible noises. 😆
Show threadgábor ugrayMar 7
@bytex64 out of curiosity, what is the frequency of these noises? i can't hear them at all.
Show threadChipMar 7
@twilliability Just guessing, maybe 5-15kHz? It’s a sweep that gets higher pitched as the voltage rises. Possibly this is a volume issue? It’s not that loud in the video, so maybe you’d hear it with headphones.
Show threadgábor ugrayMar 7
@bytex64 ah yes, headphones made the difference :) thank you!
Show threadChip
@twilliability I was doing some further analysis and I had to amplify the audio about 30dB to get a spectral plot (low end is about 6400Hz). So I guess it recorded a lot quieter than it sounded in person.
Mar 7 at 6:35pmWeb