I've observed peculiar differences between reset behavior of 805x's powered with powerful linear supplies as opposed to those powered by weak switching, or, for that matter, weak linear supplies. I think if the Vcc risetime is short enough, then things work "better" (forgive me for not having a precise characterization) than with the slow or noisilsy rising waveform on Vcc.

I was using a hand-built supply constructed in the '70's, with a 5-volt output regulated up to 30 Amperes, and, until the transformer finally caught fire, it drove all these circuits very well, hence, I never encountered the peculiar reset behavior that has been common subject for discusison in this forum.

In a "pinch" I switched to a "lightweight" supply capable of only about 1.5 or 2 Amperes, certainly enough for a circuit purportedly requiring only 50 mA, but the erratic reset behavior became apparent quite soon. I subsequently switched to a 10-Amp capable switcher and found the same problem. Later, I used a 7.5-Amp-rated linear 5-volt supply, and the problem, once again, was gone.

Perhaps one should try a precision-comparator-based switchon Vcc, that supplies Vcc to the "downstream" circuitry only after there have been no variations above 50-60 mV for 100 ms or so, and then switch on that Vcc with a rise time of, say, 50-100 microseconds. I may give this a try myself, sometime in the future, but probably not this coming week.

RE