| Electronics > Projects, Designs, and Technical Stuff |
| Wide range voltage detector |
| (1/1) |
| 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. |
| Navigation |
| Message Index |