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Wide range voltage detector
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foxabilo:
Evening all,

I have a project where the input is in the form of a couple of input terminals and the potential difference between them can be from 3.3v DC to 240v AC and I need to let a micro controller know if the inputs are energised.

I have shoved the inputs into a rectifier put it through a 220K and a zener diode to clamp it with a BJT to pull a 100k load down to GND and the input to the microcontroller all works great.

Now I want to try and opto isolate it just to be double safe, but of course the output from the 220K+rectifier from 3.3V is nowhere near enough to drive an opto , any ideas?

Cheers

Foxa
ogden:

--- Quote from: foxabilo on December 14, 2018, 11:04:55 pm ---the output from the 220K+rectifier from 3.3V is nowhere near enough to drive an opto , any ideas?

--- End quote ---

Use isolated DC-DC 5v->5v module, add some kind of amplifier between clamp and opto.
unitedatoms:
You can try using current limiter based on lnd150 fets.
https://www.eevblog.com/forum/beginners/mains-zero-crossing/
foxabilo:

--- Quote from: unitedatoms on December 14, 2018, 11:26:06 pm ---You can try using current limiter based on lnd150 fets.
https://www.eevblog.com/forum/beginners/mains-zero-crossing/

--- End quote ---

Now that is a nice starting point, let me guess though, no depleted FET models in spice , still have the issue of not enough ompf to drive an opto for the full 340 volt (dc) range though.  :-//
foxabilo:
Scratch that, I getcha now, as the depletion fet starts to conduct any high voltages currents it turns itself off at a point set by the feedback resistor and .... yea I get it .... Very smart that.
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