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| Problem reading multiple mains voltages with microcontroller. |
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| schmitt trigger:
I second what Richard Crowley mentions in his previous post. A small transformer is your best friend. Edit; In your schematic above this post, the NEUTRAL line will see 330 Vpk from the bridge rectifier’s negative terminal GND. |
| microherb:
--- Quote from: Richard Crowley on May 14, 2019, 09:30:35 am ---Nothing but a transformer will safely isolate you from the mains. Otherwise, you are playing with fire, quite literally. It doesn't have to be a very big transformer. I use the little transformers recycled out of old LINEAR wall-warts. This is when it pays to have a well-stocked junk box. --- End quote --- Thanks, yes transformer is good for isolation, smallest one seems to be about 1VA, footprint is a bit large for the application, it's a production design not a one off so I would need to find something available for purchase at a reasonable price. |
| Marco:
--- Quote from: microherb on May 14, 2019, 10:20:47 pm ---Traditionally, there is a capacitor across the low side of the flyback transformer to the switcher ground (Bridge neg) for EMC. I take it that is still OK with the low side of the output now tied to neutral? --- End quote --- Sure, the direct connection to neutral is going to win over anything the capacitor can do. |
| Richard Crowley:
There are opto-isolators used for voltage feedback on SMPS circuits. With that kind of device, surely you could devise a circuit that would sample a calibrated fraction of the mains voltage. For example: |
| microherb:
--- Quote from: Richard Crowley on May 15, 2019, 01:46:51 am ---There are opto-isolators used for voltage feedback on SMPS circuits. With that kind of device, surely you could devise a circuit that would sample a calibrated fraction of the mains voltage. For example: --- End quote --- Thanks Richard, do you have a source for the device in that document? |
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