Electronics > Beginners
Floating probe! For $2.50
JS:
Other use could be injection amplifier, for the LF wiuld be better than any transformer coming down to DC.
--- Quote from: Yansi on September 10, 2018, 07:38:55 pm ---I don't see too many uses (if any) for this thing.
At least switch the coupler to something appropriate, such as IL300.
Or just buy an analog isolation amplifier! For example Si8920 costs under $4 and has pretty darn good linearity, is even differential and the bandwidth is at least as good as your circuit. (probably better).
//EDIT: BW is a bit under 1MHz. Also the CMTI of 75kV/us is far better than what you would ever get from a nonshielded (even shielded) optocoupler.
--- End quote ---
Yes, better and specialized parts makes for better circuit and easier to design, no doubts! If I could get some I will.
JS
Gyro:
If you want to continue with the opto approach, the Broadcom HNCR200 linear opto is good for about 1.5MHz.
JS:
--- Quote from: Gyro on September 10, 2018, 07:49:07 pm ---If you want to continue with the opto approach, the Broadcom HNCR200 linear opto is good for about 1.5MHz.
--- End quote ---
I couldn't find any reference to the propagation delay in the data-sheet, that will limit the application of this circuit inside the feedback loop. Taking it out of the feedback loop will make tracking and offset compensation a real problem, there are some designs with that approach and might work reasonable fine for some applications, but drift will be bad. In any case it looks like I'm close to the limit of the 4N35. 6N136 is much faster too and I think I can get them, but not locally either. I've seen a project here with one of those, I should check how well it did, the switching takes 0.3µs typ and 1µs max, but this is not switching so specs means very little. All specs are with output voltage with a finite resistnace, not current in a virtual earth config as I'm using them, so I expect to get a bit over of those specs.
JS
Gyro:
No, you're right the datasheet is light on information. The 1.5MHz bandwidth is quoted for the Fig 16 application circuit (the transistor one). I'm not sure how linear that one would be.
It sounds as if sourcing the part isn't going to be an option for you at the moment anyway.
JS:
--- Quote from: Gyro on September 10, 2018, 08:35:59 pm ---No, you're right the datasheet is light on information. The 1.5MHz bandwidth is quoted for the Fig 16 application circuit (the transistor one). I'm not sure how linear that one would be.
It sounds as if sourcing the part isn't going to be an option for you at the moment anyway.
--- End quote ---
Fig 12 makes a more similar thing to what I've made, using opamps would make for a more libear design I guess. Not too crazy about linearity for an 8 bit converter anyway... If they are using it like this, the propagation delay must be really low, otherwhise it will become unstable, note the lack of compensation other than the optocoupler itself, I think that's pushing a bit too much.
I could get a HCNR200 for the small amount of $20 plus shipping... The 4N35 is $0.50 here for reference. I will anotate that part for my next order overseas, but it's likely to be for the next year or close to that...
JS
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