O̶S̶M̶U̶ ̶R̶e̶v̶.̶0̶
Added 2018-05-25 09:18:15 +0000 UTCI've tried various ways of extending the voltage range of the LT1970 which I wanted to build the OSMU around:
- The NI way based on this http://www.ni.com/white-paper/4297/en/ It looked like I could just add equivalent circuitry for negative output voltages, but what I came up with had huge transverse current.
- Photoelectric gate drivers like this https://imgur.com/a/jTHDeaf sort of work, but the only ones I've been able to test have a fast-discharge feature which makes them super unstable
- I am trying current mirrors now https://imgur.com/a/o2131i0 but with those the circuit is almost as large as a fully discrete implementation
All signs are pointing the way of a fully discrete implementation. It's cheaper, more professional, performance isn't depending on obscure ICs etc. AND everyone I've talked to would prefer that.
What about isolated DACs and ADCs? I wanted to use these isolation amplifiers http://www.ti.com/lit/ds/symlink/amc1301.pdf but I think there are better options. 8 MHz SPI is not too uncommon and even in full duplex mode with 6 or more slaves I think that'd give me sufficient data throughput. Anybody happen to know an integrated SPI 2-ch DAC + 2-ch ADC? Something like http://www.ti.com/lit/ds/symlink/amc7812.pdf but smaller? :)
I've spent a lot of time finding the smallest 10A relays for current range switching: https://www.mouser.de/ProductDetail/Fujitsu/FTR-P6GN012WA?qs=AcmJtBVhzkRfw7wxTo3Y4A== But those are of course horrible, wildly varying contact resistances even within the same part!
All in all: There is almost no component left the way I imagined it in the original design = more PCBs ... yay 🎉
Comments
What our industrial control company does for isolation is use an "normal" ADC on the far side of a adum5401 and just feed the data lines across the isolation barrier. Maybe that would work for you? We use all analog devices parts for the analog frontend. I've been happy with them.
Dillon Nichols
2018-05-25 11:43:59 +0000 UTCI'd like to mount the output stage board directly on heat sink and use only SMD parts with thermal pads for that reason. I think that's the coolest 😐🤨🤔😖🤣 and easiest and maybe even best cooling strategy these days. The board should be small so that I can use a small heat sink. The digital board will probably be a different PCB, but it would also be possible to use 3 separate output boards, maybe even a high voltage, a high current and a general purpose one?
Marco Reps
2018-05-25 11:32:02 +0000 UTClol, that how i feel
Prying
2018-05-25 11:07:58 +0000 UTCThis is way over my head, but in 2 places you seem to be looking for smaller parts, could you elaborate on that? Does it have to be small? If its about the price of the PCBs, maybe you could design it to be split between 2 smaller pcbs?
Marco Vujevic
2018-05-25 11:04:41 +0000 UTC
