On quick inspection, I’m a little uncomfortable with IC2 comparing USB voltage to the 3.3V output, it seems kind of like the decision on how to generate the 3.3V depends on the existence of the 3.3V, so maybe an unintended feedback going on. As long as USB voltage is present, it should power the regulators via Schottky diode D1. But without USB voltage, couldn’t both inputs to the comparator be approx. zero? So does it turn Q1 on or not? Or do you get an unstable situation? Seems like once Q1 turns on there should be 3.3V present and things should be OK, but still feeling uncomfortable about the situation. Maybe like Chuck said, manually drive the gate of Q1 and see if things work as planned.
I also have to ask, is this actually connected to 12V direct from a car battery? With a bazillion amps available? If so, I’d kind of like to see some resistance between Q1 and C6 to limit the current. Not saying this is the cause of your problem. From: AF <af-boun...@af.afmug.com> On Behalf Of can...@believewireless.net Sent: Friday, March 1, 2019 1:13 PM To: AnimalFarm Microwave Users Group <af@af.afmug.com> Subject: Re: [AFMUG] OT: EE Consultant Schematics attached. The main issue I'm having is when powered via USB, everything works fine. When powered via a 12V car battery, the chips seem to not have enough power. There are two comparator circuits, one to monitor USB/Batt and report how the unit is being powered. The 2nd actually provides the power. One chip will occasionally draw ~150-400ma of power causing the board to lock up. Chips are powered via Vin. What I don't understand is why everything works perfectly on USB but has issues when powered via 12V. On Tue, Feb 26, 2019 at 11:53 AM <ch...@wbmfg.com <mailto:ch...@wbmfg.com> > wrote: Circle of stability, miller capacitance all good stuff. From: Mark Radabaugh Sent: Tuesday, February 26, 2019 9:48 AM To: AnimalFarm Microwave Users Group Subject: Re: [AFMUG] OT: EE Consultant Oh sure, now you probably want me to believe transistors have states other than off and on. Mark On Feb 26, 2019, at 11:20 AM, Ken Hohhof <af...@kwisp.com <mailto:af...@kwisp.com> > wrote: > And good luck finding an analog circuit guy anymore ;-) That’s what I was. Not much demand, that’s why I’ve been doing other things for over 20 years. Actually made the switch to engineering management in the 80’s but still did some design work for another 10 years because all the engineers wanted to do digital and processor designs. I still have the books, the brain is rusty though. I tried to convince the new engineers that high speed digital design meant knowing analog, RF and microstrip techniques, but they weren’t buying it. Getting their products through regulatory emissions testing did give them a bit of religion. I still remember laying out PCBs using red and blue tape. From: AF <af-boun...@af.afmug.com <mailto:af-boun...@af.afmug.com> > On Behalf Of Mark Radabaugh Sent: Tuesday, February 26, 2019 9:09 AM To: AnimalFarm Microwave Users Group <af@af.afmug.com <mailto:af@af.afmug.com> > Subject: Re: [AFMUG] OT: EE Consultant Yep - I’m qualified to answer some things and would be totally lost on others. EE has become a huge field with many many disciplines. And good luck finding an analog circuit guy anymore ;-) Mark On Feb 26, 2019, at 9:56 AM, Ken Hohhof <af...@kwisp.com <mailto:af...@kwisp.com> > wrote: Analog? Digital? Even with those there tend to be specialties like emissions, safety, PLD/ASIC design, microprocessor/microcontroller, RF, etc. Or do you need a generalist? From: AF <af-boun...@af.afmug.com <mailto:af-boun...@af.afmug.com> > On Behalf Of can...@believewireless.net <mailto:can...@believewireless.net> Sent: Tuesday, February 26, 2019 8:33 AM To: AnimalFarm Microwave Users Group <af@af.afmug.com <mailto:af@af.afmug.com> > Subject: [AFMUG] OT: EE Consultant Having an issue with a circuit design, anyone know a good electrical engineer they can recommend? -- AF mailing list AF@af.afmug.com <mailto:AF@af.afmug.com> http://af.afmug.com/mailman/listinfo/af_af.afmug.com -- AF mailing list AF@af.afmug.com <mailto:AF@af.afmug.com> http://af.afmug.com/mailman/listinfo/af_af.afmug.com _____ -- AF mailing list AF@af.afmug.com <mailto:AF@af.afmug.com> http://af.afmug.com/mailman/listinfo/af_af.afmug.com -- AF mailing list AF@af.afmug.com <mailto:AF@af.afmug.com> http://af.afmug.com/mailman/listinfo/af_af.afmug.com
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