| ??? 03/29/05 17:17 Read: times |
#90617 - Is optoisolation fundamentally dangerous Responding to: ???'s previous message |
Kai Klaas said:
Geert said:
However, such help-contacts are quite expensive and I was wondering if you could 'sense' the output of the relais and bring this info (down-converted and separated by an opto-coupler, for instance) to the input of a detection circuit (0-5Vdc inputs), so that you exactly know the state of the relais in all possible situations. Hallo Geert, I agree with Erik, opto isolation might be too dangerous. There can be thousands of volts on mains! I would suggest you the following circuit: Kai, What makes optoisolation too dangerous? I understand Erik's concern about high voltages on pins close together, but there are ways to get around that. I do realize that the optoisolator I mentioned does not guarantee particularly great isolation, but there are certainly others that have higher ratings; this device is just convenient due the way it conditions the AC waveform. Also, it generally seems possible to obtain satisfactory results from optoisolators (especially ones without special conditioning circuitry) when running relatively low currents through their LEDs. Given this, and the fact that LEDs can withstand significant brief pulse currents, it seems unlikely that an optoisolator configured with a proper input resistor is likely to be damaged even by significant transients on the mains. --Sasha Jevtic |
