Ed wrote:
It seems to me that a low voltage secondary should be OK by using a fast comparator IC rather than a transistor to decide - the gain of the IC allows for much smaller detection levels, so the equivalent zero-crossing velocity could be the same. An IC tripping in a 10 mV band should provide the same effective ZC velocity at 12 V input as a transistor working around 100 mV with 120 V input. Or am I missing something?
When the switching band gets that small, device noise, input offset voltage drift, and other errors have a proportionally greater effect. I actually built a similar circuit with a 12v transformer and an LT1720 comparator, and it had worse jitter than the two-transistor circuit with a 120v feed. In this case, there is no substitute for starting with a higher-slew-rate signal. (Yes, the LT1720 did marginally better than the two-transistor circuit when both were fed from 120v -- but the fussiness of working with a fast comparator and the small gain over the two-transistor circuit made the latter the better choice, particularly in a design being put "out there" for others to build.)
Best regards, Charles _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
