> Why would you need a soft / slow rise time on the anode cut off to reduce > switching noise when the cathodes are toggled repeatedly by the 74141? Surely > that introduces just the same switching noise that would be produced with > just a high side switching FET or BJT? Or does the 74141 feature a slow > transition on its output? I can appreciate the optical isolation for the high > side switching as being a nice part of the opto-couple solution though!
It's the sequence of events that makes it work. The cathodes are switched (hard) by the 74141, but no current flows (and noise is not radiated) as the anode isn't powered yet. Then the anode is turned on (soft) by the optocoupler, and the current rises gently, producing minimal radiated noise. When it's time to switch the digit off, the same thing happens in reverse, the anode is turned off (soft) by the optocoupler, smoothly reducing the current, then the cathodes are again switched while the current is off, thereby not producing switching noise. - John -- You received this message because you are subscribed to the Google Groups "neonixie-l" group. To post to this group, send an email to [email protected]. To unsubscribe from this group, send email to [email protected]. For more options, visit https://groups.google.com/groups/opt_out.
