I am designing a data acquisition circuit. The I/O's are TTL compatible, the I/O's get damaged when ever a high voltage spike(50 V,
On a sunny day (10 Feb 2007 11:12:35 -0800) it happened "M Ihsan Baig" wrote in :
Several exist for example: Optocoupler. Transorb.
Digital or analog? A series resistor and a clamp into a CMOS input will take care of some really severe transients on digital lines. If you like living dangerously, just the series resistor might be okay (probably you'll want a pullup or pulldown on the input in either case).
Best regards, Spehro Pefhany
For modest spikes, MC1489A is a common Schmitt trigger inverter that has no problem with +/- 20V input (and responds to TTL levels). That's about as robust as a cheap IC gets, you can add discrete components to go to higher tolerances (diode clamp to ground, transzorb or zener, even fuses and spark gaps).
I've always just used reverse-biased diodes to the rails, with optionally a small (maybe 100 ohms) resistor or a small choke.
That's how they do it in video games, and I've never seen one fail at the inputs. (I used to fix video games.)
Cheers! Rich
Have something to add? Share your thoughts — no account required.
Ask the community — no account required